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Sample records for pd quasiparticle random

  1. Finite amplitude method for the quasiparticle random-phase approximation

    SciTech Connect

    Avogadro, Paolo; Nakatsukasa, Takashi

    2011-07-15

    We present the finite amplitude method (FAM), originally proposed in Ref. [17], for superfluid systems. A Hartree-Fock-Bogoliubov code may be transformed into a code of the quasiparticle-random-phase approximation (QRPA) with simple modifications. This technique has advantages over the conventional QRPA calculations, such as coding feasibility and computational cost. We perform the fully self-consistent linear-response calculation for the spherical neutron-rich nucleus {sup 174}Sn, modifying the hfbrad code, to demonstrate the accuracy, feasibility, and usefulness of the FAM.

  2. Separable pairing force for relativistic quasiparticle random-phase approximation

    SciTech Connect

    Tian Yuan; Ma Zhongyu; Ring, Peter

    2009-06-15

    We have introduced a separable pairing force, which was adjusted to reproduce the pairing properties of the Gogny force in nuclear matter. This separable pairing force is able to describe in relativistic Hartree-Bogoliubov (RHB) calculations the pairing properties in the ground state of finite nuclei on almost the same footing as the original Gogny interaction. In this work we investigate excited states using the Relativistic Quasiparticle Random-Phase Approximation (RQRPA) with the same separable pairing force. For consistency the Goldstone modes and the convergence with various cutoff parameters in this version of RQRPA are studied. The first excited 2{sup +} states for the chain of Sn isotopes with Z=50 and the chain of isotones with N=82 isotones are calculated in RQRPA together with the 3{sup -} states of Sn isotopes. By comparing our results with experimental data and with the results of the original Gogny force we find that this simple separable pairing interaction is very successful in depicting the pairing properties of vibrational excitations.

  3. Pairing within the self-consistent quasiparticle random-phase approximation at finite temperature

    SciTech Connect

    Dang, N. Dinh; Hung, N. Quang

    2008-06-15

    An approach to pairing in finite nuclei at nonzero temperature is proposed, which incorporates the effects due to the quasiparticle-number fluctuation (QNF) around Bardeen-Cooper-Schrieffer (BCS) mean field and dynamic coupling to quasiparticle-pair vibrations within the self-consistent quasiparticle random-phase approximation (SCQRPA). The numerical calculations of pairing gap, total energy, and heat capacity were carried out within a doubly folded multilevel model as well as realistic nuclei {sup 56}Fe and {sup 120}Sn. The results obtained show that, under the effect of QNF, in the region of moderate and strong couplings, the sharp transition between the superconducting and normal phases is smoothed out, resulting in a thermal pairing gap, which does not collapse at the BCS critical temperature, but has a tail, which extends to high temperature. The dynamic coupling of quasiparticles to SCQRPA vibrations significantly improves the agreement with the results of exact calculations and those obtained within the finite-temperature quantal Monte Carlo method for the total energy and heat capacity. It also causes a deviation of the quasiparticle occupation numbers from the Fermi-Dirac distributions for free fermions.

  4. Infinite-randomness fixed points for chains of non-Abelian quasiparticles.

    PubMed

    Bonesteel, N E; Yang, Kun

    2007-10-01

    One-dimensional chains of non-Abelian quasiparticles described by SU(2)k Chern-Simons-Witten theory can enter random singlet phases analogous to that of a random chain of ordinary spin-1/2 particles (corresponding to k-->infinity). For k=2 this phase provides a random singlet description of the infinite-randomness fixed point of the critical transverse field Ising model. The entanglement entropy of a region of size L in these phases scales as S(L) approximately lnd/3 log(2)L for large L, where d is the quantum dimension of the particles. PMID:17930652

  5. Thermodynamic properties of hot nuclei within the self-consistent quasiparticle random-phase approximation

    SciTech Connect

    Hung, N. Quang; Dang, N. Dinh

    2010-10-15

    The thermodynamic properties of hot nuclei are described within the canonical and microcanonical ensemble approaches. These approaches are derived based on the solutions of the BCS and self-consistent quasiparticle random-phase approximation at zero temperature embedded into the canonical and microcanonical ensembles. The results obtained agree well with the recent data extracted from experimental level densities by the Oslo group for {sup 94}Mo, {sup 98}Mo, {sup 162}Dy, and {sup 172}Yb nuclei.

  6. Implementation of the finite amplitude method for the relativistic quasiparticle random-phase approximation

    NASA Astrophysics Data System (ADS)

    Nikšić, T.; Kralj, N.; Tutiš, T.; Vretenar, D.; Ring, P.

    2013-10-01

    A new implementation of the finite amplitude method (FAM) for the solution of the relativistic quasiparticle random-phase approximation (RQRPA) is presented, based on the relativistic Hartree-Bogoliubov (RHB) model for deformed nuclei. The numerical accuracy and stability of the FAM-RQRPA is tested in a calculation of the monopole response of 22O. As an illustrative example, the model is applied to a study of the evolution of monopole strength in the chain of Sm isotopes, including the splitting of the giant monopole resonance in axially deformed systems.

  7. Quasiparticle-random-phase approximation treatment of the transverse wobbling mode reconsidered

    NASA Astrophysics Data System (ADS)

    Frauendorf, S.; Dönau, F.

    2015-12-01

    The quasiparticle-random-phase approximation is used to study the properties of the wobbling bands in 163Lu. Assuming that the wobbling mode represents pure isoscalar orientation oscillations results in too low wobbling frequencies and transition probabilities between the one- and zero-phonon wobbling bands that are strongly collective but yet too weak for B (E2 ) out and too strong for B (M1 ) out . The inclusion of an LL interaction, which couples the wobbling mode to the scissors mode, generates the right upshift of the wobbling frequencies and the right suppression of the B (M1 ) out values toward the experimental values, but does not change the B (E2 ) out values. In analogy to the quenching of low-energy E 1 transition by coupling to the isovector giant dipole resonance, a general reduction of the M 1 transitions between quasiparticle configurations caused by coupling to the scissors mode is suggested. The small B (E2 ) out values are related to small triaxiality of the density distribution, which is found by all mean field calculations for the triaxial strongly deformed nuclei in the mass 160 region.

  8. Linear response of light deformed nuclei investigated by self-consistent quasiparticle random-phase approximation

    SciTech Connect

    Losa, C.; Doessing, T.; Pastore, A.; Vigezzi, E.; Broglia, R. A.

    2010-06-15

    We present a calculation of the properties of vibrational states in deformed, axially-symmetric even-even nuclei, within the framework of a fully self-consistent quasiparticle random phase approximation (QRPA). The same Skyrme energy density and density-dependent pairing functionals are used to calculate the mean field and the residual interaction in the particle-hole and particle-particle channels. We have tested our software in the case of spherical nuclei against fully self-consistent calculations published in the literature, finding excellent agreement. We investigate the consequences of neglecting the spin-orbit and Coulomb residual interactions in QRPA. Furthermore we discuss the improvement obtained in the QRPA result associated with the removal of spurious modes. Isoscalar and isovector responses in the deformed {sup 24-26}Mg, {sup 34}Mg isotopes are presented and compared to experimental findings.

  9. Canonical and microcanonical ensemble descriptions of thermal pairing within BCS and quasiparticle random-phase approximation

    SciTech Connect

    Hung, N. Quang; Dang, N. Dinh

    2010-05-15

    We propose a description of pairing properties in finite systems within the canonical and microcanonical ensembles. The approach is derived by solving the BCS and self-consistent quasiparticle random-phase approximation with the Lipkin-Nogami particle-number projection at zero temperature. The obtained eigenvalues are embedded into the canonical and microcanonical ensembles. The results obtained are found in quite good agreement with the exact solutions of the doubly-folded equidistant multilevel pairing model as well as the experimental data for {sup 56}Fe nucleus. The merit of the present approach resides in its simplicity and its application to a wider range of particle number, where the exact solution is impracticable.

  10. Self-consistent quasiparticle random-phase approximation for a multilevel pairing model

    SciTech Connect

    Hung, N. Quang; Dang, N. Dinh

    2007-11-15

    Particle-number projection within the Lipkin-Nogami (LN) method is applied to the self-consistent quasiparticle random-phase approximation (SCQRPA), which is tested in an exactly solvable multilevel pairing model. The SCQRPA equations are numerically solved to find the energies of the ground and excited states at various numbers {omega} of doubly degenerate equidistant levels. The use of the LN method allows one to avoid the collapse of the BCS (QRPA) to obtain the energies of the ground and excited states as smooth functions of the interaction parameter G. The comparison between results given by different approximations such as the SCRPA, QRPA, LNQRPA, SCQRPA, and LNSCQRPA is carried out. Although the use of the LN method significantly improves the agreement with the exact results in the intermediate coupling region, we found that in the strong coupling region the SCQRPA results are closest to the exact ones.

  11. Quasiparticle random-phase approximation with interactions from the Similarity Renormalization Group

    SciTech Connect

    Hergert, H.; Papakonstantinou, P.; Roth, R.

    2011-06-15

    We have developed a fully consistent framework for calculations in the quasiparticle random-phase approximation (QRPA) with NN interactions from the Similarity Renormalization Group (SRG) and other unitary transformations of realistic interactions. The consistency of our calculations, which use the same Hamiltonian to determine the Hartree-Fock-Bogoliubov ground states and the residual interaction for QRPA, guarantees an excellent decoupling of spurious strength, without the need for empirical corrections. While work is under way to include SRG-evolved 3N interactions, we presently account for some 3N effects by means of a linearly density-dependent interaction, whose strength is adjusted to reproduce the charge radii of closed-shell nuclei across the whole nuclear chart. As a first application, we perform a survey of the monopole, dipole, and quadrupole response of the calcium isotopic chain and of the underlying single-particle spectra, focusing on how their properties depend on the SRG parameter {lambda}. Unrealistic spin-orbit splittings suggest that spin-orbit terms from the 3N interaction are called for. Nevertheless, our general findings are comparable to results from phenomenological QRPA calculations using Skyrme or Gogny energy density functionals. Potentially interesting phenomena related to low-lying strength warrant more systematic investigations in the future.

  12. Giant resonances in {sup 238}U within the quasiparticle random-phase approximation with the Gogny force

    SciTech Connect

    Peru, S.; Gosselin, G.; Martini, M.; Dupuis, M.; Hilaire, S.

    2011-01-15

    Fully consistent axially-symmetric deformed quasiparticle random-phase approximation (QRPA) calculations have been performed, using the same Gogny D1S effective force for both the Hartree-Fock-Bogolyubov mean field and QRPA matrix. New implementation of this approach leads to the applicability of QRPA to heavy deformed nuclei. Giant resonances and low-energy collective states for monopole, dipole, quadrupole, and octupole modes are predicted for the heavy deformed nucleus {sup 238}U and compared with experimental data.

  13. Calculation of delayed-neutron energy spectra in a quasiparticle random-phase approximation-Hauser-Feshbach model

    SciTech Connect

    Kawano, T.; Moeller, P.; Wilson, W. B.

    2008-11-15

    Theoretical {beta}-delayed-neutron spectra are calculated based on the Quasiparticle Random-Phase Approximation (QRPA) and the Hauser-Feshbach statistical model. Neutron emissions from an excited daughter nucleus after {beta} decay to the granddaughter residual are more accurately calculated than in previous evaluations, including all the microscopic nuclear structure information, such as a Gamow-Teller strength distribution and discrete states in the granddaughter. The calculated delayed-neutron spectra agree reasonably well with those evaluations in the ENDF decay library, which are based on experimental data. The model was adopted to generate the delayed-neutron spectra for all 271 precursors.

  14. Role of deformation on giant resonances within the quasiparticle random-phase approximation and the Gogny force

    SciTech Connect

    Peru, S.; Goutte, H.

    2008-04-15

    Fully consistent axially-symmetric-deformed quasiparticle random phase approximation (QRPA) calculations have been performed, in which the same Gogny D1S effective force has been used for both the Hartree-Fock-Bogolyubov mean field and the QRPA approaches. Giant resonances calculated in deformed {sup 26-28}Si and {sup 22-24}Mg nuclei as well as in the spherical {sup 30}Si and {sup 28}Mg isotopes are presented. Theoretical results for isovector-dipole and isoscalar monopole, quadrupole, and octupole responses are presented and the impact of the intrinsic nuclear deformation is discussed.

  15. Neutrino reactions on La138 and Ta180 via charged and neutral currents by the quasiparticle random-phase approximation

    NASA Astrophysics Data System (ADS)

    Cheoun, Myung-Ki; Ha, Eunja; Hayakawa, T.; Kajino, Toshitaka; Chiba, Satoshi

    2010-09-01

    The cosmological origins of the two heaviest odd-odd nuclei La138 and Ta180 are believed to be closely related to the neutrino process. We investigate in detail neutrino-induced reactions on the nuclei. Charged current (CC) reactions Ba138(νe,e-)La138 and Hf180(νe,e-)Ta180 are calculated using the standard quasi-particle random phase approximation (QRPA) with neutron-proton pairing as well as neutron-neutron and proton-proton pairing correlations. For the neutral current (NC) reactions La139(ν,ν')La139* and Ta181(ν,ν')Ta181*, we generate ground and excited states of the odd-even target nuclei La139 and Ta181 by operating one quasiparticle to even-even nuclei Ba138 and Hf180, which are assumed as the BCS ground state. Numerical results for CC reactions are shown to be consistent with recent semiempirical data deduced from the Gamow-Teller strength distributions measured in the (He3,t) reaction. Results for NC reactions are estimated to be about 4 to 5 times smaller than the results for CC reactions. Finally, cross sections weighted by the incident neutrino flux in the core-collapse supernova are presented for further applications to the network calculations for relevant nuclear abundances.

  16. Quasiparticle random-phase approximation and {beta}-decay physics: Higher-order approximations in a boson formalism

    SciTech Connect

    Sambataro, M.; Suhonen, J.

    1997-08-01

    The quasiparticle random-phase approximation (QRPA) is reviewed and higher-order approximations are discussed with reference to {beta}-decay physics. The approach is fully developed in a boson formalism. Working within a schematic model, we first illustrate a fermion-boson mapping procedure and apply it to construct boson images of the fermion Hamiltonian at different levels of approximation. The quality of these images is tested through a comparison between approximate and exact spectra. Standard QRPA equations are derived in correspondence with the quasi-boson limit of the first-order boson Hamiltonian. The use of higher-order Hamiltonians is seen to improve considerably the stability of the approximate solutions. The mapping procedure is also applied to Fermi {beta} operators: exact and approximate transition amplitudes are discussed together with the Ikeda sum rule. The range of applicabilty of the QRPA formalism is analyzed. {copyright} {ital 1997} {ital The American Physical Society}

  17. Systematics of the first 2{sup +} excitation in spherical nuclei with the Skyrme quasiparticle random-phase approximation

    SciTech Connect

    Terasaki, J.; Engel, J.; Bertsch, G. F.

    2008-10-15

    We use the quasiparticle random-phase approximation (QRPA) and the Skyrme interactions SLy4 and SkM* to systematically calculate energies and transition strengths for the lowest 2{sup +} state in spherical even-even nuclei. The SkM* functional, applied to 178 spherical nuclei between Z=10 and 90, produces excitation energies that are on average 11% higher than experimental values, with residuals that fluctuate about the average by -35% to +55%. The predictions of SkM* and SLy4 have significant differences, in part because of differences in the calculated ground state deformations; SkM* performs better in both the average and dispersion of energies. Comparing the QRPA results with those of generator-coordinate-method (GCM) calculations, we find that the QRPA reproduces trends near closed shells better than the GCM, and that it overpredicts the energies less severely in general.

  18. Continuum quasiparticle random-phase approximation for astrophysical direct neutron capture reactions on neutron-rich nuclei

    NASA Astrophysics Data System (ADS)

    Matsuo, Masayuki

    2015-03-01

    I formulate a many-body theory to calculate the cross section of direct radiative neutron capture reaction by means of the Hartree-Fock-Bogoliubov mean-field model and the continuum quasiparticle random-phase approximation (QRPA). A focus is put on very-neutron-rich nuclei and low-energy neutron kinetic energy in the range from 1 keV to several MeV, which is relevant to the rapid neutron capture process of nucleosynthesis. I begin with the photoabsorption cross section and the E 1 strength function. Next, in order to apply the reciprocity theorem, I decompose the cross section into partial cross sections corresponding to different channels of one- and two-neutron emission decays of photo-excited states. A numerical example is shown for the photo-absorption of 142Sn and the neutron capture of 141Sn .

  19. Large-scale deformed quasiparticle random-phase approximation calculations of the γ -ray strength function using the Gogny force

    NASA Astrophysics Data System (ADS)

    Martini, M.; Péru, S.; Hilaire, S.; Goriely, S.; Lechaftois, F.

    2016-07-01

    Valuable theoretical predictions of nuclear dipole excitations in the whole chart are of great interest for different nuclear applications, including in particular nuclear astrophysics. Here we present large-scale calculations of the E 1 γ -ray strength function obtained in the framework of the axially symmetric deformed quasiparticle random-phase approximation based on the finite-range Gogny force. This approach is applied to even-even nuclei, the strength function for odd nuclei being derived by interpolation. The convergence with respect to the adopted number of harmonic oscillator shells and the cutoff energy introduced in the 2-quasiparticle (2 -q p ) excitation space is analyzed. The calculations performed with two different Gogny interactions, namely D1S and D1M, are compared. A systematic energy shift of the E 1 strength is found for D1M relative to D1S, leading to a lower energy centroid and a smaller energy-weighted sum rule for D1M. When comparing with experimental photoabsorption data, the Gogny-QRPA predictions are found to overestimate the giant dipole energy by typically ˜2 MeV. Despite the microscopic nature of our self-consistent Hartree-Fock-Bogoliubov plus QRPA calculation, some phenomenological corrections need to be included to take into account the effects beyond the standard 2 -q p QRPA excitations and the coupling between the single-particle and low-lying collective phonon degrees of freedom. For this purpose, three prescriptions of folding procedure are considered and adjusted to reproduce experimental photoabsorption data at best. All of them are shown to lead to somewhat similar predictions of the E 1 strength, both at low energies and for exotic neutron-rich nuclei. Predictions of γ -ray strength functions and Maxwellian-averaged neutron capture rates for the whole Sn isotopic chain are also discussed and compared with previous theoretical calculations.

  20. Low-energy dipole excitations in neon isotopes and N=16 isotones within the quasiparticle random-phase approximation and the Gogny force

    SciTech Connect

    Martini, M.; Peru, S.; Dupuis, M.

    2011-03-15

    Low-energy dipole excitations in neon isotopes and N=16 isotones are calculated with a fully consistent axially-symmetric-deformed quasiparticle random phase approximation (QRPA) approach based on Hartree-Fock-Bogolyubov (HFB) states. The same Gogny D1S effective force has been used both in HFB and QRPA calculations. The microscopical structure of these low-lying resonances, as well as the behavior of proton and neutron transition densities, are investigated in order to determine the isoscalar or isovector nature of the excitations. It is found that the N=16 isotones {sup 24}O, {sup 26}Ne, {sup 28}Mg, and {sup 30}Si are characterized by a similar behavior. The occupation of the 2s{sub 1/2} neutron orbit turns out to be crucial, leading to nontrivial transition densities and to small but finite collectivity. Some low-lying dipole excitations of {sup 28}Ne and {sup 30}Ne, characterized by transitions involving the {nu}1d{sub 3/2} state, present a more collective behavior and isoscalar transition densities. A collective proton low-lying excitation is identified in the {sup 18}Ne nucleus.

  1. Deformation effects on the gamow-teller transitions in 76Ge and 76Se by using the deformed Quasi-Particle Random-Phase Approximation

    NASA Astrophysics Data System (ADS)

    Ha, Eunja; Cheoun, Myung-Ki; Kim, K. S.

    2015-10-01

    With the advent of high technology in analyzing the Gamow-Teller (GT) excited states beyond the one nucleon emission threshold, the quenching of the GT strength to the Ikeda sum rule can be recovered by using the high-lying GT states. Moreover, in some nuclei, GT peaks that are stronger than any other peaks appear explicitly in the high-lying excited states. In the current study, we have addressed these high-lying GT (-) excited states within a framework of the deformed quasi-particle random-phase approximation (DQRPA). These high-lying GT (-) excited states are generated due to an increase in particle numbers around the Fermi surface due to an increase in the chemical potential owing to a certain deformation of the nuclei. On the contrary, among the GT(+) excited states, the low-lying ones were favored by an increase in the deformation. The main GT(+/-) transitions were also changed drastically by the deformation. A detailed mechanism leading to the changes in the GT transitions is discussed by studying the shell evolution and the consequent change in the particle numbers in the smearing region caused by the deformation in typical doublebeta-decay nuclei, 76Ge and 76Se.

  2. β -decay rates of odd-mass neutron-rich isotopes in the deformed quasiparticle random-phase approximation with realistic interactions

    NASA Astrophysics Data System (ADS)

    Ni, Dongdong; Ren, Zhongzhou

    2015-09-01

    The deformed quasiparticle random-phase approximation with realistic nucleon-nucleon interactions is extended for the β- decay of odd-mass neutron-rich Kr, Sr, Zr, and Mo isotopes, from their longest-lived isotopes to the experimentally unknown nuclei. The particle-particle and particle-hole channels of residual interactions are handled in large single-particle model spaces, based on the Brückner G matrix with charge-dependent Bonn nucleon-nucleon forces. Both allowed Gamow-Teller and first-forbidden transitions are considered and different treatments for odd-mass systems are emphasized. The sensitivity of the calculated results to the single-particle level scheme and the particle-particle strength is discussed. The calculated Gamow-Teller strengths are analyzed, together with the contributions from first-forbidden transitions. The calculated half-lives are found to agree well with the experimental data over the orders of magnitude from 10-2 to 103 s.

  3. Two decay paths for calculating the nuclear matrix element of neutrinoless double-β decay using quasiparticle random-phase approximation

    NASA Astrophysics Data System (ADS)

    Terasaki, J.

    2016-02-01

    It is possible to employ virtual decay paths, including two-particle transfer, to calculate the nuclear matrix element of neutrinoless double-β decay under the closure approximation, in addition to the true double-β path. In the quasiparticle random-phase approximation (QRPA) approach, it is necessary to introduce the product wave functions of the like-particle and proton-neutron QRPA ground states, for achieving consistency between the calculations of the true and virtual paths. Using these different paths, the problem of whether or not these two methods give equivalent nuclear matrix elements (NMEs) is investigated. It is found that the two results are inequivalent, resulting from the different many-body correlations included in the two QRPA methods, i.e., the use of the product wave functions alone is not sufficient. The author proposes introduction of the proton-neutron pairing interaction with an adequate strength in the double-β -path method, which carries less many-body correlations without this supplemental interaction, for obtaining the NME equivalent to that of the two-particle-transfer-path method. The validity of the proposed modified approach is examined.

  4. A Fully Automated Diabetes Prevention Program, Alive-PD: Program Design and Randomized Controlled Trial Protocol

    PubMed Central

    Azar, Kristen MJ; Block, Torin J; Romanelli, Robert J; Carpenter, Heather; Hopkins, Donald; Palaniappan, Latha; Block, Clifford H

    2015-01-01

    Background In the United States, 86 million adults have pre-diabetes. Evidence-based interventions that are both cost effective and widely scalable are needed to prevent diabetes. Objective Our goal was to develop a fully automated diabetes prevention program and determine its effectiveness in a randomized controlled trial. Methods Subjects with verified pre-diabetes were recruited to participate in a trial of the effectiveness of Alive-PD, a newly developed, 1-year, fully automated behavior change program delivered by email and Web. The program involves weekly tailored goal-setting, team-based and individual challenges, gamification, and other opportunities for interaction. An accompanying mobile phone app supports goal-setting and activity planning. For the trial, participants were randomized by computer algorithm to start the program immediately or after a 6-month delay. The primary outcome measures are change in HbA1c and fasting glucose from baseline to 6 months. The secondary outcome measures are change in HbA1c, glucose, lipids, body mass index (BMI), weight, waist circumference, and blood pressure at 3, 6, 9, and 12 months. Randomization and delivery of the intervention are independent of clinic staff, who are blinded to treatment assignment. Outcomes will be evaluated for the intention-to-treat and per-protocol populations. Results A total of 340 subjects with pre-diabetes were randomized to the intervention (n=164) or delayed-entry control group (n=176). Baseline characteristics were as follows: mean age 55 (SD 8.9); mean BMI 31.1 (SD 4.3); male 68.5%; mean fasting glucose 109.9 (SD 8.4) mg/dL; and mean HbA1c 5.6 (SD 0.3)%. Data collection and analysis are in progress. We hypothesize that participants in the intervention group will achieve statistically significant reductions in fasting glucose and HbA1c as compared to the control group at 6 months post baseline. Conclusions The randomized trial will provide rigorous evidence regarding the efficacy of

  5. Photoelectron diffraction studies of Cu on Pd(111) random surface alloys

    SciTech Connect

    Siervo, A. de; Landers, R.; Soares, E. A.; Kleiman, G.G.

    2005-03-15

    The study of surface alloys is motivated by their use in many applications of different segments of industry, such as in the search for new catalysts and sensors, in surface protection against corrosion, in lowering friction, and in testing electronic devices. An important aspect of surface alloys studies is that of the precise quantification of segregation and diffusion processes as well as the determination of surface structure. In this paper we report a combined low-energy electron diffraction and photoelectron diffraction (PED) (using synchrotron radiation) study of surface alloy formation when Cu ultrathin films are evaporated onto Pd(111) single-crystal surfaces. We present results for two different coverages (1 and 3 ML) and three annealing temperatures (300, 600, and 800 K). For these preparation conditions, a random alloy phase with different concentrations seems to form in the first few layers. Through the analysis of PED data performed using a multiple scattering formalism and the average T-matrix approximation it was possible to determine the atomic structure and the atomic concentration of the first three layers.

  6. Condensing Non-Abelian Quasiparticles

    SciTech Connect

    Hermanns, M.

    2010-02-05

    A most interesting feature of certain fractional quantum Hall states is that their quasiparticles obey non-Abelian fractional statistics. So far, candidate non-Abelian wave functions have been constructed from conformal blocks in cleverly chosen conformal field theories. In this work we present a hierarchy scheme by which we can construct daughter states by condensing non-Abelian quasiparticles (as opposed to quasiholes) in a parent state, and show that the daughters have a non-Abelian statistics that differs from the parent. In particular, we discuss the daughter of the bosonic, spin-polarized Moore-Read state at nu=4/3 as an explicit example.

  7. Relativistic quasiparticle time blocking approximation: Dipole response of open-shell nuclei

    NASA Astrophysics Data System (ADS)

    Litvinova, E.; Ring, P.; Tselyaev, V.

    2008-07-01

    The self-consistent relativistic quasiparticle random-phase approximation (RQRPA) is extended by the quasiparticle-phonon coupling (QPC) model using the quasiparticle time blocking approximation (QTBA). The method is formulated in terms of the Bethe-Salpeter equation (BSE) in the two-quasiparticle space with an energy-dependent two-quasiparticle residual interaction. This equation is solved either in the basis of Dirac states forming the self-consistent solution of the ground state or in the momentum representation. Pairing correlations are treated within the Bardeen-Cooper-Schrieffer (BCS) model with a monopole-monopole interaction. The same NL3 set of the coupling constants generates the Dirac-Hartree-BCS single-quasiparticle spectrum, the static part of the residual two-quasiparticle interaction and the quasiparticle-phonon coupling amplitudes. A quantitative description of electric dipole excitations in the chain of tin isotopes (Z=50) with the mass numbers A=100,106,114,116,120, and 130 and in the chain of isotones with (N=50) Sr88, Zr90, Mo92 is performed within this framework. The RQRPA extended by the coupling to collective vibrations generates spectra with a multitude of 2q⊗phonon (two quasiparticles plus phonon) states providing a noticeable fragmentation of the giant dipole resonance as well as of the soft dipole mode (pygmy resonance) in the nuclei under investigation. The results obtained for the photo absorption cross sections and for the integrated contributions of the low-lying strength to the calculated dipole spectra agree very well with the available experimental data.

  8. Effect of spin fluctuations on quasiparticles in simple metals

    NASA Astrophysics Data System (ADS)

    Lischner, Johannes; Bazhirov, Timur; MacDonald, Allan; Cohen, Marvin; Louie, Steven

    2014-03-01

    We present a first-principles theory for quasiparticle excitations in condensed matter systems that includes their interaction with spin fluctuations. We apply this theory to sodium and lithium. Despite several previous studies, the importance of spin fluctuations in these materials and, in particular, their effect on the occupied band width remains unclear. We show that the coupling to spin fluctuations does not significantly change the occupied band width, but gives an important contribution to the quasiparticle lifetime. To obtain quantitative agreement with experiment for the occupied band width, we find that it is necessary to include vertex corrections beyond the random-phase approximation in the screening by charge fluctuations. S. G. L. acknowledges support by a Simons Foundation Fellowship in Theoretical Physics. This work was supported by NSF Grant No. DMR10-1006184 and by DOE Grant No. DE-AC02-05CH11231.

  9. Qubit dephasing due to quasiparticle tunneling

    NASA Astrophysics Data System (ADS)

    Zanker, Sebastian; Marthaler, Michael

    2015-05-01

    We study dephasing of a superconducting qubit due to quasiparticle tunneling through a Josephson junction. While qubit decay due to tunneling processes is well understood within a golden rule approximation, pure dephasing due to BCS quasiparticles gives rise to a divergent golden rule rate. We calculate qubit dephasing due to quasiparticle tunneling beyond lowest-order approximation in coupling between qubit and quasiparticles. Summing up a certain class of diagrams, we show that qubit dephasing due to purely longitudinal coupling to quasiparticles leads to dephasing ˜exp[-x (t )] where x (t ) ∝t3 /2 for short-time scales and x (t )∝t ln(t ) for long-time scales.

  10. Quasiparticle interference from magnetic impurities

    NASA Astrophysics Data System (ADS)

    Derry, Philip G.; Mitchell, Andrew K.; Logan, David E.

    2015-07-01

    Fourier transform scanning tunneling spectroscopy (FT-STS) measures the scattering of conduction electrons from impurities and defects, giving information about the electronic structure of both the host material and adsorbed impurities. We interpret such FT-STS measurements in terms of the quasiparticle interference (QPI), here investigating in detail the QPI due to single magnetic impurities adsorbed on a range of representative nonmagnetic host surfaces, and contrasting with the case of a simple scalar impurity or point defect. We demonstrate how the electronic correlations present for magnetic impurities markedly affect the QPI, showing, e.g., a large intensity enhancement due to the Kondo effect, and universality at low temperatures/scanning energies. The commonly used joint density of states interpretation of FT-STS measurements is also considered, and shown to be insufficient in many cases, including that of magnetic impurities.

  11. Exchange interaction between magnetic impurities on surfaces of Cu(x)Pd(1-x) and Cu(x)Au(1-x) random substitutional alloys.

    PubMed

    Ujfalussy, B; Simon, E

    2014-07-01

    We present fully relativistic first principles calculations of the exchange interactions between magnetic impurities deposited on the (1 1 1) surfaces of CuxPd1-x and CuxAu1-x random substitutional alloys, described using the coherent potential approximation. We show that as with pure surfaces of Cu and Au, where Shockley-type surface states mediate an RKKY-type interaction, a surface state and its dispersion can be obtained from studying the Bloch spectral function. In the second part of the paper we show how the details of the interaction are determined by the properties and dispersion of the surface states of the host material. We find an extra exponential decay in the range of the interactions compared to the 1/R(2) decay on surfaces of pure metals. The similar topology of the Fermi surface of Cu and Au allows us to scale the spin-orbit coupling and to study the Bychkov-Rashba splitting. Alternatively, the entirely different topology of the Cu and Pd Fermi surfaces allows us to study changes in the surface-state dispersion of the RKKY interaction between surface impurities. PMID:24934437

  12. Exact-exchange-based quasiparticle calculations

    SciTech Connect

    Aulbur, Wilfried G.; Staedele, Martin; Goerling, Andreas

    2000-09-15

    One-particle wave functions and energies from Kohn-Sham calculations with the exact local Kohn-Sham exchange and the local density approximation (LDA) correlation potential [EXX(c)] are used as input for quasiparticle calculations in the GW approximation (GWA) for eight semiconductors. Quasiparticle corrections to EXX(c) band gaps are small when EXX(c) band gaps are close to experiment. In the case of diamond, quasiparticle calculations are essential to remedy a 0.7 eV underestimate of the experimental band gap within EXX(c). The accuracy of EXX(c)-based GWA calculations for the determination of band gaps is as good as the accuracy of LDA-based GWA calculations. For the lowest valence band width a qualitatively different behavior is observed for medium- and wide-gap materials. The valence band width of medium- (wide-) gap materials is reduced (increased) in EXX(c) compared to the LDA. Quasiparticle corrections lead to a further reduction (increase). As a consequence, EXX(c)-based quasiparticle calculations give valence band widths that are generally 1-2 eV smaller (larger) than experiment for medium- (wide-) gap materials. (c) 2000 The American Physical Society.

  13. Comparing quasiparticle GW+DMFT and LDA+DMFT for the test bed material SrVO3

    NASA Astrophysics Data System (ADS)

    Taranto, C.; Kaltak, M.; Parragh, N.; Sangiovanni, G.; Kresse, G.; Toschi, A.; Held, K.

    2013-10-01

    We have implemented the quasiparticle GW+dynamical mean field theory (DMFT) approach in the Vienna ab initio simulation package. To this end, a quasiparticle Hermitization of the G0W0 self-energy a lá Kotani-Schilfgaarde is employed, and the interaction values are obtained from the locally unscreened random phase approximation (RPA) using a projection onto Wannier orbitals. We compare quasiparticle GW+DMFT and local density approximation (LDA)+DMFT against each other and against experiment for SrVO3. We observe a partial compensation of stronger electronic correlations due to the reduced GW bandwidth and weaker correlations due to a larger screening of the RPA interaction, so that the obtained spectra are quite similar and agree well with experiment. Noteworthy, the quasiparticle GW+DMFT better reproduces the position of the lower Hubbard side band.

  14. Quasiparticles near domain walls in hexagonal superconductors

    NASA Astrophysics Data System (ADS)

    Mukherjee, S. P.; Samokhin, K. V.

    2016-02-01

    We calculate the energy spectrum of quasiparticles trapped by a domain wall separating different time-reversal symmetry-breaking ground states in a hexagonal superconductor, such as UPt3. The bound-state energy is found to be strongly dependent on the gap symmetry, the domain-wall orientation, the quasiparticle's direction of semiclassical propagation, and the phase difference between the domains. We calculate the corresponding density of states and show how one can use its prominent features, in particular, the zero-energy singularity, to distinguish between different pairing symmetries.

  15. Quasiparticles near domain walls in hexagonal superconductors

    NASA Astrophysics Data System (ADS)

    Mukherjee, Soumya; Samokhin, Kirill

    We calculate the energy spectrum of quasiparticles trapped by a domain wall separating different time reversal symmetry-breaking ground states in a hexagonal superconductor, such as UPt3. The bound state energy is found to be strongly dependent on the gap symmetry, the domain wall orientation, the quasiparticle's direction of semiclassical propagation, and the phase difference between the domains. We calculate the corresponding density of states and show how one can use its prominent features, in particular, the zero-energy singularity, to distinguish between different pairing symmetries. Discovery Grant from the Natural Sciences and Engineering Research Council of Canada.

  16. Quasiparticle excitations of adsorbates on doped graphene

    NASA Astrophysics Data System (ADS)

    Lischner, Johannes; Wickenburg, Sebastian; Wong, Dillon; Karrasch, Christoph; Wang, Yang; Lu, Jiong; Omrani, Arash A.; Brar, Victor; Tsai, Hsin-Zon; Wu, Qiong; Corsetti, Fabiano; Mostofi, Arash; Kawakami, Roland K.; Moore, Joel; Zettl, Alex; Louie, Steven G.; Crommie, Mike

    Adsorbed atoms and molecules can modify the electronic structure of graphene, but in turn it is also possible to control the properties of adsorbates via the graphene substrate. In my talk, I will discuss the electronic structure of F4-TCNQ molecules on doped graphene and present a first-principles based theory of quasiparticle excitations that captures the interplay of doping-dependent image charge interactions between substrate and adsorbate and electron-electron interaction effects on the molecule. The resulting doping-dependent quasiparticle energies will be compared to experimental scanning tunnelling spectra. Finally, I will also discuss the effects of charged adsorbates on the electronic structure of doped graphene.

  17. Chemical potential beyond the quasiparticle mean field

    SciTech Connect

    Dinh Dang, N.; Hung, N. Quang

    2010-03-15

    The effects of quantal and thermal fluctuations beyond the BCS quasiparticle mean field on the chemical potential are studied within a model, which consists of N particles distributed amongst {Omega} doubly folded equidistant levels interacting via a pairing force with parameter G. The results obtained at zero and finite temperatures T within several approaches, which include the fluctuations beyond the BCS theory, are compared with the exact results. The chemical potential, defined as the Lagrangian multiplier to preserve the average number of particles, is compared with the corresponding quantity, which includes the effect from fluctuations of particle and quasiparticle numbers beyond the BCS quasiparticle mean field. The analysis of the results shows that the latter differs significantly from the former as functions of G and T. The chemical potential loses its physical meaning in the system with a fixed number of particles or after eliminating quantal fluctuations of particle (quasiparticle) numbers by means of particle number projection. The validity of the criterion for the signature of the transition to Bose-Einstein condensation, which occurs in infinite systems when the chemical potential hits the bottom of the energy spectrum, is reexamined for the finite multilevel model.

  18. Using Quasiparticle Poisoning To Detect Photons

    NASA Technical Reports Server (NTRS)

    Echternach, Pierre; Day, Peter

    2006-01-01

    According to a proposal, a phenomenon associated with excitation of quasiparticles in certain superconducting quantum devices would be exploited as a means of detecting photons with exquisite sensitivity. The phenomenon could also be exploited to perform medium-resolution spectroscopy. The proposal was inspired by the observation that Coulomb blockade devices upon which some quantum logic gates are based are extremely sensitive to quasiparticles excited above the superconducting gaps in their leads. The presence of quasiparticles in the leads can be easily detected via the charge states. If quasiparticles could be generated in the leads by absorption of photons, then the devices could be used as very sensitive detectors of electromagnetic radiation over the spectral range from x-rays to submillimeter waves. The devices in question are single-Cooper-pair boxes (SCBs), which are mesoscopic superconducting devices developed for quantum computing. An SCB consists of a small superconducting island connected to a reservoir via a small tunnel junction and connected to a voltage source through a gate capacitor. An SCB is an artificial two-level quantum system, the Hamiltonian of which can be controlled by the gate voltage. One measures the expected value of the charge of the eigenvectors of this quantum system by use of a radio-frequency single-electron transistor. A plot of this expected value of charge as a function of gate voltage resembles a staircase that, in the ideal case, consists of steps of height 2 e (where e is the charge of one electron). Experiments have shown that depending on the parameters of the device, quasiparticles in the form of "broken" Cooper pairs present in the reservoir can tunnel to the island, giving rise to steps of 1 e. This effect is sometimes called "poisoning." Simulations have shown that an extremely small average number of quasiparticles can generate a 1-e periodic signal. In a device according to the proposal, this poisoning would be

  19. Gap-engineered quasiparticle traps in the fluxonium artificial atom

    NASA Astrophysics Data System (ADS)

    Serniak, K.; de Lange, G.; Vool, U.; Hays, M.; Burkhart, L. D.; Gao, Y. Y.; Wang, C.; Sliwa, K. M.; Pop, I. M.; Frunzio, L.; Glazman, L. I.; Schoelkopf, R. J.; Devoret, M. H.

    Recent experiments have shown that the density of quasiparticles in superconducting quantum circuits exceeds the expected thermal density. In Josephson junction based superconducting qubits, these non-equilibrium quasiparticles can tunnel through the junctions of the circuit, causing decoherence. Quasiparticle traps aim to reduce the density of quasiparticles near the junctions, and therefore the rate of energy loss and dephasing due to tunneling events. These traps must be designed to not introduce any additional losses in the qubit. In this talk we will discuss recent progress in the design and implementation of quasiparticle traps in the fluxonium artificial atom. Work supported by ARO, ONR, YINQE, and the European Union.

  20. Superconducting resonators with trapped vortices under direct injection of quasiparticles

    NASA Astrophysics Data System (ADS)

    Nsanzineza, Ibrahim; Patel, Umesh; Dodge, K. R.; McDermott, R. F.; Plourde, B. L. T.

    Nonequilibrium quasiparticles and trapped magnetic flux vortices can significantly impact the performance of superconducting microwave resonant circuits and qubits at millikelvin temperatures. Quasiparticles result in excess loss, reducing resonator quality factors and qubit lifetimes. Vortices trapped near regions of large microwave currents also contribute excess loss. However, vortices located in current-free areas in the resonator or in the ground plane of a device can actually trap quasiparticles and lead to a reduction in the quasiparticle loss. We will describe experiments involving the controlled trapping of vortices in superconducting resonators with direct injection of quasiparticles using Normal metal-Insulator-Superconductor (NIS)-tunnel junctions.

  1. Normal Metal Quasiparticle Traps in 3D-Transmon Qubits

    NASA Astrophysics Data System (ADS)

    Burkhart, Luke D.; Gao, Yvonne Y.; Wang, Chen; Serniak, Kyle; de Lange, Gijs; Chu, Yiwen; Vool, Uri; Frunzio, Luigi; Devoret, Michel H.; Catelani, Gianluigi; Glazman, Leonid I.; Schoelkopf, Robert J.

    Quasiparticles are a known source of decoherence in Josephson-junction based superconducting qubits. While equilibrium quasiparticles should not be present in devices operated at dilution refrigeration temperatures well below the superconducting energy gap, non-thermal quasiparticles have been observed in many different superconducting qubits, including 3D-transmons and fluxonium qubits. Vortices induced by applied magnetic fields have been shown to improve non-equilibrium quasiparticle decay rates and improve coherence times by creating regions of the superconductor with vanishing energy gap, which act as quasiparticle traps. We aim to further mitigate quasiparticle-induced limits on coherence by engineering strong trapping via the introduction of normal metal to the superconducting qubit. In this talk, we present recent results regarding normal metal quasiparticle traps in 3D-transmon qubits. Work supported by ARO, A*STAR.

  2. Quasiparticle-continuum level repulsion in a quantum magnet

    DOE PAGESBeta

    Plumb, K. W.; Hwang, Kyusung; Qiu, Y.; Harriger, Leland W.; Granroth, G.  E.; Kolesnikov, Alexander I.; Shu, G. J.; Chou, F. C.; Rüegg, Ch.; Kim, Yong Baek; et al

    2015-11-30

    When the energy eigenvalues of two coupled quantum states approach each other in a certain parameter space, their energy levels repel each other and level crossing is avoided. Such level repulsion, or avoided level crossing, is commonly used to describe the dispersion relation of quasiparticles in solids. But, little is known about the level repulsion when more than two quasiparticles are present; for example, in a strongly interacting quantum system where a quasiparticle can spontaneously decay into a many-particle continuum. Here we show that even in this case level repulsion exists between a long-lived quasiparticle state and a continuum. Here,more » we observe a renormalization of the quasiparticle dispersion relation due to the presence of the continuum of multi-quasiparticle states, in our fine-resolution neutron spectroscopy study of magnetic quasiparticles in the frustrated quantum magnet BiCu2PO6.« less

  3. Quasiparticle-continuum level repulsion in a quantum magnet

    SciTech Connect

    Plumb, K. W.; Hwang, Kyusung; Qiu, Y.; Harriger, Leland W.; Granroth, G.  E.; Kolesnikov, Alexander I.; Shu, G. J.; Chou, F. C.; Rüegg, Ch.; Kim, Yong Baek; Kim, Young-June

    2015-11-30

    When the energy eigenvalues of two coupled quantum states approach each other in a certain parameter space, their energy levels repel each other and level crossing is avoided. Such level repulsion, or avoided level crossing, is commonly used to describe the dispersion relation of quasiparticles in solids. But, little is known about the level repulsion when more than two quasiparticles are present; for example, in a strongly interacting quantum system where a quasiparticle can spontaneously decay into a many-particle continuum. Here we show that even in this case level repulsion exists between a long-lived quasiparticle state and a continuum. Here, we observe a renormalization of the quasiparticle dispersion relation due to the presence of the continuum of multi-quasiparticle states, in our fine-resolution neutron spectroscopy study of magnetic quasiparticles in the frustrated quantum magnet BiCu2PO6.

  4. Quasiparticle-continuum level repulsion in a quantum magnet

    NASA Astrophysics Data System (ADS)

    Plumb, K. W.; Hwang, Kyusung; Qiu, Y.; Harriger, Leland W.; Granroth, G. E.; Kolesnikov, Alexander I.; Shu, G. J.; Chou, F. C.; Rüegg, Ch.; Kim, Yong Baek; Kim, Young-June

    2016-03-01

    When the energy eigenvalues of two coupled quantum states approach each other in a certain parameter space, their energy levels repel each other and level crossing is avoided. Such level repulsion, or avoided level crossing, is commonly used to describe the dispersion relation of quasiparticles in solids. However, little is known about the level repulsion when more than two quasiparticles are present; for example, in a strongly interacting quantum system where a quasiparticle can spontaneously decay into a many-particle continuum. Here we show that even in this case level repulsion exists between a long-lived quasiparticle state and a continuum. In our fine-resolution neutron spectroscopy study of magnetic quasiparticles in the frustrated quantum magnet BiCu2PO6, we observe a renormalization of the quasiparticle dispersion relation due to the presence of the continuum of multi-quasiparticle states.

  5. Quasiparticle interactions in frustrated Heisenberg chains

    NASA Astrophysics Data System (ADS)

    Vanderstraeten, Laurens; Haegeman, Jutho; Verstraete, Frank; Poilblanc, Didier

    2016-06-01

    Interactions between elementary excitations in quasi-one-dimensional antiferromagnets are of experimental relevance and their quantitative theoretical treatment has been a theoretical challenge for many years. Using matrix product states, one can explicitly determine the wave functions of the one- and two-particle excitations, and, consequently, the contributions to dynamical correlations. We apply this framework to the (nonintegrable) frustrated dimerized spin-1/2 chain, a model for generic spin-Peierls systems, where low-energy quasiparticle excitations are bound states of topological solitons. The spin structure factor involving two quasiparticle scattering states is obtained in the thermodynamic limit with full momentum and frequency resolution. This allows very subtle features in the two-particle spectral function to be revealed which, we argue, could be seen, e.g., in inelastic neutron scattering of spin-Peierls compounds under a change of the external pressure.

  6. Quantum Numbers of Textured Hall Effect Quasiparticles

    SciTech Connect

    Nayak, C.; Wilczek, F.

    1996-11-01

    We propose a class of variational wave functions with slow variation in spin and charge density and simple vortex structure at infinity, which properly generalize both the Laughlin quasiparticles and baby Skyrmions. We argue, on the basis of these wave functions and a spin-statistics relation in the relevant effective field theory, that the spin of the corresponding quasiparticle has a fractional part related in a universal fashion to the properties of the bulk state. We propose a direct experimental test of this claim. We show that certain spin-singlet quantum Hall states can be understood as arising from primary polarized states by Skyrmion condensation. {copyright} {ital 1996 The American Physical Society.}

  7. Superfluid 4He dynamics beyond quasiparticle excitations

    NASA Astrophysics Data System (ADS)

    Beauvois, K.; Campbell, C. E.; Dawidowski, J.; Fâk, B.; Godfrin, H.; Krotscheck, E.; Lauter, H.-J.; Lichtenegger, T.; Ollivier, J.; Sultan, A.

    2016-07-01

    The dynamics of superfluid 4He at and above the Landau quasiparticle regime is investigated by high-precision inelastic neutron scattering measurements of the dynamic structure factor. A highly structured response is observed above the familiar phonon-maxon-roton spectrum, characterized by sharp thresholds for phonon-phonon, maxon-roton, and roton-roton coupling processes. The experimental dynamic structure factor is compared to the calculation of the same physical quantity by a dynamic many-body theory including three-phonon processes self-consistently. The theory is found to provide a quantitative description of the dynamics of the correlated bosons for energies up to about three times that of the Landau quasiparticles.

  8. Anisotropic System of Quasiparticles in Superfluid Helium

    SciTech Connect

    Adamenko, I.N.; Nemchenko, K.E.; Slipko, V.A.; Wyatt, A.F.G.

    2006-02-17

    The thermodynamic properties of anisotropic quasiparticle systems of He II are considered for all degrees of anisotropy. It is shown that the thermodynamic functions of a strongly anisotropic phonon-roton system are mainly determined by rotons at all temperatures. Analytical expressions for the roton thermodynamic functions are obtained for all degrees of anisotropy. The maximum anisotropy is limited by the criterion for thermodynamic stability, which is here derived for the whole temperature range.

  9. Robustness of superconducting quantum modes against direct quasiparticle injection

    NASA Astrophysics Data System (ADS)

    Patel, U.; Nsanzineza, I.; Vavilov, M. G.; Plourde, B. L. T.; McDermott, R.

    Classical Josephson digital logic based on Single Flux Quantum (SFQ) pulses offers a path to high-fidelity coherent control of large-scale superconducting quantum machines. However, an SFQ pulse driver generates nonequilibrium quasiparticles that contribute to qubit relaxation, and steps must be taken to protect the qubit from this decoherence channel. Here we describe experiments to characterize the robustness of high-Q superconducting linear resonators and qubits against direct quasiparticle injection. We use NIS junctions and SFQ elements to controllably inject quasiparticles into the groundplane of superconducting resonator and qubit chips, and we characterize the quasiparticle contribution to dissipation. We examine the effectiveness of groundplane cuts, normal metal quasiparticle traps, and spatially-varying superconducting gaps at protecting the quantum modes against quasiparticle loss. Finally, we discuss strategies for the integration of multiqubit circuits with on-chip SFQ control elements.

  10. Quasiparticle properties of Ge(111)-2 times 1 surface

    SciTech Connect

    Zhu, X.; Louie, S.G.

    1992-08-01

    We have studied from first principles the quasiparticle properties of the 2 {times} 1 reconstructed (111) surface of Ge. Quasiparticle energies are calculated using the GW expansion of the electron self energy operator. The calculations explain a spectrum of experimental results obtained from photoemission, inverse photoemission, optical absorption, scanning tunneling microscopy, etc., for this surface. We also present a quasiparticle theory for the photoelectric threshold and examine the effects of many body corrections for this quantity.

  11. Registration of PD 05064, PD 05069, PD 05070, and PD 05071 germplasm lines of cotton

    Technology Transfer Automated Retrieval System (TEKTRAN)

    PD 05064, PD 05069, PD 05070, and PD 05071 are noncommercial breeding lines of cotton jointly released by the Agricultural Research Service, United States Department of Agriculture, the Clemson University Experiment Station, and Cotton Incorporated in 2014. PD 05064, PD 05069, PD 05070, and PD 05071...

  12. Effect of spin fluctuations on quasiparticle excitations: First-principles theory and application to sodium and lithium

    NASA Astrophysics Data System (ADS)

    Lischner, Johannes; Bazhirov, Timur; MacDonald, Allan H.; Cohen, Marvin L.; Louie, Steven G.

    2014-02-01

    We present first-principles calculations for quasiparticle excitations in sodium and lithium, including the effects of charge and spin fluctuations. We employ the Overhauser-Kukkonen form for the electron self-energy arising from spin fluctuations and demonstrate that the coupling of electrons to spin fluctuations gives an important contribution to the quasiparticle lifetime but does not significantly reduce the occupied bandwidth. Including correlation effects beyond the random-phase approximation in the screening from charge fluctuations yields good agreement with experiment.

  13. Quasiparticle band structure of HgSe

    SciTech Connect

    Rohlfing, M.; Louie, S.G.

    1998-04-01

    Motivated by a recent discussion about the existence of a fundamental gap in HgSe [Phys. Rev. Lett. {bold 78}, 3165 (1997)], we calculate the quasiparticle band structure of HgSe within the GW approximation for the electron self-energy. The band-structure results show that HgSe is a semimetal, which is in agreement with most experimental data. We observe a strong wave-vector dependence of the self-energy of the lowest conduction band, leading to an increased dispersion and a small effective mass. This may help to interpret recent photoemission spectroscopy measurements. {copyright} {ital 1998} {ital The American Physical Society}

  14. Charge of a quasiparticle in a superconductor

    PubMed Central

    Ronen, Yuval; Cohen, Yonatan; Kang, Jung-Hyun; Haim, Arbel; Rieder, Maria-Theresa; Heiblum, Moty; Mahalu, Diana; Shtrikman, Hadas

    2016-01-01

    Nonlinear charge transport in superconductor–insulator–superconductor (SIS) Josephson junctions has a unique signature in the shuttled charge quantum between the two superconductors. In the zero-bias limit Cooper pairs, each with twice the electron charge, carry the Josephson current. An applied bias VSD leads to multiple Andreev reflections (MAR), which in the limit of weak tunneling probability should lead to integer multiples of the electron charge ne traversing the junction, with n integer larger than 2Δ/eVSD and Δ the superconducting order parameter. Exceptionally, just above the gap eVSD ≥ 2Δ, with Andreev reflections suppressed, one would expect the current to be carried by partitioned quasiparticles, each with energy-dependent charge, being a superposition of an electron and a hole. Using shot-noise measurements in an SIS junction induced in an InAs nanowire (with noise proportional to the partitioned charge), we first observed quantization of the partitioned charge q = e*/e=n, with n = 1–4, thus reaffirming the validity of our charge interpretation. Concentrating next on the bias region eVSD∼2Δ, we found a reproducible and clear dip in the extracted charge to q ∼0.6, which, after excluding other possibilities, we attribute to the partitioned quasiparticle charge. Such dip is supported by numerical simulations of our SIS structure. PMID:26831071

  15. Charge of a quasiparticle in a superconductor.

    PubMed

    Ronen, Yuval; Cohen, Yonatan; Kang, Jung-Hyun; Haim, Arbel; Rieder, Maria-Theresa; Heiblum, Moty; Mahalu, Diana; Shtrikman, Hadas

    2016-02-16

    Nonlinear charge transport in superconductor-insulator-superconductor (SIS) Josephson junctions has a unique signature in the shuttled charge quantum between the two superconductors. In the zero-bias limit Cooper pairs, each with twice the electron charge, carry the Josephson current. An applied bias VSD leads to multiple Andreev reflections (MAR), which in the limit of weak tunneling probability should lead to integer multiples of the electron charge ne traversing the junction, with n integer larger than 2Δ/eVSD and Δ the superconducting order parameter. Exceptionally, just above the gap eVSD ≥ 2Δ, with Andreev reflections suppressed, one would expect the current to be carried by partitioned quasiparticles, each with energy-dependent charge, being a superposition of an electron and a hole. Using shot-noise measurements in an SIS junction induced in an InAs nanowire (with noise proportional to the partitioned charge), we first observed quantization of the partitioned charge q = e*/e = n, with n = 1-4, thus reaffirming the validity of our charge interpretation. Concentrating next on the bias region eVSD ~ 2Δ, we found a reproducible and clear dip in the extracted charge to q ~ 0.6, which, after excluding other possibilities, we attribute to the partitioned quasiparticle charge. Such dip is supported by numerical simulations of our SIS structure. PMID:26831071

  16. Quasiparticle Aggregation in the Fractional Quantum Hall Effect

    DOE R&D Accomplishments Database

    Laughlin, R. B.

    1984-10-10

    Quasiparticles in the Fractional Quantum Hall Effect behave qualitatively like electrons confined to the lowest landau level, and can do everything electrons can do, including condense into second generation Fractional Quantum Hall ground states. I review in this paper the reasoning leading to variational wavefunctions for ground state and quasiparticles in the 1/3 effect. I then show how two-quasiparticle eigenstates are uniquely determined from symmetry, and how this leads in a natural way to variational wavefunctions for composite states which have the correct densities (2/5, 2/7, ...). I show in the process that the boson, anyon and fermion representations for the quasiparticles used by Haldane, Halperin, and me are all equivalent. I demonstrate a simple way to derive Halperin`s multiple-valued quasiparticle wavefunction from the correct single-valued electron wavefunction. (auth)

  17. Coherent Suppression of Quasiparticle Dissipation in Superconducting Artificial Atom

    NASA Astrophysics Data System (ADS)

    Pop, Ioan M.

    2015-03-01

    We demonstrate immunity to quasiparticle dissipation in a Josephson junction. At the foundation of this protection rests a prediction by Brian Josephson from fifty years ago: the particle-hole interference of superconducting quasiparticles when tunneling across a Josephson junction. The junction under study is the central element of a fluxonium artificial atom, which we place in an extremely low loss environment and measure using radio-frequency dispersive techniques. Furthermore, by using a quantum limited amplifier (a Josephson Parametric Converter) we can observe quantum jumps between the 0 and 1 states of the qubit in thermal equilibrium with the environment. The distribution of the times in-between the quantum jumps reveals quantitative information about the population and dynamics of quasiparticles. The data is entirely consistent with the hypothesis that our system is sensitive to single quasiparticle excitations, which opens new perspectives for quasiparticle monitoring in low temperature devices. Work supported by: IARPA, ARO, and ONR.

  18. Quasiparticle interference, quasiparticle interactions, and the origin of the charge density wave in 2H–NbSe2

    DOE PAGESBeta

    Arguello, C. J.; Rosenthal, E. P.; Andrade, E. F.; Jin, W.; Yeh, P. C.; Zaki, N.; Jia, S.; Cava, R. J.; Fernandes, R. M.; Millis, A. J.; et al

    2015-01-21

    We show that a small number of intentionally introduced defects can be used as a spectroscopic tool to amplify quasiparticle interference in 2H-NbSe₂, that we measure by scanning tunneling spectroscopic imaging. We show from the momentum and energy dependence of the quasiparticle interference that Fermi surface nesting is inconsequential to charge density wave formation in 2H-NbSe₂. Thus, we demonstrate that by combining quasiparticle interference data with additional knowledge of the quasiparticle band structure from angle resolved photoemission measurements, one can extract the wavevector and energy dependence of the important electronic scattering processes thereby obtaining direct information both about the fermiologymore » and the interactions. In 2H-NbSe₂, we use this combination to show that the important near-Fermi-surface electronic physics is dominated by the coupling of the quasiparticles to soft mode phonons at a wave vector different from the CDW ordering wave vector.« less

  19. Finite quasiparticle lifetime in disordered superconductors.

    SciTech Connect

    Zemlicka, M.; Neilinger, P.; Trgala, M; Rehak, M; Manca, D.; Grajcar, M.; Szabo, P.; Samuely, P.; Gazi, S.; Hubner, U.; Vinokur, V. M.; Il'ichev, E.

    2015-12-08

    We investigate the complex conductivity of a highly disordered MoC superconducting film with k(F)l approximate to 1, where k(F) is the Fermi wave number and l is the mean free path, derived from experimental transmission characteristics of coplanar waveguide resonators in a wide temperature range below the superconducting transition temperature T-c. We find that the original Mattis-Bardeen model with a finite quasiparticle lifetime, tau, offers a perfect description of the experimentally observed complex conductivity. We show that iota is appreciably reduced by scattering effects. Characteristics of the scattering centers are independently found by scanning tunneling spectroscopy and agree with those determined from the complex conductivity.

  20. Nuclear response theory for spin-isospin excitations in a relativistic quasiparticle-phonon coupling framework

    NASA Astrophysics Data System (ADS)

    Robin, Caroline; Litvinova, Elena

    2016-07-01

    A new theoretical approach to spin-isospin excitations in open-shell nuclei is presented. The developed method is based on the relativistic meson-exchange nuclear Lagrangian of Quantum Hadrodynamics and extends the response theory for superfluid nuclear systems beyond relativistic quasiparticle random phase approximation in the proton-neutron channel (pn-RQRPA). The coupling between quasiparticle degrees of freedom and collective vibrations (phonons) introduces a time-dependent effective interaction, in addition to the exchange of pion and ρ -meson taken into account without retardation. The time-dependent contributions are treated in the resonant time-blocking approximation, in analogy to the previously developed relativistic quasiparticle time-blocking approximation (RQTBA) in the neutral (non-isospin-flip) channel. The new method is called proton-neutron RQTBA (pn-RQTBA) and is applied to the Gamow-Teller resonance in a chain of neutron-rich nickel isotopes 68-78Ni . A strong fragmentation of the resonance along with quenching of the strength, as compared to pn-RQRPA, is obtained. Based on the calculated strength distribution, beta-decay half-lives of the considered isotopes are computed and compared to pn-RQRPA half-lives and to experimental data. It is shown that a considerable improvement of the half-life description is obtained in pn-RQTBA because of the spreading effects, which bring the lifetimes to a very good quantitative agreement with data.

  1. Quasiparticle bands and spectra of Ga2O3 polymorphs

    NASA Astrophysics Data System (ADS)

    Furthmüller, J.; Bechstedt, F.

    2016-03-01

    Within the framework of density functional theory and Hedin's G W approximation for single-particle excitations, we present quasiparticle band structures and densities of states for two gallium oxide polymorphs: rhombohedral α -Ga2O3 and monoclinic β -Ga2O3 . The gap problem is attacked. In addition, their electron effective mass tensors are given. Solving the Bethe-Salpeter equation we also calculate excitonic optical spectra of the two polymorphs. The treatment of excitonic effects allows for a trustable prediction of optical properties from the band gap to the ultraviolet region. In addition, for few other polymorphs we also discuss the frequency-dependent dielectric tensor within the independent-particle approximation (random phase approximation) and densities of states on density functional level. We demonstrate that apart from subtle details, the overall densities of states and optical spectra, in particular the isotropically averaged spectra, are rather similar for all polymorphs, while the electronic dielectric constants vary with the structure. For all polymorphs, complete sets of elastic constants are given.

  2. Quasiparticles in the pseudogap Phase of Underdoped Cuprate

    SciTech Connect

    Yang, K.; Yang, H; Johnson, P; Rice, T; Zhang, F

    2009-01-01

    Recent angle-resolved photoemission (Yang H.-B. et al., Nature, 456 (2008) 77) and scanning tunneling microscopy (Kohsaka Y. et al., Nature, 454 (2008) 1072) measurements on underdoped cuprates have yielded new spectroscopic information on quasiparticles in the pseudogap phase. New features of the normal state such as particle-hole asymmetry, maxima in the energy dispersion, and accompanying drops in the spectral weight of quasiparticles agree with the ansatz of Yang et al. for the single-particle propagator in the pseudogap phase. The coherent quasiparticle dispersion and reduced asymmetry in the tunneling density of states in the superconducting state can also be described by this propagator.

  3. Decays of 110Rh and 112Rh to the near neutron midshell isotopes 110Pd and 112Pd

    NASA Astrophysics Data System (ADS)

    Lhersonneau, G.; Wang, J. C.; Hankonen, S.; Dendooven, P.; Jones, P.; Julin, R.; Äystö, J.

    1999-07-01

    The decays 110Rh and 112Rh have been investigated using on-line mass separation with the ion-guide technique. Extended decay schemes have been constructed for both the low- and high-spin states in 112Rh. Mixing ratios for the collective transitions from the 2+2 and 3+1 states in 112Pd have been measured by γ-γ angular correlation. The presence of two sets of 0+ and 2+ states in the 1.1-1.4 MeV range suggests the existence of an intruder band, the energy of which is the lowest in 110Pd with two neutrons fewer than the midshell. The quasiparticle levels at 2195 and 2755 keV are assigned I=4 and I=5, respectively. The corresponding levels in 110Pd are a new level at 2261 keV and the 2805 keV level. Systematics of logft values and excitation energies of these quasiparticle levels is remarkably smooth. The strong β feeding to the I=5 quasiparticle state can be regarded as similar to the main branch in the decay of odd Rh isotopes, while a neutron is a spectator.

  4. Subgap resonant quasiparticle transport in normal-superconductor quantum dot devices

    NASA Astrophysics Data System (ADS)

    Gramich, J.; Baumgartner, A.; Schönenberger, C.

    2016-04-01

    We report thermally activated transport resonances for biases below the superconducting energy gap in a carbon nanotube quantum dot (QD) device with a superconducting Pb and a normal metal contact. These resonances are due to the superconductor's finite quasi-particle population at elevated temperatures and can only be observed when the QD life-time broadening is considerably smaller than the gap. This condition is fulfilled in our QD devices with optimized Pd/Pb/In multi-layer contacts, which result in reproducibly large and "clean" superconducting transport gaps with a strong conductance suppression for subgap biases. We show that these gaps close monotonically with increasing magnetic field and temperature. The accurate description of the subgap resonances by a simple resonant tunneling model illustrates the ideal characteristics of the reported Pb contacts and gives an alternative access to the tunnel coupling strengths in a QD.

  5. Phonon Quasiparticles and Anharmonic Free Energy in Complex Systems

    NASA Astrophysics Data System (ADS)

    Zhang, Dong-Bo; Sun, Tao; Wentzcovitch, Renata M.

    2014-02-01

    We use a hybrid strategy to obtain anharmonic frequency shifts and lifetimes of phonon quasiparticles from first principles molecular dynamics simulations in modest size supercells. This approach is effective irrespective of crystal structure complexity and facilitates calculation of full anharmonic phonon dispersions, as long as phonon quasiparticles are well defined. We validate this approach to obtain anharmonic effects with calculations in MgSiO3 perovskite, the major Earth forming mineral phase. First, we reproduce irregular thermal frequency shifts of well characterized Raman modes. Second, we combine the phonon gas model (PGM) with quasiparticle frequencies and reproduce free energies obtained using thermodynamic integration. Combining thoroughly sampled quasiparticle dispersions with the PGM we then obtain first-principles anharmonic free energy in the thermodynamic limit (N→∞).

  6. Rate of tunneling nonequilibrium quasiparticles in superconducting qubits

    NASA Astrophysics Data System (ADS)

    Ansari, Mohammad H.

    2015-04-01

    In superconducting qubits the lifetime of quantum states cannot be prolonged arbitrarily by decreasing temperature. At low temperature quasiparticles tunneling between the electromagnetic environment and superconducting islands takes the condensate state out of equilibrium due to charge imbalance. We obtain the tunneling rate from a phenomenological model of non-equilibrium, where nonequilibrium quasiparticle tunnelling stimulates a temperature-dependent chemical potential shift in the superconductor. As a result we obtain a non-monotonic behavior for relaxation rate as a function of temperature. Depending on the fabrication parameters for some qubits, the lowest tunneling rate of nonequilibrium quasiparticles can take place only near the onset temperature below which nonequilibrium quasiparticles dominate over equilibrium one. Our theory also indicates that such tunnelings can influence the probability of transitions in qubits through a coupling to the zero-point energy of phase fluctuations.

  7. Phonon quasiparticles and anharmonic free energy in complex systems.

    PubMed

    Zhang, Dong-Bo; Sun, Tao; Wentzcovitch, Renata M

    2014-02-01

    We use a hybrid strategy to obtain anharmonic frequency shifts and lifetimes of phonon quasiparticles from first principles molecular dynamics simulations in modest size supercells. This approach is effective irrespective of crystal structure complexity and facilitates calculation of full anharmonic phonon dispersions, as long as phonon quasiparticles are well defined. We validate this approach to obtain anharmonic effects with calculations in MgSiO3 perovskite, the major Earth forming mineral phase. First, we reproduce irregular thermal frequency shifts of well characterized Raman modes. Second, we combine the phonon gas model (PGM) with quasiparticle frequencies and reproduce free energies obtained using thermodynamic integration. Combining thoroughly sampled quasiparticle dispersions with the PGM we then obtain first-principles anharmonic free energy in the thermodynamic limit (N→∞). PMID:24580631

  8. Polyakov loop and gluon quasiparticles in Yang-Mills thermodynamics

    NASA Astrophysics Data System (ADS)

    Ruggieri, M.; Alba, P.; Castorina, P.; Plumari, S.; Ratti, C.; Greco, V.

    2012-09-01

    We study the interpretation of lattice data about the thermodynamics of the deconfinement phase of SU(3) Yang-Mills theory, in terms of gluon quasiparticles propagating in a background of a Polyakov loop. A potential for the Polyakov loop, inspired by the strong coupling expansion of the QCD action, is introduced; the Polyakov loop is coupled to transverse gluon quasiparticles by means of a gaslike effective potential. This study is useful to identify the effective degrees of freedom propagating in the gluon medium above the critical temperature. A main general finding is that a dominant part of the phase transition dynamics is accounted for by the Polyakov loop dynamics; hence, the thermodynamics can be described without the need for diverging or exponentially increasing quasiparticle masses as T→Tc, at variance respect to standard quasiparticle models.

  9. One-quasiparticle states in odd-Z heavy nuclei

    SciTech Connect

    Adamian, G. G.; Antonenko, N. V.; Kuklin, S. N.; Scheid, W.

    2010-11-15

    The isotopic dependencies of one-quasiparticle states in Es and Md are treated. In {sup 253,255}Lr, the energies of the lowest one-quasiproton states are calculated. The one-quasiparticle isomer states are revealed in the nuclei of an {alpha}-decay chain starting from {sup 269}Rg. The {alpha} decays from some isomer states are predicted. The population of isomer states in the complete fusion reactions is discussed.

  10. Quasiparticle energy studies of bulk semiconductors, surfaces and nanotubes

    SciTech Connect

    Blase, X.F.

    1994-12-01

    Effects of many-body effects on electronic excitation energies (quasiparticle band structure) of these materials are explored. GW approximation, including local field effects, for self-energy operator is used to calculate quasi-particle energies. The newly discovered carbon nanotubes are studied; structural stability and band structures are calculated. BN nanotubes are also studied, and their stability is predicted. Unexpected electronic features are predicted for both systems. Filling of carbon nanotubes with metal atoms and the doping of BN nanotubes by carbon and other impurites is also studied. The occupied surface states at H/Si(111)-(1{times}1) surface are studied; it is shown that the electronic structure requires a full quasiparticle calculation even for this simple chemisorption system. The core level shift of the Si 2p levels for atoms near the H/Si(111)-(1{times}1) surface is calculated; a simple first order perturbation theory using pseudopotential and the local density approximation gives good results for the photoemission spectra of the core electrons. The quasiparticle energies of bulk hexagonal BN and those of an isolated BN sheet are studied; this provides an understanding of the quasiparticle band structure of BN nanotubes. A nearly free electron state with a wavefunction in the interlayer or vacuum region composes the bottom of the conduction bands. A mixed-space formalism is presented for calculating the dynamical screening effects and electron self-energy operator in solids; this provides an efficient algorithm to calculate quasiparticle energies for large systems.

  11. Shooting quasiparticles from Andreev bound states in a superconducting constriction

    SciTech Connect

    Riwar, R.-P.; Houzet, M.; Meyer, J. S.; Nazarov, Y. V.

    2014-12-15

    A few-channel superconducting constriction provides a set of discrete Andreev bound states that may be populated with quasiparticles. Motivated by recent experimental research, we study the processes in an a.c. driven constriction whereby a quasiparticle is promoted to the delocalized states outside the superconducting gap and flies away. We distinguish two processes of this kind. In the process of ionization, a quasiparticle present in the Andreev bound state is transferred to the delocalized states leaving the constriction. The refill process involves two quasiparticles: one flies away while another one appears in the Andreev bound state. We notice an interesting asymmetry of these processes. The electron-like quasiparticles are predominantly emitted to one side of the constriction while the hole-like ones are emitted to the other side. This produces a charge imbalance of accumulated quasiparticles, that is opposite on opposite sides of the junction. The imbalance may be detected with a tunnel contact to a normal metal lead.

  12. Shooting quasiparticles from Andreev bound states in a superconducting constriction

    NASA Astrophysics Data System (ADS)

    Riwar, R.-P.; Houzet, M.; Meyer, J. S.; Nazarov, Y. V.

    2014-12-01

    A few-channel superconducting constriction provides a set of discrete Andreev bound states that may be populated with quasiparticles. Motivated by recent experimental research, we study the processes in an a.c. driven constriction whereby a quasiparticle is promoted to the delocalized states outside the superconducting gap and flies away. We distinguish two processes of this kind. In the process of ionization, a quasiparticle present in the Andreev bound state is transferred to the delocalized states leaving the constriction. The refill process involves two quasiparticles: one flies away while another one appears in the Andreev bound state. We notice an interesting asymmetry of these processes. The electron-like quasiparticles are predominantly emitted to one side of the constriction while the hole-like ones are emitted to the other side. This produces a charge imbalance of accumulated quasiparticles, that is opposite on opposite sides of the junction. The imbalance may be detected with a tunnel contact to a normal metal lead.

  13. Quasiparticle Level Alignment for Photocatalytic Interfaces.

    PubMed

    Migani, Annapaoala; Mowbray, Duncan J; Zhao, Jin; Petek, Hrvoje; Rubio, Angel

    2014-05-13

    Electronic level alignment at the interface between an adsorbed molecular layer and a semiconducting substrate determines the activity and efficiency of many photocatalytic materials. Standard density functional theory (DFT)-based methods have proven unable to provide a quantitative description of this level alignment. This requires a proper treatment of the anisotropic screening, necessitating the use of quasiparticle (QP) techniques. However, the computational complexity of QP algorithms has meant a quantitative description of interfacial levels has remained elusive. We provide a systematic study of a prototypical interface, bare and methanol-covered rutile TiO2(110) surfaces, to determine the type of many-body theory required to obtain an accurate description of the level alignment. This is accomplished via a direct comparison with metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS), and two-photon photoemission (2PP) spectroscopy. We consider GGA DFT, hybrid DFT, and G0W0, scQPGW1, scQPGW0, and scQPGW QP calculations. Our results demonstrate that G0W0, or our recently introduced scQPGW1 approach, are required to obtain the correct alignment of both the highest occupied and lowest unoccupied interfacial molecular levels (HOMO/LUMO). These calculations set a new standard in the interpretation of electronic structure probe experiments of complex organic molecule/semiconductor interfaces. PMID:26580537

  14. Signatures of Weyl semimetals in quasiparticle interference

    NASA Astrophysics Data System (ADS)

    Mitchell, Andrew K.; Fritz, Lars

    2016-01-01

    Impurities act as in situ probes of nontrivial electronic structure, causing real-space modulations in the density of states detected by scanning tunneling spectroscopy on the sample surface. We show that distinctive topological features of Weyl semimetals can be revealed in the Fourier transform of this map, interpreted in terms of quasiparticle interference (QPI). We develop an exact Green's function formalism and apply it to generalized models of Weyl semimetals with an explicit surface. The type of perturbation lifting the Dirac node degeneracy to produce the three-dimensional bulk Weyl phase determines the specific QPI signatures appearing on the surface. QPI Fermi arcs may or may not appear, depending on the relative surface orientation and quantum interference effects. Line nodes give rise to tube projections of width controlled by the bias voltage. We consider the effect of crystal warping, distinguishing dispersive arclike features from true Fermi arcs. Finally, we demonstrate that the commonly used joint-density-of-states approach fails qualitatively, and cannot describe QPI extinction.

  15. Nodal Quasiparticle in Pseudogapped Colossal Magnetoresistive Manganites

    SciTech Connect

    Mannella, N.

    2010-06-02

    A characteristic feature of the copper oxide high-temperature superconductors is the dichotomy between the electronic excitations along the nodal (diagonal) and antinodal (parallel to the Cu-O bonds) directions in momentum space, generally assumed to be linked to the d-wave symmetry of the superconducting state. Angle-resolved photoemission measurements in the superconducting state have revealed a quasiparticle spectrum with a d-wave gap structure that exhibits a maximum along the antinodal direction and vanishes along the nodal direction. Subsequent measurements have shown that, at low doping levels, this gap structure persists even in the high-temperature metallic state, although the nodal points of the superconducting state spread out in finite Fermi arcs. This is the so-called pseudogap phase, and it has been assumed that it is closely linked to the superconducting state, either by assigning it to fluctuating superconductivity or by invoking orders which are natural competitors of d-wave superconductors. Here we report experimental evidence that a very similar pseudogap state with a nodal-antinodal dichotomous character exists in a system that is markedly different from a superconductor: the ferromagnetic metallic groundstate of the colossal magnetoresistive bilayer manganite La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7}. Our findings therefore cast doubt on the assumption that the pseudogap state in the copper oxides and the nodal-antinodal dichotomy are hallmarks of the superconductivity state.

  16. QCD critical point in a quasiparticle model

    SciTech Connect

    Srivastava, P. K.; Tiwari, S. K.; Singh, C. P.

    2010-07-01

    Recent theoretical investigations have unveiled a rich structure in the quantum chromodynamics phase diagram, which consists of quark-gluon plasma and the hadronic phases but also supports the existence of a crossover transition ending at a critical end point (CEP). We find a too large variation in the determination of the coordinates of the CEP in the temperature (T) baryon chemical potential ({mu}{sub B}) plane; and, therefore, its identification in the current heavy-ion experiments becomes debatable. Here we use an equation of state for a deconfined quark-gluon plasma using a thermodynamically-consistent quasiparticle model involving noninteracting quarks and gluons having thermal masses. We further use a thermodynamically-consistent excluded-volume model for the hadron gas, which was recently proposed by us. Using these equations of state, a first-order deconfining phase transition is constructed using Gibbs's criteria. This leads to an interesting finding that the phase transition line ends at a critical end point (CEP) beyond which a crossover region exists. Using our thermal hadron gas model, we obtain a chemical freeze out curve, and we find that the CEP lies in close proximity to this curve as proposed by some authors. The coordinates of CEP are found to lie within the reach of Relativistic heavy-ion collider experiment.

  17. Quasiparticle Level Alignment for Photocatalytic Interfaces

    SciTech Connect

    Migani, Annapaola; Mowbray, Duncan J.; Zhao, Jin; Petek, Hrvoje; Rubio, Angel

    2014-05-13

    Electronic level alignment at the interface between an adsorbed molecular layer and a semiconducting substrate determines the activity and efficiency of many photocatalytic materials. Standard density functional theory (DFT)-based methods have proven unable to provide a quantitative description of this level alignment. This requires a proper treatment of the anisotropic screening, necessitating the use of quasiparticle (QP) techniques. However, the computational complexity of QP algorithms has meant a quantitative description of interfacial levels has remained elusive. We provide a systematic study of a prototypical interface, bare and methanol-covered rutile TiO2(110) surfaces, to determine the type of many-body theory required to obtain an accurate description of the level alignment. This is accomplished via a direct comparison with metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS), and two-photon photoemission (2PP) spectroscopy. We consider GGA DFT, hybrid DFT, and G0W0, scQPGW1, scQPGW0, and scQPGW QP calculations. Our results demonstrate that G0W0, or our recently introduced scQPGW1 approach, are required to obtain the correct alignment of both the highest occupied and lowest unoccupied interfacial molecular levels (HOMO/LUMO). These calculations set a new standard in the interpretation of electronic structure probe experiments of complex organic molecule/semiconductor interfaces.

  18. A Randomized, Double-Blind, Placebo-Controlled Assessment of BMS-936558, a Fully Human Monoclonal Antibody to Programmed Death-1 (PD-1), in Patients with Chronic Hepatitis C Virus Infection

    PubMed Central

    Gardiner, David; Lalezari, Jay; Lawitz, Eric; DiMicco, Michael; Ghalib, Rheem; Reddy, K. Rajender; Chang, Kyong-Mi; Sulkowski, Mark; Marro, Steven O’; Anderson, Jeffrey; He, Bing; Kansra, Vikram; McPhee, Fiona; Wind-Rotolo, Megan; Grasela, Dennis; Selby, Mark; Korman, Alan J.; Lowy, Israel

    2013-01-01

    Expression of the programmed death 1 (PD-1) receptor and its ligands are implicated in the T cell exhaustion phenotype which contributes to the persistence of several chronic viral infections, including human hepatitis C virus (HCV). The antiviral potential of BMS-936558 (MDX-1106) – a fully human anti-PD-1 monoclonal immunoglobulin-G4 that blocks ligand binding – was explored in a proof-of-concept, placebo-controlled single-ascending-dose study in patients (N = 54) with chronic HCV infection. Interferon-alfa treatment-experienced patients (n = 42) were randomized 5∶1 to receive a single infusion of BMS-936558 (0.03, 0.1, 0.3, 1.0, 3.0 mg/kg [n = 5 each] or 10 mg/kg [n = 10]) or of placebo (n = 7). An additional 12 HCV treatment-naïve patients were randomized to receive 10 mg/kg BMS-936558 (n = 10) or placebo (n = 2). Patients were followed for 85 days post-dose. Five patients who received BMS-936558 (0.1 [n = 1] or 10 mg/kg) and one placebo patient achieved the primary study endpoint of a reduction in HCV RNA ≥0.5 log10 IU/mL on at least 2 consecutive visits; 3 (10 mg/kg) achieved a >4 log10 reduction. Two patients (10 mg/kg) achieved HCV RNA below the lower limit of quantitation (25 IU/mL), one of whom (a prior null-responder) remained RNA-undetectable 1 year post-study. Transient reductions in CD4+, CD8+ and CD19+ cells, including both naïve and memory CD4+ and CD8+ subsets, were observed at Day 2 without evidence of immune deficit. No clinically relevant changes in immunoglobulin subsets or treatment-related trends in circulating cytokines were noted. BMS-936558 exhibited dose-related exposure increases, with a half-life of 20–24 days. BMS-936558 was mostly well tolerated. One patient (10 mg/kg) experienced an asymptomatic grade 4 ALT elevation coincident with the onset of a 4-log viral load reduction. Six patients exhibited immune-related adverse events of mild-to-moderate intensity, including two cases of

  19. Recombination and propagation of quasiparticles in cuprate superconductors

    SciTech Connect

    Gedik, Nuh

    2004-05-20

    Rapid developments in time-resolved optical spectroscopy have led to renewed interest in the nonequilibrium state of superconductors and other highly correlated electron materials. In these experiments, the nonequilibrium state is prepared by the absorption of short (less than 100 fs) laser pulses, typically in the near-infrared, that perturb the density and energy distribution of quasiparticles. The evolution of the nonequilibrium state is probed by time resolving the changes in the optical response functions of the medium that take place after photoexcitation. Ultimately, the goal of such experiments is to understand not only the nonequilibrium state, but to shed light on the still poorly understood equilibrium properties of these materials. We report nonequilibrium experiments that have revealed aspects of the cup rates that have been inaccessible by other techniques. Namely, the diffusion and recombination coefficients of quasiparticles have been measured in both YBa{sub 2}Cu{sub 3}O{sub 6.5} and Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x} using time-resolved optical spectroscopy. Dependence of these measurements on doping, temperature and laser intensity is also obtained. To study the recombination of quasiparticles, we measure the change in reflectivity {Delta}R which is directly proportional to the nonequilibrium quasiparticle density created by the laser. From the intensity dependence, we estimate {beta}, the inelastic scattering coefficient and {gamma}{sub th} thermal equilibrium quasiparticle decay rate. We also present the dependence of recombination measurements on doping in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x}. Going from underdoped to overdoped regime, the sign of {Delta}R changes from positive to negative right at the optimal doping. This is accompanied by a change in dynamics. The decay of {Delta}R stops being intensity dependent exactly at the optimal doping. We provide possible interpretations of these two observations. To study the propagation of

  20. Evaluation of overlaps between arbitrary fermionic quasiparticle vacua

    NASA Astrophysics Data System (ADS)

    Avez, B.; Bender, M.

    2012-03-01

    We derive an expression that allows for the unambiguous evaluation of the overlap between two arbitrary quasiparticle vacua, including its sign. Our expression is based on the Pfaffian of a skew-symmetric matrix, extending the overlap formula recently proposed by Robledo [Phys. Rev. CPRVCAN0556-281310.1103/PhysRevC.79.021302 79, 021302(R) (2009)] to the most general case of quasiparticle vacua, including the one of the overlap between two different blocked n-quasiparticle states for either even or odd systems. The powerfulness of the method is illustrated for a few typical matrix elements that appear in realistic angular-momentum-restored generator coordinate method calculations when breaking time-reversal invariance and using the full model space of occupied single-particle states.

  1. Deformed nuclear state as a quasiparticle-pair condensate

    SciTech Connect

    Dobaczewski, J.; Skalski, J.

    1988-07-01

    The deformed nuclear states, obtained in terms of the Hartree-Fock plus Bardeen-Cooper-Schrieffer (BCS) method with the Skyrme SIII interaction, are approximated by condensates of the low-angular-momentum quasiparticle and particle pairs. It is shown that the quasiparticle pairs, which are essentially the particle-hole nuclear excitations, provide for a better approximation than the valence particle pairs. In both cases, the inclusion of J = 0, 2, and 4 components is necessary to reproduce the Hartree-Fock plus BCS equilibrium deformation and deformation energy.

  2. Controlling quasiparticle excitations in a trapped Bose-Einstein condensate

    SciTech Connect

    Woo, S.J.; Choi, S.; Bigelow, N.P.

    2005-08-15

    We describe an approach to quantum control of the quasiparticle excitations in a trapped Bose-Einstein condensate based on adiabatic and diabatic changes in the trap anisotropy. We describe our approach in the context of the Landau-Zener transition at the avoided crossings in the quasiparticle excitation spectrum. We find also that there can be population oscillation between different modes at the specific aspect ratios of the trapping potential at which the mode energies are almost degenerate. These effects may have implications in the expansion of an excited condensate as well as the dynamics of a moving condensate in an atomic waveguide with a varying width.

  3. PD-1/PD-L1 inhibitors.

    PubMed

    Sunshine, Joel; Taube, Janis M

    2015-08-01

    Tumors may adopt normal physiologic checkpoints for immunomodulation leading to an imbalance between tumor growth and host surveillance. Antibodies targeting the PD-1/PD-L1 checkpoint have shown dynamic and durable tumor regressions, suggesting a rebalancing of the host-tumor interaction. Nivolumab and pembrolizumab are the anti-PD-1 antibodies that are currently the furthest in clinical development, and anti-PD-L1 agents under investigation include MPDL3280A, MEDI4736, and BMS-936559. These agents have been used to treat advanced melanoma, non-small cell lung cancer, renal cell carcinoma, bladder cancer and Hodgkin lymphoma, amongst other tumor types. In this article, we review the updated response results for early clinical trials, note recent FDA actions regarding this class of agents, and summarize results across trials looking at PD-L1 status as a predictor of response to anti-PD-1/PD-L1. PMID:26047524

  4. Quasiparticle collapsing in an anisotropic t -J ladder

    NASA Astrophysics Data System (ADS)

    Zhu, Zheng; Weng, Zheng-Yu

    2015-12-01

    Quasiparticle collapsing is a central issue in the study of strongly correlated electron systems. In the one-dimensional case, the quasiparticle collapsing in a form of spin-charge separation has been well established, but the problem remains elusive in dimensions higher than one. By using the density matrix renormalization group (DMRG) algorithm, we show that in an anisotropic two-leg t -J ladder, an injected single hole behaves like a well-defined quasiparticle in the strong rung limit but undergoes a "phase transition" with the effective mass diverging at a quantum critical point (QCP) towards the isotropic limit. After the transition, the quasiparticle collapses into a loosely bound object of a charge (holon) and a spin-1/2 (spinon) accompanied by an unscreened phase string as well as a substantially enhanced binding energy between two doped holes. A phase diagram of multileg ladders is further obtained, which extrapolates the QCP towards the two-dimensional limit. The underlying mechanism generic for any dimensions is also discussed.

  5. Lightwave-driven quasiparticle collisions on a subcycle timescale.

    PubMed

    Langer, F; Hohenleutner, M; Schmid, C P; Poellmann, C; Nagler, P; Korn, T; Schüller, C; Sherwin, M S; Huttner, U; Steiner, J T; Koch, S W; Kira, M; Huber, R

    2016-05-12

    Ever since Ernest Rutherford scattered α-particles from gold foils, collision experiments have revealed insights into atoms, nuclei and elementary particles. In solids, many-body correlations lead to characteristic resonances--called quasiparticles--such as excitons, dropletons, polarons and Cooper pairs. The structure and dynamics of quasiparticles are important because they define macroscopic phenomena such as Mott insulating states, spontaneous spin- and charge-order, and high-temperature superconductivity. However, the extremely short lifetimes of these entities make practical implementations of a suitable collider challenging. Here we exploit lightwave-driven charge transport, the foundation of attosecond science, to explore ultrafast quasiparticle collisions directly in the time domain: a femtosecond optical pulse creates excitonic electron-hole pairs in the layered dichalcogenide tungsten diselenide while a strong terahertz field accelerates and collides the electrons with the holes. The underlying dynamics of the wave packets, including collision, pair annihilation, quantum interference and dephasing, are detected as light emission in high-order spectral sidebands of the optical excitation. A full quantum theory explains our observations microscopically. This approach enables collision experiments with various complex quasiparticles and suggests a promising new way of generating sub-femtosecond pulses. PMID:27172045

  6. Kondo physics from quasiparticle poisoning in Majorana devices

    NASA Astrophysics Data System (ADS)

    Plugge, S.; Zazunov, A.; Eriksson, E.; Tsvelik, A. M.; Egger, R.

    2016-03-01

    We present a theoretical analysis of quasiparticle poisoning in Coulomb-blockaded Majorana fermion systems tunnel-coupled to normal-conducting leads. Taking into account finite-energy quasiparticles, we derive the effective low-energy theory and present a renormalization group analysis. We find qualitatively new effects when a quasiparticle state with very low energy is localized near a tunnel contact. For M =2 attached leads, such "dangerous" quasiparticle poisoning processes cause a spin S =1 /2 single-channel Kondo effect, which can be detected through a characteristic zero-bias anomaly conductance peak in all Coulomb blockade valleys. For more than two attached leads, the topological Kondo effect of the unpoisoned system becomes unstable. A strong-coupling bosonization analysis indicates that at low energy the poisoned lead is effectively decoupled and hence, for M >3 , the topological Kondo fixed point re-emerges, though now it involves only M -1 leads. As a consequence, for M =3 , the low-energy fixed point becomes trivial corresponding to decoupled leads.

  7. Nonequilibrium electron dynamics: Formation of the quasiparticle peak

    NASA Astrophysics Data System (ADS)

    Sayyad, Sharareh; Eckstein, Martin

    We characterize how the narrow quasiparticle band of the one-band Hubbard model forms out of a bad metallic state in a time-dependent metal-insulator transition, using nonequilibrium slave-rotor dynamical mean field theory. Our results exhibit a nontrivial electronic timescale which is much longer than the width of the quasiparticle peak itself. To study this timescale, we perform a fast ramp from the insulating phase into the metallic region of the phase diagram, resulting in a highly excited state, and study the equilibration of the system with a weakly coupled phononic bath. The slow relaxation behavior is explained by surveilling the interplay between spinon and rotor degrees of freedom. Since the system is initially prepared in an insulating phase, the quasi-particle peak emerges when spinons catch up the metal-insulator crossover region, which is reached earlier by the rotor. At this point, spinon and rotor become weakly coupled, and the resulting very slow equilibration of the spinon is a bottleneck for the dynamics. After the birth of the quasiparticle peak, its height enhances by the construction of the low-energy spectrum of the rotor, which then lacks behind the relaxation of the spinon.

  8. Kondo physics from quasiparticle poisoning in Majorana devices

    DOE PAGESBeta

    Plugge, S.; Tsvelik, A. M.; Zazunov, A.; Eriksson, E.; Egger, R.

    2016-03-24

    Here, we present a theoretical analysis of quasiparticle poisoning in Coulomb-blockaded Majorana fermion systems tunnel-coupled to normal-conducting leads. Taking into account finite-energy quasiparticles, we derive the effective low-energy theory and present a renormalization group analysis. We find qualitatively new effects when a quasiparticle state with very low energy is localized near a tunnel contact. For M = 2 attached leads, such “dangerous” quasiparticle poisoning processes cause a spin S = 1/2 single-channel Kondo effect, which can be detected through a characteristic zero-bias anomaly conductance peak in all Coulomb blockade valleys. For more than two attached leads, the topological Kondo effectmore » of the unpoisoned system becomes unstable. A strong-coupling bosonization analysis indicates that at low energy the poisoned lead is effectively decoupled and hence, for M > 3, the topological Kondo fixed point re-emerges, though now it involves only M–1 leads. As a consequence, for M = 3, the low-energy fixed point becomes trivial corresponding to decoupled leads.« less

  9. Suppressing decoherence of superconducting qubits by trapping non-equilibrium quasiparticles

    NASA Astrophysics Data System (ADS)

    Gao, Yvonne; Wang, Chen; Pop, I. M.; Vool, U.; Axline, C.; Brecht, T.; Heeres, R. W.; Frunzio, L.; Devoret, M. H.; Catelani, G.; Glazman, L. I.; Schoelkopf, R. J.

    2015-03-01

    We report a counter-intuitive observation that vortices can improve the coherence of superconducting qubits by suppressing non-equilibrium quasiparticles. This effect is systematically studied by measuring the magnetic-field dependence of qubit coherence times and quasiparticle lifetimes in transmons with different geometries in a 3D cQED architecture. Varying quasiparticle dynamics by vortices allows separation of dissipation mechanisms and measurement of the stray generation rate of quasiparticles in our devices. More details are described in Ref. Our results indicate that quasiparticles contribute significantly to qubit decoherence. Hence suppression of quasiparticle density in the device is essential for further improvement of coherence times of superconducting qubits and we will present recent results aimed at alleviating decoherence due to quasiparticles.

  10. Nonperturbative renormalization group calculation of quasiparticle velocity and dielectric function of graphene

    NASA Astrophysics Data System (ADS)

    Bauer, Carsten; Rückriegel, Andreas; Sharma, Anand; Kopietz, Peter

    2015-09-01

    Using a nonperturbative functional renormalization group approach, we calculate the renormalized quasiparticle velocity v (k ) and the static dielectric function ɛ (k ) of suspended graphene as functions of an external momentum k . Our numerical result for v (k ) can be fitted by v (k ) /vF=A +B ln(Λ0/k ) , where vF is the bare Fermi velocity, Λ0 is an ultraviolet cutoff, and A =1.37 , B =0.51 for the physically relevant value (e2/vF=2.2 ) of the coupling constant. In contrast to calculations based on the static random-phase approximation, we find that ɛ (k ) approaches unity for k →0 . Our result for v (k ) agrees very well with a recent measurement by Elias et al. [Nat. Phys. 7, 701 (2011), 10.1038/nphys2049].

  11. Real-time measurement of quasiparticle tunneling in a single-junction transmon qubit using feedback

    NASA Astrophysics Data System (ADS)

    Ristè, Diego; Bultink, Niels; Tiggelman, Marijn; Schouten, Raymond; Lehnert, Konrad; Dicarlo, Leonardo

    2013-03-01

    With coherence times of superconducting qubits now exceeding 100 μs , the contribution of quasiparticle (QP) tunneling to qubit relaxation and dephasing becomes potentially relevant. We report the real-time measurement of QP tunneling across the single junction of a 3D transmon qubit. We integrate recent developments in projective qubit readout with 99 % fidelity and feedback-based reset to transform the qubit into a charge-parity detector with 6 μs resolution. We detect a symmetric random telegraph signal matching a QP tunneling time of 0 . 8 ms . By measuring the correlation function of charge parity conditioned on specific initial and final qubit states, we determine that most QP tunneling does not induce qubit transitions, in contradiction with recent theory. We extract a QP-induced qubit relaxation time T1qp ~ 3 ms , decidedly not limiting the measured T1 = 0 . 14 ms . Research supported by NWO, FOM, and EU Project SOLID.

  12. Quasiparticle-phonon interaction in the theory of finite Fermi systems

    SciTech Connect

    Kamerdzhiev, S. P.; Avdeenkov, A. V.; Voitenkov, D. A.

    2011-10-15

    Within the Green's function method and on the basis of the method developed by V.A. Khodel for analyzing anharmonic effects, effects of quasiparticle-phonon interaction in the second order in the amplitude of phonon production are studied in two problems as a natural development of A.B. Migdal's theory of finite Fermi systems. Transitions between excited states and static moments of magic and nonmagic nuclei in excited states, each of which is described in the random-phase approximation, are considered. The results for this problem are found to differ considerably from those in the quasiparticle random-phase approximation. The inclusion of all second-order anharmonic effects in the extended theory of finite Fermi systems that extends the standard theory of finite Fermi systems to the case of taking into account quasiparticle-phonon interaction in order to describe excited states, but which does not take into account all such effects, is also considered. They are taken into account at a level that makes it possible to calculate static moments of odd nuclei-more precisely, the respective equation for the vertex function, which, in the theory of finite Fermi systems, is a basic ingredient that describes the interaction of a nucleus with an external field, is derived. Some numerical results obtained within the recently implemented self-consistent version of the extended theory of finite Fermi systems are also presented for 15 stable and unstable tin isotopes. These results give sufficient grounds to conclude that phenomenological systematics are inapplicable to giant dipole resonances in neutron-rich isotopes. The cross sections for radiative neutron capture that are calculated by usingmicroscopic strength functions for the neutron-rich isotopes 132Sn and 150Sn differ strongly from the cross sections calculated on the basis of a phenomenological description of giant dipole resonances. These results are of paramount importance for astrophysics and for the theory of

  13. γ vibrational band and quasiparticle excitations in 80Sr

    NASA Astrophysics Data System (ADS)

    Sienko, T. A.; Lister, C. J.; Kaye, R. A.

    2003-06-01

    Non-yrast states in 80Sr were populated in the 24Mg(58Ni,2p)80Sr reaction at 200 MeV and their γ decays investigated using Gammasphere, in order to investigate shape softness and quasiparticle excitations. A large data set was collected which was A and Z gated, using the Argonne Fragment Mass Analyzer and a focal plane ion chamber. The excellent channel selection enhanced the sensitivity to energetically nonfavored configurations. Several new rotational bands were found, and many conflicts between previous experiments were resolved. In particular, the gamma vibrational band is now clearly delineated, and more than ten quasiparticle bandheads have been identified. At the highest spins, evidence for a long-predicted shape change was found.

  14. Finite temperature quasiparticle self-consistent GW approximation

    SciTech Connect

    Vanschilfgaarde, Mark; Leonard, Fran­cois; Desjarlais, Michael Paul; Kotani, Takao; Faleev, Sergey V

    2005-10-01

    We present a new ab initio method for electronic structure calculations of materials at finite temperature (FT) based on the all-electron quasiparticle self-consistent GW (QPscGW) approximation and Keldysh time-loop Green's function approach. We apply the method to Si, Ge, GaAs, InSb, and diamond and show that the band gaps of these materials universally decrease with temperature in contrast with the local density approximation (LDA) of density functional theory (DFT) where the band gaps universally increase. At temperatures of a few eV the difference between quasiparticle energies obtained in FT-QPscGW and FT-LDA approaches significantly reduces. This result suggests that existing simulations of very high temperature materials based on the FT-LDA are more justified then it might appear from well-known LDA band gap errors at zero-temperature.

  15. Quasi-Particle Self-Consistent GW for Molecules.

    PubMed

    Kaplan, F; Harding, M E; Seiler, C; Weigend, F; Evers, F; van Setten, M J

    2016-06-14

    We present the formalism and implementation of quasi-particle self-consistent GW (qsGW) and eigenvalue only quasi-particle self-consistent GW (evGW) adapted to standard quantum chemistry packages. Our implementation is benchmarked against high-level quantum chemistry computations (coupled-cluster theory) and experimental results using a representative set of molecules. Furthermore, we compare the qsGW approach for five molecules relevant for organic photovoltaics to self-consistent GW results (scGW) and analyze the effects of the self-consistency on the ground state density by comparing calculated dipole moments to their experimental values. We show that qsGW makes a significant improvement over conventional G0W0 and that partially self-consistent flavors (in particular evGW) can be excellent alternatives. PMID:27168352

  16. Quasiparticle spin resonance and coherence in superconducting aluminium

    PubMed Central

    Quay, C. H. L.; Weideneder, M.; Chiffaudel, Y.; Strunk, C.; Aprili, M.

    2015-01-01

    Conventional superconductors were long thought to be spin inert; however, there is now increasing interest in both (the manipulation of) the internal spin structure of the ground-state condensate, as well as recently observed long-lived, spin-polarized excitations (quasiparticles). We demonstrate spin resonance in the quasiparticle population of a mesoscopic superconductor (aluminium) using novel on-chip microwave detection techniques. The spin decoherence time obtained (∼100 ps), and its dependence on the sample thickness are consistent with Elliott–Yafet spin–orbit scattering as the main decoherence mechanism. The striking divergence between the spin coherence time and the previously measured spin imbalance relaxation time (∼10 ns) suggests that the latter is limited instead by inelastic processes. This work stakes out new ground for the nascent field of spin-based electronics with superconductors or superconducting spintronics. PMID:26497744

  17. Quasiparticle and excitonic gaps of one-dimensional carbon chains.

    PubMed

    Mostaani, E; Monserrat, B; Drummond, N D; Lambert, C J

    2016-06-01

    We report diffusion quantum Monte Carlo (DMC) calculations of the quasiparticle and excitonic gaps of hydrogen-terminated oligoynes and extended polyyne. The electronic gaps are found to be very sensitive to the atomic structure in these systems. We have therefore optimised the geometry of polyyne by directly minimising the DMC energy with respect to the lattice constant and the Peierls-induced carbon-carbon bond-length alternation. We find the bond-length alternation of polyyne to be 0.136(2) Å and the excitonic and quasiparticle gaps to be 3.30(7) and 3.4(1) eV, respectively. The DMC zone-centre longitudinal optical phonon frequency of polyyne is 2084(5) cm(-1), which is consistent with Raman spectroscopic measurements for large oligoynes. PMID:27104222

  18. Quasiparticle spin resonance and coherence in superconducting aluminium

    NASA Astrophysics Data System (ADS)

    Quay, C. H. L.; Weideneder, M.; Chiffaudel, Y.; Strunk, C.; Aprili, M.

    2015-10-01

    Conventional superconductors were long thought to be spin inert; however, there is now increasing interest in both (the manipulation of) the internal spin structure of the ground-state condensate, as well as recently observed long-lived, spin-polarized excitations (quasiparticles). We demonstrate spin resonance in the quasiparticle population of a mesoscopic superconductor (aluminium) using novel on-chip microwave detection techniques. The spin decoherence time obtained (~100 ps), and its dependence on the sample thickness are consistent with Elliott-Yafet spin-orbit scattering as the main decoherence mechanism. The striking divergence between the spin coherence time and the previously measured spin imbalance relaxation time (~10 ns) suggests that the latter is limited instead by inelastic processes. This work stakes out new ground for the nascent field of spin-based electronics with superconductors or superconducting spintronics.

  19. Shear viscosity over entropy density ratio with extended quasiparticles

    NASA Astrophysics Data System (ADS)

    Horváth, M.; Jakovác, A.

    2016-03-01

    We consider an effective field theory description of beyond-quasiparticle excitations aiming to associate the transport properties of the system with the spectral density of states. Tuning various properties of the many-particle correlations, we investigate how the robust microscopic features are translated into the macroscopic observables like shear viscosity and entropy density. The liquid-gas crossover is analysed using several examples. A thermal constraint on the fluidity measure η /s is discussed.

  20. Josephson effect and quasiparticle states in d-wave superconductors

    SciTech Connect

    Tanaka, Yukio; Kashiwaya, Satoshi

    1996-12-31

    A general formula for the Josephson current in a d-wave/insulator/d-wave-superconductor junction is presented by taking account of the zero-energy states formed around the interfaces. For a fixed phase difference between the two superconductors, the current component becomes either positive or negative depending on the injection angle of the quasiparticle. Anomalous temperature dependences are predicted in the maximum Josephson current and in the free energy minima.

  1. Quasiparticle electronic structure of bismuth telluride in the GW approximation

    NASA Astrophysics Data System (ADS)

    Kioupakis, Emmanouil; Tiago, Murilo L.; Louie, Steven G.

    2010-12-01

    The quasiparticle band structure of bismuth telluride (Bi2Te3) , an important thermoelectric material that exhibits topologically insulating surface states, is calculated from first principles in the GW approximation. The quasiparticle energies are evaluated in fine detail in the first Brillouin zone using a Wannier-function interpolation method, allowing the accurate determination of the location of the band extrema (which is in the mirror plane) as well as the values of the quasiparticle band gap (0.17 eV) and effective-mass tensors. Spin-orbit interaction effects were included. The valence band exhibits two distinct maxima in the mirror plane that differ by just 1 meV, giving rise to one direct and one indirect band gap of very similar magnitude. The effective-mass tensors are in reasonable agreement with experiment. The Wannier interpolation coefficients can be used for the tight-binding parametrization of the band structure. Our work elucidates the electronic structure of Bi2Te3 and sheds light on its exceptional thermoelectric and topologically insulating properties.

  2. Lightwave-driven quasiparticle collisions on a subcycle timescale

    NASA Astrophysics Data System (ADS)

    Langer, F.; Hohenleutner, M.; Schmid, C. P.; Poellmann, C.; Nagler, P.; Korn, T.; Schüller, C.; Sherwin, M. S.; Huttner, U.; Steiner, J. T.; Koch, S. W.; Kira, M.; Huber, R.

    2016-05-01

    Ever since Ernest Rutherford scattered α-particles from gold foils, collision experiments have revealed insights into atoms, nuclei and elementary particles. In solids, many-body correlations lead to characteristic resonances—called quasiparticles—such as excitons, dropletons, polarons and Cooper pairs. The structure and dynamics of quasiparticles are important because they define macroscopic phenomena such as Mott insulating states, spontaneous spin- and charge-order, and high-temperature superconductivity. However, the extremely short lifetimes of these entities make practical implementations of a suitable collider challenging. Here we exploit lightwave-driven charge transport, the foundation of attosecond science, to explore ultrafast quasiparticle collisions directly in the time domain: a femtosecond optical pulse creates excitonic electron–hole pairs in the layered dichalcogenide tungsten diselenide while a strong terahertz field accelerates and collides the electrons with the holes. The underlying dynamics of the wave packets, including collision, pair annihilation, quantum interference and dephasing, are detected as light emission in high-order spectral sidebands of the optical excitation. A full quantum theory explains our observations microscopically. This approach enables collision experiments with various complex quasiparticles and suggests a promising new way of generating sub-femtosecond pulses.

  3. Quasiparticle electronic structure of bismuth telluride in the GW approximation

    SciTech Connect

    Kioupakis, Emmanouil; Tiago, Murilo L; Louie, Steven G.

    2010-01-01

    The quasiparticle band structure of bismuth telluride Bi2Te3 , an important thermoelectric material that exhibits topologically insulating surface states, is calculated from first principles in the GW approximation. The quasiparticle energies are evaluated in fine detail in the first Brillouin zone using a Wannier-function interpo- lation method, allowing the accurate determination of the location of the band extrema which is in the mirror plane as well as the values of the quasiparticle band gap 0.17 eV and effective-mass tensors. Spin-orbit interaction effects were included. The valence band exhibits two distinct maxima in the mirror plane that differ by just 1 meV, giving rise to one direct and one indirect band gap of very similar magnitude. The effective- mass tensors are in reasonable agreement with experiment. The Wannier interpolation coefficients can be used for the tight-binding parametrization of the band structure. Our work elucidates the electronic structure of Bi2Te3 and sheds light on its exceptional thermoelectric and topologically insulating properties.

  4. Real Spin in Pseudospin Quasiparticles of Bilayer Quantum Hall systems

    NASA Astrophysics Data System (ADS)

    Roostaei, Bahman; Fertig, H. A.; Mullen, Kieran

    2005-03-01

    Recent experiments have observed enhanced nuclear spin relaxation in double layer quantum Hall systems near the phase boundary between compressible and incompressible states(1). We investigate the electronic spin structure of such systems by calculating the groundstate close to ν= 1 using the Hartree-Fock approximation. This state is a quasiparticle lattice, and we examine the possibility of optimizing its energy by allowing the real spin to tilt away from the majority direction in the quasiparticle cores, analogous to what has been suggested in field theoretic studies of single quasiparticles(2). A broken symmetry of these states introduces low energy spin modes which may couple to the nuclear spins. We calculate both the spin and pseudospin textures for the system near the transition and discuss whether they can account for the observed relaxation rates.1) I.B. Spielman et al., cond-mat/0410092; N. Kumada et al., cond-mat/04104952) S. Ghosh and R. Rajaraman, Phys. Rev. B63, 035304 (2001); Z.F. Izawa and G. Tsitsishvili, cond- mat/0311406.Grants: NSF MRSEC DMR-0080054, NSF EPS-9720651 and NSF DMR- 0454699

  5. Quark susceptibility in a generalized dynamical quasiparticle model

    NASA Astrophysics Data System (ADS)

    Berrehrah, H.; Cassing, W.; Bratkovskaya, E.; Steinert, Th.

    2016-04-01

    The quark susceptibility χq at zero and finite quark chemical potential provides a critical benchmark to determine the quark-gluon-plasma (QGP) degrees of freedom in relation to the results from lattice QCD (lQCD) in addition to the equation of state and transport coefficients. Here we extend the familiar dynamical quasiparticle model (DQPM) to partonic propagators that explicitly depend on the three-momentum with respect to the partonic medium at rest in order to match perturbative QCD (pQCD) at high momenta. Within the extended dynamical quasiparticle model (DQPM*) we reproduce simultaneously the lQCD results for the quark number density and susceptibility and the QGP pressure at zero and finite (but small) chemical potential μq. The shear viscosity η and the electric conductivity σe from the extended quasiparticle model (DQPM*) also turn out to be in close agreement with lattice results for μq=0 . The DQPM*, furthermore, allows one to evaluate the momentum p , temperature T , and chemical potential μq dependencies of the partonic degrees of freedom also for larger μq, which are mandatory for transport studies of heavy-ion collisions in the regime 5 <√{sN N}<10 GeV.

  6. Anti-PD-1/PD-L1 antibody therapy for pretreated advanced nonsmall-cell lung cancer

    PubMed Central

    Zhou, Guo-Wu; Xiong, Ye; Chen, Si; Xia, Fan; Li, Qiang; Hu, Jia

    2016-01-01

    Abstract Background: Anti-PD-1/PD-L1 antibody therapy is a promising clinical treatment for nonsmall-cell lung cancer (NSCLC). However, whether anti-PD-1/PD-L1 antibody therapy can provide added benefits for heavily pretreated patients with advanced NSCLC and whether the efficacy of anti-PD-1/PD-L1 antibody therapy relates to the tumor PD-L1 expression level remain controversial. Thus, this meta-analysis evaluated the efficacy and safety of anti-PD-1/PD-L1 antibody therapy for pretreated patients with advanced NSCLC. Methods: Randomized clinical trials were retrieved by searching the PubMed, EMBASE, ASCO meeting abstract, clinicaltrial.gov, and Cochrane library databases. The pooled hazard ratios (HRs) for overall survival (OS) and progression-free survival (PFS), and odds ratios for the overall response rate and adverse events (AEs) were calculated by STATA software. Results: Three randomized clinical trials involving 1141 pretreated patients with advanced NSCLC were included. These trials all compared the efficacy and safety of anti-PD-1/PD-L1 antibodies (nivolumab and MPDL3280A) with docetaxel. The results suggested that, for all patients, anti-PD-1/PD-L1 therapy could acquire a greater overall response (odds ratio = 1.50, 95% CI: 1.08–2.07, P = 0.015, P for heterogeneity [Ph] = 0.620) and longer OS (HR = 0.71, 95% CI: 0.61–0.81, P < 0.001, Ph = 0.361) than docetaxel, but not PFS (HR = 0.83, 95% CI: 0.65–1.06, P = 0.134; Ph = 0.031). Subgroup analyses according to the tumor PD-L1 expression level showed that anti-PD-1/PD-L1 therapy could significantly improve both OS and PFS in patients with high expressions of PD-L1, but not in those with low expressions. Generally, the rates of grade 3 or 4 AEs of anti-PD-1/PD-L1 therapy were significantly lower than that of docetaxel. However, the risks of pneumonitis and hypothyroidism were significantly higher. Conclusion: Anti-PD-1/PD-L1 antibody therapy may significantly improve

  7. Experiments on Interaction of Quasiparticles with Two-Level-Systems in a Superconducting Phase Qubit

    NASA Astrophysics Data System (ADS)

    Bilmes, Alexander; Lisenfeld, Jürgen; Heimes, Andreas; Zanker, Sebastian; Schön, Gerd; Ustinov, Alexey

    2015-03-01

    Two-Level-Systems (TLS) are one of the main sources of decoherence in superconducting qubits. Some individual and coherent TLS, present in the tunnel barrier of the qubit's Josephson junction, can be coherently operated via the qubit. In the past, experiments on superconducting glasses indicated that quasiparticles may give rise to TLS energy loss similar to Korringa relaxation. We will present experiments in which we use a phase qubit to explore the interaction of single TLS with non-equilibrium quasiparticles. We have implemented in-situ quasiparticle injection by using an on-chip dc-SQUID that is pulse-biased beyond its critical current. The quasiparticle density is calibrated by measuring associated characteristic changes to the qubit resonance frequency and energy relaxation rate. The coherence times of individual TLS is measured in dependence of the non-equilibrium quasiparticle density and compared to thermally generated quasiparticles. PI, KIT, Wolfgang-Gaede-Strasse 1, 76131 Karlsruhe, Germany.

  8. Simultaneous quasiparticle and Josephson tunneling in BSCCO-2212 break junctions.

    SciTech Connect

    Ozyuzer, L.

    1998-10-27

    Tunneling measurements are reported for superconductor-insulator-superconductor (SIS) break junctions on underdoped, optimally-doped, and overdoped single crystals of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} (Bi-2212). The junction I-V characteristics exhibit well-defined quasiparticle current jumps at eV = 2A as well as hysteretic Josephson currents. The quasiparticle branch has been analyzed in the framework of d{sub x{sup 2}-y{sup 2}} (d-wave) superconductivity and indicates that there is preferential tunneling along the lobe directions of the d-wave gap. For overdoped Bi-2212 with T{sub c} = 62 K, the Josephson current is measured as a function of junction resistance, R{sub n}, which varied by two orders of magnitude (1 k{Omega} to 100 k{Omega}). I{sub c}R{sub n} product is proportional to the 0.47 power of I{sub c} and displays a maximum of 7.0 mV. When the hole doping is decreased from overdoped (T{sub c} = 62 K) to the underdoped regime (T{sub c} = 70 K), the average I{sub c}R{sub n} product increases as does the quasiparticle gap. The maximum I{sub c}R{sub n} is {approximately} 40% of the {Delta}/e at each doping level, with a value as high as 25 mV in underdoped Bi-2212.

  9. Electronic structure from relativistic quasiparticle self-consistent GW calculations

    NASA Astrophysics Data System (ADS)

    Blügel, Stefan

    Most theoretical studies of topological insulators (TIs) are based on tight-binding descriptions and density functional theory (DFT). But recently, many-body calculations within the GW approximation attract much attention in the study of these materials. We present an implementation of the quasiparticle self-consistent (QS) GW method where the spin-orbit coupling (SOC) is fully taken into account in each iteration rather than added a posteriori. Within the all-electron FLAPW formalism, we show DFT, one-shot GW , and QS GW calculations for several, well-known TIs. We present a comparison of the calculations to photoemission spectroscopy and show that the GW corrected bands agree much better with experiment. For example, we show that Bi2Se3 is a direct gap semiconductor, in contrast to what was believed for many years by interpreting experimental results on the basis of DFT and that small strains in Bi can lead to a semimetal-to-semiconductor or trivial-to-topological transitions. Quasiparticle calculations for low-dimensional systems are still very demanding. In order to study the topological surface states with an approach based on GW , we use Wannier functions to construct a Hamiltonian that reproduces the many-body band structure of the bulk, and that is used to construct a slab Hamiltonian. With this approach, we discuss the effect of quasiparticle corrections on the surface states of TIs and on the interaction between bulk and surface states Work was funded by the Virtual Institute for Topological Insulators of the Helmholtz Association and carried out in collaboration with Irene Aguilera, Gustav Bihlmayer, and Christoph Friedrich.

  10. Disappearance of quasiparticles in a Bose lattice gas

    NASA Astrophysics Data System (ADS)

    Chen, David; Meldgin, Carolyn; Russ, Philip; DeMarco, Brian; Mueller, Erich

    2016-08-01

    We use a momentum-space hole-burning technique implemented via stimulated Raman transitions to measure the momentum relaxation time for a gas of bosonic atoms trapped in an optical lattice. By changing the lattice potential depth, we observe a smooth crossover between relaxation times larger and smaller than the bandwidth. The latter condition violates the Mott-Ioffe-Regel bound and indicates a breakdown of the quasiparticle picture. We produce a simple kinetic model that quantitatively predicts these relaxation times. Finally, we introduce a cooling technique based upon our hole-burning technique.

  11. Dynamics of Hubbard-Band Quasiparticles in Disordered Optical Lattices

    NASA Astrophysics Data System (ADS)

    Scarola, Vito; Demarco, Brian

    Recent experiments use transport of degenerate Fermi gases in optical lattices (Kondov et al. Phys. Rev. Lett. 114, 083002 (2015) to probe the interplay of disorder and strong interactions. These experiments find evidence for an intriguing insulating phase where quantum diffusion is completely suppressed by strong disorder. Quantitative interpretation of these experiments remains an open problem that requires inclusion of non-zero entropy, strong interaction, and trapping in an Anderson-Hubbard model. We construct a theory of dynamics of Hubbard-band quasiparticles tailored to trapped optical lattice experiments. We compare the theory directly with center-of-mass transport experiments of Kondov et al. with no fitting parameters. The close agreement between theory and experiments shows that the suppression of transport is only partly due to finite entropy effects. We argue that the complete suppression of transport is consistent with short-time, finite size precursors of Anderson localization of Hubbard-band quasiparticles. The combination of our theoretical framework and optical lattice experiments offers an important platform for studying localization in isolated many-body quantum systems. V.W.S. acknowledges support from AFOSR under Grant FA9550-11-1-0313.

  12. Quasiparticles and Fermi liquid behaviour in an organic metal

    PubMed Central

    Kiss, T.; Chainani, A.; Yamamoto, H.M.; Miyazaki, T.; Akimoto, T.; Shimojima, T.; Ishizaka, K.; Watanabe, S.; Chen, C.-T.; Fukaya, A.; Kato, R.; Shin, S.

    2012-01-01

    Many organic metals display exotic properties such as superconductivity, spin-charge separation and so on and have been described as quasi-one-dimensional Luttinger liquids. However, a genuine Fermi liquid behaviour with quasiparticles and Fermi surfaces have not been reported to date for any organic metal. Here, we report the experimental Fermi surface and band structure of an organic metal (BEDT-TTF)3Br(pBIB) obtained using angle-resolved photoelectron spectroscopy, and show its consistency with first-principles band structure calculations. Our results reveal a quasiparticle renormalization at low energy scales (effective mass m*=1.9 me) and ω2 dependence of the imaginary part of the self energy, limited by a kink at ~50 meV arising from coupling to molecular vibrations. The study unambiguously proves that (BEDT-TTF)3Br(pBIB) is a quasi-2D organic Fermi liquid with a Fermi surface consistent with Shubnikov-de Haas results. PMID:23011143

  13. Extinction of quasiparticle interference in underdoped cuprates with coexisting order

    NASA Astrophysics Data System (ADS)

    Andersen, Brian M.; Hirschfeld, P. J.

    2009-04-01

    Scanning tunneling spectroscopy (STS) measurements [Y. Kohsaka , Nature (London) 454, 1072 (2008)] have shown that dispersing quasiparticle interference (QPI) peaks in Fourier-transformed conductance maps disappear as the bias voltage exceeds a certain threshold corresponding to the coincidence of the contour of constant quasiparticle energy with the period-doubled (e.g., antiferromagnetic) zone boundary. Here we show that this may be caused by coexisting order present in the d -wave superconducting phase. We show explicitly how QPI peaks are extinguished in the situation with coexisting long-range spin-density wave order and discuss the connection with the more realistic case where short-range order is created by quenched disorder. Since it is the localized QPI peaks rather than the underlying antinodal states themselves which are destroyed at a critical bias, our proposal resolves a conflict between STS and photoemission spectroscopy regarding the nature of these states. We also study the momentum-summed density of states in the coexisting phase and show how the competing order produces a kink inside the “V”-shaped d -wave superconducting gap in agreement with recent STS measurements [J. W. Alldredge , Nat. Phys. 4, 319 (2008)].

  14. Quasiparticle Trapping in Microwave Kinetic Inductance Strip Detectors

    NASA Astrophysics Data System (ADS)

    Moore, D. C.; Mazing, B. A.; Golwala, S.; Bumble, B.; Gao, J.; Young, B. A.; McHugth, S.; Day, P. K.; LeDuc, H. G.; Zmuidzinas, J.

    2009-12-01

    Microwave Kinetic Inductance Detectors (MKIDs) are thin-film, superconducting resonators, which are attractive for making large detector arrays due to their natural frequency domain multiplexing at GHz frequencies. For X-ray to IR wavelengths, MKIDs can provide high-resolution energy and timing information for each incoming photon. By fabricating strip detectors consisting of a rectangular absorber coupled to MKIDs at each end, high quantum efficiency and spatial resolution can be obtained. A similar geometry is being pursued for phonon sensing in a WIMP dark matter detector. Various materials have been tested including tantalum, tin, and aluminum for the absorbing strip, and aluminum, titanium, and aluminum manganese for the MKID. Initial Ta/Al X-ray devices have shown energy resolutions as good as 62 eV at 6 keV. A Ta/Al UV strip detector with an energy resolution of 0.8 eV at 4.9 eV has been demonstrated, but we find the coupling of the MKIDs to the absorbers is unreliable for these thinner devices. We report on progress probing the thicknesses at which the absorber/MKID coupling begins to degrade by using a resonator to inject quasiparticles directly into the absorber. In order to eliminate the absorber/MKID interface, a modified design for implanted AlMn/Al UV strip detectors was developed, and results showing good transmission of quasiparticles from the absorber to MKID in these devices are presented.

  15. Pump probe spectroscopy of quasiparticle dynamics in cuprate superconductors

    SciTech Connect

    Segre, Gino P.

    2001-05-01

    Pump probe spectroscopy is used to examine the picosecond response of a BSCCO thin film, and two YBCO crystals in the near infrared. The role of pump fluence and temperature have been closely examined in an effort to clarify the mechanism by which the quasiparticles rejoin the condensate. BSCCO results suggest that the recombination behavior is consistent with the d-wave density of states in that quasiparticles appear to relax to the nodes immediately before they rejoin the condensate. The first substantial investigation of polarized pump probe response in detwinned YBCO crystals is also reported. Dramatic doping dependent anisotropies along the a and b axes are observed in time and temperature resolved studies. Among many results, we highlight the discovery of an anomalous temperature and time dependence of a- axis response in optimally doped YBCO. We also report on the first observation of the photoinduced response in a magnetic field. We find the amplitude of the response, and in some cases, the dynamics considerably changed with the application of a 6T field. Finally, we speculate on two of the many theoretical directions stimulated by our results. We find that the two-fluid model suggests a mechanism to explain how changes at very low energies are visible to a high-energy probe. Also discussed are basic recombination processes which may play a role in the observed decay.

  16. Optical-lattice-influenced geometry of quasi-two-dimensional binary condensates and quasiparticle spectra

    NASA Astrophysics Data System (ADS)

    Suthar, K.; Angom, D.

    2016-06-01

    We explore the collective excitation of two-species Bose-Einstein condensates (TBECs) confined in quasi-two-dimensional optical lattices. For this we use a set of coupled discrete nonlinear Schrödinger equations to describe the system and we employ Hartree-Fock-Bogoliubov theory with the Popov approximation to analyze the quasiparticle spectra at zero temperature. The ground-state geometry, evolution of quasiparticle energies, structure of quasiparticle amplitudes, and dispersion relations are examined in detail. We observe that the TBEC acquires a side-by-side density profile when it is tuned from the miscible to the immiscible phase. In addition, the quasiparticle energies are softened as the system is tuned towards phase separation, but harden after phase separation and mode degeneracies are lifted. In terms of structure, in the miscible phase the quasiparticles have well-defined azimuthal quantum numbers, but that is not the case for the immiscible phase.

  17. Charge separation at nanoscale interfaces: Energy-level alignment including two-quasiparticle interactions

    SciTech Connect

    Li, Huashan; Lin, Zhibin; Lusk, Mark T. Wu, Zhigang

    2014-10-21

    The universal and fundamental criteria for charge separation at interfaces involving nanoscale materials are investigated. In addition to the single-quasiparticle excitation, all the two-quasiparticle effects including exciton binding, Coulomb stabilization, and exciton transfer are considered, which play critical roles on nanoscale interfaces for optoelectronic applications. We propose a scheme allowing adding these two-quasiparticle interactions on top of the single-quasiparticle energy level alignment for determining and illuminating charge separation at nanoscale interfaces. Employing the many-body perturbation theory based on Green's functions, we quantitatively demonstrate that neglecting or simplifying these crucial two-quasiparticle interactions using less accurate methods is likely to predict qualitatively incorrect charge separation behaviors at nanoscale interfaces where quantum confinement dominates.

  18. Quasiparticle Self-Recombination in Double STJs Strip X-ray Detectors

    SciTech Connect

    Andrianov, V. A.; Gorkov, V. P.

    2009-12-16

    The quasiparticle self-recombination was considered in the frame of 2D diffusion model of the strip X-ray detectors. The detector consists of a long superconducting strip, which is ended by the trapping layers and superconducting tunnel junctions at each end. The model takes into account the 2D-diffusion of the excess quasiparticles, quasiparticle trapping at the tunnel junctions and quasiparticle losses in the volume of the strip and at the strip boundaries. Self-recombination was described by a quadratic term. As the analytical solution is absent, the numeric calculations were carried out. It has been shown that the self-recombination as well as quasiparticle losses at the strip boundaries caused the dependence of the signals on the photon absorption site in transverse direction. The latter worsens the energy resolution and transforms the spectral line of the detector to nongaussian shape.

  19. G6PD Deficiency

    MedlinePlus

    Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a genetic disorder that is most common in males. About 1 in 10 African American males in the United States has it. G6PD deficiency mainly affects red blood cells, which carry oxygen ...

  20. Friedel oscillations as a probe of fermionic quasiparticles

    NASA Astrophysics Data System (ADS)

    Dalla Torre, Emanuele G.; Benjamin, David; He, Yang; Dentelski, David; Demler, Eugene

    2016-05-01

    When immersed in a sea of electrons, local impurities give rise to density modulations known as Friedel oscillations. In spite of the generality of this phenomenon, the exact shape of these modulations is usually computed only for noninteracting electrons with a quadratic dispersion relation. In actual materials, Friedel oscillations are a viable way to access the properties of electronic quasiparticles, including their dispersion relation, lifetime, and pairing. In this work we analyze the signatures of Friedel oscillations in STM and x-ray scattering experiments, focusing on the concrete example of cuprate superconductors. We identify signatures of Friedel oscillations seeded by impurities and vortices, and explain experimental observations that have been previously attributed to a competing charge order.

  1. Quasiparticle and optical properties of polythiophene-derived polymers

    NASA Astrophysics Data System (ADS)

    Samsonidze, Georgy; Ribeiro, Filipe J.; Cohen, Marvin L.; Louie, Steven G.

    2014-07-01

    Electron donor conjugated polymers blended with electron acceptor fullerene derivatives is one of the promising technologies for organic photovoltaics. However, with the energy conversion efficiency of only 9% in a single bulk heterojunction device structure, these solar cells are not yet competitive with conventional inorganic semiconductor technology. Some of the limitations are large optical band gaps and small electron affinities of polymers preventing the absorption of infrared radiation and leading to energy losses during charge separation at the donor-acceptor interface, respectively. In this work, we compute from first principles the quasiparticle and optical spectra of several different thiophene-, ethyne-, and vinylene-based copolymers using the GW method and the GW plus Bethe-Salpeter equation approach. One of the polymers is identified which has a preferential alignment of the energy levels at the interface with fullerene molecule compared to the reference case of polythiophene.

  2. Quasiparticle Interference Imaging on SmB6

    NASA Astrophysics Data System (ADS)

    Pirie, Harris; He, Yang; Hamidian, Mohammad; Yee, Michael; Kim, Dae-Jeong; Fisk, Zachary; Hoffman, Jennifer

    Theoretical interest in SmB6 as a possible topological Kondo insulator with spin-textured Dirac surface states spanning the bulk hybridization gap has been well supported by recent transport, quantum oscillation, and spin-resolved ARPES experiments. However, the influence of surface reconstruction and polarization on the observed dispersion remains unclear. Scanning tunneling microscopy (STM) and spectroscopy (STS) enable simultaneous measurement of local real- and momentum-space structure through quasiparticle interference (QPI) imaging. We use QPI imaging to detect and measure the dispersion of states near the hybridization gap on a non-polar, 2 × 1 reconstructed surface of SmB6. We compare these results with recent theoretical predictions to gain insight into the low energy excitations of SmB6. This work was supported by the US National Science Foundation under the Grant DMR-1410480.

  3. Nuclear shell structure and response with quasiparticle-vibration coupling

    NASA Astrophysics Data System (ADS)

    Litvinova, Elena; Ring, Peter

    Extensions of the covariant density functional theory by quasiparticle-vibration coupling (QVC) are discussed. The formalism for one-body and two-body propagators in the nuclear medium allows calculations of single-particle energies and spectroscopic factors as well as the response to various types of excitations. In both cases QVC leads to a fragmentation of states, in agreement with experimental observations. Peculiarities of various 2p2h coupling schemes in the nuclear response function are discussed. The theory of the spin-isospin response includes both QVC and pion exchange and provides a framework for calculations of beta-decay, electron capture and charge-exchange reaction characteristics. The presented approaches are illustrated by realistic calculations for medium-mass and heavy nuclei.

  4. Intact quasiparticles at an unconventional quantum critical point

    NASA Astrophysics Data System (ADS)

    Sutherland, M. L.; O'Farrell, E. C. T.; Toews, W. H.; Dunn, J.; Kuga, K.; Nakatsuji, S.; Machida, Y.; Izawa, K.; Hill, R. W.

    2015-07-01

    We report measurements of in-plane electrical and thermal transport properties in the limit T →0 near the unconventional quantum critical point in the heavy-fermion metal β -YbAlB4 . The high Kondo temperature TK≃200 K in this material allows us to probe transport extremely close to the critical point, at unusually small values of T /TK<5 ×10-4 . Here we find that the Wiedemann-Franz law is obeyed at the lowest temperatures, implying that the Landau quasiparticles remain intact in the critical region. At finite temperatures we observe a non-Fermi-liquid T -linear dependence of inelastic-scattering processes to energies lower than those previously accessed. These processes have a weaker temperature dependence than in comparable heavy fermion quantum critical systems, revealing a temperature scale of T ˜0.3 K which signals a sudden change in the character of the inelastic scattering.

  5. Multiple magnetic impurities on surfaces: Scattering and quasiparticle interference

    NASA Astrophysics Data System (ADS)

    Mitchell, Andrew K.; Derry, Philip G.; Logan, David E.

    2015-06-01

    We study systems of multiple interacting quantum impurities deposited on a metallic surface in a three-dimensional host. For the real-space two-impurity problem, using numerical renormalization group calculations, a rich range of behavior is shown to arise due to the interplay between Kondo physics and effective Ruderman-Kittel-Kasuya-Yosida interactions—provided the impurity separation is small. Such calculations allow identification of the minimum impurity separation required for a description in terms of independent impurities, and thereby the onset of the "dilute-impurity limit" in many-impurity systems. A "dilute-cluster" limit is also identified in systems with higher impurity density, where interimpurity interactions are important only within independent clusters. We calculate the quasiparticle interference due to two and many impurities, and explore the consequences of the independent impurity and cluster paradigms. Our results provide a framework to investigate the effects of disorder due to interacting impurities at experimentally relevant surface coverages.

  6. Quasiparticle Interactions in Neutron Matter for Applications in Neutron Stars

    NASA Technical Reports Server (NTRS)

    Wambach, J; Ainsworth, T. L.; Pines, D.

    1993-01-01

    A microscopic model for the quasiparticle interaction in neutron matter is presented. Both-particle (pp) and particle-hole (ph) correlations are included. The pp correlations are treated in semi-empirical way, while ph correlations are incorporated by solving coupled two-body equations for particle-hole interaction and the scattering amplitude of the Fermi sphere. The resulting integral equations self-consistently sum the ph reducible diagrams. Antisymmetry is kept at all stages and hence the forward-scattering sum rules for the scattering amplitude are obeyed. Results for Landau parameters and transport coefficients in a density regime representing the crust of a neutron star are presented. We also estimate the (1)S(sub 0) gap parameter for neutron superfluidity and comment briefly on neutron-star implications.

  7. Quasiparticle relaxation mechanisms in superconductor/ferromagnet bilayers.

    PubMed

    Attanasio, Carmine; Cirillo, Carla

    2012-02-29

    In this paper we review some recent results obtained on superconducting/ferromagnetic (S/F) structures when measuring the dynamic instabilities of the vortex lattice at high driving currents. The role played on the non-equilibrium properties of the hybrids by both the ferromagnetic and the superconducting materials has been analyzed with a special focus on the values and the temperature dependence of the quasiparticle relaxation times, τ(E). Knowledge of the relaxation mechanisms in these systems is extremely important in view of possible applications since it can drive the optimal choice of both materials to realize, in particular, ultrafast superconducting single photon detectors based on S/F hybrid structures. PMID:22314798

  8. Source conductance scaling for high frequency superconducting quasiparticle receivers

    NASA Technical Reports Server (NTRS)

    Ke, Qing; Feldman, M. J.

    1992-01-01

    It has been suggested that the optimum source conductance G(sub s) for the superconductor-insulator-superconductor (SIS) quasiparticle mixer should have a l/f dependence. This would imply that the critical current density of SIS junctions used for mixing should increase as frequency squared, a stringent constraint on the design of submillimeter SIS mixers, rather than in simple proportion to frequency as previously believed. We have used Tucker's quantum theory of mixing for extensive numerical calculations to determine G(sub s) for an optimized SIS receiver. We find that G(sub s) is very roughly independent of frequency (except for the best junctions at low frequency), and discuss the implications of our results for the design of submillimeter SIS mixers.

  9. Quasiparticle scattering image in hidden order phases and chiral superconductors

    NASA Astrophysics Data System (ADS)

    Thalmeier, Peter; Akbari, Alireza

    2016-02-01

    The technique of Bogoliubov quasiparticle interference (QPI) has been successfully used to investigate the symmetry of unconventional superconducting gaps, also in heavy fermion compounds. It was demonstrated that QPI can distinguish between the d-wave singlet candidates in CeCoIn5. In URu2Si2 presumably a chiral d-wave singlet superconducting (SC) state exists inside a multipolar hidden order (HO) phase. We show that hidden order leaves an imprint on the symmetry of QPI pattern that may be used to determine the essential question whether HO in URu2Si2 breaks the in-plane rotational symmetry or not. We also demonstrate that the chiral d-wave SC gap leads to a crossover to a quasi-2D QPI spectrum below Tc which sharpens the HO features. Furthermore we investigate the QPI image of chiral p-wave multigap superconductor Sr2RuO4.

  10. Aspects of nodal quasiparticle transport in high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Smith, Michael F.

    Various low-temperature thermodynamic and transport properties of high TC superconductors at temperatures well below TC are studied theoretically under the assumption that the low-energy excited states can be regarded as independent Bogolubov quasiparticles near the nodes of the superconducting order parameter. In the limiting case of temperatures well above that corresponding to the impurity scattering rate, a Boltzmann-equation description of the quasiparticle distribution is used to study thermal and electrical transport for several scattering mechanisms. In particular, the dominant scattering mechanism for the relaxation of microwave electrical currents well below TC is identified, and the observed temperature dependence of the microwave conductivity data in optimally-doped YBa2Cu3O7-delta thus explained. The Knight shift and nuclear spin relaxation rate at temperatures well above the impurity scattering rate are also calculated and compared with available data. In the opposite limiting case of temperatures well below that corresponding to the impurity scattering rate, the sound attenuation and electron-phonon heat transfer rate are calculated. A model for the electron-phonon interaction in square-lattice tight-binding materials is developed and used to explain the huge measured anisotropy of the normal-state sound attenuation in the unconventional superconductor Sr2RuO4 and to rule out certain candidates for the order parameter symmetry of this material. A calculation of the electron-phonon heat transfer rate for d-wave superconductors gives the dependence of this quantity on various material parameters. Finally, the result for the electron-phonon heat transfer rate is used to explain the origin of the anomalous downturns in the thermal conductivity that have been observed in both the normal and superconducting state of cuprate superconductors, most notably in Pr2-xCe xCuO7-delta.

  11. Quasiparticle spectrum and plasmonic excitations in the topological insulator Sb2Te3

    NASA Astrophysics Data System (ADS)

    Nechaev, I. A.; Aguilera, I.; De Renzi, V.; di Bona, A.; Lodi Rizzini, A.; Mio, A. M.; Nicotra, G.; Politano, A.; Scalese, S.; Aliev, Z. S.; Babanly, M. B.; Friedrich, C.; Blügel, S.; Chulkov, E. V.

    2015-06-01

    We report first-principles G W results on the dispersion of the bulk band-gap edges in the three-dimensional topological insulator Sb2Te3 . We find that, independently of the reference density-functional-theory band structure and the crystal-lattice parameters used, the one-shot G W corrections enlarge the fundamental band gap, bringing its value in close agreement with experiment. We conclude that the G W corrections cause the displacement of the valence-band maximum (VBM) to the Γ point, ensuring that the surface-state Dirac point lies above the VBM. We extend our study to the analysis of the electron-energy-loss spectrum (EELS) of bulk Sb2Te3 . In particular, we perform energy-filtered transmission electron microscopy and reflection EELS measurements. We show that the random-phase approximation with the G W quasiparticle energies and taking into account virtual excitations from the semicore states leads to good agreement with our experimental data.

  12. Decoherence and Decay of Two-level Systems due to Non-equilibrium Quasiparticles

    NASA Astrophysics Data System (ADS)

    Zanker, Sebastian; Marthaler, Michael; Schön, Gerd; Institut für Theoretische Festkörperphysik Team

    It is frequently observed that even at very low temperatures the number of quasiparticles in superconducting materials is higher than predicted by standard BCS-theory. These quasiparticles can interact with two-level systems, such as superconducting qubits or two-level systems (TLS) in the amorphous oxide layer of a Josephson junction. This interaction leads to decay and decoherence of the TLS, with specific results, such as the time dependence, depending on the distribution of quasiparticles and the form of the interaction. We study the resulting decay laws for different experimentally relevant protocols. This work was supported by the German-Israeli Foundation for Scientific Research and Development (GIF).

  13. Resonant tunneling and the quasiparticle lifetime in graphene/boron nitride/graphene heterostructures

    NASA Astrophysics Data System (ADS)

    Guerrero-Becerra, Karina A.; Tomadin, Andrea; Polini, Marco

    2016-03-01

    Tunneling of quasiparticles between two nearly aligned graphene sheets produces resonant current-voltage characteristics because of the quasiexact conservation of in-plane momentum. We claim that, in this regime, vertical transport in graphene/boron nitride/graphene heterostructures carries precious information on electron-electron interactions and the quasiparticle spectral function of the two-dimensional electron system in graphene. We present extensive microscopic calculations of the tunneling spectra with the inclusion of quasiparticle lifetime effects and elucidate the range of parameters (interlayer bias, temperature, twist angle, and gate voltage) under which electron-electron interaction physics emerges.

  14. Particle-number conserving analysis for the 2-quasiparticle and high-K multi-quasiparticle states in doubly-odd 174,176Lu

    NASA Astrophysics Data System (ADS)

    Li, Bing-Huan; Zhang, Zhen-Hua; Lei, Yi-An

    2013-01-01

    Two-quasiparticle bands and low-lying excited high-K four-, six-, and eight-quasiparticle bands in the doubly-odd174,176 Lu are analyzed by using the cranked shell model (CSM) with the pairing correlations treated by a particle-number conserving (PNC) method, in which the blocking effects are taken into account exactly. The proton and neutron Nilsson level schemes for174,176, Lu are taken from the adjacent odd-A Lu and Hf isotopes, which are adopted to reproduce the experimental bandhead energies of the one-quasiproton and one-quasineutron bands of these odd-A Lu and Hf nuclei, respectively. Once the quasiparticle configurations are determined, the experimental bandhead energies and the moments of inertia of these two- and multi-quasiparticle bands are well reproduced by PNC-CSM calculations. The Coriolis mixing of the low-K (K=|Ω1-Ω2|) two-quasiparticle band of the Gallagher-Moszkowski doublet with one nucleon in the Ω=1/2 orbital is analyzed.

  15. PD-1, PD-L1 and PD-L2 expression in mouse prostate cancer

    PubMed Central

    Yang, Shijie; Zhang, Qiuyang; Liu, Sen; Wang, Alun R; You, Zongbing

    2016-01-01

    Programmed cell death protein 1 (PD-1) and its ligands PD-L1 and PD-L2 play critical roles in maintaining an immunosuppressive tumor microenvironment. The purpose of the present study was to assess expression of PD-1, PD-L1, and PD-L2 in mouse prostate tumors. A total of 33 mouse prostate tumors derived from Pten-null mice were examined using immunohistochemical staining for PD-1, PD-L1, and PD-L2. The animals were either with interleukin-17 receptor c (Il-17rc) wild-type or knockout genotype, or fed with regular diet or high-fat diet to 30 weeks of age. We found that Il-17rc wild-type mouse prostate tumors had significantly higher levels of PD-1, PD-L1, and PD-L2 than Il-17rc knockout mouse prostate tumors. High-fat diet-induced obese mice had significantly higher levels of PD-1, PD-L1, and PD-L2 in their prostate tumors than lean mice fed with regular diet. Increased expression of PD-1, PD-L1, and PD-L2 was associated with increased number of invasive prostate tumors formed in the Il-17rc wild-type and obese mice compared to the Il-17rc knockout and lean mice, respectively. Our findings suggest that expression of PD-1, PD-L1, and PD-L2 may enhance development of mouse prostate cancer through creating an immunosuppressive tumor microenvironment. PMID:27069956

  16. Development of a Spatially Resolved ^3He Quasi-Particle Detector

    NASA Astrophysics Data System (ADS)

    Barquist, C. S.; Zheng, P.; Jiang, W. G.; Lee, Y.; Yoon, Y. K.; Schumann, T.; Nogan, J.; Lilly, M.

    2016-05-01

    Andreev surface bound sates are known to exist on the boundaries of superfluid ^3He-B. However, the detailed nature of their interaction with bulk quasi-particles is not well known. In a manner similar to angle-resolved photo-emission spectroscopy, surface states can be probed by measuring the change in momentum of bulk quasi-particles scattered from the surface. In order to make such a measurement, we have designed a spatially resolved quasi-particle detector. The detector consists of an array of micro-machined resonators, which are sensitive to quasi-particle flux. The detector is based on previously developed micro-machined resonators, which have been successfully used to study superfluid ^3He-B and ^4He. Presented here is the design of the detector and the fabrication procedure.

  17. Phonon Quasi-Particles and Anharmonic Free Energy in Complex Systems

    NASA Astrophysics Data System (ADS)

    Zhang, Dong-Bo; Sun, Tao; Wentzcovitch, Renata

    2014-03-01

    We use a hybrid strategy to obtain anharmonic frequency shifts and lifetimes of phonon quasi-particles from first principles molecular dynamics simulations in modest size supercells. This approach is effective irrespective of crystal structure complexity and facilitates calculation of full anharmonic phonon dispersions, as long as phonon quasi-particles are well defined. We validate this approach to obtaining anharmonic effects with calculations in MgSiO3-perovskite, the major Earth forming mineral phase. First, we reproduce irregular temperature induced frequency shifts of well characterized Raman modes. Second, we combine the phonon gas model (PGM) with quasi-particle frequencies and reproduce free energies obtained using a direct approach such as thermodynamic integration. Using thoroughly sampled quasi-particle dispersions with the PGM we then obtain first-principles anharmonic free energy in the thermodynamic limit (N --> ∞) . Research supported by Abu Dhabi-Minnesota Institute for Research Excellence (ADMIRE) and NSF grant EAR-1047629.

  18. Tunable quasiparticle trapping in Meissner and vortex states of mesoscopic superconductors

    NASA Astrophysics Data System (ADS)

    Taupin, M.; Khaymovich, I. M.; Meschke, M.; Mel'Nikov, A. S.; Pekola, J. P.

    2016-03-01

    Nowadays, superconductors serve in numerous applications, from high-field magnets to ultrasensitive detectors of radiation. Mesoscopic superconducting devices, referring to those with nanoscale dimensions, are in a special position as they are easily driven out of equilibrium under typical operating conditions. The out-of-equilibrium superconductors are characterized by non-equilibrium quasiparticles. These extra excitations can compromise the performance of mesoscopic devices by introducing, for example, leakage currents or decreased coherence time in quantum devices. By applying an external magnetic field, one can conveniently suppress or redistribute the population of excess quasiparticles. In this article, we present an experimental demonstration and a theoretical analysis of such effective control of quasiparticles, resulting in electron cooling both in the Meissner and vortex states of a mesoscopic superconductor. We introduce a theoretical model of quasiparticle dynamics, which is in quantitative agreement with the experimental data.

  19. Normal State Spectral Lineshapes of Nodal Quasiparticles in Single Layer Bi2201 Superconductor

    SciTech Connect

    Lanzara, A.

    2010-04-30

    A detailed study of the normal state photoemission lineshapes and quasiparticle dispersion for the single layer Bi{sub 2}Sr{sub 2-x}La{sub x}CuO{sub 6+{delta}}(Bi2201) superconductor is presented. We report the first experimental evidence of a double peak structure and a dip of spectral intensity in the energy distribution curves (EDCs) along the nodal direction. The double peak structure is well identified in the normal state, up to ten times the critical temperature. As a result of the same self-energy effect, a strong mass renormalization of the quasiparticle dispersion, i.e. kink, and an increase of the quasiparticle lifetime in the normal state are also observed. Our results provide unambiguous evidence on the existence of bosonic excitation in the normal state, and support a picture where nodal quasiparticles are strongly coupled to the lattice.

  20. Tunable quasiparticle trapping in Meissner and vortex states of mesoscopic superconductors

    PubMed Central

    Taupin, M.; Khaymovich, I. M.; Meschke, M.; Mel'nikov, A. S.; Pekola, J. P.

    2016-01-01

    Nowadays, superconductors serve in numerous applications, from high-field magnets to ultrasensitive detectors of radiation. Mesoscopic superconducting devices, referring to those with nanoscale dimensions, are in a special position as they are easily driven out of equilibrium under typical operating conditions. The out-of-equilibrium superconductors are characterized by non-equilibrium quasiparticles. These extra excitations can compromise the performance of mesoscopic devices by introducing, for example, leakage currents or decreased coherence time in quantum devices. By applying an external magnetic field, one can conveniently suppress or redistribute the population of excess quasiparticles. In this article, we present an experimental demonstration and a theoretical analysis of such effective control of quasiparticles, resulting in electron cooling both in the Meissner and vortex states of a mesoscopic superconductor. We introduce a theoretical model of quasiparticle dynamics, which is in quantitative agreement with the experimental data. PMID:26980225

  1. A Quasiparticle Detector for Quantum Turbulence Imaging in Superfluid 3 He-B

    NASA Astrophysics Data System (ADS)

    Fisher, Shaun; Bradley, Ian; Clovevcko, Marcel; Ahlstrom, Sean; Guise, Ed; Haley, Rich; Holt, Steve; Pickett, George; Schanon, Roch; Tsepelin, Viktor; Woods, Andrew

    2014-03-01

    We describe the development of a two-dimensional quasiparticle detector to visualise quantum turbulence in superfluid 3He-B at ultra-low temperatures. The detector consists of 25 pixels each containing a miniature quartz tuning fork. The damping on each fork provides a measure of the local quasiparticle flux. The detector is illuminated by a beam of ballistic quasiparticles generated from a near-by black-body radiator. Vortices have a large cross-section for Andreev reflecting ballistic quasiparticles at low temperatures. We generate a tangle of vortices (quantum turbulence) in the path of the beam using a vibrating wire resonator. The vortices cast a shadow onto the face of the detector due to the Andreev reflection. This allows us to image the vortex tangle and to investigate the tangle dynamics. We describe the detector and present some preliminary results.

  2. Tunable quasiparticle trapping in Meissner and vortex states of mesoscopic superconductors.

    PubMed

    Taupin, M; Khaymovich, I M; Meschke, M; Mel'nikov, A S; Pekola, J P

    2016-01-01

    Nowadays, superconductors serve in numerous applications, from high-field magnets to ultrasensitive detectors of radiation. Mesoscopic superconducting devices, referring to those with nanoscale dimensions, are in a special position as they are easily driven out of equilibrium under typical operating conditions. The out-of-equilibrium superconductors are characterized by non-equilibrium quasiparticles. These extra excitations can compromise the performance of mesoscopic devices by introducing, for example, leakage currents or decreased coherence time in quantum devices. By applying an external magnetic field, one can conveniently suppress or redistribute the population of excess quasiparticles. In this article, we present an experimental demonstration and a theoretical analysis of such effective control of quasiparticles, resulting in electron cooling both in the Meissner and vortex states of a mesoscopic superconductor. We introduce a theoretical model of quasiparticle dynamics, which is in quantitative agreement with the experimental data. PMID:26980225

  3. Thermal Transport by Ballistic Quasiparticles in Superfluid 3He-B in the Low Temperature Limit

    SciTech Connect

    Bradley, D. I.; Fisher, S. N.; Guenault, A. M.; Haley, R. P.; Martin, H.; Pickett, G. R.; Roberts, J. E.; Tsepelin, V.

    2006-09-07

    In the temperature range below 0.2Tc, the gas of thermal excitations from the superfluid 3He-B ground state is in the ultra-dilute ballistic regime. Here we discuss preliminary measurements of the transport properties of this quasiparticle gas in a cell of cylindrical geometry with dimensions much smaller than any mean free path. The vertical cylinder, constructed from epoxy-coated paper, has vibrating wire resonator (VWR) heaters and thermometers at the top and bottom, and a small aperture at the top which provides the only exit for quasiparticles. Using the thermometer VWRs, we measure the difference in quasiparticle density between the top and bottom of the tube when we excite the top or bottom VWR heater. This gives information about the transport of energy along the cylindrical 3He sample and hence about the scattering behaviour involved when a quasiparticle impinges on the cylinder wall.

  4. Quasiparticle theory of transport coefficients for hadronic matter at finite temperature and baryon density

    NASA Astrophysics Data System (ADS)

    Albright, M.; Kapusta, J. I.

    2016-01-01

    We develop a flexible quasiparticle theory of transport coefficients of hot hadronic matter at finite baryon density. We begin with a hadronic quasiparticle model which includes a scalar and a vector mean field. Quasiparticle energies and the mean fields depend on temperature and baryon chemical potential. Starting with the quasiparticle dispersion relation, we derive the Boltzmann equation and use the Chapman-Enskog expansion to derive formulas for the shear and bulk viscosities and thermal conductivity. We obtain both relaxation-time approximation formulas and more general integral equations. Throughout the work, we explicitly enforce the Landau-Lifshitz conditions of fit and ensure the theory is thermodynamically self-consistent. The derived formulas should be useful for predicting the transport coefficients of the hadronic phase of matter produced in heavy-ion collisions at the Relativistic Heavy Ion Collider and at other accelerators.

  5. Anomalous Quasiparticles on the Domain Wall Between Topological Insulators and Spin Ice Compounds

    NASA Astrophysics Data System (ADS)

    Kanazawa, I.; Sasaki, T.

    We have discussed the behavior of anomalous quasiparticle with fractional electronic charge on the domain wall between topological insulators and spin ice compounds from the standpoint of the field-theoretical formula.

  6. Quasiparticle and Optical Excitations in Solid Ne and Ar: GW and BSE Approximations

    SciTech Connect

    Patterson, Charles H.; Galamic-Mulaomerovic, S.

    2007-12-26

    The GW approximation and the Bethe-Salpeter equation (BSE) have been used to calculate quasiparticle and optical excitations in solid Ne and Ar. Absolute positions of quasiparticle and quasihole energies are found to be in very good agreement with experimental values. Binding energies of Frenkel excitons for these systems calculated using the BSE are also in good agreement with experiment. Splitting of excitons into longitudinal and transverse modes is calculated and found to be approximately twice the experimentally measured value.

  7. One and two quasiparticle state densities in the ESM: Combinatorial approach vs. exact results

    SciTech Connect

    Noy, R.C.; Silvera, M.P.; Martinez, R.P.

    1994-12-31

    An exact method proposed by Zhang and Yang to calculate the effect of Pauli exclusion principle in particle-hole state densities is used to derive closed formulas for one and two quasiparticle state densities. Analytical results are tested against exact combinatorial calculation in the framework of BCS theory using equidistant shell model spectra. Relationship between particle-hole and quasiparticle state densities is discussed.

  8. Quasiparticle Self-Recombination in Superconducting Tunnel Junction X-ray Detectors

    NASA Astrophysics Data System (ADS)

    Andrianov, V. A.; Gorkov, V. P.

    2016-07-01

    The mathematical modelling of the X-ray detectors based on superconducting tunnel junctions was performed taking into account diffusion of nonequilibrium quasiparticles, quasiparticle tunnelling and losses, self-recombination and exchange 2Δ -phonons. The effects of recombination were examined in detail. The dependence of the signal on the photon energy and the energy resolution of the detectors were considered. A new analytical expression for a contribution of self-recombination to the signal was obtained.

  9. Connecting neutron star observations to the high density equation of state of a quasiparticle model

    NASA Astrophysics Data System (ADS)

    Yan, Yan; Cao, Jing; Luo, Xin-Lian; Sun, Wei-Min; Zong, Hongshi

    2012-12-01

    The observation of the 1.97±0.04 solar-mass neutronlike star gives constraint on the equation of state of cold, condensed matter. In this paper, the equation of state for both the pure quark star and the hybrid star with a quark core described by the quasiparticle model are considered. The parameters of the quasiparticle model that affect the mass of both the quark star and the hybrid star can be constrained by the observation.

  10. Behavior of one-quasiparticle levels in odd isotonic chains of heavy nuclei

    SciTech Connect

    Adamian, G. G.; Antonenko, N. V.; Kuklin, S. N.; Malov, L. A.; Lu, B. N.; Zhou, S. G.

    2011-08-15

    The low-lying one-quasiparticle states are studied in the isotonic chains with N=147, 149, 151, 153, and 155 within the microscopic-macroscopic and self-consistent approaches. The energies of one-quasiparticle states change rather smoothly in the isotonic chains if there is no cross of the proton subshell. The {alpha}-decay schemes of several nuclei are suggested. The isomeric states in the odd isotopes of Fm and No are discussed.

  11. Harmonic and reactive behavior of the quasiparticle tunnel current in SIS junctions

    NASA Astrophysics Data System (ADS)

    Rashid, H.; Desmaris, V.; Pavolotsky, A.; Belitsky, V.

    2016-04-01

    In this paper, we show theoretically and experimentally that the reactive quasiparticle tunnel current of the superconductor tunnel junction could be directly measured at specific bias voltages for the higher harmonics of the quasiparticle tunnel current. We used the theory of quasiparticle tunneling to study the higher harmonics of the quasiparticle tunnel current in superconducting tunnel junction in the presence of rf irradiation. The impact of the reactive current on the harmonic behavior of the quasiparticle tunnel current was carefully studied by implementing a practical model with four parameters to model the dc I-V characteristics of the superconducting tunnel junction. The measured reactive current at the specific bias voltage is in good agreement with our theoretically calculated reactive current through the Kramers-Kronig transform. This study also shows that there is an excellent correspondence between the behavior of the predicted higher harmonics using the previously established theory of quasiparticle tunnel current in superconducting tunnel junctions by J.R. Tucker and M.J. Feldman and the measurements presented in this paper.

  12. Synthesis and characterization of Pd(0), PdS, and Pd@PdO core-shell nanoparticles by solventless thermolysis of a Pd-thiolate cluster

    NASA Astrophysics Data System (ADS)

    Jose, Deepa; Jagirdar, Balaji R.

    2010-09-01

    Colloids of palladium nanoparticles have been prepared by the solvated metal atom dispersion (SMAD) method. The as-prepared Pd colloid consists of particles with an average diameter of 2.8±0.1 nm. Digestive ripening of the as-prepared Pd colloid, a process involving refluxing the as-prepared colloid at or near the boiling point of the solvent in the presence of a passivating agent, dodecanethiol resulted in a previously reported Pd-thiolate cluster, [Pd(SC 12H 25) 2] 6 but did not render the expected narrowing down of the particle size distribution. Solventless thermolysis of the Pd-thiolate complex resulted in various Pd systems such as Pd(0), PdS, and Pd@PdO core-shell nanoparticles thus demonstrating its versatility. These Pd nanostructures have been characterized using high-resolution electron microscopy and powder X-ray diffraction methods.

  13. ARPES view of orbitally resolved quasiparticle lifetimes in iron pnictides

    NASA Astrophysics Data System (ADS)

    Brouet, Véronique; LeBoeuf, David; Lin, Ping-Hui; Mansart, Joseph; Taleb-Ibrahimi, Amina; Le Fèvre, Patrick; Bertran, François; Forget, Anne; Colson, Dorothée

    2016-02-01

    We study with angle-resolved photoemission spectroscopy (ARPES) the renormalization and quasiparticle lifetimes of the dx y and dx z/dy z orbitals in two iron pnictides, LiFeAs and Ba (Fe0.92Co0.08 )2As2 (Co8). We find that both quantities depend on orbital character rather than on the position on the Fermi surface (for example, hole or electron pocket). In LiFeAs, the renormalizations are larger for dx y, while they are similar for both types of orbitals in Co8. The most salient feature, which proved robust against all the ARPES caveats we could think of, is that the lifetimes for dx y exhibit a markedly different behavior than those for dx z/dy z. They have smaller values near EF and exhibit larger ω and temperature dependences. While the behavior of dx y is compatible with a Fermi-liquid description, that is not the case for dx z/dy z. This situation should have important consequences for the physics of iron pnictides, which have not been considered up to now. More generally, it raises interesting questions about how a Fermi-liquid regime can be established in a multiband system with small effective bandwidths.

  14. Planar Quasiparticle Tunneling Spectroscopy of Bi2212 Single Crystals

    NASA Astrophysics Data System (ADS)

    Aubin, H.; Pugel, D. E.; Greene, L. H.; Jian, S.; Hinks, D.

    2000-03-01

    Using techniques of quasi-particle planar tunneling spectroscopy, the in-plane density of states of the high-Tc superconductor Bi2212 is investigated. The 0.3 mm thick single crystals used allow tunneling into crystal faces of various crystallographic orientations, and a newly-developed technique allows for exposing these crystal faces with little damage. The planar tunnel junction is fabricated with the insulating dielectric CaF2 as the tunnel barrier and a noble metal counter-electrode. The tunneling conductance measured with the current injected perpendicular to the copper-oxide planes differs substantially from that measured with the current injected parallel to the planes. The in-plane tunneling density of states exhibits a zero-bias conductance peak which is attributed to the formation of an Andreev bound state, as predicted to occur at the ab-plane oriented surface of a d-wave superconductor. Tunneling spectra as a function of temperature, magnetic field and crystallographic orientation will be presented. These results will be discussed and compared with those obtained previously on YBCO-based tunnel junctions. This research was supported by the NSF-STCS (NSF-DMR 91-20000). DGH acknowledges support by the US DOE (W-31-109-ENG-38).

  15. Maximally-localized Wannier functions for GW quasiparticles

    NASA Astrophysics Data System (ADS)

    Hamann, D. R.; Vanderbilt, David

    2009-03-01

    Recent efforts carrying the GW many-body approximation to self-consistency have given improved electronic structure results.^1 Maximally-localized Wannier functions^2 formed from the quasiparticle wave functions^3 provide an efficient and highly accurate basis for interpolating the SCGW bands from a coarse Brillouin-zone mesh to symmetry lines. Since the MLWF's correspond to chemists' bond orbitals, they potentially also provide insight into the qualitative effects of the improved treatment of correlations in SCGW compared to LDA. We report results on SrTiO3, solid Ar, and molecular CO. Band interpolation is accurate and effective for both solids. Small shifts in the degree of hybridization can be visualized for some of the SrTiO3 and CO MLWF's. In Ar, individual conduction-band Bloch functions were found to have large differences between LDA and SCGW.^1 However, a manifold of 9 d and spd-hybrid MLWF's which proved to be the minimum necessary for the lower conduction bands showed minimal differences in the two cases. A fully-functional interface to the WANNIER90 library within the SCGW-capable ABINIT code has been implemented and will be publicly available in the near future. 1. F. Bruneval et al., Phys. Rev. B 74, 045102 (2006). 2. N. Marzari and D. Vanderbilt, Phys. Rev. B 56, 12 847 (1997). 3. M. van Schilfgaarde et al., Phys. Rev. Lett. 96, 226402 (2006).

  16. Collectivity of 98Pd

    NASA Astrophysics Data System (ADS)

    Fransen, C.; Blazhev, A.; Dewald, A.; Jolie, J.; Mü; cher, D.; Möller, O.; Pissulla, T.

    2009-01-01

    The N = 52 nucleus 98Pd was investigated at the Cologne TANDEM accelerator both with the Cologne plunger using the recoil distance Doppler-shift method (RDDS) and with the Cologne HORUS spectrometer for a γγ angular correlation experiment. For the first time lifetimes of yrast states and highly excited low-spin states were measured in 98Pd and the low-spin level scheme was extended. From our data we were able to interpret 98Pd as a nucleus that exhibits some collective features, but is obviously much less collective than the neighboring N = 52 isotones 94Mo and 96Ru due to its closeness to doubly-magic 100Sn.

  17. Synthesis and characterization of Pd(0), PdS, and Pd-PdO core-shell nanoparticles by solventless thermolysis of a Pd-thiolate cluster

    SciTech Connect

    Jose, Deepa; Jagirdar, Balaji R.

    2010-09-15

    Colloids of palladium nanoparticles have been prepared by the solvated metal atom dispersion (SMAD) method. The as-prepared Pd colloid consists of particles with an average diameter of 2.8{+-}0.1 nm. Digestive ripening of the as-prepared Pd colloid, a process involving refluxing the as-prepared colloid at or near the boiling point of the solvent in the presence of a passivating agent, dodecanethiol resulted in a previously reported Pd-thiolate cluster, [Pd(SC{sub 12}H{sub 25}){sub 2}]{sub 6} but did not render the expected narrowing down of the particle size distribution. Solventless thermolysis of the Pd-thiolate complex resulted in various Pd systems such as Pd(0), PdS, and Pd-PdO core-shell nanoparticles thus demonstrating its versatility. These Pd nanostructures have been characterized using high-resolution electron microscopy and powder X-ray diffraction methods. - Graphical abstract: Solventless thermolysis of a single palladium-thiolate cluster affords various Pd systems such as Pd(0), Pd-PdO core-shell, and PdS nanoparticles demonstrating the versatility of the precursor and the methodology.

  18. G6PD: The Test

    MedlinePlus

    ... is it used? Glucose-6-phosphate dehydrogenase (G6PD) enzyme testing is used to screen for and help ... and the District of Columbia. G6PD is an enzyme found in all cells, including red blood cells ( ...

  19. Emergence of massless Dirac quasiparticles in correlated hydrogenated graphene with broken sublattice symmetry

    NASA Astrophysics Data System (ADS)

    Seki, Kazuhiro; Shirakawa, Tomonori; Zhang, Qinfang; Li, Tao; Yunoki, Seiji

    2016-04-01

    Using the variational cluster approximation (VCA) and the cluster perturbation theory, we study the finite-temperature phase diagram of a half-depleted periodic Anderson model on the honeycomb lattice at half-filling for a model of graphone, i.e., single-side hydrogenated graphene. The ground state of this model is found to be ferromagnetic (FM) semimetal. The origin of this FM state is attributed to the instability of a flat band located at the Fermi energy in the noninteracting limit and is smoothly connected to the Lieb-Mattis-type ferromagnetism. The spin-wave dispersion in the FM state is linear in momentum at zero temperature but becomes quadratic at finite temperatures, implying that the FM state is fragile against thermal fluctuations. Indeed, our VCA calculations find that the paramagnetic (PM) state dominates the finite-temperature phase diagram. More surprisingly, we find that massless Dirac quasiparticles with the linear energy dispersion emerge at the Fermi energy upon introducing the electron correlation U at the impurity sites in the PM phase. The Dirac Fermi velocity is found to be highly correlated to the quasiparticle weight of the emergent massless Dirac quasiparticles at the Fermi energy and monotonically increases with U . These unexpected massless Dirac quasiparticles are also examined with the Hubbard-I approximation and the origin is discussed in terms of the spectral weight redistribution involving a large energy scale of U . Considering an effective quasiparticle Hamiltonian which reproduces the single-particle excitations obtained by the Hubbard-I approximation, we argue that the massless Dirac quasiparticles are protected by the electron correlation. Our finding therefore provides a unique example of the emergence of massless Dirac quasiparticles due to dynamical electron correlations without breaking any spatial symmetry. The experimental implications of our results for graphone as well as a graphene sheet on transition-metal substrates

  20. The application of the fractional exclusion statistics to the BCS theory-A redefinition of the quasiparticle energies

    NASA Astrophysics Data System (ADS)

    Anghel, Dragoş-Victor; Nemnes, George Alexandru

    2016-09-01

    The effective energy of a superconductor Eeff(T) at temperature T is defined as the difference between the total energy at temperature T and the total energy at 0 K. We call the energy of the condensate, Ec, the difference between Eeff and the sum of the quasiparticle energies Eqp. Ec, Eqp, as well as the BCS quasiparticle energy ɛ are positive and depend on the gap energy Δ, which, in turn, depends on the populations of the quasiparticle states (equivalently, they depend on T). So, from the energetic point of view, the superconductor is a Fermi liquid of interacting quasiparticles. We show that the choice of quasiparticles is not unique, but there is an infinite range of possibilities. Some of these possibilities have been explored in the context of the fractional exclusion statistics (FES), which is a general method of describing interacting particle systems as ideal gases. We apply FES here and transform the Fermi liquid of BCS excitations into an ideal gas by redefining the quasiparticle energies. The new FES quasiparticles exhibit the same energy gap as the BCS quasiparticles, but a different DOS, which is finite at any quasiparticle energy. We also discuss the effect of the remnant electron-electron interaction (electron-electron interaction beyond the BCS pairing model) and show that this can stabilize the BCS condensate, increasing the critical temperature.

  1. Quasiparticles of strongly correlated Fermi liquids at high temperatures and in high magnetic fields

    SciTech Connect

    Shaginyan, V. R.

    2011-08-15

    Strongly correlated Fermi systems are among the most intriguing, best experimentally studied and fundamental systems in physics. There is, however, lack of theoretical understanding in this field of physics. The ideas based on the concepts like Kondo lattice and involving quantum and thermal fluctuations at a quantum critical point have been used to explain the unusual physics. Alas, being suggested to describe one property, these approaches fail to explain the others. This means a real crisis in theory suggesting that there is a hidden fundamental law of nature. It turns out that the hidden fundamental law is well forgotten old one directly related to the Landau-Migdal quasiparticles, while the basic properties and the scaling behavior of the strongly correlated systems can be described within the framework of the fermion condensation quantum phase transition (FCQPT). The phase transition comprises the extended quasiparticle paradigm that allows us to explain the non-Fermi liquid (NFL) behavior observed in these systems. In contrast to the Landau paradigm stating that the quasiparticle effective mass is a constant, the effective mass of new quasiparticles strongly depends on temperature, magnetic field, pressure, and other parameters. Our observations are in good agreement with experimental facts and show that FCQPT is responsible for the observed NFL behavior and quasiparticles survive both high temperatures and high magnetic fields.

  2. A Quasiparticle Detector for Imaging Quantum Turbulence in Superfluid He-B

    NASA Astrophysics Data System (ADS)

    Ahlstrom, S. L.; Bradley, D. I.; Fisher, S. N.; Guénault, A. M.; Guise, E. A.; Haley, R. P.; Holt, S.; Kolosov, O.; McClintock, P. V. E.; Pickett, G. R.; Poole, M.; Schanen, R.; Tsepelin, V.; Woods, A. J.

    2014-06-01

    We describe the development of a two-dimensional quasiparticle detector for use in visualising quantum turbulence in superfluid He-B at ultra-low temperatures. The detector consists of a matrix of pixels, each a 1 mm diameter hole in a copper block containing a miniature quartz tuning fork. The damping on each fork provides a measure of the local quasiparticle flux. The detector is illuminated by a beam of ballistic quasiparticles generated from a nearby black-body radiator. A comparison of the damping on the different forks provides a measure of the cross-sectional profile of the beam. Further, we generate a tangle of vortices (quantum turbulence) in the path of the beam using a vibrating wire resonator. The vortices cast a shadow onto the face of the detector due to the Andreev reflection of quasiparticles in the beam. This allows us to image the vortices and to investigate their dynamics. Here we give details of the design and construction of the detector and show some preliminary results for one row of pixels which demonstrates its successful application to measuring quasiparticle beams and quantum turbulence.

  3. Bogoliubov quasiparticles coupled to the antiferromagnetic spin mode in a vortex core

    NASA Astrophysics Data System (ADS)

    Berthod, C.

    2015-12-01

    In copper- and iron-based unconventional superconductors, the Bogoliubov quasiparticles interact with a spin resonance at momentum (π ,π ) . This interaction is revealed by specific signatures in the quasiparticle spectroscopies, like kinks in photoemission and dips in tunneling. We study these signatures, as they appear inside and around a vortex core in the local density of states (LDOS), a property accessible experimentally by scanning tunneling spectroscopy. Our model retains the whole nonlocal structure of the self-energy in space and time and is therefore not amenable to a Hamiltonian treatment using Bogoliubov-de Gennes equations. The interaction with the spin resonance does not suppress the zero-bias peak at the vortex center, although it reduces its spectral weight; neither does it smear out the vortex LDOS, but rather it adds structure to it. Some of the signatures we find may have been already measured in FeSe, but remained unnoticed. We compare the LDOS as a function of both energy and position with and without coupling to the spin resonance and observe, in particular, that the quasiparticle interference patterns around the vortex are strongly damped by the coupling. We study in detail the transfer of spectral weight induced both locally and globally by the interaction and also by the formation of the vortex. Finally, we introduce a new way of imaging the quasiparticles in real space, which combines locality and momentum-space sensitivity. This approach allows one to access quasiparticle properties that are not contained in the LDOS.

  4. Phase Stability for the Pd-Si System: First-Principles, Experiments, and Solution-Based Modeling

    NASA Astrophysics Data System (ADS)

    Zhou, S. H.; Huo, Y.; Napolitano, Ralph E.

    2016-01-01

    The relative stabilities of the compounds in the binary Pd-Si system were assessed using first-principles calculations and experimental methods. Calculations of lattice parameters and enthalpy of formation indicate that Pd5Si-{μ }, Pd9Si_2-{α }, Pd_3Si-{β }, Pd_2Si-{γ }, and PdSi-{δ } are the stable phases at 0 K (-273 °C). X-ray diffraction analyses (XRD) and electron probe microanalysis (EPMA) of the as-solidified and heat-treated samples support the computational findings, except that the PdSi-{δ } phase was not observed at low temperature. Considering both experimental data and first-principles results, the compounds Pd5Si-{μ }, Pd9Si2-{α }, Pd3Si-{β }, and Pd_2Si-{γ } are treated as stable phases down to 0 K (-273 °C), while the PdSi-{δ } is treated as being stable over a limited range, exhibiting a lower bound. Using these findings, a comprehensive solution-based thermodynamic model is formulated for the Pd-Si system, permitting phase diagram calculation. The liquid phase is described using a three-species association model and other phases are treated as solid solutions, where a random substitutional model is adopted for Pd-fcc and Si-dia, and a two-sublattice model is employed for Pd5Si-{μ }, Pd9Si_2-{α }, Pd_3Si-{β }, Pd_2Si-{γ }, and PdSi-{δ }. Model parameters are fitted using available experimental data and first-principles data, and the resulting phase diagram is reported over the full range of compositions.

  5. Phase Stability for the Pd-Si System. First-Principles, Experiments, and Solution-Based Modeling

    DOE PAGESBeta

    Zhou, S. H.; Huo, Y.; Napolitano, Ralph E.

    2015-11-05

    Relative stabilities of the compounds in the binary Pd-Si system were assessed using first-principles calculations and experimental methods. Calculations of lattice parameters and enthalpy of formation indicate that Pd5Si-μ, Pd9Si2-α, Pd3 Si-β, Pd2 Si-γ, and PdSi-δ are the stable phases at 0 K (-273 °C). X-ray diffraction analyses (XRD) and electron probe microanalysis (EPMA) of the as-solidified and heat-treated samples support the computational findings, except that the PdSi-δ phase was not observed at low temperature. Considering both experimental data and first-principles results, the compounds Pd 5 Si-μ, Pd9 Si2-α, Pd3Si-β, and Pd2Si-γ are treated as stable phases down to 0more » K (-273 °C), while the PdSi-δ is treated as being stable over a limited range, exhibiting a lower bound. Using these findings, a comprehensive solution-based thermodynamic model is formulated for the Pd-Si system, permitting phase diagram calculation. Moreover, the liquid phase is described using a three-species association model and other phases are treated as solid solutions, where a random substitutional model is adopted for Pd-fcc and Si-dia, and a two-sublattice model is employed for Pd5Si-μ, Pd9Si2-α, Pd3Si-β, Pd2Si-γ, and PdSi-δ. Model parameters are fitted using available experimental data and first-principles data, and the resulting phase diagram is reported over the full range of compositions.« less

  6. Effect of magnetic field on quasiparticle branches of intrinsic Josephson junctions with ferromagnetic layer.

    SciTech Connect

    Ozyuzer, L.; Ozdemir, M.; Kurter, C.; Hinks, D. G.; Gray, K. E.

    2007-01-01

    The interlayer tunneling spectroscopy has been performed on micron-sized mesa arrays of HgBr{sub 2} intercalated superconducting Bi2212 single crystals. A ferromagnetic multilayer (Au/Co/Au) is deposited on top of the mesas. The spin-polarized current is driven along the c-axis of the mesas through a ferromagnetic Co layer and the hysteretic quasiparticle branches are observed at 4.2 K. Magnetic field evolution of hysteretic quasiparticle branches is obtained to examine the effect of injected spin-polarized current on intrinsic Josephson junction characteristics. It is observed that there is a gradual distribution in quasiparticle branches with the application of magnetic field and increasing field reduces the switching current progressively.

  7. Quasiparticle electronic structure of bulk and slab Bi2Se3 and Bi2Te3

    NASA Astrophysics Data System (ADS)

    Barker, Bradford; Deslippe, Jack; Yazyev, Oleg; Louie, Steven G.

    2014-03-01

    We present ab initio calculations of the quasiparticle electronic band structure of three-dimensional topological insulator materials Bi2Se3 and Bi2Te3. The mean-field DFT calculation is performed with fully relativistic pseudopotentials, generating spinor wavefunctions in a plane-wave basis. Quasiparticle properties are computed with a one-shot ab initio GW calculation. We use both bulk and slab forms of the materials to better understand the quasiparticle band gaps and Fermi velocities of the topological surface states of these materials. This work was supported by NSF grant No. DMR10-1006184 and U.S. DOE under Contract No. DE-AC02-05CH11231. Computational resources have been provided by DOE at LBNL's NERSC facility and the NSF through XSEDE resources at NICS.

  8. Biased impurity tunneling current emission spectrum in the presence of quasi-particle interaction

    NASA Astrophysics Data System (ADS)

    Maslova, N. S.; Arseyev, P. I.; Mantsevich, V. N.

    2016-09-01

    We performed theoretical investigations of the tunneling current noise spectra through single-level impurity in the presence of quasi-particle (electron-phonon) interaction by means of the non-equilibrium Green function formalism. We demonstrated a fundamental link between quantum noise in tunneling contact and light emission processes. We calculated tunneling current noise spectra through a single level impurity atom both in the presence and in the absence of quasi-particle interaction for a finite bias voltage and identified it as a source of experimentally observed light emission from bias STM contacts. The results turn out to be sensitive to the tunneling contact parameters. Our findings provide important insight into the nature of non-equilibrium electronic transport in tunneling junctions with quasi-particle interaction.

  9. Quasiparticle parity lifetime of bound states in a hybrid superconductor-semiconductor quantum dot

    NASA Astrophysics Data System (ADS)

    Higginbotham, Andrew; Albrecht, Sven; Kirsanskas, Gediminas; Chang, Willy; Kuemmeth, Ferdinand; Krogstrup, Peter; Jespersen, Thomas; Nygård, Jesper; Flensberg, Karsten; Marcus, Charles

    2015-03-01

    We measure quasiparticle transport in an InAs nanowire that is half-covered with epitaxial superconducting aluminum, then locally gated to form a quantum dot. We observe negative differential conductance at finite source-drain bias, and temperature dependent even-odd alternations in the Coulomb blockade peak spacings at zero bias. These observations can be understood in terms of a mid-gap semiconductor discrete state and a continuum of BCS quasiparticle states. Comparing with simple models, we bound the discrete state's parity lifetime and the quasiparticle temperature. These results indicate that parity fluctuations are slow, and imply Majorana qubit poisoning times on the order of a millisecond. Additional results indicate that the bound states move to zero energy in a magnetic field, qualitatively consistent with expectations for Majorana fermions in a finite system. Research supported by Microsoft Station Q, Danish National Research Foundation, Villum Foundation, Lundbeck Foundation, and the European Commission.

  10. Boundary conformal field theory and tunneling of edge quasiparticles in non-Abelian topological states

    SciTech Connect

    Fendley, Paul; Fisher, Matthew P.A.; Nayak, Chetan

    2009-07-15

    We explain how (perturbed) boundary conformal field theory allows us to understand the tunneling of edge quasiparticles in non-Abelian topological states. The coupling between a bulk non-Abelian quasiparticle and the edge is due to resonant tunneling to a zero mode on the quasiparticle, which causes the zero mode to hybridize with the edge. This can be reformulated as the flow from one conformally invariant boundary condition to another in an associated critical statistical mechanical model. Tunneling from one edge to another at a point contact can split the system in two, either partially or completely. This can be reformulated in the critical statistical mechanical model as the flow from one type of defect line to another. We illustrate these two phenomena in detail in the context of the {nu}=5/2 quantum Hall state and the critical Ising model. We briefly discuss the case of Fibonacci anyons and conclude by explaining the general formulation and its physical interpretation.

  11. Microscopic Model of Quasiparticle Wave Packets in Superfluids, Superconductors, and Paired Hall States

    NASA Astrophysics Data System (ADS)

    Parameswaran, S. A.; Kivelson, S. A.; Shankar, R.; Sondhi, S. L.; Spivak, B. Z.

    2012-12-01

    We study the structure of Bogoliubov quasiparticles, bogolons, the fermionic excitations of paired superfluids that arise from fermion (BCS) pairing, including neutral superfluids, superconductors, and paired quantum Hall states. The naive construction of a stationary quasiparticle in which the deformation of the pair field is neglected leads to a contradiction: it carries a net electrical current even though it does not move. However, treating the pair field self-consistently resolves this problem: in a neutral superfluid, a dipolar current pattern is associated with the quasiparticle for which the total current vanishes. When Maxwell electrodynamics is included, as appropriate to a superconductor, this pattern is confined over a penetration depth. For paired quantum Hall states of composite fermions, the Maxwell term is replaced by a Chern-Simons term, which leads to a dipolar charge distribution and consequently to a dipolar current pattern.

  12. Quasi-particle spectrum in trilayer graphene: Role of onsite coulomb interaction and interlayer coupling

    NASA Astrophysics Data System (ADS)

    Kumar, Sanjay; Ajay

    2015-01-01

    Stacking dependent quasi-particle spectrum and density of states (DOS) in trilayer (ABC-, ABA- and AAA-stacked) graphene are analyzed using mean-field Green's function equations of motion method. Interlayer coupling (t1) is found to be responsible for the splitting of quasi-particle peaks in each stacking order. Coulomb interaction suppresses the trilayer splitting and generates a finite gap at Fermi level in ABC- while a tiny gap in ABA-stacked trilayer graphene. Influence of t⊥ is prominent for AAA-stacking as compared to ABC- and ABA-stacking orders. The theoretically obtained quasi-particle energies and DOS has been viewed in terms of recent angle resolved photoemission spectroscopic (ARPES) and scanning tunneling microscopic (STM) data available on these systems.

  13. Tunneling into thin superconducting films: Interface-induced quasiparticle lifetime reduction

    NASA Astrophysics Data System (ADS)

    Löptien, P.; Zhou, L.; Khajetoorians, A. A.; Wiebe, J.; Wiesendanger, R.

    2016-01-01

    Scanning tunneling spectroscopy measurements of superconducting thin lanthanum films grown on a normal metal tungsten substrate reveal an extraordinarily large broadening of the coherence peaks. The observed broadening corresponds to very short electron-like quasiparticle lifetimes in the tunneling process. A thorough analysis considering the different relaxation processes reveals that the dominant mechanism is an efficient quasiparticle relaxation at the interface between the superconducting film and the underlying substrate. This process is of general relevance to scanning tunneling spectroscopy studies on thin superconducting films and enables measurements of film thicknesses via a spectroscopic method.

  14. Measurement of quasiparticle transport in aluminum films using tungsten transition-edge sensors

    SciTech Connect

    Yen, J. J. Shank, B.; Cabrera, B.; Moffatt, R.; Redl, P.; Young, B. A.; Tortorici, E. C.; Brink, P. L.; Cherry, M.; Tomada, A.; Kreikebaum, J. M.

    2014-10-20

    We report on experimental studies of phonon sensors which utilize quasiparticle diffusion in thin aluminum films connected to tungsten transition-edge-sensors (TESs) operated at 35 mK. We show that basic TES physics and a simple physical model of the overlap region between the W and Al films in our devices enables us to accurately reproduce the experimentally observed pulse shapes from x-rays absorbed in the Al films. We further estimate quasiparticle loss in Al films using a simple diffusion equation approach. These studies allow the design of phonon sensors with improved performance.

  15. Proposal to measure the quasiparticle poisoning time of Majorana bound states

    NASA Astrophysics Data System (ADS)

    Colbert, Jacob R.; Lee, Patrick A.

    2014-04-01

    We propose a method of measuring the fermion parity lifetime of Majorana fermion modes due to quasiparticle poisoning. We model quasiparticle poisoning by coupling the Majorana modes to electron reservoirs, explicitly breaking parity conservation in the system. This poisoning broadens and shortens the resonance peak associated with Majorana modes. In a two-lead geometry, the poisoning decreases the correlation in current noise between the two leads from the maximal value characteristic of crossed Andreev reflection. The latter measurement allows for calculation of the poisoning rate even if the temperature is much higher than the resonance width.

  16. Emergent exclusion statistics of quasiparticles in two-dimensional topological phases

    NASA Astrophysics Data System (ADS)

    Hu, Yuting; Stirling, Spencer D.; Wu, Yong-Shi

    2014-03-01

    We demonstrate how the generalized Pauli exclusion principle emerges for quasiparticle excitations in 2D topological phases. As an example, we examine the Levin-Wen model with the Fibonacci data (specified in the text), and construct the number operator for fluxons living on plaquettes. By numerically counting the many-body states with fluxon number fixed, the matrix of exclusion statistics parameters is identified and is shown to depend on the spatial topology (sphere or torus) of the system. Our work reveals the structure of the (many-body) Hilbert space and some general features of thermodynamics for quasiparticle excitations in topological matter.

  17. Tunneling spectroscopy of quasiparticle bound states in a spinful Josephson junction.

    PubMed

    Chang, W; Manucharyan, V E; Jespersen, T S; Nygård, J; Marcus, C M

    2013-05-24

    The spectrum of a segment of InAs nanowire, confined between two superconducting leads, was measured as function of gate voltage and superconducting phase difference using a third normal-metal tunnel probe. Subgap resonances for odd electron occupancy-interpreted as bound states involving a confined electron and a quasiparticle from the superconducting leads, reminiscent of Yu-Shiba-Rusinov states-evolve into Kondo-related resonances at higher magnetic fields. An additional zero-bias peak of unknown origin is observed to coexist with the quasiparticle bound states. PMID:23745916

  18. Trapping hot quasi-particles in a high-power superconducting electronic cooler

    NASA Astrophysics Data System (ADS)

    Nguyen, H. Q.; Aref, T.; Kauppila, V. J.; Meschke, M.; Winkelmann, C. B.; Courtois, H.; Pekola, J. P.

    2013-08-01

    The performance of hybrid superconducting electronic coolers is usually limited by the accumulation of hot quasi-particles in their superconducting leads. This issue is all the more stringent in large-scale and high-power devices, as required by the applications. Introducing a metallic drain connected to the superconducting electrodes via a fine-tuned tunnel barrier, we efficiently remove quasi-particles and obtain electronic cooling from 300 mK down to 130 mK with a 400 pW cooling power. A simple thermal model accounts for the experimental observations.

  19. PD trivia: Making learning fun.

    PubMed

    Kennedy, Liana

    2006-01-01

    Nurses are educators. It is the aim of every educator that his or her teaching should translate into learning. Effective teaching is especially of importance in assuring that patients learn to perform their own peritoneal dialysis (PD). In facilitating an environment where learning can occur, making learning fun is the objective. It is with this mandate that PD Trivia was created. PD Trivia is an interactive game created to facilitate and reinforce learning. PD Trivia consists of 100 essential questions to making PD a success at home. Evaluations at the peritoneal dialysis clinic have revealed excellent quantitative and qualitative results of this simple but comprehensive teaching tool for effective learning of PD. PMID:17061697

  20. Analysis of the renormalization of the quasiparticle dispersion in high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Li, Jian-Xin; Wang, Z. D.

    2005-03-01

    Based on the slave-boson approach to the bilayer t-t^'- J model, the renormalization of the quasiparticle dispersion in high-Tc cuprates is investigated by examining both interactions of fermions with spin fluctuations and phonons. It is shown that both interactions can give rise to a kink in the dispersion around the antinodes of the d-wave gap (near (,) and (0,π)). However, three remarkable differences caused by these interactions are found, namely the peak/dip/hump structure in the quasiparticle lineshape, the doping dependence of the quasiparticle weight, and the role played by the interlayer coupling on the formation of the antinodal kink. These differences are suggested to serve as a discriminance to single out the main residual interaction in the superconducting state. A comparison to the recent angle-resolved photoemission (ARPES) experiments shows that the coupling to the spin resonance dominates for quasiparticles around the antinodes. ^1National Laboratory of Solid State of Microstructure and Department of Physics, Nanjing University, Nanjing 210093, China^2Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, China^3The Interdisciplinary Center of Theoretical Studies, Chinese Academy of Science, Beijing 100080, China.

  1. Decay spectroscopy of 160Sm: The lightest four-quasiparticle K isomer

    NASA Astrophysics Data System (ADS)

    Patel, Z.; Podolyák, Zs.; Walker, P. M.; Regan, P. H.; Söderström, P.-A.; Watanabe, H.; Ideguchi, E.; Simpson, G. S.; Nishimura, S.; Browne, F.; Doornenbal, P.; Lorusso, G.; Rice, S.; Sinclair, L.; Sumikama, T.; Wu, J.; Xu, Z. Y.; Aoi, N.; Baba, H.; Bello Garrote, F. L.; Benzoni, G.; Daido, R.; Dombrádi, Zs.; Fang, Y.; Fukuda, N.; Gey, G.; Go, S.; Gottardo, A.; Inabe, N.; Isobe, T.; Kameda, D.; Kobayashi, K.; Kobayashi, M.; Komatsubara, T.; Kojouharov, I.; Kubo, T.; Kurz, N.; Kuti, I.; Li, Z.; Liu, H. L.; Matsushita, M.; Michimasa, S.; Moon, C.-B.; Nishibata, H.; Nishizuka, I.; Odahara, A.; Şahin, E.; Sakurai, H.; Schaffner, H.; Suzuki, H.; Takeda, H.; Tanaka, M.; Taprogge, J.; Vajta, Zs.; Xu, F. R.; Yagi, A.; Yokoyama, R.

    2016-02-01

    The decay of a new four-quasiparticle isomeric state in 160Sm has been observed using γ-ray spectroscopy at the RIBF, RIKEN. The four-quasiparticle state is assigned a 2 π ⊗ 2 ν π5/2- [ 532 ], π5/2+ [ 413 ], ν5/2- [ 523 ], ν7/2+ [ 633 ] configuration. The half-life of this (11+) state is measured to be 1.8(4) μs. The (11+) isomer decays into a rotational band structure, based on a (6-) ν5/2- [ 523 ] ⊗ ν7/2+ [ 633 ] bandhead, consistent with the gK -gR values. This decays to a (5-) two-proton quasiparticle state, which in turn decays to the ground state band. Potential energy surface and blocked-BCS calculations were performed in the deformed midshell region around 160Sm. They reveal a significant influence from β6 deformation and that 160Sm is the best candidate for the lightest four-quasiparticle K isomer to exist in this region. The relationship between reduced hindrance and isomer excitation energy for E1 transitions from multiquasiparticle states is considered with the new data from 160Sm. The E1 data are found to agree with the existing relationship for E2 transitions.

  2. Quasiparticle energies and lifetimes in a metallic chain model of a tunnel junction.

    PubMed

    Szepieniec, Mark; Yeriskin, Irene; Greer, J C

    2013-04-14

    As electronics devices scale to sub-10 nm lengths, the distinction between "device" and "electrodes" becomes blurred. Here, we study a simple model of a molecular tunnel junction, consisting of an atomic gold chain partitioned into left and right electrodes, and a central "molecule." Using a complex absorbing potential, we are able to reproduce the single-particle energy levels of the device region including a description of the effects of the semi-infinite electrodes. We then use the method of configuration interaction to explore the effect of correlations on the system's quasiparticle peaks. We find that when excitations on the leads are excluded, the device's highest occupied molecular orbital and lowest unoccupied molecular orbital quasiparticle states when including correlation are bracketed by their respective values in the Hartree-Fock (Koopmans) and ΔSCF approximations. In contrast, when excitations on the leads are included, the bracketing property no longer holds, and both the positions and the lifetimes of the quasiparticle levels change considerably, indicating that the combined effect of coupling and correlation is to alter the quasiparticle spectrum significantly relative to an isolated molecule. PMID:24981526

  3. Tunneling Spectroscopy Study of Spin-Polarized Quasiparticle Injection Effects in Cuparate/Manganite Heterostructures

    NASA Technical Reports Server (NTRS)

    Wei, J. Y. T.; Yeh, N. C.; Vasquez, R. P.

    1998-01-01

    Scanning tunneling spectroscopy was performed at 4.2K on epitaxial thin-film heterostructures comprising YBa2Cu3O7 and La0.7Ca0.3MnO3, to study the microscopic effects of spin-polarized quasiparticle injection from the half-metallic ferromagnetic manganite on the high-Tc cuprate superconductor.

  4. Ab initio quasiparticle bandstructure of ABA and ABC-stacked graphene trilayers

    NASA Astrophysics Data System (ADS)

    Menezes, Marcos; Capaz, Rodrigo; Louie, Steven

    2013-03-01

    We obtain the quasiparticle band structure of ABA and ABC-stacked graphene trilayers through ab initio density functional theory (DFT) and many-body quasiparticle calculations within the GW approximation. To interpret our results, we fit the DFT and GW π bands to a low energy tight-binding model, which is found to reproduce very well the observed features near the K point. The values of the extracted hopping parameters are reported and compared with available theoretical and experimental data. For both stackings, the quasiparticle corrections lead to a renormalization of the Fermi velocity, an effect also observed in previous calculations on monolayer graphene. They also increase the separation between the higher energy bands, which is proportional to the nearest neighbor interlayer hopping parameter γ1. Both features are brought to closer agreement with experiment through the quasiparticle corrections. Finally, other effects, such as trigonal warping, electron-hole assymetry and energy gaps are discussed in terms of the associated parameters. This work was supported by the Brazilian funding agencies: CAPES, CNPq, FAPERJ and INCT-Nanomateriais de Carbono. It was also supported by NSF grant No. DMR10-1006184 and U.S. DOE under Contract No. DE-AC02-05CH11231.

  5. Quasiparticle Tunneling in the Fractional Quantum Hall effect at filling fraction ν=5/2

    NASA Astrophysics Data System (ADS)

    Radu, Iuliana P.

    2009-03-01

    In a two-dimensional electron gas (2DEG), in the fractional quantum Hall regime, the quasiparticles are predicted to have fractional charge and statistics, as well as modified Coulomb interactions. The state at filling fraction ν=5/2 is predicted by some theories to have non-abelian statistics, a property that might be exploited for topological quantum computing. However, alternative models with abelian properties have been proposed as well. Weak quasiparticle tunneling between counter-propagating edges is one of the methods that can be used to learn about the properties of the state and potentially distinguish between models describing it. We employ an electrostatically defined quantum point contact (QPC) fabricated on a high mobility GaAs/AlGaAs 2DEG to create a constriction where quasiparticles can tunnel between counter-propagating edges. We study the temperature and dc bias dependence of the tunneling conductance, while preserving the same filling fraction in the constriction and the bulk of the sample. The data show scaling of the bias-dependent tunneling over a range of temperatures, in agreement with the theory of weak quasiparticle tunneling, and we extract values for the effective charge and interaction parameter of the quasiparticles. The ranges of values obtained are consistent with those predicted by certain models describing the 5/2 state, indicating as more probable a non-abelian state. This work was done in collaboration with J. B. Miller, C. M. Marcus, M. A. Kastner, L. N. Pfeiffer and K. W. West. This work was supported in part by the Army Research Office (W911NF-05-1-0062), the Nanoscale Science and Engineering Center program of NSF (PHY-0117795), NSF (DMR-0701386), the Center for Materials Science and Engineering program of NSF (DMR-0213282) at MIT, the Microsoft Corporation Project Q, and the Center for Nanoscale Systems at Harvard University.

  6. Ultrafast momentum-dependent quasiparticle dynamics in high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Bovensiepen, Uwe

    2013-03-01

    Femtosecond time- and angle-resolved photoelectron spectroscopy trARPES facilitates insight into electronic relaxation and electronic structure of non-equilibrium states of matter. Hot electrons and holes relax in metals on ultrafast time scales due to the screened Coulomb interaction. In superconductors the relaxation rates of quasiparticles at energies close to the superconducting gap edge are reduced because of the loss of quasiparticle states near EF. Since in the superconducting state the relaxation of optically excited carriers proceeds partly by Cooper pair reformation, the study of the quasiparticle dynamics bears the potential to analyze the interaction responsible for Cooper pair formation. Results of trARPES will be discussed for optimally doped Bi2Sr2CaCu2O8+δ in the superconducting state and on EuFe2As2 in the antiferromagnetic state. In the cuprate system we find a predominant excitation of quasiparticles at momenta near the antinode. We show furthermore, that at excitation densities of several 10 μJ/cm2 quasiparticle relaxation is dominated by Cooper pair reformation, which again proceeds near the antinode. In the Fe-pnictide material we monitor a difference in the relaxation rate for electrons and holes near the Fermi momentum, which disappears above the Neel temperature. We conclude that this anisotropic relaxation of electrons and holes is a consequence of the optical modification of the antiferromagnetic order. Analysis of energy transfer from electrons to phonons allows to determine the momentum averaged electron-phonon coupling constant λ. We find values below 0.25 for Bi2Sr2CaCu2O8+δ and below 0.15 for EuFe2As2. We acknowledge funding through the Deutsche Forschungsgemeinschaft through BO 1823/2, SPP 1458 and the Alexander von Humboldt foundation.

  7. Strongly correlated electron materials. I. Theory of the quasiparticle structure

    SciTech Connect

    Lopez-Aguilar, F.; Costa-Quintana, J.; Puig-Puig, L. )

    1993-07-01

    In this paper we give a method for analyzing the renormalized electronic structure of the Hubbard systems. The first step is the determination of effective interactions from the random-phase approximation (RPA) and from an extended RPA (ERPA) that introduces vertex effects within the bubble polarization. The second step is the determination of the density of states deduced from the spectral functions. Its analysis leads us to conclude that these systems can exhibit three types of resonances in their electronic structures: the lower-, middle-, and upper-energy resonances. Furthermore, we analyze the conditions for which there is only one type of resonance and the causes that lead to the disappearance of the heavy-fermion state. We finally introduce the RPA and ERPA effective interactions within the strong-coupling theory and we give the conditions for obtaining coupling and superconductivity.

  8. Constitution and thermodynamics of the Mo-Ru, Mo-Pd, Ru-Pd and Mo-Ru-Pd systems

    NASA Astrophysics Data System (ADS)

    Kleykamp, H.

    1989-09-01

    The constitution of the Mo-Ru, Mo-Pd and Ru-Pd systems was reinvestigated between 800 and 2000°C. The Mo-Ru system is of the eutectic type, a σ-phase Mo 5Ru 3 exists between 1915 and 1143°C. The Mo-Pd system is characterized by an hcp phase Mo 9Pd 11 and by two peritectic reactions, β- Mo( Pd) + L = Mo9Pd11andMo9Pd11 + L = α- Pd( Mo). Mo 9Pd 11 decomposes eutectoidally at 1370°C. The Ru-Pd system is simple peritectic. The continuous series of the hcp solid solutions between Mo 9Pd 11 and ɛ-Ru(Mo, Pd) in the ternary Mo-Ru-Pd system observed at 1700°C are suppressed below 1370°C near the Mo-Pd boundary system by the formation of a narrow α + β + ɛ three-phase field. Relative partial molar Gibbs energies of Mo, Mo and Ru in the respective binary systems and of Mo in the ternary system were measured by the EMF method with a Zr(Ca)O 2 electrolyte. xsΔ ḠMo∞ quantities were evaluated at 1200 K which give -43 kJ/mol Mo in Ru and -94 kJ/mol Mo in Pd at infinite dilution. Gibbs energies of formation of the Mo-Ru and Mo-Pd systems were calculated.

  9. Enhanced interlayer exchange coupling in antiferromagnetically coupled ultrathin (Co70Fe30/Pd) multilayers

    NASA Astrophysics Data System (ADS)

    Meng, Zhaoliang; Qiu, Jinjun; Han, Guchang; Teo, Kie Leong

    2015-12-01

    We report the studies of magnetization reversal and magnetic interlayer coupling in synthetic antiferromagnetic (SAF) [Pd/Co70Fe30]9/Ru(tRu)/Pd(tPd)/[Co70Fe30/Pd]9 structure as functions of inserted Pd layer (tPd) and Ru layer (tRu) thicknesses. We found the exchange coupling field (Hex) and perpendicular magnetic anisotropy (PMA) can be controlled by both the tPd and tRu, The Hex shows a Ruderman-Kittel-Kasuya-Yosida-type oscillatory decay dependence on tRu and a maximum interlayer coupling strength Jex = 0.522 erg/cm2 is achieved at tPd + tRu ≈ 0.8 nm in the as-deposited sample. As it is known that a high post-annealing stability of SAF structure is required for magnetic random access memory applications, the dependence of Hex and PMA on the post-annealing temperature (Ta) is also investigated. We found that both high PMA of the top Co70Fe30/Pd multilayer is maintained and Hex is enhanced with increasing Ta up to 350 °C for tRu > 0.7 nm in our SAF structure.

  10. Shape vibration and quasiparticle excitations in the lowest 0+ excited state in erbium isotopes

    NASA Astrophysics Data System (ADS)

    Chen, Fang-Qi; Egido, J. Luis

    2016-06-01

    The ground and first excited 0+ states of the -172Er156 isotopes are analyzed in the framework of the generator coordinate method. The shape parameter β is used to generate wave functions with different deformations which together with the two-quasiparticle states built on them provide a set of states. An angular momentum and particle number projection of the latter spawn the basis states of the generator coordinate method. With this ansatz and using the separable pairing plus quadrupole interaction we obtain a good agreement with the experimental spectra and E 2 transition rates up to moderate spin values. The structure of the wave functions suggests that the first excited 0+ states in the soft Er isotopes are dominated by shape fluctuations, while in the well deformed Er isotopes the two-quasiparticle states are more relevant. In between, both degrees of freedom are necessary.

  11. Inflationary Quasiparticle Creation and Thermalization Dynamics in Coupled Bose-Einstein Condensates.

    PubMed

    Posazhennikova, Anna; Trujillo-Martinez, Mauricio; Kroha, Johann

    2016-06-01

    A Bose gas in a double-well potential, exhibiting a true Bose-Einstein condensate (BEC) amplitude and initially performing Josephson oscillations, is a prototype of an isolated, nonequilibrium many-body system. We investigate the quasiparticle (QP) creation and thermalization dynamics of this system by solving the time-dependent Keldysh-Bogoliubov equations. We find avalanchelike QP creation due to a parametric resonance between BEC and QP oscillations, followed by slow, exponential relaxation to a thermal state at an elevated temperature, controlled by the initial excitation energy of the oscillating BEC above its ground state. The crossover between the two regimes occurs because of an effective decoupling of the QP and BEC oscillations. This dynamics is analogous to elementary particle creation in models of the early universe. The thermalization in our setup occurs because the BEC acts as a grand canonical reservoir for the quasiparticle system. PMID:27314725

  12. Long-Range Spin-Polarized Quasiparticle Transport in Mesoscopic Al Superconductors with a Zeeman Splitting

    NASA Astrophysics Data System (ADS)

    Hübler, F.; Wolf, M. J.; Beckmann, D.; v. Löhneysen, H.

    2012-11-01

    We report on nonlocal transport in multiterminal superconductor-ferromagnet structures, which were fabricated by means of e-beam lithography and shadow evaporation techniques. In the presence of a significant Zeeman splitting of the quasiparticle states, we find signatures of spin transport over distances of several μm, exceeding other length scales such as the coherence length, the normal-state spin-diffusion length, and the charge-imbalance length. The relaxation length of the spin signal shows a nearly linear increase with magnetic field, hinting at a freeze-out of relaxation by the Zeeman splitting. We propose that the relaxation length is given by the recombination length of the quasiparticles rather than a renormalized spin-diffusion length.

  13. Witnessing the formation and relaxation of dressed quasi-particles in a strongly correlated electron system

    NASA Astrophysics Data System (ADS)

    Novelli, Fabio; de Filippis, Giulio; Cataudella, Vittorio; Esposito, Martina; Vergara, Ignacio; Cilento, Federico; Sindici, Enrico; Amaricci, Adriano; Giannetti, Claudio; Prabhakaran, Dharmalingam; Wall, Simon; Perucchi, Andrea; Dal Conte, Stefano; Cerullo, Giulio; Capone, Massimo; Mishchenko, Andrey; Grüninger, Markus; Nagaosa, Naoto; Parmigiani, Fulvio; Fausti, Daniele

    2014-10-01

    The non-equilibrium approach to correlated electron systems is often based on the paradigm that different degrees of freedom interact on different timescales. In this context, photo-excitation is treated as an impulsive injection of electronic energy that is transferred to other degrees of freedom only at later times. Here, by studying the ultrafast dynamics of quasi-particles in an archetypal strongly correlated charge-transfer insulator (La2CuO4+δ), we show that the interaction between electrons and bosons manifests itself directly in the photo-excitation processes of a correlated material. With the aid of a general theoretical framework (Hubbard-Holstein Hamiltonian), we reveal that sub-gap excitation pilots the formation of itinerant quasi-particles, which are suddenly dressed by an ultrafast reaction of the bosonic field.

  14. Properties of quark matter in a new quasiparticle model with QCD running coupling

    NASA Astrophysics Data System (ADS)

    Lu, ZhenYan; Peng, GuangXiong; Xu, JianFeng; Zhang, ShiPeng

    2016-06-01

    The running of the QCD coupling in the effective mass causes thermodynamic inconsistency problem in the conventional quasiparticle model. We provide a novel treatment which removes the inconsistency by an effective bag constant. The chemical potential dependence of the renormalization subtraction point is constrained by the Cauchy condition in the chemical potential space. The stability and microscopic properties of strange quark matter are then studied within the completely self-consistent quasiparticle model, and the obtained equation of state of quark matter is applied to the investigation of strange stars. It is found that our improved model can describe well compact stars with mass about two times the solar mass, which indicates that such massive compact stars could be strange stars.

  15. Non-exponential energy decay and quasi-particle fluctuations in a superconducting flux qubit

    NASA Astrophysics Data System (ADS)

    Gustavsson, Simon; Yan, Fei; Catelani, Gianluigi; Kamal, Archana; Bylander, Jonas; Yoshihara, Fumiki; Nakamura, Yasunobu; Orlando, Terry; Oliver, Wiliam

    2015-03-01

    We measure pronounced non-exponential energy relaxation in a superconducting flux qubit, observing a decay function that exhibits a fast initial decay followed by a much slower decay for long times. When applying a sequence of pi pulses to the qubit and measuring the decay after the last pi pulse, we observe strong modifications to the decay function, including a slow-down of the fast initial decay and a three-fold increase of the 1/e-time. If we attribute the non-exponential decay to quasiparticle number fluctuations, we speculate that the improvements in T1 are due to a qubit-mediated shuffling of quasiparticles between the metallic islands of the device, which will eventually pump them away from the Josephson junctions to a larger ground plane where their contribution to qubit energy relaxation become negligible.

  16. Quasiparticle Scattering Rate and Antiferromagnetic Excitations in YBa_2Cu_3O_7.

    NASA Astrophysics Data System (ADS)

    Stojković, Branko P.; Blumberg, G.; Klein, M. V.

    1996-03-01

    In quasi-two-dimensional d-wave superconductors Van Hove singularities close to the Fermi surface lead to magnetic quasi-particle excitations.(G. Blumberg, B. P. Stojković and M. V. Klein, preprint.) Assuming a model electron-magnon interaction and realistic electronic band structure for YBa_2Cu_3O_7, we calculate the inelastic electronic scattering rate in both normal and superconducting states. In agreement with the momentum dependent spectral function broadening observed in YBCO in the superconducting state by photoemission spectroscopy, we find different quasiparticle scattering rates as a function of energy and temperature for different regions of the Brillouin zone. We calculate the magnetic excitation spectra in momentum space and use them to discuss the implications of our results for NMR, inelastic neutron scattering, and Raman spectroscopy.

  17. Efficient quasiparticle band-structure calculations for cubic and noncubic crystals

    SciTech Connect

    Wenzien, B.; Cappellini, G.; Bechstedt, F.

    1995-05-15

    An efficient method developed for the calculation of quasiparticle corrections to density-functional-theory--local-density-approximation (DFT-LDA) band structures of diamond and zinc-blende materials is generalized for crystals with other cubic, hexagonal, tetragonal, and orthorhombic Bravais lattices. Local-field effects are considered in the framework of a LDA-like approximation. The dynamical screening is treated by expanding the self-energy linearly in energy. The anisotropy of the inverse dielectric matrix is taken into account. The singularity of the Coulomb potential in the screened-exchange part of the electronic self-energy is treated using auxiliary functions of the appropriate symmetry. An application to the electronic quasiparticle band structure of wurtzite 2{ital H}-SiC is presented within the approach of norm-conserving, nonlocal, fully separable pseudopotentials and a plane-wave expansion of the wave functions for the underlying DFT-LDA.

  18. Coherent quasiparticles with a small fermi surface in lightly doped Sr(3)Ir(2)O(7).

    PubMed

    de la Torre, A; Hunter, E C; Subedi, A; McKeown Walker, S; Tamai, A; Kim, T K; Hoesch, M; Perry, R S; Georges, A; Baumberger, F

    2014-12-19

    We characterize the electron doping evolution of (Sr_{1-x}La_{x})_{3}Ir_{2}O_{7} by means of angle-resolved photoemission. Concomitant with the metal insulator transition around x≈0.05 we find the emergence of coherent quasiparticle states forming a closed small Fermi surface of volume 3x/2, where x is the independently measured La concentration. The quasiparticle weight Z remains large along the entire Fermi surface, consistent with the moderate renormalization of the low-energy dispersion, and no pseudogap is observed. This indicates a conventional, weakly correlated Fermi liquid state with a momentum independent residue Z≈0.5 in lightly doped Sr_{3}Ir_{2}O_{7}. PMID:25554897

  19. Structure of three-quasiparticle isomers in {sup 169}Ho and {sup 171}Tm

    SciTech Connect

    Dracoulis, G. D.; Lane, G. J.; Hughes, R. O.; Kondev, F. G.; Chiara, C. J.; Watanabe, H.; Seweryniak, D.; Zhu, S.; Carpenter, M. P.; Janssens, R. V. F.; Lauritsen, T.; Lister, C. J.; McCutchan, E. A.; Stefanescu, I.; Chowdhury, P.

    2010-09-15

    A three-quasiparticle isomer with {tau}=170(8) {mu}s and K{sup {pi}=} (19/2{sup +}) has been identified in the neutron-rich isotope {sup 169}Ho. The isomer decays with K-forbidden transitions to members of a band associated with the 7/2{sup -}[523] proton configuration, whose structure is characterized through analysis of the in-band {gamma}-ray branching ratios. In the isotone {sup 171}Tm, the rotational band based on the known 19/2{sup +}, three-quasiparticle isomer has also been observed. Alternative one-proton two-neutron configurations for the isomer in {sup 169}Ho are discussed in terms of multiquasiparticle calculations and through a comparison with the structures observed in {sup 171}Tm.

  20. Witnessing the formation and relaxation of dressed quasi-particles in a strongly correlated electron system.

    PubMed

    Novelli, Fabio; De Filippis, Giulio; Cataudella, Vittorio; Esposito, Martina; Vergara, Ignacio; Cilento, Federico; Sindici, Enrico; Amaricci, Adriano; Giannetti, Claudio; Prabhakaran, Dharmalingam; Wall, Simon; Perucchi, Andrea; Dal Conte, Stefano; Cerullo, Giulio; Capone, Massimo; Mishchenko, Andrey; Grüninger, Markus; Nagaosa, Naoto; Parmigiani, Fulvio; Fausti, Daniele

    2014-01-01

    The non-equilibrium approach to correlated electron systems is often based on the paradigm that different degrees of freedom interact on different timescales. In this context, photo-excitation is treated as an impulsive injection of electronic energy that is transferred to other degrees of freedom only at later times. Here, by studying the ultrafast dynamics of quasi-particles in an archetypal strongly correlated charge-transfer insulator (La2CuO(4+δ)), we show that the interaction between electrons and bosons manifests itself directly in the photo-excitation processes of a correlated material. With the aid of a general theoretical framework (Hubbard-Holstein Hamiltonian), we reveal that sub-gap excitation pilots the formation of itinerant quasi-particles, which are suddenly dressed by an ultrafast reaction of the bosonic field. PMID:25290587

  1. Fast decay of a three-quasiparticle isomer in {sup 171}Tm

    SciTech Connect

    Walker, P. M.; Wood, R. J.; El-Masri, H. M.; Wheldon, C.; Dracoulis, G. D.; Kibedi, T.; Bark, R. A.; Davidson, P. M.; Lane, G. J.; Moon, C.; Bruce, A. M.; Orce, J. N.; Estevez, F. M. Prados; Byrne, A. P.; Wilson, A. N.

    2009-04-15

    Incomplete-fusion reactions have been used to study high-spin states in {sup 171}Tm. Gamma rays and conversion electrons were measured using pulsed-beam conditions for enhanced isomer sensitivity. A K{sup {pi}}=19/2{sup +}, three-quasiparticle isomer was identified, with a half-life of 1.7(2){mu}s. The faster than expected transition rates from the isomer can be understood as being due to a chance near-degeneracy, with mixing between the isomeric state and the I{sup {pi}}=19/2{sup +} member of the one-quasiparticle rotational band to which it decays. The implied mixing matrix element is 12(2) eV.

  2. Inflationary Quasiparticle Creation and Thermalization Dynamics in Coupled Bose-Einstein Condensates

    NASA Astrophysics Data System (ADS)

    Posazhennikova, Anna; Trujillo-Martinez, Mauricio; Kroha, Johann

    2016-06-01

    A Bose gas in a double-well potential, exhibiting a true Bose-Einstein condensate (BEC) amplitude and initially performing Josephson oscillations, is a prototype of an isolated, nonequilibrium many-body system. We investigate the quasiparticle (QP) creation and thermalization dynamics of this system by solving the time-dependent Keldysh-Bogoliubov equations. We find avalanchelike QP creation due to a parametric resonance between BEC and QP oscillations, followed by slow, exponential relaxation to a thermal state at an elevated temperature, controlled by the initial excitation energy of the oscillating BEC above its ground state. The crossover between the two regimes occurs because of an effective decoupling of the QP and BEC oscillations. This dynamics is analogous to elementary particle creation in models of the early universe. The thermalization in our setup occurs because the BEC acts as a grand canonical reservoir for the quasiparticle system.

  3. Quasiparticle-mediated spin Hall effect in a superconductor.

    PubMed

    Wakamura, T; Akaike, H; Omori, Y; Niimi, Y; Takahashi, S; Fujimaki, A; Maekawa, S; Otani, Y

    2015-07-01

    In some materials the competition between superconductivity and magnetism brings about a variety of unique phenomena such as the coexistence of superconductivity and magnetism in heavy-fermion superconductors or spin-triplet supercurrent in ferromagnetic Josephson junctions. Recent observations of spin-charge separation in a lateral spin valve with a superconductor evidence that these remarkable properties are applicable to spintronics, although there are still few works exploring this possibility. Here, we report the experimental observation of the quasiparticle-mediated spin Hall effect in a superconductor, NbN. This compound exhibits the inverse spin Hall (ISH) effect even below the superconducting transition temperature. Surprisingly, the ISH signal increases by more than 2,000 times compared with that in the normal state with a decrease of the injected spin current. The effect disappears when the distance between the voltage probes becomes larger than the charge imbalance length, corroborating that the huge ISH signals measured are mediated by quasiparticles. PMID:25985459

  4. Two-quasiparticle states in {sup 250}Bk studied by decay scheme and transfer reaction spectroscopy

    SciTech Connect

    Ahmad, I.; Kondev, F. G.; Koenig, Z. M.; McHarris, Wm. C.; Yates, S. W.

    2008-05-15

    Two-quasiparticle states in {sup 250}Bk were investigated with decay scheme studies and the single-neutron transfer reaction {sup 249}Bk(d,p){sup 250}Bk. Mass-separated sources of {sup 254}Es were used for {alpha} singles and {alpha}-{gamma} coincidence measurements. These studies, plus previous studies of {sup 254}Es{sup m} {alpha} decay and the {sup 249}Bk(n,{gamma}) reaction, provide spins and parities of the observed levels. The transfer reaction {sup 249}Bk(d,p){sup 250}Bk was used to deduce neutron single-particle components of the observed bands. Six pairs of singlet and triplet states, formed by the coupling of proton and neutron one-quasiparticle states, were identified. The splitting energies between the triplet and singlet states were found to be in agreement with previous calculations.

  5. Probing Bogoliubov Quasiparticles in Superfluid ^3He with a `Vibrating-Wire Like' MEMS Device

    NASA Astrophysics Data System (ADS)

    Defoort, M.; Dufresnes, S.; Ahlstrom, S. L.; Bradley, D. I.; Haley, R. P.; Guénault, A. M.; Guise, E. A.; Pickett, G. R.; Poole, M.; Woods, A. J.; Tsepelin, V.; Fisher, S. N.; Godfrin, H.; Collin, E.

    2016-05-01

    We have measured the interaction between superfluid ^3He-B and a micro-machined goalpost-shaped device at temperatures below 0.2 T_c. The measured damping follows well the theory developed for vibrating wires, in which the Andreev reflection of quasiparticles in the flow field around the moving structure leads to a nonlinear frictional force. At low velocities, the damping force is proportional to velocity, while it tends to saturate for larger excitations. Above a velocity of 2.6 mm s^{-1}, the damping abruptly increases, which is interpreted in terms of Cooper-pair breaking. Interestingly, this critical velocity is significantly lower than that reported with other mechanical probes immersed in superfluid ^3He. Furthermore, we report on a nonlinear resonance shape for large motion amplitudes that we interpret as an inertial effect due to quasiparticle friction, but other mechanisms could possibly be invoked as well.

  6. Quasiparticle electronic structure of Bi2Se3 via the sc-COHSEX+GW approach

    NASA Astrophysics Data System (ADS)

    Barker, Bradford A.; Deslippe, Jack; Yazyev, Oleg; Louie, Steven G.

    We present ab initio calculations of the quasiparticle electronic band structure of three-dimensional topological insulator material Bi2Se3 using the full spinor GW approach. The mean-field is initially computed at the DFT level in the local density approximation (LDA) using fully-relativistic pseudopotentials. We then improve the mean-field electronic structure by solving Dyson's equation in the static COHSEX approximation, self-consistently updating the eigenvalues, eigenvectors, and dielectric screening. After a few iterations, we then perform a GW calculation to determine the quasiparticle energies. We compare our calculated results to experimental values of the band gaps and effective masses. This work was supported by NSF Grant No. DMR15-1508412 and U.S. DOE under Contract No. DE-AC02-05CH11231. Computational resources have been provided by DOE at LBNL's NERSC facility and the NSF through XSEDE resources at NICS.

  7. Coherent quasiparticles with a small Fermi Surface in lightly doped Sr3Ir2O7

    NASA Astrophysics Data System (ADS)

    de la Torre, Alberto; McKeown Walker, Siobhan; Tamai, Anna; Hunter, Emily; Subedi, Alaska; Kim, Timur; Hoesch, Moritz; Perry, Robin; Georges, Antoine; Baumberger, Felix

    2015-03-01

    We characterize the electron doping evolution of (Sr1-xLax)Ir2O7 by means of angle-resolved photoemission. Concomitant with the metal insulator transition around x ~ 0 . 05 we find the emergence of coherent quasiparticle states forming a closed small Fermi surface of volume 3 x / 2 , where x is the independently measured La concentration. The quasiparticle weight Z remains large along the entire Fermi surface, consistent with the moderate renormalization of the low-energy dispersion and no pseudogap is observed. This indicates a conventional, weakly correlated Fermi liquid state with a momentum independent residue Z ~ 0 . 5 in lightly doped Sr3Ir2O7, in stark contrast with underdoped cuprates.

  8. Coherent Quasiparticles with a Small Fermi Surface in Lightly Doped Sr3Ir2O7

    NASA Astrophysics Data System (ADS)

    de la Torre, A.; Hunter, E. C.; Subedi, A.; McKeown Walker, S.; Tamai, A.; Kim, T. K.; Hoesch, M.; Perry, R. S.; Georges, A.; Baumberger, F.

    2014-12-01

    We characterize the electron doping evolution of (Sr1 -xLax)3Ir2O7 by means of angle-resolved photoemission. Concomitant with the metal insulator transition around x ≈0.05 we find the emergence of coherent quasiparticle states forming a closed small Fermi surface of volume 3 x /2 , where x is the independently measured La concentration. The quasiparticle weight Z remains large along the entire Fermi surface, consistent with the moderate renormalization of the low-energy dispersion, and no pseudogap is observed. This indicates a conventional, weakly correlated Fermi liquid state with a momentum independent residue Z ≈0.5 in lightly doped Sr3Ir2O7 .

  9. Parity switching and decoherence by quasiparticles in single-junction transmons

    NASA Astrophysics Data System (ADS)

    Catelani, Gianluigi

    2014-03-01

    Transmons are at present among the most coherent superconducting qubits, reaching quality factors of order 106 both in 3D and 2D architectures. These high quality factors enable detailed investigations of decoherence mechanisms. An intrinsic decoherence process originates from the coupling between the qubit degree of freedom and the quasiparticles that tunnel across Josephson junctions. In a transmon, tunneling of a single quasiparticle is associated with a change in parity. I will discuss the theory of the parity switching rate in single-junction transmons, compare it with recent measurements, and consider the role of parity switching in limiting the coherence time. Partial support by the EU under REA grant agreement CIG-618258 is acknowledged.

  10. Structure of three-quasiparticle isomers in {sup 169}Ho and {sup 171}Tm.

    SciTech Connect

    Dracoulis, G. D.; Lane, G. J.; Hughes, R. O.; Kondev, F. G.; Watanabe, H.; Seweryniak, D.; Zhu, S.; Carpenter, M. P.; Chiara, C. J.; Janssens, R. V. F.; Lauritsen, T.; Lister, C. J.; McCutchan, E. A.; Stefanescu, I.; Chowdhury, P.

    2010-09-17

    A three-quasiparticle isomer with {tau}=170(8) {micro}s and K{sup {pi}} = (19/2{sup +}) has been identified in the neutron-rich isotope {sup 169}Ho. The isomer decays with K-forbidden transitions to members of a band associated with the 7/2-[523] proton configuration, whose structure is characterized through analysis of the in-band {gamma}-ray branching ratios. In the isotone {sup 171}Tm, the rotational band based on the known 19/2{sup +}, three-quasiparticle isomer has also been observed. Alternative one-proton two-neutron configurations for the isomer in {sup 169}Ho are discussed in terms of multiquasiparticle calculations and through a comparison with the structures observed in {sup 171}Tm.

  11. Volume dependent quasiparticle spectral weight in NiS2-xSex system

    NASA Astrophysics Data System (ADS)

    Marini, C.; Perucchi, A.; Dore, P.; Topwal, D.; Sarma, D. D.; Lupi, S.; Postorino, P.

    2012-05-01

    We discuss the evolution of Infrared reflectivity at room temperature under various pressures (P) and Se alloying concentration in the strongly correlated NiS2-xSex pyrite. Measurements gave a complete picture of the optical response of the system on approaching the P-induced and Se-induced metallic state. A peculiar non-monotonic (V-shaped) volume dependence was found for the quasiparticle spectral weight of both pure and Se-doped compounds.

  12. Anomalous Quasiparticle Symmetries and Non-Abelian Defects on Symmetrically Gapped Surfaces of Weak Topological Insulators

    NASA Astrophysics Data System (ADS)

    Mross, David F.; Essin, Andrew; Alicea, Jason; Stern, Ady

    2016-01-01

    We show that boundaries of 3D weak topological insulators can become gapped by strong interactions while preserving all symmetries, leading to Abelian surface topological order. The anomalous nature of weak topological insulator surfaces manifests itself in a nontrivial action of symmetries on the quasiparticles; most strikingly, translations change the anyon types in a manner impossible in strictly 2D systems with the same symmetry. As a further consequence, screw dislocations form non-Abelian defects that trap Z4 parafermion zero modes.

  13. Analytical results for quasiparticle excitations in the Fractional Quantum Hall Effect regime

    NASA Astrophysics Data System (ADS)

    Bentalha, Z.

    2016-07-01

    In this work, quasiparticle energies for systems with N = 3 , 4 , 5 , 6 and 7 electrons are calculated analytically in both Laughlin and composite fermions (CF) theories by considering the electron-electron interaction potential. The exact results we have obtained for the first and the second excited states agree with previous numerical results. This study shows that at this level the CF-wave function has lower energy in comparison with Laughlin wave function energy.

  14. Spectral Function and Quasiparticle Damping of Interacting Bosons in Two Dimensions

    SciTech Connect

    Sinner, Andreas; Kopietz, Peter; Hasselmann, Nils

    2009-03-27

    We employ the functional renormalization group to study dynamical properties of the two-dimensional Bose gas. Our approach is free of infrared divergences, which plague the usual diagrammatic approaches, and is consistent with the exact Nepomnyashchy identity, which states that the anomalous self-energy vanishes at zero frequency and momentum. We recover the correct infrared behavior of the propagators and present explicit results for the spectral line shape, from which we extract the quasiparticle dispersion and dampi0008.

  15. A quasiparticle-trap-assisted transition-edge sensor for phonon-mediated particle detection

    NASA Astrophysics Data System (ADS)

    Irwin, K. D.; Nam, S. W.; Cabrera, B.; Chugg, B.; Young, B. A.

    1995-11-01

    We have demonstrated the operation of composite superconducting tungsten and aluminum transition-edge sensors which take advantage of quasiparticle trapping and electrothermal feedback. We call these devices W/Al QETs (quasiparticle-trap-assisted electrothermal feedback transition-edge sensors). The quasiparticle trapping mechanism makes it possible to instrument large surface areas without increasing sensor heat capacity, thus allowing larger absorbers and reducing phonon collection times. The sensor consists of a 30-nm-thick superconducting tungsten thin film with Tc˜80 mK deposited on a high-purity silicon substrate. The W film is patterned into 200 parallel lines segments, each 2 μm wide and 800 μm long. Eight superconducting aluminum thin film pads are electrically connected to each segment, and cover a much larger surface area than the W. When phonons from particle interactions in the silicon crystal impinge on an aluminum pad, Cooper pairs are broken, forming quasiparticles which diffuse to the tungsten lines where they are rapidly thermalized. The W film is voltage biased, and self-regulates in temperature within its superconducting transition region by electrothermal feedback. Heat deposited in the film causes a current pulse of ˜100 μs duration, which is measured with a series array of dc superconducting quantum interference devices. We have demonstrated an energy resolution of <350 eV full width at half-maximum for 6 keV x rays incident on the backside of a 1 cm×1 cm×1 mm (0.25 g) silicon absorber, the highest resolution that has been reported for a fast (<1 ms pulse duration) calorimetric detector with an absorber mass≳0.1 g. Applications of this technology include dark matter searches and neutrino detection.

  16. Four-Quasiparticle High-K States in Neutron-Deficient Lead and Polonium Nuclei

    NASA Astrophysics Data System (ADS)

    Shi, Yue; Xu, Furong

    2012-06-01

    Configuration-constrained potential energy surface calculations have been performed to investigate four-quasiparticle high-K configurations in neutron-deficient lead and polonium isotopes. A good agreement between the calculations and the experimental data has been found for the excitation energy of the observed Kπ = 19- state in 188Pb. Several lowly excited high-K states are predicted, and the large oblate deformation and low energy indicate high-K isomerism in these nuclei.

  17. Quasiparticle and optical properties of rutile and anatase TiO2

    NASA Astrophysics Data System (ADS)

    Kang, Wei; Hybertsen, Mark S.

    2010-08-01

    Quasiparticle excitation energies and optical properties of TiO2 in the rutile and anatase structures are calculated using many-body perturbation-theory methods. Calculations are performed for a frozen crystal lattice; electron-phonon coupling is not explicitly considered. In the GW method, several approximations are compared and it is found that inclusion of the full frequency dependence as well as explicit treatment of the Ti semicore states are essential for accurate calculation of the quasiparticle energy-band gap. The calculated quasiparticle energies are in good agreement with available photoemission and inverse photoemission experiments. The results of the GW calculations, together with the calculated static screened Coulomb interaction, are utilized in the Bethe-Salpeter equation to calculate the dielectric function γ2(ω) for both the rutile and anatase structures. The results are in good agreement with experimental observations, particularly the onset of the main absorption features around 4 eV. For comparison to low-temperature optical-absorption measurements that resolve individual excitonic transitions in rutile, the low-lying discrete excitonic energy levels are calculated with electronic screening only. The lowest energy exciton found in the energy gap of rutile has a binding energy of 0.13 eV. In agreement with experiment, it is not dipole allowed but the calculated exciton energy exceeds that measured in absorption experiments by about 0.22 eV and the scale of the exciton binding energy is also too large. The quasiparticle energy alignment of rutile is calculated for nonpolar (110) surfaces. In the GW approximation, the valence-band maximum is 7.8 eV below the vacuum level, showing a small shift from density-functional theory results.

  18. Quasi-particles ultrafastly releasing kink bosons to form Fermi arcs in a cuprate superconductor

    PubMed Central

    Ishida, Y.; Saitoh, T.; Mochiku, T.; Nakane, T.; Hirata, K.; Shin, S.

    2016-01-01

    In a conventional framework, superconductivity is lost at a critical temperature (Tc) because, at higher temperatures, gluing bosons can no longer bind two electrons into a Cooper pair. In high-Tc cuprates, it is still unknown how superconductivity vanishes at Tc. We provide evidence that the so-called ≲70-meV kink bosons that dress the quasi-particle excitations are playing a key role in the loss of superconductivity in a cuprate. We irradiated a 170-fs laser pulse on Bi2Sr2CaCu2O8+δ and monitored the responses of the superconducting gap and dressed quasi-particles by time- and angle-resolved photoemission spectroscopy. We observe an ultrafast loss of superconducting gap near the d-wave node, or light-induced Fermi arcs, which is accompanied by spectral broadenings and weight redistributions occurring within the kink binding energy. We discuss that the underlying mechanism of the spectral broadening that induce the Fermi arc is the undressing of quasi-particles from the kink bosons. The loss mechanism is beyond the conventional framework, and can accept the unconventional phenomena such as the signatures of Cooper pairs remaining at temperatures above Tc. PMID:26728626

  19. Quasiparticle degrees of freedom versus the perfect fluid as descriptors of the quark-gluon plasma

    SciTech Connect

    Levy, L. A. Linden; Nagle, J. L.; Rosen, C.; Steinberg, P.

    2008-10-15

    The hot nuclear matter created at the Relativistic Heavy Ion Collider has been characterized by near-perfect fluid behavior. We demonstrate that this stands in contradiction to the identification of quantum chromodynamics quasiparticles with the thermodynamic degrees of freedom in the early (fluid) stage of heavy-ion collisions. The empirical observation of constituent quark 'n{sub q}' scaling of elliptic flow [PHENIX, A. Adare et al., Phys. Rev. Lett. 98, 162301 (2007)] is juxtaposed with the lack of such scaling behavior in hydrodynamic fluid calculations followed by Cooper-Frye freeze-out to hadrons. As the hydrodynamic fluid expands, increasing viscous effects may allow for a short time period of 'quasiparticle transport' prior to hadronization. However, without a detailed understanding of the transitions between these time stages, the 'n{sub q}' scaling is not a necessary consequence of this prescription. Also, if the duration of this stage is too short, it may not support well-defined quasiparticles. By comparing and contrasting the coalescence of quarks into hadrons with the similar process of producing light nuclei from nucleons, it is shown that the observation of 'n{sub q}' scaling in the final state does not necessarily imply that the constituent degrees of freedom were the relevant ones in the initial state.

  20. Decay and Fission Hindrance of Two- and Four-Quasiparticle K Isomers in 254Rf

    NASA Astrophysics Data System (ADS)

    David, H. M.; Chen, J.; Seweryniak, D.; Kondev, F. G.; Gates, J. M.; Gregorich, K. E.; Ahmad, I.; Albers, M.; Alcorta, M.; Back, B. B.; Baartman, B.; Bertone, P. F.; Bernstein, L. A.; Campbell, C. M.; Carpenter, M. P.; Chiara, C. J.; Clark, R. M.; Cromaz, M.; Doherty, D. T.; Dracoulis, G. D.; Esker, N. E.; Fallon, P.; Gothe, O. R.; Greene, J. P.; Greenlees, P. T.; Hartley, D. J.; Hauschild, K.; Hoffman, C. R.; Hota, S. S.; Janssens, R. V. F.; Khoo, T. L.; Konki, J.; Kwarsick, J. T.; Lauritsen, T.; Macchiavelli, A. O.; Mudder, P. R.; Nair, C.; Qiu, Y.; Rissanen, J.; Rogers, A. M.; Ruotsalainen, P.; Savard, G.; Stolze, S.; Wiens, A.; Zhu, S.

    2015-09-01

    Two isomers decaying by electromagnetic transitions with half-lives of 4.7(1.1) and 247 (73 ) μ s have been discovered in the heavy 254Rf nucleus. The observation of the shorter-lived isomer was made possible by a novel application of a digital data acquisition system. The isomers were interpreted as the Kπ=8- , ν2(7 /2+[624 ],9 /2-[734 ]) two-quasineutron and the Kπ=1 6+, 8-ν2(7 /2+[624 ],9 /2-[734 ])⊗8-π2(7 /2-[514 ],9 /2+[624 ]) four-quasiparticle configurations, respectively. Surprisingly, the lifetime of the two-quasiparticle isomer is more than 4 orders of magnitude shorter than what has been observed for analogous isomers in the lighter N =150 isotones. The four-quasiparticle isomer is longer lived than the 254Rf ground state that decays exclusively by spontaneous fission with a half-life of 23.2 (1.1 ) μ s . The absence of sizable fission branches from either of the isomers implies unprecedented fission hindrance relative to the ground state.

  1. Probing the Unconventional Superconducting State of LiFeAs by Quasiparticle Interference

    NASA Astrophysics Data System (ADS)

    Hänke, Torben; Sykora, Steffen; Schlegel, Ronny; Baumann, Danny; Harnagea, Luminita; Wurmehl, Sabine; Daghofer, Maria; Büchner, Bernd; van den Brink, Jeroen; Hess, Christian

    2012-03-01

    A crucial step in revealing the nature of unconventional superconductivity is to investigate the symmetry of the superconducting order parameter. Scanning tunneling spectroscopy has proven a powerful technique to probe this symmetry by measuring the quasiparticle interference (QPI) which sensitively depends on the superconducting pairing mechanism. A particularly well-suited material to apply this technique is the stoichiometric superconductor LiFeAs as it features clean, charge neutral cleaved surfaces without surface states and a relatively high Tc˜18K. Our data reveal that in LiFeAs the quasiparticle scattering is governed by a van Hove singularity at the center of the Brillouin zone which is in stark contrast to other pnictide superconductors where nesting is crucial for both scattering and s± superconductivity. Indeed, within a minimal model and using the most elementary order parameters, calculations of the QPI suggest a dominating role of the holelike bands for the quasiparticle scattering. Our theoretical findings do not support the elementary singlet pairing symmetries s++, s±, and d wave. This brings to mind that the superconducting pairing mechanism in LiFeAs is based on an unusual pairing symmetry such as an elementary p wave (which provides optimal agreement between the experimental data and QPI simulations) or a more complex order parameter (e.g., s+id wave symmetry).

  2. Modulation of the penetration depth of Nb and NbN films by quasiparticle injection

    SciTech Connect

    Track, E.K.; Radparvar, M.; Faris, S.M.

    1989-03-01

    A novel approach to modulating the inductance of a superconducting microstrip is described. This approach could be the basis for numerous practical applications, such as phase shifters and high frequency tuning elements. The physical mechanisms involved are quasiparticle injection, gap suppression, and penetration depth modulation. In this current, the authors have investigated the modulation of the penetration depth of niobium and niobium nitride films by excess quasiparticle injection. To this effect, all-niobium and all-niobium-nitride SQUID circuits are designed and fabricated. These circuits allow quasiparticle injection into the inductive element of the SQUID. This injection is achieved by 1. optical irradiation through an opening in a Nb reflective layer which partially masks the rest of the circuit, and 2. electronic current injection through a tunnel junction overlaid on the microstrip inductance. Penetration depth modulation is achieved with both methods. The magnitude of the effect varies from 10% to over 200% change in inductance. These results and their dependence on temperature and on the parameters of the control mechanism (light intensity, amount of current injection, etc.) are presented and discussed.

  3. Fermionic q-deformation and its connection to thermal effective mass of a quasiparticle

    NASA Astrophysics Data System (ADS)

    Algin, Abdullah; Senay, Mustafa

    2016-04-01

    A fermionic deformation scheme is applied to a study on the low-temperature quantum statistical behavior of a quasifermion gas model with intermediate statistics. Such a model does not satisfy the Pauli exclusion principle, and its quantum statistical properties are based on a formalism of the fermionic q-calculus. For low temperatures, several thermostatistical functions of the model such as the chemical potential, the heat capacity, and the entropy are derived by means of a function of the model deformation parameter q. The effect of fermionic q-deformation on the low-temperature thermostatistical properties of the model are discussed in detail. Our results show that the present deformed (quasi)fermion model provides remarkable connections of the model deformation parameter q, first, with the thermal effective mass of a quasiparticle, and second, with the temperature parameter. Hence, it turns out that the model deformation parameter q has also a role controlling the strength of effective quasiparticle interactions in the model. Finally, we conclude that this work can be useful for understanding the details of interaction mechanism of fermions such as quasiparticle states emergent in the fractional quantum Hall effect.

  4. The birth of a quasiparticle in silicon observed in time-frequency space.

    PubMed

    Hase, Muneaki; Kitajima, Masahiro; Constantinescu, Anca Monia; Petek, Hrvoje

    2003-11-01

    The concept of quasiparticles in solid-state physics is an extremely powerful tool for describing complex many-body phenomena in terms of single-particle excitations. Introducing a simple particle, such as an electron, hole or phonon, deforms a many-body system through its interactions with other particles. In this way, the added particle is 'dressed' or 'renormalized' by a self-energy cloud that describes the response of the many-body system, so forming a new entity--the quasiparticle. Using ultrafast laser techniques, it is possible to impulsively generate bare particles and observe their subsequent dressing by the many-body interactions (that is, quasiparticle formation) on the time and energy scales governed by the Heisenberg uncertainty principle. Here we describe the coherent response of silicon to excitation with a 10-femtosecond (10(-14) s) laser pulse. The optical pulse interacts with the sample by way of the complex second-order nonlinear susceptibility to generate a force on the lattice driving coherent phonon excitation. Transforming the transient reflectivity signal into frequency-time space reveals interference effects leading to the coherent phonon generation and subsequent dressing of the phonon by electron-hole pair excitations. PMID:14603313

  5. Localization of Bogoliubov quasiparticles in interacting Bose gases with correlated disorder

    NASA Astrophysics Data System (ADS)

    Lugan, P.; Sanchez-Palencia, L.

    2011-07-01

    We study the Anderson localization of Bogoliubov quasiparticles (elementary many-body excitations) in a weakly interacting Bose gas of chemical potential μ subjected to a disordered potential V. We introduce a general mapping (valid for weak inhomogeneous potentials in any dimension) of the Bogoliubov-de Gennes equations onto a single-particle Schrödinger-like equation with an effective potential. For disordered potentials, the Schrödinger-like equation accounts for the scattering and localization properties of the Bogoliubov quasiparticles. We derive analytically the localization lengths for correlated disordered potentials in the one-dimensional geometry. Our approach relies on a perturbative expansion in V/μ, which we develop up to third order, and we discuss the impact of the various perturbation orders. Our predictions are shown to be in very good agreement with direct numerical calculations. We identify different localization regimes: For low energy, the effective disordered potential exhibits a strong screening by the quasicondensate density background, and localization is suppressed. For high-energy excitations, the effective disordered potential reduces to the bare disordered potential, and the localization properties of quasiparticles are the same as for free particles. The maximum of localization is found at intermediate energy when the quasicondensate healing length is of the order of the disorder correlation length. Possible extensions of our work to higher dimensions are also discussed.

  6. Quantum confinement and quasiparticle corrections in α-HgS from first principles

    NASA Astrophysics Data System (ADS)

    Lanzillo, Nicholas A.; Roy, Sujit; Nayak, Saroj K.

    2015-06-01

    Using a combination of density functional theory and many-body GW corrections, we calculate the quasiparticle band gap of bulk α-HgS and investigate the effect of quantum confinement on the geometric, electronic and optical structures. The basic structural unit of α-HgS is a one-dimensional helical chain consisting of covalently bound Hg and S atoms. When isolated to just a single helix or to a few-helix configuration, we find that α-HgS becomes a wide-gap semiconductor with a quasiparticle band gap as large as 7.0 eV, in contrast to the bulk structure with a direct quasiparticle band gap of 2.8 eV and an indirect gap of 2.14 eV. This dramatic increase in the band gap is attributed to quantum confinement effects on the geometry and intra-helix bonding. Shifts in the band gaps are also reflected as shifts in the low-energy optical absorption spectra calculated via density functional theory. As more helical chains are added, the band gap decreases sharply while the geometry becomes more bulk-like. This work illustrates the strong effects of quantum confinement in low-dimensional α-HgS nanostructures.

  7. Quasi-particles ultrafastly releasing kink bosons to form Fermi arcs in a cuprate superconductor.

    PubMed

    Ishida, Y; Saitoh, T; Mochiku, T; Nakane, T; Hirata, K; Shin, S

    2016-01-01

    In a conventional framework, superconductivity is lost at a critical temperature (Tc) because, at higher temperatures, gluing bosons can no longer bind two electrons into a Cooper pair. In high-Tc cuprates, it is still unknown how superconductivity vanishes at Tc. We provide evidence that the so-called ≲ 70-meV kink bosons that dress the quasi-particle excitations are playing a key role in the loss of superconductivity in a cuprate. We irradiated a 170-fs laser pulse on Bi2Sr2CaCu2O(8+δ) and monitored the responses of the superconducting gap and dressed quasi-particles by time- and angle-resolved photoemission spectroscopy. We observe an ultrafast loss of superconducting gap near the d-wave node, or light-induced Fermi arcs, which is accompanied by spectral broadenings and weight redistributions occurring within the kink binding energy. We discuss that the underlying mechanism of the spectral broadening that induce the Fermi arc is the undressing of quasi-particles from the kink bosons. The loss mechanism is beyond the conventional framework, and can accept the unconventional phenomena such as the signatures of Cooper pairs remaining at temperatures above Tc. PMID:26728626

  8. Microstructures and perpendicular magnetic properties of Co/Pd multilayers on various metal/MgO seed-layers

    NASA Astrophysics Data System (ADS)

    Kim, Sanghoon; Lee, Sangho; Kim, Joonyong; Kang, Jaeyong; Hong, Jongill

    2011-04-01

    We studied the effects of metal/MgO seeds (metal = Ta, Ru, or Pd) on the crystalline structure and perpendicular magnetic properties of Co/Pd multilayers to investigate the possibility of developing a (100) texture with sufficiently high perpendicular anisotropy and small switching field distributions for applications such as patterned media and perpendicular magnetic random access memories. The Pd/MgO or the MgO seed successfully promoted a (100) texture of Co/Pd multilayers. In particular, the Pd/MgO seed developed a strong (100) texture in the Co/Pd multilayer and resulted in perpendicular magnetic anisotropies ˜2 × 106 erg/cm3. On the other hand, the Co/Pd multilayer with the Ta/MgO or the Ru/MgO seed showed a strong (111) texture, inducing a perpendicular magnetic anisotropy higher than that of the (100) textured films. The coercive fields of Co/Pd multilayers with the (111) texture were over 4 kOe and higher than those with the (100) texture, which were ˜2 kOe when they were patterned into 2 × 2 μm2 islands. The switching field distributions of the Co/Pd multilayers with the (100) texture were smaller than those of the Co/Pd multilayers with the (111) texture. Our findings suggest that the Pd/MgO or the MgO seed can be a template suitable for device applications.

  9. Clinical and prognostic significance of PD-1 and PD-L1 expression in sarcomas.

    PubMed

    Paydas, Semra; Bagir, Emine Kilic; Deveci, Mehmet Ali; Gonlusen, Gulfiliz

    2016-08-01

    Programmed death-1 (PD-1) and programmed death-ligand 1 (PD-L1) are new targets in cancer immunotherapy in recent years. The aim of this study is to evaluate the PD-1/PD-L1 expressions in sarcomas and to determine association between PD-1/PD-L1 expressions and clinical/pathological properties in some sarcoma subtypes. Formalin-fixed, paraffin-embedded tissue samples from 65 cases with sarcomas were analyzed. Immunohistochemical staining was performed to detect the PD-1 and PD-L1 expressions in tumor tissue and microenvironment, separately. PD-1 expression in tumor tissue and microenvironment was detected in 11 (17 %) and 8 (12 %) cases, respectively. PD-L1 expression in tumor tissue and microenvironment was detected in 19 (29 %) and 20 cases (30 %), respectively. None of the 5 Ewing sarcomas involving bone showed PD-1/PD-L1 expression, while 2 of 3 cases with Ewing sarcomas involving soft tissue showed PD-1 and PD-L1 expression. Among 5 cases with Kaposi sarcoma, four showed PD-1 and/or PD-L1 expression in tumor or microenvironment. PD-1/PD-L1 expressions were detected 3 of 6 cases with pleomorphic sarcoma, 2 of 4 cases with peripheral nerve sheath tumors and 1 of 4 cases with synovial sarcoma. Interestingly, strongest PD-1/PD-L1 expressions in our study group were detected in 2 sarcoma cases with the history of giant cell tumor. PD-1 and PD-L1 expressions are up to 30 % of the cases with sarcomas. It may be rational to target programmed death pathway in Kaposi sarcoma, pleomorphic sarcoma and peripheral nerve sheath tumors. Strong expression of PD-1/PD-L1 in cases with previous giant cell bone tumor has been found to be interesting and must be studied in giant cell tumor samples. PMID:27421997

  10. PD-L1 and Survival in Solid Tumors: A Meta-Analysis

    PubMed Central

    Li, Lijun; Chai, Ying; Huang, Jian

    2015-01-01

    Background Numerous agents targeting PD-L1/PD-1 check-point are in clinical development. However, the correlation between PD-L1expression and prognosis of solid tumor is still in controversial. Here, we elicit a systematic review and meta-analysis to investigate the potential value of PD-L1 in the prognostic prediction in human solid tumors. Methods Electronic databases were searched for studies evaluating the expression of PD-L1 and overall survival (OS) of patients with solid tumors. Odds ratios (ORs) from individual studies were calculated and pooled by using a random-effect model, and heterogeneity and publication bias analyses were also performed. Results A total of 3107 patients with solid tumor from 28 published studies were included in the meta-analysis. The median percentage of solid tumors with PD-L1 overexpression was 52.5%. PD-L1 overexpression was associated with worse OS at both 3 years (OR = 2.43, 95% confidence interval (CI) = 1.60 to 3.70, P < 0.0001) and 5 years (OR = 2.23, 95% CI = 1.40 to 3.55, P = 0.0008) of solid tumors. Among the tumor types, PD-L1 was associated with worse 3 year-OS of esophageal cancer, gastric cancer, hepatocellular carcinoma, and urothelial cancer, and 5 year-OS of esophageal cancer, gastric cancer and colorectal cancer. Conclusions These results suggest that expression of PD-L1 is associated with worse survival in solid tumors. However, the correlations between PD-L1 and prognosis are variant among different tumor types. More studies are needed to investigate the clinical value of PD-L1 expression in prognostic prediction and treatment option. PMID:26114883

  11. Differential induction of PD-1/PD-L1 in Neuroimmune cells by drug of abuse.

    PubMed

    Mishra, Vikas; Schuetz, Heather; Haorah, James

    2015-01-01

    Interaction of programmed cell death protein 1 (PD-1) and programmed death-ligand 1 (PD-L1) plays a critical role in regulating the delicate balance between protective immunity and tolerance. Human neuroimmune cells express very low or undetectable levels of PD-1/PD-L1 in normal physiological condition.We seek to examine if exposure of these cells to drug of abuse such as methamphetamine (METH) alters the profile of PD-1/PD-L1 levels, thereby dampens the innate immune response of the host cells. Thus, we assessed the changes in the levels of PD-1/PD-L1 in primary human macrophages, brain endothelial cells (hBECs), astrocytes, microglia, and neurons after exposure to METH. We observed that stimulation of these neuroimmune cells by METH responded differentially to PD-1/PD-L1 expression. Stimulation of macrophage culture with 50 μM of METH exhibited immediate gradual upregulation of PD-L1, while increase in PD-1 took 2-4 hours later than PD-L1. The response of hBECs to PD-1/PD-L1 induction occurred at 24 hours, while increase of PD-1/PD-L1 levels in neurons and microglia was immediate following METH exposure. We found that astrocytes expressed moderate levels of endogenous PD-1/PD-L1, which was diminished by METH exposure. Our findings show a differential expression of PD-1/PD-L1 in neuroimmune cells in response to METH stimulation, suggesting that PD-1/PD-L1 interplay in these cell types could orchestrate the intercellular interactive communication for neuronal death or protection in the brain environment. PMID:26330898

  12. Differential induction of PD-1/PD-L1 in Neuroimmune cells by drug of abuse

    PubMed Central

    Mishra, Vikas; Schuetz, Heather; Haorah, James

    2015-01-01

    Interaction of programmed cell death protein 1 (PD-1) and programmed death-ligand 1 (PD-L1) plays a critical role in regulating the delicate balance between protective immunity and tolerance. Human neuroimmune cells express very low or undetectable levels of PD-1/PD-L1 in normal physiological condition.We seek to examine if exposure of these cells to drug of abuse such as methamphetamine (METH) alters the profile of PD-1/PD-L1 levels, thereby dampens the innate immune response of the host cells. Thus, we assessed the changes in the levels of PD-1/PD-L1 in primary human macrophages, brain endothelial cells (hBECs), astrocytes, microglia, and neurons after exposure to METH. We observed that stimulation of these neuroimmune cells by METH responded differentially to PD-1/PD-L1 expression. Stimulation of macrophage culture with 50 μM of METH exhibited immediate gradual upregulation of PD-L1, while increase in PD-1 took 2-4 hours later than PD-L1. The response of hBECs to PD-1/PD-L1 induction occurred at 24 hours, while increase of PD-1/PD-L1 levels in neurons and microglia was immediate following METH exposure. We found that astrocytes expressed moderate levels of endogenous PD-1/PD-L1, which was diminished by METH exposure. Our findings show a differential expression of PD-1/PD-L1 in neuroimmune cells in response to METH stimulation, suggesting that PD-1/PD-L1 interplay in these cell types could orchestrate the intercellular interactive communication for neuronal death or protection in the brain environment. PMID:26330898

  13. Collectivity of {sup 98}Pd

    SciTech Connect

    Fransen, C.; Blazhev, A.; Dewald, A.; Jolie, J.; Muecher, D.; Pissulla, T.; Moeller, O.

    2009-01-28

    The N = 52 nucleus {sup 98}Pd was investigated at the Cologne TANDEM accelerator both with the Cologne plunger using the recoil distance Doppler-shift method (RDDS) and with the Cologne HORUS spectrometer for a {gamma}{gamma} angular correlation experiment. For the first time lifetimes of yrast states and highly excited low-spin states were measured in {sup 98}Pd and the low-spin level scheme was extended. From our data we were able to interpret {sup 98}Pd as a nucleus that exhibits some collective features, but is obviously much less collective than the neighboring N = 52 isotones {sup 94}Mo and {sup 96}Ru due to its closeness to doubly-magic {sup 100}Sn.

  14. Phase Stability for the Pd-Si System. First-Principles, Experiments, and Solution-Based Modeling

    SciTech Connect

    Zhou, S. H.; Huo, Y.; Napolitano, Ralph E.

    2015-11-05

    Relative stabilities of the compounds in the binary Pd-Si system were assessed using first-principles calculations and experimental methods. Calculations of lattice parameters and enthalpy of formation indicate that Pd5Si-μ, Pd9Si2-α, Pd3 Si-β, Pd2 Si-γ, and PdSi-δ are the stable phases at 0 K (-273 °C). X-ray diffraction analyses (XRD) and electron probe microanalysis (EPMA) of the as-solidified and heat-treated samples support the computational findings, except that the PdSi-δ phase was not observed at low temperature. Considering both experimental data and first-principles results, the compounds Pd 5 Si-μ, Pd9 Si2-α, Pd3Si-β, and Pd2Si-γ are treated as stable phases down to 0 K (-273 °C), while the PdSi-δ is treated as being stable over a limited range, exhibiting a lower bound. Using these findings, a comprehensive solution-based thermodynamic model is formulated for the Pd-Si system, permitting phase diagram calculation. Moreover, the liquid phase is described using a three-species association model and other phases are treated as solid solutions, where a random substitutional model is adopted for Pd-fcc and Si-dia, and a two-sublattice model is employed for Pd5Si-μ, Pd9Si2-α, Pd3Si-β, Pd2Si-γ, and PdSi-δ. Model parameters are fitted using available experimental data and first-principles data, and the resulting phase diagram is reported over the full range of compositions.

  15. Quasiparticle energies, excitonic effects, and dielectric screening in transparent conducting oxides

    NASA Astrophysics Data System (ADS)

    Schleife, André

    Using the power of high-performance super computers, computational materials scientists nowadays employ highly accurate quantum-mechanical approaches to reliably predict materials properties. In particular, many-body perturbation theory is an excellent framework for performing theoretical spectroscopy on novel materials including transparent conducting oxides, since this framework accurately describes quasiparticle and excitonic effects.We recently used hybrid exchange-correlation functionals and an efficient implementation of the Bethe-Salpeter approach to investigate several important transparent conducting oxides. Despite their exceptional potential for applications in photovoltaics and optoelectronics their optical properties oftentimes remain poorly understood: Our calculations explain the optical spectrum of bixbyite indium oxide over a very large photon energy range, which allows us to discuss the importance of quasiparticle and excitonic effects at low photon energies around the absorption onset, but also for excitations up to 40 eV. We show that in this regime the energy dependence of the electronic self energy cannot be neglected. Furthermore, we investigated the influence of excitonic effects on optical absorption for lanthanum-aluminum oxide and hafnium oxide. Their complicated conduction band structures require an accurate description of quasiparticle energies and we find that for these strongly polar materials, a contribution of the lattice polarizability to dielectric screening needs to be taken into account. We discuss how this affects the electron-hole interaction and find a strong influence on excitonic effects.The deep understanding of electronic excitations that can be obtained using these modern first-principles techniques, eventually will allow for computational materials design, e.g. of band gaps, densities of states, and optical properties of transparent conducting oxides and other materials with societally important applications.

  16. Light quasiparticles dominate electronic transport in molecular crystal field-effect transistors

    SciTech Connect

    Li, Z. Q.; Podzorov, V.; Sai, N.; Martin, Michael C.; Gershenson, M. E.; Di Ventra, M.; Basov, D. N.

    2007-03-01

    We report on an infrared spectroscopy study of mobile holes in the accumulation layer of organic field-effect transistors based on rubrene single crystals. Our data indicate that both transport and infrared properties of these transistors at room temperature are governed by light quasiparticles in molecular orbital bands with the effective masses m[small star, filled]comparable to free electron mass. Furthermore, the m[small star, filled]values inferred from our experiments are in agreement with those determined from band structure calculations. These findings reveal no evidence for prominent polaronic effects, which is at variance with the common beliefs of polaron formation in molecular solids.

  17. Robust determination of the superconducting gap sign structure via quasiparticle interference

    NASA Astrophysics Data System (ADS)

    Hirschfeld, P. J.; Altenfeld, D.; Eremin, I.; Mazin, I. I.

    2015-11-01

    Phase-sensitive measurements of the superconducting gap in Fe-based superconductors have proven more difficult than originally anticipated. While quasiparticle interference (QPI) measurements based on scanning tunneling spectroscopy are often proposed as definitive tests of gap structure, the analysis typically relies on details of the model employed. Here we point out that the temperature dependence of momentum-integrated QPI data can be used to identify gap sign changes in a qualitative way, and present an illustration for s± and s++ states in a system with typical Fe-pnictide Fermi surface.

  18. Equation of state of a quasiparticle model at finite chemical potential and quark star

    NASA Astrophysics Data System (ADS)

    Tian, Ya-Lan; Yan, Yan; Li, Hua; Luo, Xin-Lian; Zong, Hong-Shi

    2012-02-01

    In this paper, we employ the equation of state (EOS) of the quasiparticle model proposed in A. M. Zhao , Mod. Phys. Lett. A 25, 47 (2010)MPLAEQ0217-732310.1142/S0217732310031361] which incorporates the effect of vacuum negative pressure to study the properties of quark stars. In our model the EOS has the correct behavior required by QCD in the small and large μ limit. We employ this EOS to calculate the mass-radii relation and mass-energy density relation of quark stars. Our results are found to be consistent with the most recent astronomical observations.

  19. Destruction of Fermi liquid quasiparticles in two dimensions by critical fluctuations

    NASA Astrophysics Data System (ADS)

    Tremblay, Andr'e.-Marie

    1996-03-01

    For almost forty years, the concepts of Fermi liquid theory have served as a basis to understand interacting fermion systems. Recently, especially in the context of high-temperature superconductors, the universal applicability of Fermi-liquid theory has been challenged. Most studies of the stability of the Fermi liquid have been done at zero temperature. However, in many physically interesting cases, a phase transition at some temperature Tc trivially precludes a zero-temperature Fermi liquid. Yet the system behaves as a Fermi liquid at finite temperature when T_cquasiparticles arises. This is especially interesting in two dimensions where the transition to a spin density wave state (SDW) occurs only at exactly zero temperature ( T_c=T_N=0) but the system enters a renormalized classical regime (RC) at a finite temperature T_X<t. After formulating the approach, (Y.M. Vilk, Liang Chen and A.-M.S. Tremblay Phys. Rev. B Rapid Comm. 49), 13 267 (1994), and J. Chem. Phys. Solids, (in press) and Y.M. Vilk and A.-M.S. Tremblay, Europhys. Lett. (in press) I use it to find under which conditions critical spin fluctuations destroy the original Fermi liquid quasiparticles in the paramagnetic state. The quasiparticles are replaced by precursors of

  20. Dilepton production by dynamical quasi-particles in the strongly interacting quark-gluon plasma

    NASA Astrophysics Data System (ADS)

    Linnyk, O.

    2011-02-01

    We address the dilepton production by the constituents of the strongly interacting quark-gluon plasma (sQGP). In order to make quantitative predictions for dilepton rates at experimentally relevant low dilepton mass (O(1GeV)) and strong coupling (αS ~ 0.5-1), we take into account non-perturbative spectral functions and self-energies of the quarks, antiquarks and gluons. For this purpose, we use parametrizations of the quark and gluon propagators provided by the dynamical quasi-particle model (DQPM) matched to reproduce lattice quantum chromodynamics (QCD) data. The DQPM describes QCD properties in terms of the single-particle Green's functions and leads to the notion of the constituents of the sQGP being effective quasi-particles, which are massive and have broad spectral functions (due to large interaction rates). By 'dressing' the quark and gluon lines with the effective propagators, we derive the off-shell cross sections for dilepton production in the reactions q+\\,\\bar{q}\\rightarrow l^+l^- (Born mechanism), q+ \\,\\bar{q}\\rightarrow g+\\,l^+l^- (quark annihilation with the gluon bremsstrahlung in the final state), q(\\bar{q})+g\\rightarrow q(\\bar{q})+ l^+l^- (gluon-Compton scattering), g\\rightarrow q+\\bar{q}+l^+l^- and q(\\bar{q})\\rightarrow q(\\bar{q})+g+l^+l^- (virtual gluon decay, virtual quark decay). In contrast to previous calculations of these cross sections, we account for virtualities of all the quarks and gluons. We find that finite masses of the effective quasi-particles not only screen the singularities typical of the perturbative cross sections with massless quarks, but also modify the shape of the dilepton production cross sections, especially at low dilepton mass Q and at the edges of the phase space. Finally, we use the calculated mass-dependent cross sections to identify the dependence of the dilepton rates on the spectral function widths of the initial and final quarks and gluons, which has not been estimated so far. The results

  1. Band Mapping and Quasiparticle Suppression in the One-Dimensional Organic Conductor TTF-TCNQ

    NASA Astrophysics Data System (ADS)

    Zwick, F.; Jérome, D.; Margaritondo, G.; Onellion, M.; Voit, J.; Grioni, M.

    1998-10-01

    Dispersing 1D bands have been observed for the first time in an organic conductor by high resolution photoemission experiments on TTF-TCNQ (tetrathiafulvalene-tetracyanoquinodimethane). Their properties are extremely unusual: the bandwidth is much larger than traditional estimates, and the quasiparticle states are strongly renormalized, with no weight at the chemical potential. A deep pseudogap around the Fermi energy persists, and even increases, up to room temperature. We also report a direct determination of kF in this material, and the observation of the opening of a Peierls gap in the low-temperature charge density wave phase.

  2. Quasiparticle band structure for the Hubbard systems: Application to. alpha. -CeAl sub 2

    SciTech Connect

    Costa-Quintana, J.; Lopez-Aguilar, F. ); Balle, S. ); Salvador, R. Supercomputer Computations Research Institute, Florida State University, Tallahassee, Florida 32306-4052 )

    1990-04-01

    A self-energy formalism for determining the quasiparticle band structure of the Hubbard systems is deduced. The self-energy is obtained from the dynamically screened Coulomb interaction whose bare value is the correlation energy {ital U}. A method for integrating the Schroedingerlike equation with the self-energy operator is given. The method is applied to the cubic Laves phase of {alpha}-CeAl{sub 2} because it is a clear Hubbard system with a very complex electronic structure and, moreover, this system provides us with sufficient experimental data for testing our method.

  3. Calculation of quasiparticle energy spectrum of silicon using the correlated Hartree-Fock method

    NASA Astrophysics Data System (ADS)

    Ishihara, Takamitsu; Yamagami, Hiroshi; Matsuzawa, Kazuya; Yasuhara, Hiroshi

    1999-06-01

    We present quasiparticle energy spectrum calculations of silicon using the correlated Hartree-Fock method proposed by Yasuhara and Takada [Phys. Rev. B 43, 7200 (1991)], in which the information on the effective mass of an electron liquid is included in the form of a nonlocal spin-parallel potential in addition to a local potential. The calculated band gaps of silicon are much improved, compared with the local density approximation values. The minimum indirect band gap is evaluated to be 1.37 eV.

  4. Impurity effects in quasiparticle spectrum of high-Tc superconductors (Review Article)

    NASA Astrophysics Data System (ADS)

    Pogorelov, Yu. G.; Santos, M. C.; Loktev, V. M.

    2011-08-01

    The revision is made of Green function methods that describe the dynamics of electronic quasiparticles in disordered superconducting systems with d-wave symmetry of order parameter. Various types of impurity perturbations are analyzed within the simplest T-matrix approximation. The extension of the common self-consistent T-matrix approximation (SCTMA) to the so-called group expansions in clusters of interacting impurity centers is discussed and hence the validity criteria for SCTMA are established. A special attention is paid to the formation of impurity resonance states and localized states near the characteristic points of energy spectrum, corresponding to nodal points on the Fermi surface.

  5. Lowest four-quasiparticle magnetic dipole band in {sup 128}Ba

    SciTech Connect

    Vogel, O.; Dewald, A.; von Brentano, P.; Gableske, J.; Kruecken, R.; Nicolay, N.; Gelberg, A.; Petkov, P.; Gizon, A.; Gizon, J.; Bazzacco, D.; Rossi Alvarez, C.; Pavan, P.; Lunardi, S.; Napoli, D.R.; Frauendorf, S.; Doenau, F.

    1997-09-01

    The four-quasiparticle magnetic dipole band in {sup 128}Ba has been investigated with the {sup 96}Zr({sup 36}S,4n){sup 128}Ba reaction at the GASP spectrometer of the Laboratori Nazionali di Legnaro. Linking transitions to the previously known positive parity states have been observed for the first time in this mass region and new transitions on top of the band have been found. The experimental results are compared to previously made tilted axis cranking calculations. {copyright} {ital 1997} {ital The American Physical Society}

  6. Spectroscopy in the second well of the {sup 148}Gd nucleus: Two quasiparticle and collective excitations

    SciTech Connect

    de Angelis, G.; Wyss, R.; Bazzacco, D.; De Poli, M.; Gadea, A.; Lunardi, S.; Napoli, D.R.; Petrache, C.M.; Rossi Alvarez, C.; Sferrazza, M.; Rubio, B. |||

    1996-02-01

    Six superdeformed (SD) bands have been observed in the nucleus {sup 148}Gd using the {gamma}-spectrometer GASP. The structure of the observed SD bands is discussed within the concept of cranked-Strutinsky-type calculations including pairing interaction. For the configuration assignments two different parametrizations of the Woods-Saxon potential are compared. Five of the observed SD bands are described in terms of quasiparticle configurations, whereas one is suggested to have vibrational-like structure. From this data a {Delta}{ital I}=2 staggering in the rotational spectrum of the yrast SD band also has been observed. {copyright} {ital 1996 The American Physical Society.}

  7. Non-analytic magnetic field dependence of quasi-particle properties of two-dimensional metals

    NASA Astrophysics Data System (ADS)

    Drukier, Casper; Lange, Philipp; Kopietz, Peter

    2015-02-01

    We show that in a weak external magnetic field H the quasi-particle residue and the renormalized electron Landé factor of two-dimensional Fermi liquids exhibit a non-analytic magnetic field dependence proportional to | H | which is due to electron-electron interactions and the Zeeman effect. We explicitly calculate the corresponding prefactors to second order in the interaction and show that they are determined by low-energy scattering processes involving only momenta close to the Fermi surface. These non-analytic terms appear in measurable quantities such as the density of states and the magnetoconductivity.

  8. Observation of a γ band based on a two-quasiparticle configuration in 70Ge

    NASA Astrophysics Data System (ADS)

    Raju, M. Kumar; Rao, P. V. Madhusudhana; Muralithar, S.; Singh, R. P.; Bhat, G. H.; Sheikh, J. A.; Tandel, S. K.; Sugathan, P.; Reddy, T. Seshi; Rao, B. V. Thirumala; Bhowmik, R. K.

    2016-03-01

    The structure of 70Ge has been studied through in-beam γ -ray spectroscopy. A new band structure is identified that leads to forking of the ground-state band into two excited bands. Band structures have been investigated using the microscopic triaxial projected shell-model approach. The observed forking is demonstrated to result from almost simultaneous band crossing of the two-neutron aligned configuration and the γ band built on this two-quasiparticle configuration with the ground-state band.

  9. Projected quasiparticle calculations for the N =82 odd-proton isotones

    SciTech Connect

    Losano, L. ); Dias, H. )

    1991-12-01

    The structure of low-lying states in odd-mass {ital N}=82 isotones (135{le}{ital A}{le}145) is investigated in terms of a number-projected one- and three-quasiparticles Tamm-Dancoff approximation. A surface-delta interaction is taken as the residual nucleon-nucleon interaction. Excitation energies, dipole and quadrupole moments, and {ital B}({ital M}1) and {ital B}({ital E}2) values are calculated and compared with the experimental data.

  10. Superconducting Gap Anisotropy and Quasiparticle Interactions: A Doping Dependent Photoemission Study

    SciTech Connect

    Mesot, J.; Norman, M.R.; Campuzano, J.C.; Mesot, J.; Campuzano, J.C.; Fretwell, H.M.; Kaminski, A.; Ding, H.; Randeria, M.; Paramekanti, A.; Takeuchi, T.; Yokoya, T.; Sato, T.; Takahashi, T.; Mochiku, T.; Kadowaki, K.

    1999-07-01

    Comparing photoemission measurements on Bi2212 with penetration depth data, we show that a description of the nodal excitations of the d -wave superconducting state in terms of noninteracting quasiparticles is inadequate, and we estimate the magnitude and doping dependence of the Landau interaction parameter which renormalizes the linear T contribution to the superfluid density. Furthermore, although consistent with d -wave symmetry, the gap with underdoping cannot be fit by the simple cos k{sub x}{minus}cos k{sub y} form, which suggests an increasing importance of long range interactions as the insulator is approached. {copyright} {ital 1999} {ital The American Physical Society }

  11. Multi-quasiparticle isomers in the vicinity of {sup 132}Sn

    SciTech Connect

    Watanabe, Hiroshi

    2010-05-12

    Nuclear isomers with multi-quasiparticle configurations near closed shells serve as valuable experimental probes which reveal the nature of residual nucleon-nucleon interactions. We have populated stable and neutron-rich odd-A antimony (Z = 51) and iodine (Z = 53) isotopes using multi-nucleon transfer and fusion-fission reactions with {sup 136}Xe beams and also using incomplete-fusion reactions with {sup 7}Li beams. The decay properties of high-spin isomers have been investigated by means of time-correlated gamma-ray and electron spectroscopy and the measurement of gamma-ray angular correlations.

  12. Multi-quasiparticle excitation: Extending shape coexistence in A{approx}190 neutron-deficient nuclei

    SciTech Connect

    Shi Yue; Liu, H. L.; Xu, F. R.; Walker, P. M.

    2010-10-15

    Multi-quasiparticle high-K states in neutron-deficient mercury, lead, and polonium isotopes have been investigated systematically by means of configuration-constrained potential-energy-surface calculations. An abundance of high-K states is predicted with both prolate and oblate shapes, which extends the shape coexistence of the mass region. Well-deformed shapes provide good conditions for the formation of isomers, as exemplified in {sup 188}Pb. Of particular interest is the prediction of low-lying 10{sup -} states in polonium isotopes, which indicate long-lived isomers.

  13. Multi-quasiparticle excitation: Extending shape coexistence in A~190 neutron-deficient nuclei

    NASA Astrophysics Data System (ADS)

    Shi, Yue; Xu, F. R.; Liu, H. L.; Walker, P. M.

    2010-10-01

    Multi-quasiparticle high-K states in neutron-deficient mercury, lead, and polonium isotopes have been investigated systematically by means of configuration-constrained potential-energy-surface calculations. An abundance of high-K states is predicted with both prolate and oblate shapes, which extends the shape coexistence of the mass region. Well-deformed shapes provide good conditions for the formation of isomers, as exemplified in Pb188. Of particular interest is the prediction of low-lying 10- states in polonium isotopes, which indicate long-lived isomers.

  14. Differential expression of PD-L1 between primary and metastatic sites in clear cell Renal Cell Carcinoma

    PubMed Central

    Callea, Marcella; Albiges, Laurence; Gupta, Mamta; Cheng, Su-Chun; Genega, Elizabeth M.; Fay, André P.; Song, Jiaxi; Carvo, Ingrid; Bhatt, Rupal S.; Atkins, Michael B.; Hodi, F. Stephen; Choueiri, Toni K.; McDermott, David F.; Freeman, Gordon J.; Signoretti, Sabina

    2015-01-01

    PD-L1 expression in primary clear cell renal cell carcinoma (ccRCC) increases the likelihood of response to anti-PD-1 inhibition, but fails to identify all responders. We hypothesized that PD-L1 levels assessed in randomly selected areas of the primary tumors may not accurately reflect expression levels in metastatic lesions, which are the target of systemic therapy. Therefore, we compared PD-L1 expression in a series of primary ccRCC and their metastases. Tissue blocks from 53 primary ccRCCs and 76 corresponding metastases were retrieved. Areas with predominant and highest nuclear grade were selected. Slides were immunostained with a validated anti-PD-L1 antibody (405.9A11). Membranous expression in tumor cells was quantified using H-score. Expression in tumor-infiltrating mononuclear cells (TIMC) was quantified using a combined score. Discordant tumor cell PD-L1 staining between primary tumors and metastases was observed in 11/53 cases (20.8%). Overall, tumor cell PD-L1 levels were not different in primary tumors and metastases (p=0.51). Tumor cell PD-L1 positivity was associated with higher T stage (p=0.03) and higher Fuhrman Nuclear Grade (FNG) (p<0.01). Within individual lesions, PD-L1 positivity was heterogeneous and almost exclusively detected in high nuclear grade areas (p<0.001). No difference was found in PD-L1 levels in TIMCs between primary tumors and metastases (p=0.82). Heterogeneity of PD-L1 expression in ccRCC suggests that its assessment as predictive biomarker for PD-1 blockade may require analysis of metastatic lesions. Notably, since PD-L1 expression was mostly detected in high nuclear grade areas, to avoid false negative results, these areas should be specifically selected for assessment. PMID:26014095

  15. Registration of PD 05035 and PD 05041 germplasm lines of cotton

    Technology Transfer Automated Retrieval System (TEKTRAN)

    PD 05035 and PD 05041 are noncommercial breeding lines of cotton jointly released by the Agricultural Research Service, United States Department of Agriculture, the Clemson University Experiment Station, and Cotton Incorporated in 2014. PD 05035 was selected from a cross of PD 93007 and ‘SG 747’, an...

  16. Registration of PD 06001 and PD 06078 germplasm lines of cotton

    Technology Transfer Automated Retrieval System (TEKTRAN)

    PD 06001 and PD 06078 are noncommercial breeding lines of cotton jointly released by the Agricultural Research Service, United States Department of Agriculture, the Clemson University Experiment Station, and Cotton Incorporated in 2014. PD 06001 is a breeding line selected from a cross of PD 93007 a...

  17. NO Adsorption on Pd(111)

    NASA Astrophysics Data System (ADS)

    Garda, Graciela R.; Ferullo, Ricardo M.; Castellani, Norberto J.

    The reactive behavior of NO on Pd(111) has been studied using a semiempirical theoretical method. The adsorption sites and the related electronic structure have been considered. In particular, the dissociation process has been studied and compared with CO. Different dissociation mechanisms have been proposed and the formation of NCO species has been considered. The results follow the trends reported in the experimental literature.

  18. First-principles study of ferromagnetism in Pd-doped and Pd- Cu-codoped BN

    NASA Astrophysics Data System (ADS)

    Wang, Q.; Wang, S.; Dai, J. F.; Li, W. X.

    2016-07-01

    In this paper, we aimed at probing the ferromagnetism properties of Pd and Pd-Cu- codoped supercell BN based on the first-principles methods. The formation energy, lattice constants, energy band structures, spin density of state, energy difference between ferromagnetism (FM) and autiferromagnetism (AFM) orderings were calculated. Formation energy calculations showed that Pd atom tended to replace B atom in the supercell. Pd-doped BN exhibited a half-metallic ferromagnetic. And the ferromagnetism arised form the strong hybridization between the Pd4d and N2p state. Pd-Cu-codoped BN also displayed a half-metallic ferromagnetic. The incorporation of Pd and Pd-Cu induced some impurity energy differences between FM and AFM orderings. It also showed that FM state was the ground state, and room temperature ferromagnetism may be expected. These results pointed out the possibility of fabricating BN based on dilute magnetic semiconductors (DMS) by doping with Pd and Pd-Cu.

  19. Human Cancer Immunotherapy with PD-1/PD-L1 Blockade

    PubMed Central

    Zheng, Peilin; Zhou, Zhiguang

    2015-01-01

    The ligation of programmed cell death-1 (PD-1) to its ligands PD-L1 and PD-L2 counteracts T-cell activation, which is critical in immune tolerance. The persistent high expression of PD-1 and PD-L1 are also observed on tumor-infiltrating lymphocytes and various tumor cells, maintaining the highly suppressive microenvironment in tumor sites and promoting tumor malignancies. The blockade of PD-1 axis with PD-L2 fusion protein or monoclonal antibodies against either PD-1 or PD-L1 has been clinically evaluated in various tumor types. This short review summarizes the progress of PD-1 axis blockade in clinical trials to evaluate its effectiveness in the antitumor immunotherapy. PMID:26448693

  20. Measuring, interpreting, and translating electron quasiparticle - Phonon interactions on the surfaces of the topological insulators bismuth selenide and bismuth telluride

    NASA Astrophysics Data System (ADS)

    Howard, Colin

    The following dissertation presents a comprehensive study of the interaction between Dirac fermion quasiparticles (DFQs) and surface phonons on the surfaces of the topological insulators Bi2Se3 and Bi2Te 3. Inelastic helium atom surface scattering (HASS) spectroscopy and time of flight (TOF) techniques were used to measure the surface phonon dispersion of these materials along the two high-symmetry directions of the surface Brillouin zone (SBZ). Two anomalies common to both materials are exhibited in the experimental data. First, there is an absence of Rayleigh acoustic waves on the surface of these materials, pointing to weak coupling between the surface charge density and the surface acoustic phonon modes and potential applications for soundproofing technologies. Secondly, both materials exhibit an out-of-plane polarized optical phonon mode beginning at the SBZ center and dispersing to lower energy with increasing wave vector along both high-symmetry directions of the SBZ. This trend terminates in a V-shaped minimum at a wave vector corresponding to 2 kF for each material, after which the dispersion resumes its upward trend. This phenomenon constitutes a strong Kohn anomaly and can be attributed to the interaction between the surface phonons and DFQs. To quantify the coupling between the optical phonons experiencing strong renormalization and the DFQs at the surface, a phenomenological model was constructed based within the random phase approximation. Fitting the theoretical model to the experimental data allowed for the extraction of the matrix elements of the coupling Hamiltonian and the modifications to the surface phonon propagator encoded in the phonon self energy. This allowed, for the first time, calculation of phonon mode-specific quasiparticle-phonon coupling lambdanu( q) from experimental data. Additionally, an averaged coupling parameter was determined for both materials yielding bar lambdaTe ≈ 2 and bar lambdaSe ≈ 0.7. These values are

  1. Design innovations and baseline findings in a long-term Parkinson’s trial: NET-PD LS-1

    PubMed Central

    2012-01-01

    Background Based on the pre-clinical and the results of a phase 2 futility study, creatine was selected for an efficacy trial in Parkinson’s disease (PD). We present the design rationale and a description of the study cohort at baseline. Methods A randomized, multicenter, double-blind, parallel group, placebo controlled Phase 3 study of creatine (10 gm daily) in participants with early, treated PD, the Long-term Study – 1 (LS-1) is being conducted by the NINDS Exploratory Trials in Parkinson’s Disease (NET-PD) network. The study utilizes a global statistical test (GST) encompassing multiple clinical rating scales to provide a multidimensional assessment of disease progression. Results A total of 1,741 PD participants from 45 sites in the U.S. and Canada were randomized 1:1 to either 10-gm creatine/day or matching placebo. Participants are being evaluated for a minimum of 5 years. The LS-1 baseline cohort includes participants treated with dopaminergic therapy and generally mild PD. Conclusions LS-1 represents the largest cohort of patients with early treated PD ever enrolled in a clinical trial. The GST approach should provide high power to test the hypothesis that daily administration of creatine (10gm/day) is more effective than placebo in slowing clinical decline in PD between baseline and the 5 year follow-up visit against the background of dopaminergic therapy and best PD care. PMID:23079770

  2. The rate of quasiparticle recombination probes the onset of coherence in cuprate superconductors

    DOE PAGESBeta

    Hinton, J. P.; Thewalt, E.; Alpichshev, Z.; Mahmood, F.; Koralek, J. D.; Chan, M. K.; Veit, M. J.; Dorow, C. J.; Barisic, N.; Kemper, A. F.; et al

    2016-04-13

    In the underdoped copper-oxides, high-temperature superconductivity condenses from a nonconventional metallic ”pseudogap” phase that exhibits a variety of non-Fermi liquid properties. Recently, it has become clear that a charge density wave (CDW) phase exists within the pseudogap regime. This CDW coexists and competes with superconductivity (SC) below the transition temperature Tc, suggesting that these two orders are intimately related. Here we show that the condensation of the superfluid from this unconventional precursor is reflected in deviations from the predictions of BSC theory regarding the recombination rate of quasiparticles. We report a detailed investigation of the quasiparticle (QP) recombination lifetime, τqp,more » as a function of temperature and magnetic field in underdoped HgBa2CuO4+δ (Hg-1201) and YBa2Cu3O6+x (YBCO) single crystals by ultrafast time-resolved reflectivity. We find that τqp(T) exhibits a local maximum in a small temperature window near Tc that is prominent in underdoped samples with coexisting charge order and vanishes with application of a small magnetic field. We explain this unusual, non-BCS behavior by positing that Tc marks a transition from phase-fluctuating SC/CDW composite order above to a SC/CDW condensate below. Lastly, our results suggest that the superfluid in underdoped cuprates is a condensate of coherently-mixed particle-particle and particle-hole pairs.« less

  3. The rate of quasiparticle recombination probes the onset of coherence in cuprate superconductors

    PubMed Central

    Hinton, J. P.; Thewalt, E.; Alpichshev, Z.; Mahmood, F.; Koralek, J. D.; Chan, M. K.; Veit, M. J.; Dorow, C. J.; Barišić, N.; Kemper, A. F.; Bonn, D. A.; Hardy, W. N.; Liang, Ruixing; Gedik, N.; Greven, M.; Lanzara, A.; Orenstein, J.

    2016-01-01

    In the underdoped copper-oxides, high-temperature superconductivity condenses from a nonconventional metallic ”pseudogap” phase that exhibits a variety of non-Fermi liquid properties. Recently, it has become clear that a charge density wave (CDW) phase exists within the pseudogap regime. This CDW coexists and competes with superconductivity (SC) below the transition temperature Tc, suggesting that these two orders are intimately related. Here we show that the condensation of the superfluid from this unconventional precursor is reflected in deviations from the predictions of BSC theory regarding the recombination rate of quasiparticles. We report a detailed investigation of the quasiparticle (QP) recombination lifetime, τqp, as a function of temperature and magnetic field in underdoped HgBa2CuO4+δ (Hg-1201) and YBa2Cu3O6+x (YBCO) single crystals by ultrafast time-resolved reflectivity. We find that τqp(T ) exhibits a local maximum in a small temperature window near Tc that is prominent in underdoped samples with coexisting charge order and vanishes with application of a small magnetic field. We explain this unusual, non-BCS behavior by positing that Tc marks a transition from phase-fluctuating SC/CDW composite order above to a SC/CDW condensate below. Our results suggest that the superfluid in underdoped cuprates is a condensate of coherently-mixed particle-particle and particle-hole pairs. PMID:27071712

  4. Ab initio quasiparticle band structure of ABA and ABC-stacked graphene trilayers

    NASA Astrophysics Data System (ADS)

    Menezes, Marcos G.; Capaz, Rodrigo B.; Louie, Steven G.

    2014-01-01

    We obtain the quasiparticle band structure of ABA and ABC-stacked graphene trilayers through ab initio density-functional theory (DFT) and many-body quasiparticle calculations within the GW approximation. To interpret our results, we fit the DFT and GW π bands to a low-energy tight-binding model, which is found to reproduce very well the observed features near the K point. The values of the extracted hopping parameters are reported and compared with available theoretical and experimental data. For both stackings, the self-energy corrections lead to a renormalization of the Fermi velocity, an effect also observed in previous calculations on monolayer graphene. They also increase the separation between the higher-energy bands, which is proportional to the nearest-neighbor interlayer hopping parameter γ1. Both features are brought to closer agreement with experiment through the self-energy corrections. Finally, other effects, such as trigonal warping, electron-hole asymmetry, and energy gaps, are discussed in terms of the associated parameters.

  5. Quasiparticle weight and renormalized Fermi velocity of graphene with long-range Coulomb interactions

    NASA Astrophysics Data System (ADS)

    Tang, Ho-Kin; Leaw, Jia Ning; Rodrigues, J. N. B.; Sengupta, P.; Assaad, F. F.; Adam, S.

    In this work, we study the effects of realistic Coulomb interactions in graphene using a projective quantum Monte Carlo simulation of electrons at half-filing on a honeycomb lattice. We compute the quasiparticle residue, the renormalized Fermi velocity and the antiferromagnetic order parameter as a function of both the long-range and short-range components of the Coulomb potential. We find that the Mott insulator transition is determined mostly by the short-range interaction and is consistent with the Gross-Neveu-Yukawa critical theory. Far from the critical point and in the semi-metallic regime, we find that the Fermi-velocity and quasiparticle residue are influenced by the long-range tail of the Coulomb potential, and for very small interaction strength are consistent with predictions of first order perturbation theory. For experimentally relevant and stronger values of the long-range interaction, our numerical data contradicts prediction from both perturbation theory and the renormalization group approaches. This work was supported by Singapore National Research Foundation (NRF-NRFF2012-01 and CA2DM mid-size Centre), Singapore Ministry of Education(Yale-NUS College R-607-265-01312 and MOE2014-T2-2-112), and DFG Grant No. AS120/9-1.

  6. Quasiparticle properties of the nonlinear Holstein model at finite doping and temperature

    NASA Astrophysics Data System (ADS)

    Li, Shaozhi; Nowadnick, Beth; Johnston, Steven

    Models with linear electron-phonon (e-ph) interactions often predict the formation of small polarons with large lattice displacements. This directly violates the approximations made in deriving the linear model, which implies that one should consider higher order terms in the interaction. Previously we have shown that even small positive nonlinear e-ph interactions dramatically suppress charge-density-wave formation and s-wave superconductivity relative to the linear model [EPL. 109, 27007 (2015)]. In this talk, we present a determinant quantum Monte Carlo study of thesingle-particle properties of quasiparticles and phonons in a two-dimensional Holstein model that includes an additional nonlinear e-ph interaction. We show that a small positive nonlinear e-ph interaction reduces the effective coupling between electrons and phonons and hardens the effective phonon frequency. Conversely, a small negative nonlinear interaction can enhance e-ph coupling resulting in heavier quasiparticles. In addition, we find that an effective linear model fails to simultaneously capture the quantitative effects of the nonlinearity of both the electronic and phononic degrees of freedom, even though it can qualitatively reproduce properties.

  7. The rate of quasiparticle recombination probes the onset of coherence in cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Hinton, J. P.; Thewalt, E.; Alpichshev, Z.; Mahmood, F.; Koralek, J. D.; Chan, M. K.; Veit, M. J.; Dorow, C. J.; Barišić, N.; Kemper, A. F.; Bonn, D. A.; Hardy, W. N.; Liang, Ruixing; Gedik, N.; Greven, M.; Lanzara, A.; Orenstein, J.

    2016-04-01

    In the underdoped copper-oxides, high-temperature superconductivity condenses from a nonconventional metallic ”pseudogap” phase that exhibits a variety of non-Fermi liquid properties. Recently, it has become clear that a charge density wave (CDW) phase exists within the pseudogap regime. This CDW coexists and competes with superconductivity (SC) below the transition temperature Tc, suggesting that these two orders are intimately related. Here we show that the condensation of the superfluid from this unconventional precursor is reflected in deviations from the predictions of BSC theory regarding the recombination rate of quasiparticles. We report a detailed investigation of the quasiparticle (QP) recombination lifetime, τqp, as a function of temperature and magnetic field in underdoped HgBa2CuO4+δ (Hg-1201) and YBa2Cu3O6+x (YBCO) single crystals by ultrafast time-resolved reflectivity. We find that τqp(T ) exhibits a local maximum in a small temperature window near Tc that is prominent in underdoped samples with coexisting charge order and vanishes with application of a small magnetic field. We explain this unusual, non-BCS behavior by positing that Tc marks a transition from phase-fluctuating SC/CDW composite order above to a SC/CDW condensate below. Our results suggest that the superfluid in underdoped cuprates is a condensate of coherently-mixed particle-particle and particle-hole pairs.

  8. Momentum-Space Imaging of the Dirac Band Structure in Molecular Graphene via Quasiparticle Interference

    NASA Astrophysics Data System (ADS)

    Stephenson, Anna; Gomes, Kenjiro K.; Ko, Wonhee; Mar, Warren; Manoharan, Hari C.

    2014-03-01

    Molecular graphene is a nanoscale artificial lattice composed of carbon monoxide molecules arranged one by one, realizing a dream of exploring exotic quantum materials by design. This assembly is done by atomic manipulation with a scanning tunneling microscope (STM) on a Cu(111) surface. To directly probe the transformation of normal surface state electrons into massless Dirac fermions, we map the momentum space dispersion through the Fourier analysis of quasiparticle scattering maps acquired at different energies with the STM. The Fourier analysis not only bridges the real-space and momentum-space data but also reveals the chiral nature of those quasiparticles, through a set of selection rules of allowed scattering involving the pseudospin and valley degrees of freedom. The graphene-like band structure can be reshaped with simple alterations to the lattice, such as the addition of a strain. We analyze the effect on the momentum space band structure of multiple types of strain on our system. Supported by DOE, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under contract DE-AC02-76SF00515.

  9. The Quasiparticle Puzzle: Reconciling ARPES and FTSTS Studies of Bi2212

    SciTech Connect

    Vishik, I.M.; Nowadnick, E.A.; Lee, W.S.; Shen, Z.X.; Moritz, B.; Devereaux, T.P.; Tanaka, K.; Sasagawa, T.; Fujii, T.; /Tokyo U.

    2009-12-17

    Angle Resolved Photoemission Spectroscopy (ARPES) probes the momentum-space electronic structure of materials, and provides invaluable information about the high-temperature superconducting cuprates. Likewise, cuprates real-space, inhomogeneous electronic structure is elucidated by Scanning Tunneling Spectroscopy (STS). Recently, STS has exploited quasiparticle interference (QPI) - wave-like electrons scattering off impurities to produce periodic interference patterns - to infer properties of the QP in momentum-space. Surprisingly, some interference peaks in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} (Bi-2212) are absent beyond the antiferromagnetic (AF) zone boundary, implying the dominance of particular scattering process. Here, we show that ARPES sees no evidence of quasiparticle (QP) extinction: QP-like peaks are measured everywhere on the Fermi surface, evolving smoothly across the AF zone boundary. This apparent contradiction stems from different natures of single-particle (ARPES) and two-particle (STS) processes underlying these probes. Using a simple model, we demonstrate extinction of QPI without implying the loss of QP beyond the AF zone boundary.

  10. Quasiparticle structure of superheavy nuclei along the α -decay chain of 288115

    NASA Astrophysics Data System (ADS)

    Bezbakh, A. N.; Kartavenko, V. G.; Adamian, G. G.; Antonenko, N. V.; Jolos, R. V.; Nesterenko, V. O.

    2015-07-01

    Background: Recent experiments on α -decay of odd-odd superheavy nuclei give important information on the structure of the low-lying states of these nuclei. For this reason, it is interesting to calculate the excitation spectra of superheavy nuclei in the framework of different approaches and compare the results with the experimental data. Purpose: To calculate the excitation energies of the two-quasiparticle states of nuclei belonging to the α -decay chain of 288115 nucleus. Method: Two different single-particle potentials, modified two-center and Skyrme-based potentials, are used to calculate the energies of two-quasiparticle states. Results: The spectra of the low-lying states are calculated. An evolution of the splitting of the pseudospin doublets and an evolution of the energies of the unique parity single-particle states with the nuclear mass number are investigated. The α -decay spectra of nuclei belonging to the α -decay chain of 288115 are obtained and compared with the experimental data. A possibility of the E 1 transitions in 276Mt following α decay of 288115 is considered. Conclusion: The E 1 transitions in 276Mt might be related to the transitions n 9 /2 [604 ]→n 11 /2 [725 ] ,n 11 /2 [725 ]→n 9 /2 [615 ] , and p 9 /2 [505 ]→p 11 /2 [615 ] . Besides the E 1 transitions, the strong M 1 and M 2 transitions are expected in 276Mt.

  11. Quasiparticle band structure of infinite hydrogen fluoride and hydrogen chloride chains

    NASA Astrophysics Data System (ADS)

    Buth, Christian

    2006-10-01

    We study the quasiparticle band structure of isolated, infinite (HF)∞ and (HCl)∞ bent (zigzag) chains and examine the effect of the crystal field on the energy levels of the constituent monomers. The chains are one of the simplest but realistic models of the corresponding three-dimensional crystalline solids. To describe the isolated monomers and the chains, we set out from the Hartree-Fock approximation, harnessing the advanced Green's function methods local molecular orbital algebraic diagrammatic construction (ADC) scheme and local crystal orbital ADC (CO-ADC) in a strict second order approximation, ADC(2,2) and CO-ADC(2,2), respectively, to account for electron correlations. The configuration space of the periodic correlation calculations is found to converge rapidly only requiring nearest-neighbor contributions to be regarded. Although electron correlations cause a pronounced shift of the quasiparticle band structure of the chains with respect to the Hartree-Fock result, the bandwidth essentially remains unaltered in contrast to, e.g., covalently bound compounds.

  12. Quasiparticle properties of the nonlinear Holstein model at finite doping and temperature

    NASA Astrophysics Data System (ADS)

    Li, Shaozhi; Nowadnick, E. A.; Johnston, S.

    2015-08-01

    We use determinant quantum Monte Carlo to study the single-particle properties of quasiparticles and phonons in a variant of the two-dimensional Holstein model that includes an additional nonlinear electron-phonon (e-ph) interaction. We find that a small positive nonlinear interaction reduces the effective coupling between the electrons and the lattice, suppresses charge-density-wave (CDW) correlations, and hardens the effective phonon frequency. Conversely, a small negative nonlinear interaction can enhance the e-ph coupling resulting in heavier quasiparticles, an increased tendency towards a CDW phase at all fillings, and a softened phonon frequency. An effective linear model with a renormalized interaction strength and phonon frequency can qualitatively capture this physics; however, the quantitative effects of the nonlinearity on both the electronic and phononic degrees of freedom cannot be captured by such a model. These results are significant for typical nonlinear coupling strengths found in real materials, indicating that nonlinearity can have an important influence on the physics of many e-ph coupled systems.

  13. Ab Initio Study of Quasiparticle and Excitonic Properties of MoS2

    NASA Astrophysics Data System (ADS)

    Qiu, Diana; Jornada, Felipe; Louie, Steven

    2013-03-01

    MoS2 is a layered, transition-metal dichalcogenide that can be cleaved into single-layer sheets, in a manner similar to graphene. Monolayer MoS2 has a direct band gap, strong spin-orbit coupling and strongly enhanced photoluminescence, compared with the bulk. MoS2's interesting electronic and optical properties mean that it could have many applications in single-layer electronic devices, but on the theoretical level, when many-electron interaction effects are included, there is still some uncertainty about the quasiparticle and excitonic properties of MoS2. We use first-principles calculations to study the quasiparticle band structure and optical absorption spectrum of MoS2 at the GW +BSE level. We include spin-orbit coupling as a perturbation either before or after the GW calculation of the band structure, and we demonstrate that our calculations are fully converged with respect to the dielectric cutoff and summation over empty bands. This work was supported by NSF grant No. DMR10-1006184 and U.S. DOE under Contract No. DE-AC02-05CH11231. Computational resources have been provided by NERSC.

  14. Quasiparticle spectra from a nonempirical optimally tuned range-separated hybrid density functional

    SciTech Connect

    Refaely-Abramson, Sivan; Sharifzadeh, Sahar; Govind, Niranjan; Autschbach, Jochen; Neaton, Jeffrey B.; Baer, Roi; Kronik, Leeor

    2012-11-28

    We present a method for obtaining quasiparticle excitation energies from a DFT-based calculation, but with accuracy that is comparable to that of many-body perturbation theory within the GW approximation. The approach uses a range-separated hybrid density functional, with asymptotically exact and short-range fractional Fock exchange. The functional contains two parameters - the range separation and the short-range Fock fraction. Both are determined non-empirically, per system, based on satisfaction of exact physical constraints for the ionization potential and many-electron self-interaction, respectively. The accuracy of the method is demonstrated on the important benchmark molecule, 3,4,9,10-perylene-tetracarboxylic-dianydride (PTCDA), where it is shown to be the only non-empirical DFT-based method comparable to GW calculations. For any finite system, we envision that the approach could be useful directly as an inexpensive alternative to GW that offers good accuracy for both frontier and non-frontier quasiparticle excitation energies, opening the door to the studyof presently out of reach large-scale systems.

  15. The rate of quasiparticle recombination probes the onset of coherence in cuprate superconductors.

    PubMed

    Hinton, J P; Thewalt, E; Alpichshev, Z; Mahmood, F; Koralek, J D; Chan, M K; Veit, M J; Dorow, C J; Barišić, N; Kemper, A F; Bonn, D A; Hardy, W N; Liang, Ruixing; Gedik, N; Greven, M; Lanzara, A; Orenstein, J

    2016-01-01

    In the underdoped copper-oxides, high-temperature superconductivity condenses from a nonconventional metallic "pseudogap" phase that exhibits a variety of non-Fermi liquid properties. Recently, it has become clear that a charge density wave (CDW) phase exists within the pseudogap regime. This CDW coexists and competes with superconductivity (SC) below the transition temperature Tc, suggesting that these two orders are intimately related. Here we show that the condensation of the superfluid from this unconventional precursor is reflected in deviations from the predictions of BSC theory regarding the recombination rate of quasiparticles. We report a detailed investigation of the quasiparticle (QP) recombination lifetime, τqp, as a function of temperature and magnetic field in underdoped HgBa2CuO(4+δ) (Hg-1201) and YBa2Cu3O(6+x) (YBCO) single crystals by ultrafast time-resolved reflectivity. We find that τqp(T) exhibits a local maximum in a small temperature window near Tc that is prominent in underdoped samples with coexisting charge order and vanishes with application of a small magnetic field. We explain this unusual, non-BCS behavior by positing that Tc marks a transition from phase-fluctuating SC/CDW composite order above to a SC/CDW condensate below. Our results suggest that the superfluid in underdoped cuprates is a condensate of coherently-mixed particle-particle and particle-hole pairs. PMID:27071712

  16. Preparation of (103)Pd brachytherapy seeds by electroless plating of (103)Pd onto carbon bars.

    PubMed

    Li, Zhong-Yong; Gao, Hui-Bo; Deng, Xue-Song; Zhou, Leng; Zhang, Wen-Hui; Han, Lian-Ge; Jin, Xiao-Hai; Cui, Hai-Ping

    2015-09-01

    A method for preparing (103)Pd brachytherapy seeds is reported. The key of the method was to deposit (103)Pd onto carbon bars by electroless plating so as to prepare source cores. After each carbon bar with (103)Pd was sealed in a titanium capsule, the (103)Pd seeds were fabricated. This paper provides valuable experiences and data for the preparation of (103)Pd brachytherapy seeds. PMID:26092353

  17. Random Walks on Random Graphs

    NASA Astrophysics Data System (ADS)

    Cooper, Colin; Frieze, Alan

    The aim of this article is to discuss some of the notions and applications of random walks on finite graphs, especially as they apply to random graphs. In this section we give some basic definitions, in Section 2 we review applications of random walks in computer science, and in Section 3 we focus on walks in random graphs.

  18. Hydrogen-induced atomic rearrangement in MgPd{sub 3}

    SciTech Connect

    Kohlmann, H. . E-mail: h.kohlmann@mx.uni-saarland.de; Renaudin, G.; Yvon, K.; Wannek, C.; Harbrecht, B.

    2005-04-15

    The hydrogenation behavior of MgPd{sub 3} has been studied by in situ X-ray powder diffraction and by neutron powder diffraction. At room temperature and p {approx}500kPa hydrogen pressure its structure is capable of incorporating up to one hydrogen atom per formula unit ({alpha}-MgPd{sub 3}H{sub {approx}}{sub 1}), thereby retaining a tetragonal ZrAl{sub 3}-type metal atom arrangement. Upon heating to 750K in a hydrogen atmosphere of 610kPa it transforms into a cubic modification with AuCu{sub 3}-type metal atom arrangement ({beta}-MgPd{sub 3}H{sub {approx}}{sub 0.7}). Neutron diffraction on the deuteride reveals an anion deficient anti-perovskite-type structure ({beta}-MgPd{sub 3}D{sub 0.67}, a=398.200(7)pm) in which octahedral sites surrounded exclusively by palladium atoms are occupied by deuterium. Complete removal of hydrogen (480K, 1Pa) stabilizes a new binary modification ({beta}-MgPd{sub 3}, a=391.78(2)pm) crystallizing with a primitive cubic AuCu{sub 3}-type structure. Mechanical treatment (grinding) transforms both {alpha} and {beta} modifications of MgPd{sub 3} into a cubic face-centered solid solution Mg{sub 0.25}Pd{sub 0.75} showing a random distribution of magnesium and palladium atoms.

  19. Sepsis-Induced Potentiation of Peritoneal Macrophage Migration is mitigated by PD-1 Gene Deficiency

    PubMed Central

    Ayala, Alfred; Elphick, Gwendolyn F.; Kim, Ye Sul; Huang, Xin; Carreira-Rosario, Arnaldo; Santos, Sadella C.; Shubin, Nicholas; Chen, Yaping; Reichner, Jonathan; Chung, Chun-Shiang

    2014-01-01

    Programmed cell death receptor (PD)-1’s effect on phagocyte function has not been extensively described. Here we report that experimental mouse sepsis, cecal ligation and puncture (CLP), induced a marked increase in peritoneal macrophage random migration/ motility/ cell spread, but these changes were lost in the absence of PD-1. Alternatively, phagocytic activity was inversely affected. In vitro cell culture imaging studies, with the macrophage cell line J774, documented that blocking PD-1 with antibody led to aggregation of cytoskeletal proteins alphaactinin and F-actin. Further experiments looking at ex vivo peritoneal macrophages from mice illustrated that a similar pattern of alpha-actinin and F-actin was evident on cells from wild-type CLP mice but not PD-1 −/− CLP mouse cells. We also observed that fMLP-induced migration by J774 cells was markedly attenuated using PD-1 blocking antibodies, a non-selective phosphatase inhibitor and a selective Rap1 inhibitor. Finally, peritoneal macrophages derived from CLP as opposed to Sham mice demonstrated aspects of both cell surface co-localization with CD11b and internalization of PD-1 within vacuoles independent of CD11b staining. Together, we believe the data support a role for PD-1 in mediating aspects of innate macrophage immune dysfunction during sepsis, heretofore unappreciated. PMID:24247196

  20. Electronic Structure of NiPdP Amorphous Metals

    NASA Astrophysics Data System (ADS)

    Swihart, J. C.; Nicholson, D. M. C.; Shelton, W. A.; Wang, Y.

    1996-03-01

    The understanding of the structure, properties and required cooling rates for bulk amorphous alloys is hindered by the the large number of constituents in the typical alloy. One of the compositionally simplest systems that can be cast into bulk specimens is Ni_0.4Pd_0.4P_0.2. Furthermore, the thoroughly studied structure of amorphous Ni_0.8P_0.2 provides a useful starting point for its investigation. We use the locally selfconsistent multiple scattering (LSMS) method to determine the electronic structure, mass density, and energy as Pd is substituted at random for Ni in the Ni_0.8P_0.2 amorphous structure. Work supported by Laboratory Directors Research Development program at Oak Ridge National Laboratory, Division of Materials Science, and the Mathematical Information and Computational Science Division of the Office of Computational Technology Research, US DOE under subcontract DEAC05-84OR21400 with Lockheed-Martin Energy Systems, Inc.

  1. Coexistence of Antiferromagnetism and Superconductivity in Heavy Fermion Cerium Compound Ce3PdIn11

    PubMed Central

    Kratochvílová, M.; Prokleška, J.; Uhlířová, K.; Tkáč, V.; Dušek, M.; Sechovský, V.; Custers, J.

    2015-01-01

    Many current research efforts in strongly correlated systems focus on the interplay between magnetism and superconductivity. Here we report on coexistence of both cooperative ordered states in recently discovered stoichiometric and fully inversion symmetric heavy fermion compound Ce3PdIn11 at ambient pressure. Thermodynamic and transport measurements reveal two successive magnetic transitions at T1 = 1.67 K and TN = 1.53 K into antiferromagnetic type of ordered states. Below Tc = 0.42 K the compound enters a superconducting state. The large initial slope of dBc2/dT ≈ – 8.6 T/K indicates that heavy quasiparticles form the Cooper pairs. The origin of the two magnetic transitions and the coexistence of magnetism and superconductivity is briefly discussed in the context of the coexistence of the two inequivalent Ce-sublattices in the unit cell of Ce3PdIn11 with different Kondo couplings to the conduction electrons. PMID:26514364

  2. Hydrogen electrosorption into Pd-Cd nanostructures.

    PubMed

    Adams, Brian D; Ostrom, Cassandra K; Chen, Aicheng

    2010-05-18

    Hydrogen-absorbing materials are crucial for both the purification and storage of hydrogen. Pd and Pd-based alloys have been studied extensively for their use as both hydrogen dissociation catalysts and hydrogen selective membrane materials. It is known that incorporating metal atoms of different sizes into the Pd lattice has a major impact on the hydrogen absorption process. In this paper, hydrogen electrosorption into nanostructured Pd-Cd alloys has been studied for different compositions of Cd that varied from 0 to 15 at. %. The low cost of Cd makes it an attractive material to combine with Pd for hydrogen sorption. A combination of chronoamperometry and cyclic voltammetric experiments was used to determine the ratio of the H/(Pd + Cd) and the kinetics of hydrogen sorption into these Pd-Cd alloys at different potentials. It was found that the maximum H/(Pd + Cd) value was 0.66 for pure Pd, and this decreased with increasing the amount of Cd. Also, the alpha (solid solution) to beta phase (metal hydride) hydrogen transition was determined to be the slowest step in the absorption process and was practically eliminated when an optimum amount of Cd atoms was doped (i.e., Pd-Cd(15%)). With increasing the amount of Cd, more hydrogen was absorbed into the Pd-Cd nanostructures at the higher potentials (the alpha phase region). The faster kinetics, along with the decrease in the phase transition of hydrogen sorption into the Pd-Cd nanostructures when compared to pure Pd, makes the Pd-Cd nanostructures attractive for use as a hydrogen dissociation catalytic capping layer for other metal hydrides or as a hydrogen selective membrane. PMID:20099788

  3. [Perioperative Management of PD Patients].

    PubMed

    Reichmann, H

    2016-07-01

    Both patients and caregivers but also treating physicians are concerned about complications along with surgical interventions. A major problem is abrupt cessation of anti-Parkinson medication, which leads to manifold disturbances, sometimes even to an akinetic crisis. There are several means to guarantee continuous dopaminergic stimulation even in patients that are not allowed to take medication orally before they undergo surgery. Amongst others rectally applied levodopa, amantadine infusions, and especially the use of a rotigotine patch are good means to overcome oral intake. Perioperative management is important due to the fact that in Germany alone each year more than 10 000 PD patients undergo surgery. Main reasons for this are fractures, but also elective interventions. Further emergency situations that cause treatment as an inpatient are psychosis, motoric disability, but also pneumonia and cardiovascular disturbances. In contrast PD patients suffer less often from cancer. PMID:27276074

  4. Strain effects on ensemble populations in AuPd/Pd(100) surface alloys

    NASA Astrophysics Data System (ADS)

    Stephens, J. Adam; Hwang, Gyeong S.

    2013-10-01

    The effects of applied strain on the arrangement of atoms in AuPd/Pd(100) surface alloys are studied using Monte Carlo simulations and cluster expansion Hamiltonians. The strain effects are found to be significant, with heteronuclear (Au-Pd) interactions more strongly enhanced by biaxial compression than homonuclear (Pd-Pd) ones. In particular, compressive strain causes an increase in the population of Pd monomers and second nearest-neighbor pairs of Pd monomers, both of which have been identified previously as important ensembles for various catalytic reactions. We also discuss the origin of these effects using density functional theory calculations of the surface electronic structure of strained AuPd/Pd(100).Our findings may suggest an additional means of employing strain to tune the catalytic properties of surface alloys.

  5. Quasiparticle band gap of organic-inorganic hybrid perovskites: Crystal structure, spin-orbit coupling, and self-energy effects

    NASA Astrophysics Data System (ADS)

    Gao, Weiwei; Gao, Xiang; Abtew, Tesfaye; Sun, Yiyang; Zhang, Shengbai; Zhang, Peihong

    The quasiparticle band gaps of organic-inorganic hybrid perovskites are often determined (and can be controlled) by various factors, complicating predictive materials optimization. Here we report a comprehensive investigation on the band gap formation mechanism in CH3NH3PbI3 by decoupling various contributing factors which ultimately determine their electronic structure and quasiparticle band gap. Four major factors, namely, quasiparticle self-energy, spin-orbit coupling, volume (lattice constant) effects, and structural distortions due to the presence of organic molecules, and their influences on the quasiparticle band structure of organometal hybrid perovskites are illustrated. We find that although methylammonium cations do not contribute directly to the electronic states near band edges, they play an important role in defining the band gap through a lattice distortion mechanism and by controlling the overall lattice constants (thus the chemical bonding of the optically active PbI3-). The spin-orbit coupling effects drastically reduce the electron and hole effective masses in these systems, which is beneficial for high carrier mobilities and small exciton binding energies. This work is supported by the National Natural Science Foundation of China (Grant No. 11328401), NSF (Grant No. DMR-0946404 and DMR-1506669), and the SUNY Networks of Excellence.

  6. Spin-flip scattering of critical quasiparticles and the phase diagram of YbRh2Si2

    NASA Astrophysics Data System (ADS)

    Wölfle, Peter; Abrahams, Elihu

    2015-10-01

    Several observed transport and thermodynamic properties of the heavy-fermion compound YbRh2Si2 in the quantum critical regime are unusual and suggest that the fermionic quasiparticles are critical, characterized by a scale-dependent diverging effective mass. A theory based on the concept of critical quasiparticles scattering off antiferromagnetic spin fluctuations in a strong-coupling regime has been shown to successfully explain the unusual existing data and to predict a number of so far unobserved properties. In this paper, we point out a new feature of a magnetic field-tuned quantum critical point of a heavy-fermion metal: anomalies in the transport and thermodynamic properties caused by the freezing out of spin-flip scattering of critical quasiparticles and the scattering off collective spin excitations. We show a steplike behavior as a function of magnetic field of, e.g., the Hall coefficient and magnetoresistivity results, which accounts quantitatively for the observed behavior of these quantities. That behavior has been described as a crossover line T*(H ) in the T -H phase diagram of YbRh2Si2 . Whereas some authors have interpreted this observation as signaling the breakdown of Kondo screening and an associated abrupt change of the Fermi surface, our results suggest that the T* line may be quantitatively understood within the picture of robust critical quasiparticles.

  7. Quasiparticle band structure of the almost-gapless transition-metal-based Heusler semiconductors

    NASA Astrophysics Data System (ADS)

    Tas, M.; Şaşıoǧlu, E.; Galanakis, I.; Friedrich, C.; Blügel, S.

    2016-05-01

    Transition-metal-based Heusler semiconductors are promising materials for a variety of applications ranging from spintronics to thermoelectricity. Employing the G W approximation within the framework of the FLAPW method, we study the quasiparticle band structure of a number of such compounds being almost gapless semiconductors. We find that in contrast to the s p -electron based semiconductors such as Si and GaAs, in these systems, the many-body corrections have a minimal effect on the electronic band structure and the energy band gap increases by less than 0.2 eV, which makes the starting point density functional theory (DFT) a good approximation for the description of electronic and optical properties of these materials. Furthermore, the band gap can be tuned either by the variation of the lattice parameter or by the substitution of the s p -chemical element.

  8. Quasiparticle interference of the Fermi arcs and surface-bulk connectivity of a Weyl semimetal.

    PubMed

    Inoue, Hiroyuki; Gyenis, András; Wang, Zhijun; Li, Jian; Oh, Seong Woo; Jiang, Shan; Ni, Ni; Bernevig, B Andrei; Yazdani, Ali

    2016-03-11

    Weyl semimetals host topologically protected surface states, with arced Fermi surface contours that are predicted to propagate through the bulk when their momentum matches that of the surface projections of the bulk's Weyl nodes. We used spectroscopic mapping with a scanning tunneling microscope to visualize quasiparticle scattering and interference at the surface of the Weyl semimetal TaAs. Our measurements reveal 10 different scattering wave vectors, which can be understood and precisely reproduced with a theory that takes into account the shape, spin texture, and momentum-dependent propagation of the Fermi arc surface states into the bulk. Our findings provide evidence that Weyl nodes act as sinks for electron transport on the surface of these materials. PMID:26965625

  9. Adaptation of the Landau-Migdal quasiparticle pattern to strongly correlated Fermi systems

    SciTech Connect

    Khodel, V. A.; Clark, J. W.; Zverev, M. V.

    2011-09-15

    A quasiparticle pattern advanced in Landau's first article on Fermi-liquid theory is adapted to elucidate the properties of a class of strongly correlated Fermi systems characterized by a Lifshitz phase diagram featuring a quantum critical point (QCP) where the density of states diverges. The necessary condition for stability of the Landau Fermi-Liquid state is shown to break down in such systems, triggering a cascade of topological phase transitions that lead, without symmetry violation, to states with multi-connected Fermi surfaces. The end point of this evolution is found to be an exceptional state whose spectrum of single-particle excitations exhibits a completely flat portion at zero temperature. Analysis of the evolution of the temperature dependence of the single-particle spectrum yields results that provide a natural explanation of classical behavior of this class of Fermi systems in the QCP region.

  10. Interpretation of scanning tunneling quasiparticle interference and impurity states in cuprates.

    PubMed

    Kreisel, A; Choubey, Peayush; Berlijn, T; Ku, W; Andersen, B M; Hirschfeld, P J

    2015-05-29

    We apply a recently developed method combining first principles based Wannier functions with solutions to the Bogoliubov-de Gennes equations to the problem of interpreting STM data in cuprate superconductors. We show that the observed images of Zn on the surface of Bi_{2}Sr_{2}CaCu_{2}O_{8} can only be understood by accounting for the tails of the Cu Wannier functions, which include significant weight on apical O sites in neighboring unit cells. This calculation thus puts earlier crude "filter" theories on a microscopic foundation and solves a long-standing puzzle. We then study quasiparticle interference phenomena induced by out-of-plane weak potential scatterers, and show how patterns long observed in cuprates can be understood in terms of the interference of Wannier functions above the surface. Our results show excellent agreement with experiment and enable a better understanding of novel phenomena in the cuprates via STM imaging. PMID:26066452

  11. Compressed Sensing in Scanning Tunneling Microscopy/Spectroscopy for Observation of Quasi-Particle Interference

    NASA Astrophysics Data System (ADS)

    Nakanishi-Ohno, Yoshinori; Haze, Masahiro; Yoshida, Yasuo; Hukushima, Koji; Hasegawa, Yukio; Okada, Masato

    2016-09-01

    We applied a method of compressed sensing to the observation of quasi-particle interference (QPI) by scanning tunneling microscopy/spectroscopy to improve efficiency and save measurement time. To solve an ill-posed problem owing to the scarcity of data, the compressed sensing utilizes the sparseness of QPI patterns in momentum space. We examined the performance of a sparsity-inducing algorithm called least absolute shrinkage and selection operator (LASSO), and demonstrated that LASSO enables us to recover a double-circle QPI pattern of the Ag(111) surface from a dataset whose size is less than that necessary for the conventional Fourier transformation method. In addition, the smallest number of data required for the recovery is discussed on the basis of cross validation.

  12. Quasiparticle Properties of a Mobile Impurity in a Bose-Einstein Condensate

    NASA Astrophysics Data System (ADS)

    Christensen, Rasmus Søgaard; Levinsen, Jesper; Bruun, Georg M.

    2015-10-01

    We develop a systematic perturbation theory for the quasiparticle properties of a single impurity immersed in a Bose-Einstein condensate. Analytical results are derived for the impurity energy, effective mass, and residue to third order in the impurity-boson scattering length. The energy is shown to depend logarithmically on the scattering length to third order, whereas the residue and the effective mass are given by analytical power series. When the boson-boson scattering length equals the boson-impurity scattering length, the energy has the same structure as that of a weakly interacting Bose gas, including terms of the Lee-Huang-Yang and fourth order logarithmic form. Our results, which cannot be obtained within the canonical Fröhlich model of an impurity interacting with phonons, provide valuable benchmarks for many-body theories and for experiments.

  13. The Stationary Dirac Equation as a Generalized Pauli Equation for Two Quasiparticles

    NASA Astrophysics Data System (ADS)

    Chuprikov, Nikolay L.

    2015-06-01

    By analyzing the Dirac equation with static electric and magnetic fields it is shown that Dirac's theory is nothing but a generalized one-particle quantum theory compatible with the special theory of relativity. This equation describes a quantum dynamics of a single relativistic fermion, and its solution is reduced to solution of the generalized Pauli equation for two quasiparticles which move in the Euclidean space with their effective masses holding information about the Lorentzian symmetry of the four-dimensional space-time. We reveal the correspondence between the Dirac bispinor and Pauli spinor (two-component wave function), and show that all four components of the Dirac bispinor correspond to a fermion (or all of them correspond to its antiparticle). Mixing the particle and antiparticle states is prohibited. On this basis we discuss the paradoxical phenomena of Zitterbewegung and the Klein tunneling.

  14. Investigation of magnetic phases in parent compounds of iron-chalcogenides via quasiparticle scattering interference

    NASA Astrophysics Data System (ADS)

    Kamble, Bhaskar; Akbari, Alireza; Eremin, Ilya

    2016-04-01

    We employ a five-orbital tight-binding model to develop the mean-field solution for various possible spin density wave states in the iron-chalcogenides. The quasiparticle interference (QPI) technique is applied to detect signatures of these states due to scatterings arising from non-magnetic impurities. Apart from the experimentally observed double-striped structure with ordering vector (π/2,π/2) , the QPI method is investigated for the extended-stripe as well as the orthogonal double-stripe phase. We discuss QPI as a possible tool to detect and classify various magnetic structures with different electronic structure reconstruction within the framework of the \\text{Fe}1+y\\text{Te} compound.

  15. Mixed quantum-classical versus full quantum dynamics: Coupled quasiparticle-oscillator system

    NASA Astrophysics Data System (ADS)

    Schanz, Holger; Esser, Bernd

    1997-05-01

    The relation between the dynamical properties of a coupled quasiparticle-oscillator system in the mixed quantum-classical and fully quantized descriptions is investigated. The system is considered as a model for applying a stepwise quantization. Features of the nonlinear dynamics in the mixed description such as the presence of a separatrix structure or regular and chaotic motion are shown to be reflected in the evolu- tion of the quantum state vector of the fully quantized system. In particular, it is demonstrated how wave packets propagate along the separatrix structure of the mixed description, and that chaotic dynamics leads to a strongly entangled quantum state vector. Special emphasis is given to viewing the system from a dyn- amical Born-Oppenheimer approximation defining integrable reference oscillators, and elucidating the role of the nonadiabatic couplings which complement this approximation into a rigorous quantization scheme.

  16. Nodal Quasiparticle Meltdown in Ultra-High Resolution Pump-Probe Angle-Resolved Photoemission

    SciTech Connect

    Graf, Jeff; Jozwiak, Chris; Smallwood, Chris L.; Eisaki, H.; Kaindl, Robert A.; Lee, Dung-Hai; Lanzara, Alessandra

    2011-06-03

    High-T{sub c} cuprate superconductors are characterized by a strong momentum-dependent anisotropy between the low energy excitations along the Brillouin zone diagonal (nodal direction) and those along the Brillouin zone face (antinodal direction). Most obvious is the d-wave superconducting gap, with the largest magnitude found in the antinodal direction and no gap in the nodal direction. Additionally, while antin- odal quasiparticle excitations appear only below T{sub c}, superconductivity is thought to be indifferent to nodal excitations as they are regarded robust and insensitive to T{sub c}. Here we reveal an unexpected tie between nodal quasiparticles and superconductivity using high resolution time- and angle-resolved photoemission on optimally doped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} . We observe a suppression of the nodal quasiparticle spectral weight following pump laser excitation and measure its recovery dynamics. This suppression is dramatically enhanced in the superconducting state. These results reduce the nodal-antinodal dichotomy and challenge the conventional view of nodal excitation neutrality in superconductivity. The electronic structures of high-Tc cuprates are strongly momentum-dependent. This is one reason why the momentum-resolved technique of angle-resolved photoemission spectroscopy (ARPES) has been a central tool in the field of high-temperature superconductivity. For example, coherent low energy excitations with momenta near the Brillouin zone face, or antinodal quasiparticles (QPs), are only observed below T{sub c} and have been linked to superfluid density. They have therefore been the primary focus of ARPES studies. In contrast, nodal QPs, with momenta along the Brillouin zone diagonal, have received less attention and are usually regarded as largely immune to the superconducting transition because they seem insensitive to perturbations such as disorder, doping, isotope exchange, charge ordering, and temperature. Clearly

  17. Massive Dirac quasiparticles in the optical absorbance of graphene, silicene, germanene, and tinene

    NASA Astrophysics Data System (ADS)

    Matthes, Lars; Pulci, Olivia; Bechstedt, Friedhelm

    2013-10-01

    We present first-principles studies of the optical absorbance of the group IV honeycomb crystals graphene, silicene, germanene, and tinene. We account for many-body effects on the optical properties by using the non-local hybrid functional HSE06. The optical absorption peaks are blueshifted due to quasiparticle corrections, while the influence on the low-frequency absorbance remains unchanged and reduces to a universal value related to the Sommerfeld fine structure constant. At the Dirac points spin-orbit interaction opens fundamental band gaps; parabolic bands with a very small effective mass emerge. Consequently, the low-frequency absorbance is modified with a spin-orbit-induced transparency region and an increase of the absorbance at the fundamental absorption edge.

  18. Study of weakly-bound odd-A nuclei with quasiparticle blocking

    NASA Astrophysics Data System (ADS)

    Xue-Yu, Xiong; Jun-Chen, Pei; Yi-Nu, Zhang; Yi, Zhu

    2016-02-01

    The coordinate-space Hartree-Fock-Bogoliubov (HFB) approach with quasiparticle blocking has been applied to study the odd-A weakly bound nuclei 17,19B and 37Mg, in which halo structures have been reported in experiments. The Skyrme nuclear forces SLy4 and UNEDF1 have been adopted in our calculations. The results with and without blocking have been compared to demonstrate the emergence of deformed halo structures due to blocking effects. In our calculations, 19B and 37Mg have remarkable features of deformed halos. Supported by National Key Basic Research Program of China (2013CB83440), National Natural Science Foundation of China (11375016, 11235001, 11320101004) and Research Fund for Doctoral Program of Higher Education of China (20130001110001)

  19. Quasiparticle-phonon model and quadrupole mixed-symmetry states of 96Ru

    NASA Astrophysics Data System (ADS)

    Stoyanov, Ch.; Pietralla, N.

    2016-01-01

    The structure of low-lying quadrupole states of 96Ru was calculated within the Quasiparticle-Phonon Model. It is shown that symmetric and mixed-symmetry properties manifest themselves via the structure of the excited states. The first 2+ state is collective and neutron and proton transition matrix elements Mn and Mp are in-phase, while the neutron and proton transition matrix elements Mn and Mp have opposite signs for the third 2+ state. This property of the third 2+ state leads to a large M1 transition between the first and third 2+ states. It is an unambigous demonstration of the mixed-symmetry nature of the third 2+ state. The structure of the first 1+ state is calculated. The state is a member of the two-phonon multiplet generated by the coupling of the [21+]QRPA and the [22+]QRPA states.

  20. Superconductivity. Quasiparticle mass enhancement approaching optimal doping in a high-T(c) superconductor.

    PubMed

    Ramshaw, B J; Sebastian, S E; McDonald, R D; Day, James; Tan, B S; Zhu, Z; Betts, J B; Liang, Ruixing; Bonn, D A; Hardy, W N; Harrison, N

    2015-04-17

    In the quest for superconductors with higher transition temperatures (T(c)), one emerging motif is that electronic interactions favorable for superconductivity can be enhanced by fluctuations of a broken-symmetry phase. Recent experiments have suggested the existence of the requisite broken-symmetry phase in the high-T(c) cuprates, but the impact of such a phase on the ground-state electronic interactions has remained unclear. We used magnetic fields exceeding 90 tesla to access the underlying metallic state of the cuprate YBa2Cu3O(6+δ) over a wide range of doping, and observed magnetic quantum oscillations that reveal a strong enhancement of the quasiparticle effective mass toward optimal doping. This mass enhancement results from increasing electronic interactions approaching optimal doping, and suggests a quantum critical point at a hole doping of p(crit) ≈ 0.18. PMID:25814065

  1. Electron and electron-hole quasiparticle states in a driven quantum contact

    NASA Astrophysics Data System (ADS)

    Vanević, Mihajlo; Gabelli, Julien; Belzig, Wolfgang; Reulet, Bertrand

    2016-01-01

    We study the many-body electronic state created by a time-dependent drive of a mesoscopic contact. The many-body state is expressed manifestly in terms of single-electron and electron-hole quasiparticle excitations with the amplitudes and probabilities of creation which depend on the details of the applied voltage. We experimentally probe the time dependence of the constituent electronic states by using an analog of the optical Hong-Ou-Mandel correlation experiment where electrons emitted from the terminals with a relative time delay collide at the contact. The electron wave packet overlap is directly related to the current noise power in the contact. We have confirmed the time dependence of the electronic states predicted theoretically by measurements of the current noise power in a tunnel junction under harmonic excitation.

  2. Quasiparticle Properties of a Mobile Impurity in a Bose-Einstein Condensate.

    PubMed

    Christensen, Rasmus Søgaard; Levinsen, Jesper; Bruun, Georg M

    2015-10-16

    We develop a systematic perturbation theory for the quasiparticle properties of a single impurity immersed in a Bose-Einstein condensate. Analytical results are derived for the impurity energy, effective mass, and residue to third order in the impurity-boson scattering length. The energy is shown to depend logarithmically on the scattering length to third order, whereas the residue and the effective mass are given by analytical power series. When the boson-boson scattering length equals the boson-impurity scattering length, the energy has the same structure as that of a weakly interacting Bose gas, including terms of the Lee-Huang-Yang and fourth order logarithmic form. Our results, which cannot be obtained within the canonical Fröhlich model of an impurity interacting with phonons, provide valuable benchmarks for many-body theories and for experiments. PMID:26550852

  3. From dressed electrons to quasiparticles: The emergence of emergent entities in quantum field theory

    NASA Astrophysics Data System (ADS)

    Blum, Alexander S.; Joas, Christian

    2016-02-01

    In the 1970s, the reinterpretation of renormalization group techniques in terms of effective field theories and their subsequent rapid development led to a major reinterpretation of the entire renormalization program, originally formulated in the late 1940s within quantum electrodynamics (QED). A more gradual shift in its interpretation, however, occurred already in the early-to-mid-1950s when renormalization techniques were transferred to solid-state and nuclear physics and helped establish the notion of effective or quasi-particles, emergent entities that are not to be found in the original, microscopic description of the theory. We study how the methods of QED, when applied in different contexts, gave rise to this ontological reinterpretation.

  4. Collective states of non-Abelian quasiparticles in a magnetic field

    NASA Astrophysics Data System (ADS)

    Levin, Michael; Halperin, Bertrand I.

    2009-05-01

    Motivated by the physics of the Moore-Read ν=1/2 state away from half filling, we investigate collective states of non-Abelian e/4 quasiparticles in a magnetic field. We consider two types of collective states: incompressible liquids and Wigner crystals. In the incompressible liquid case, we construct a natural series of states which can be thought of as a non-Abelian generalization of the Laughlin states. These states are associated with a series of hierarchical states derived from the Moore-Read state—the simplest of which occur at filling fraction 8/17 and 7/13. Interestingly, we find that the hierarchical states are Abelian even though their parent state is non-Abelian. In the Wigner crystal case, we construct two candidate states. We find that they, too, are Abelian—in agreement with previous analysis.

  5. Middle School Mathematics PD Study: Study Design and Methodology. Paper #1

    ERIC Educational Resources Information Center

    Stancavage, Fran; Garet, Michael; Wayne, Andrew

    2010-01-01

    The PD program evaluated in this study is designed to address the problem of low student achievement in topics in rational numbers. The study focuses on seventh grade, the culminating year for teaching those topics. The study randomly assigned 77 mid- and high-poverty schools from 12 districts to treatment and control conditions and collected…

  6. Size-Dependent Disorder-Order Transformation in the Synthesis of Monodisperse Intermetallic PdCu Nanocatalysts.

    PubMed

    Wang, Chenyu; Chen, Dennis P; Sang, Xiahan; Unocic, Raymond R; Skrabalak, Sara E

    2016-06-28

    The high performance of Pd-based intermetallic nanocatalysts has the potential to replace Pt-containing catalysts for fuel-cell reactions. Conventionally, intermetallic particles are obtained through the annealing of nanoparticles of a random alloy distribution. However, this method inevitably leads to sintering of the nanoparticles and generates polydisperse samples. Here, monodisperse PdCu nanoparticles with the ordered B2 phase were synthesized by seed-mediated co-reduction using PdCu nanoparticle seeds with a random alloy distribution (A1 phase). A time-evolution study suggests that the particles must overcome a size-dependent activation barrier for the ordering process to occur. Characterization of the as-prepared PdCu B2 nanoparticles by electron microscopy techniques revealed surface segregation of Pd as a thin shell over the PdCu core. The ordered nanoparticles exhibit superior activity and durability for the oxygen reduction reaction in comparison with PdCu A1 nanoparticles. This seed-mediated co-reduction strategy produced monodisperse nanoparticles ideally suited for structure-activity studies. Moreover, the study of their growth mechanism provides insights into the size dependence of disorder-order transformations of bimetallic alloys at the nanoscale, which should enable the design of synthetic strategies toward other intermetallic systems. PMID:27214313

  7. Atomistic Modeling of Surface and Bulk Properties of Cu, Pd and the Cu-Pd System

    NASA Technical Reports Server (NTRS)

    Bozzolo, Guillermo; Garces, Jorge E.; Noebe, Ronald D.; Abel, Phillip; Mosca, Hugo O.; Gray, Hugh R. (Technical Monitor)

    2002-01-01

    The BFS (Bozzolo-Ferrante-Smith) method for alloys is applied to the study of the Cu-Pd system. A variety of issues are analyzed and discussed, including the properties of pure Cu or Pd crystals (surface energies, surface relaxations), Pd/Cu and Cu/Pd surface alloys, segregation of Pd (or Cu) in Cu (or Pd), concentration dependence of the lattice parameter of the high temperature fcc CuPd solid solution, the formation and properties of low temperature ordered phases, and order-disorder transition temperatures. Emphasis is made on the ability of the method to describe these properties on the basis of a minimum set of BFS universal parameters that uniquely characterize the Cu-Pd system.

  8. Association between PD-1/PD-L1 and T regulate cells in early recurrent miscarriage

    PubMed Central

    Li, Guiyu; Lu, Caixia; Gao, Jing; Wang, Xietong; Wu, Huanling; Lee, Chao; Xing, Baoxiang; Zhang, Qi

    2015-01-01

    In this study, we try to testify the relationship between the programmed cell death receptor-1 (PD-1)/programmed cell death ligand 1 (PD-L1) passway and Treg cells in maternal-fetal immune regulation through PD-1 blockade on lymphocytes of normal early pregnancy in vitro and investigation of the PD-1 and PD-L1 changes in early recurrent miscarriage patients. CD4+ CD25+ Treg cells and PD-1 (CD279) positive cell were detected in deciduas in early recurrent miscarriage patients by flow cytometry. And the normal early pregnant women were as controls. Meanwhile the mRNA level of PD-1 and molecular expression of PD-L1 in deciduas of early recurrent miscarriage patients were detected by real time RT-PCR test and Immunohistochemical staining respectively. Also through antibody blocking assay to block PD-1 on lymphocytes of normal early pregnancy in vitro further testify the relationship between PD-1/PD-L1 and Treg cells, the results were analyzed by flow cytometry. CD4+ CD25+ Treg cells decreased both in deciduas in RM (P < 0.05), and for all almost 100% Treg cells (CD4+ CD25+) expressed PD-1, but there was no difference between the PD-1 positive cells in decidual lymphocytes in RM and that in normal pregnancy women (P > 0.05). PD-L1 mRNA in deciduas decreased in RM (P < 0.001), but PD-1 mRNA no difference (P > 0.1). After PD-1 blockade there was no change in CD4+ CD25+ Treg cells percentage, while the CD4+ T cell percentage increased (P < 0.01), as well as the level of IFN-gamma in cells supernatant (P < 0.01). PD-1 blockade has a little influence on the number of Treg cells, and may lead to impaired Treg cells function, the decrease of PD-L1 may closely relates to the occurrence of early recurrent miscarriage and implies that Treg cells may through PD-1/PD-L1 pathway play a role of immunosuppression regulation, and the impairment of Treg cells function in recurrent early abortion cases may be due to PD-L1 decrease in deciduas or trophoblast cells rather than PD-1 change

  9. A Pd/silica composite with highly uniform Pd nanoparticles on silica lamella via layered silicate

    NASA Astrophysics Data System (ADS)

    Hao, Jing; Cui, Zhi-Min; Cao, Chang-Yan; Song, Weiguo

    2016-08-01

    Pd nanoparticles was loaded on silica lamella via layered silicate through a simple ion-exchange and in situ reduction method. The obtained Pd/silica composite has Pd nanoparticles with highly uniform size dispersed well on the silica lamella. The Pd/silica composite is active and recoverable catalyst for the hydrogenation reaction and the reaction can be completed in a short time of 2 h at room temperature and 1 atm H2 pressure.

  10. PD98059 Protects Brain against Cells Death Resulting from ROS/ERK Activation in a Cardiac Arrest Rat Model

    PubMed Central

    Nguyen Thi, Phuong Anh; Chen, Meng-Hua; Li, Nuo; Zhuo, Xiao-Jun; Xie, Lu

    2016-01-01

    The clinical and experimental postcardiac arrest treatment has not reached therapeutic success. The present study investigated the effect of PD98059 (PD) in rats subjected to cardiac arrest (CA)/cardiopulmonary resuscitation (CPR). Experimental rats were divided randomly into 3 groups: sham, CA, and PD. The rats except for sham group were subjected to CA for 5 min followed by CPR operation. Once spontaneous circulation was restored, saline and PD were injected in CA and PD groups, respectively. The survival rates and neurologic deficit scores (NDS) were observed, and the following indices of brain tissue were evaluated: ROS, MDA, SOD, p-ERK1/2/ERK1/2, caspase-3, Bax, Bcl-2, TUNEL positive cells, and double fluorescent staining of p-ERK/TUNEL. Our results indicated that PD treatment significantly reduced apoptotic neurons and improved the survival rates and NDS. Moreover, PD markedly downregulated the ROS, MDA, p-ERK, and caspase-3, Bax and upregulated SOD and Bcl-2 levels. Double staining p-ERK/TUNEL in choroid plexus and cortex showed that cell death is dependent on ERK activation. The findings in present study demonstrated that PD provides neuroprotection via antioxidant activity and antiapoptosis in rats subjected to CA/CPR. PMID:27069530

  11. Modified random phase approximation for multipole excitations at finite temperature

    SciTech Connect

    Dang, N.D. )

    1992-03-01

    The modified finite-temperature random phase approximation (FT-RPA) has been constructed by taking the influence of thermostat on the structure of quasiparticles into account. The modified FT-RPA linear response for electric quadrupole ({lambda}{sup {pi}}=2{sup +}) and octupole ({lambda}{sup {pi}}=3{sup {minus}}) excitations in {sup 58}Ni has been calculated as a function of the nuclear temperature. As compared to the conventional FT-RPA, the modified FT-RPA has given a stronger spreading for the strength distribution of quadrupole excitations at finite temperature {ital T}{le}3 MeV.

  12. Selective reduction of a Pd pincer PCP complex to well-defined Pd(0) species.

    PubMed

    Melero, Cristóbal; Martínez-Prieto, Luis M; Palma, Pilar; del Rio, Diego; Alvarez, Eleuterio; Cámpora, Juan

    2010-12-14

    Well-defined dimeric or polymeric Pd(0) complexes [Pd(μ-(iPr)PCHP)](n) (n = 2 or ∞) containing the bridging ligand α,α'-bis(diisopropylphosphino)-m-xylene ((iPr)PCHP) are produced under mild conditions when the cyclometallated PCP pincer complex ((iPr)PCP)Pd-OH reacts with methanol or isopropanol. PMID:20967320

  13. PD-1/PD-L1 blockade in cancer treatment: perspectives and issues.

    PubMed

    Hamanishi, Junzo; Mandai, Masaki; Matsumura, Noriomi; Abiko, Kaoru; Baba, Tsukasa; Konishi, Ikuo

    2016-06-01

    Recent studies showed that tumor cells 'edit' host immunity in several ways to evade immune defenses in the tumor microenvironment. This phenomenon is called "cancer immune escape." One of the most important components in this system is an immunosuppressive co-signal (immune checkpoint) mediated by the PD-1 receptor and its ligand, PD-L1. PD-1 is mainly expressed on activated T cells, whereas PD-L1 is expressed on several types of tumor cells. Preclinical studies have shown that inhibition of the interaction between PD-1 and PD-L1 enhances the T-cell response and mediates antitumor activity. Several clinical trials of PD-1/PD-L1 signal-blockade agents have exhibited dramatic antitumor efficacy in patients with certain types of solid or hematological malignancies. In this review, we highlight recent clinical trials using anti-PD-1 or anti-PD-L1 antibodies against several types of malignancies, including a trial conducted in our department, and describe the clinical perspectives and issues regarding the PD-1/PD-L1 blockade in cancer treatment. PMID:26899259

  14. Quasiparticle interference, quasiparticle interactions, and the origin of the charge density wave in 2HNbSe2

    SciTech Connect

    Arguello, C. J.; Rosenthal, E. P.; Andrade, E. F.; Jin, W.; Yeh, P. C.; Zaki, N.; Jia, S.; Cava, R. J.; Fernandes, R. M.; Millis, A. J.; Valla, T.; Osgood, Jr., R. M.; Pasupathy, A. N.

    2015-01-21

    We show that a small number of intentionally introduced defects can be used as a spectroscopic tool to amplify quasiparticle interference in 2H-NbSe₂, that we measure by scanning tunneling spectroscopic imaging. We show from the momentum and energy dependence of the quasiparticle interference that Fermi surface nesting is inconsequential to charge density wave formation in 2H-NbSe₂. Thus, we demonstrate that by combining quasiparticle interference data with additional knowledge of the quasiparticle band structure from angle resolved photoemission measurements, one can extract the wavevector and energy dependence of the important electronic scattering processes thereby obtaining direct information both about the fermiology and the interactions. In 2H-NbSe₂, we use this combination to show that the important near-Fermi-surface electronic physics is dominated by the coupling of the quasiparticles to soft mode phonons at a wave vector different from the CDW ordering wave vector.

  15. Methane Oxidation on Pd-Ceria. A DFT Study of the Combustion Mechanism over Pd, PdO and Pd-ceria Sites

    SciTech Connect

    Mayernick, Adam D.; Janik, Michael J.

    2010-12-24

    Palladium/ceria exhibits unique catalytic activity for hydrocarbon oxidation; however, the chemical and structural properties of active sites on the palladium–ceria surface are difficult to characterize. Strong interactions between palladium and the ceria support stabilize oxidized Pdδ+ species, which may contribute to the significant activity of Pd/ceria for methane oxidation. We present a density functional theory (DFT + U) investigation into methane oxidation over Pd/ceria and quantify the activity of the PdxCe1-xO2(1 1 1) mixed oxide surface in comparison with the PdO(1 0 0) and Pd(1 1 1) surfaces. The methane activation barrier is lowest over the PdxCe1-xO2(1 1 1) surface, even lower than over the Pd(1 1 1) surface or low coordinated stepped or kinked Pd sites. Subsequent reaction steps in complete oxidation, including product desorption and vacancy refilling, are considered to substantiate that methane activation remains the rate-limiting step despite the low barrier over PdxCe1-xO2(1 1 1). The low barrier over the PdxCe1-xO2(1 1 1) surface demonstrates that mixed ceria-noble metal oxides offer the potential for improved hydrocarbon oxidation performance with respect to dispersed noble metal particles on ceria.

  16. Immune biomarkers PD-1/PD-L1 and TLR3 in malignant pleural mesotheliomas.

    PubMed

    Combaz-Lair, Christelle; Galateau-Sallé, Françoise; McLeer-Florin, Anne; Le Stang, Nolwenn; David-Boudet, Laurence; Duruisseaux, Mickael; Ferretti, Gilbert R; Brambilla, Elisabeth; Lebecque, Serge; Lantuejoul, Sylvie

    2016-06-01

    Malignant pleural mesothelioma (MPM) is an aggressive tumor with no effective therapy. However PD-L1/PD-1 immunity checkpoint therapies gave encouraging results; TLR3 is a programmed death factor, which triggering up-regulates PD-L1. As PD-1/PD-L1 blocking antibodies could restore antitumor immune responses alone or in combination with TLR3 agonists, we investigated PD-L1/PD-1 and TLR3 expressions in MPM to select patients for immunotherapy. Sixty-eight pleural surgical specimens, including 58 MPM (epithelioid, n = 34; biphasic, n = 11; sarcomatoid, n = 13) and 10 benign lesions, were studied. PD-L1 expression was assessed using E1L3N and SP142 clones in tumor cells (TCs) and in tumor-infiltrating lymphocytes (TILs) (positivity threshold of 1%), and compared with overall survival. PD-1, CD3 and CD8 expression by TILs, and TLR3 expression by TCs were analyzed concomitantly. PD-L1 was more expressed by sarcomatoid subtype than by other MPM (62% versus 23% and 9% for E1L3N; 38% versus 11% for SP142) (P = .01 and .04, respectively). Specificity and sensitivity of E1L3N and SP142 were of 53% and 98%, and 90% and 86%, respectively. PD-L1 expression by TILs and TCs correlated for SP142 (P = .023), and PD-L1 SP142 expression by TCs was associated with shorter overall survival (P = .016). TLR3 was expressed in most MPM, but weakly in sarcomatoid MPM. We confirm by comparing two commercially available antibodies that PD-L1 expression is higher in sarcomatoid MPM and correlates with a shorter survival. Whereas TLR3 agonists could be tested in MPM expressing TLR3, the sarcomatoid subtype could benefit from anti-PD-L1/PD-1 therapies alone or in combination. PMID:26980049

  17. Spectroscopy and electronic structure of jet-cooled NiPd and PdPt

    NASA Astrophysics Data System (ADS)

    Taylor, Scott; Spain, Eileen M.; Morse, Michael D.

    1990-03-01

    Resonant two-photon ionization spectroscopy of jet-cooled NiPd and PdPt has revealed a dense vibronic spectrum for NiPd and a much more sparse spectrum for PdPt. Four vibrational progressions have been identified for NiPd, and three have been located for PdPt. High resolution investigations of NiPd have established a ground state bond length of r″0 =2.242±0.005 Å with Ω″=2. The observed spectra have been used to bracket the ionization potentials, giving IP(NiPd)=7.18±0.76 eV and IP(PdPt)=8.27±0.38 eV. In contrast to previous work on Ni2, NiPt, and Pt2, no abrupt onset of rapid predissociation is observed for either NiPd or PdPt. A discussion of this result in terms of the expected potential energy curves for the palladium-containing diatomics is presented, which when combined with the frequencies of the highest energy vibronic bands observed yields estimates of D0(NiPd)≊1.46 eV and D0(PdPt)≊1.98 eV. The lack of observable vibronic transitions in Pd2 above 11 375 cm-1 places D0(Pd2) below 1.41 eV, in agreement with Knudsen effusion mass spectrometry. Finally a comparison of the platinum group dimers and the coinage metal dimers is given, demonstrating the increasing importance of d-orbital contributions to the bonding in the platinum group dimers as one moves down the periodic table. The anomalous behavior of the palladium-containing diatomics is also discussed in terms of the highly stable 4d105s0, 1S0 ground state of atomic palladium.

  18. Strong lattice correlation of non-equilibrium quasiparticles in a pseudospin-1/2 Mott insulator Sr2IrO4

    DOE PAGESBeta

    Li, Yuelin; Schaller, Richard D.; Zhu, Mengze; Walko, Donald A.; Kim, Jungho; Ke, Xianglin; Miao, Ludi; Mao, Z. Q.

    2016-01-20

    In correlated oxides the coupling of quasiparticles to other degrees of freedom such as spin and lattice plays critical roles in the emergence of symmetry-breaking quantum ordered states such as high temperature superconductivity. We report a strong lattice coupling of photon-induced quasiparticles in spin-orbital coupling Mott insulator Sr2IrO4 probed via optical excitation. Combining time-resolved x-ray diffraction and optical spectroscopy techniques, we reconstruct a spatiotemporal map of the diffusion of these quasiparticles. Lastly, due to the unique electronic configuration of the quasiparticles, the strong lattice correlation is unexpected but extends the similarity between Sr2IrO4 and cuprates to a new dimension ofmore » electron-phonon coupling which persists under highly non-equilibrium conditions.« less

  19. Strong lattice correlation of non-equilibrium quasiparticles in a pseudospin-1/2 Mott insulator Sr2IrO4.

    PubMed

    Li, Yuelin; Schaller, Richard D; Zhu, Mengze; Walko, Donald A; Kim, Jungho; Ke, Xianglin; Miao, Ludi; Mao, Z Q

    2016-01-01

    In correlated oxides the coupling of quasiparticles to other degrees of freedom such as spin and lattice plays critical roles in the emergence of symmetry-breaking quantum ordered states such as high temperature superconductivity. We report a strong lattice coupling of photon-induced quasiparticles in spin-orbital coupling Mott insulator Sr2IrO4 probed via optical excitation. Combining time-resolved x-ray diffraction and optical spectroscopy techniques, we reconstruct a spatiotemporal map of the diffusion of these quasiparticles. Due to the unique electronic configuration of the quasiparticles, the strong lattice correlation is unexpected but extends the similarity between Sr2IrO4 and cuprates to a new dimension of electron-phonon coupling which persists under highly non-equilibrium conditions. PMID:26787094

  20. Strong lattice correlation of non-equilibrium quasiparticles in a pseudospin-1/2 Mott insulator Sr2IrO4

    PubMed Central

    Li, Yuelin; Schaller, Richard D.; Zhu, Mengze; Walko, Donald A.; Kim, Jungho; Ke, Xianglin; Miao, Ludi; Mao, Z. Q.

    2016-01-01

    In correlated oxides the coupling of quasiparticles to other degrees of freedom such as spin and lattice plays critical roles in the emergence of symmetry-breaking quantum ordered states such as high temperature superconductivity. We report a strong lattice coupling of photon-induced quasiparticles in spin-orbital coupling Mott insulator Sr2IrO4 probed via optical excitation. Combining time-resolved x-ray diffraction and optical spectroscopy techniques, we reconstruct a spatiotemporal map of the diffusion of these quasiparticles. Due to the unique electronic configuration of the quasiparticles, the strong lattice correlation is unexpected but extends the similarity between Sr2IrO4 and cuprates to a new dimension of electron-phonon coupling which persists under highly non-equilibrium conditions. PMID:26787094

  1. On the absence of higher generations of incompressible daughter states of composite Fermion quasiparticles

    NASA Astrophysics Data System (ADS)

    Quinn, John J.

    2016-03-01

    Jain [1] introduced a simple mean-field (MF) composite Fermion (CF) picture by attaching to each electron in a quantum Hall system a flux tube producing a Chern- Simons magnetic field b(r) = 2pϕ0 Σi δ(r - r i)ẑ. Here ϕ0 = hc/e is the quantum of flux, and the sum is over all electron coordinates r i. He then averaged the total flux and the total charge (electronic plus positive background) over the entire sample. This MF picture gave a system of noninteracting CFs in an effective magnetic field B * 0 = νB 0. It predicted incompressible quantum liquid (IQL) states at filling factors ν = n(1 + 2pn)-1 for integral values of n. Chen and Quinn [2] demonstrated that Jain’s MF CF picture predicted the total angular momentum values of the lowest energy band of states for any value of the applied magnetic field B0. Justification of when the MFCF picture was valid was given by Wojs and Quinn [3], who extended the CF hierarchy scheme of Sitko et al. [4]. The CF hierarchy gave the Jain states for integrally filled CF Landau levels (CF LLs), and the Haldane hierarchy of all odd denominator fractions when quasiparticles in the highest (partially filled) CF angular momentum shell had interactions sufficiently similar to the Coulomb interactions of electrons in the lowest Landau level. Sitko et al. showed that the predictions of the CF hierarchy scheme were not always correct. By using a simple pair angular momentum identity and the concept of fractional grandparentage, Wojs and Quinn showed that higher generations of CFs could result from the interactions of the original CF quasiparticles only if their interaction energy V QP(L 2) as a function of their pair angular momentum L 2 increased with increasing L 2 faster than L2(L2 + 1). For Laughlin quasielectrons of the ν = 1/3 IQL state this condition was not satisfied. Therefore, no second generation of CFs could occur. The observed IQL at electron filling factor ν = 4/11 can not be attributed to a daughter IQL state at

  2. Quasiparticle motion in some classical and quantum mechanical systems: Investigations of nanoscale friction and polaron mobility

    NASA Astrophysics Data System (ADS)

    Tiwari, Mukesh

    In this thesis, we investigate some topics of transport in classical and quantum systems. The classical system under study is related to friction at the nanoscale. The first model we consider is that of a dimer moving on a 1-dimensional periodic substrate; we study the role of an internal channel of dissipation on the effective damping experienced by the dimer during its motion. With the view that understanding of the processes at the microscopic scale can shed some light on the origin of frictional forces, we undertake a systematic study of the scattering of a free particle by a harmonic oscillator. This study starts from a Hamiltonian description of the system, without any phenomenological damping. The dissipation in this system results from an exchange of energy between the particle and the oscillator when they are in close proximity. This classical scattering problem becomes chaotic as a result of exchange of energy. We present, in detail, a study of the chaotic scattering process for an initially static oscillator. In the case of an initially excited oscillator, extraction of information about the chaotic set requires the construction of Smale horseshoe on an appropriate Poincare surface of section. A discussion on the construction of this chaotic invariant set is also provided in this thesis. Interacting quasiparticle-boson systems form an important part of condensed matter physics. Various approximation schemes are often employed in the study of these systems. In order to understand the response of a quasi-particle to externally applied electric fields, we study in the second part of this thesis, the 2-site quantum dimer under the semiclassical approximation. The role of initial phases and effects of resonance between phonon frequency and the frequency due to the Stark splitting of states is investigated. This thesis also contains discussions regarding the frequency response of both degenerate and nondegenerate adiabatic semiclassical models and self

  3. TiOx thin films grown on Pd(100) and Pd(111) by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Farstad, M. H.; Ragazzon, D.; Grönbeck, H.; Strømsheim, M. D.; Stavrakas, C.; Gustafson, J.; Sandell, A.; Borg, A.

    2016-07-01

    The growth of ultrathin TiOx (0≤x≤2) films on Pd(100) and Pd(111) surfaces by chemical vapor deposition (CVD), using Titanium(IV)isopropoxide (TTIP) as precursor, has been investigated by high resolution photoelectron spectroscopy, low energy electron diffraction and scanning tunneling microscopy. Three different TiOx phases and one Pd-Ti alloy phase have been identified for both surfaces. The Pd-Ti alloy phase is observed at the initial stages of film growth. Density functional theory (DFT) calculations for Pd(100) and Pd(111) suggest that Ti is alloyed into the second layer of the substrate. Increasing the TTIP dose yields a wetting layer comprising Ti2 + species (TiOx, x ∼0.75). On Pd(100), this phase exhibits a mixture of structures with (3 × 5) and (4 × 5) periodicity with respect to the Pd(100) substrate, while an incommensurate structure is formed on Pd(111). Most importantly, on both surfaces this phase consists of a zigzag pattern similar to observations on other reactive metal surfaces. Further increase in coverage results in growth of a fully oxidized (TiO2) phase on top of the partially oxidized layer. Preliminary investigations indicate that the fully oxidized phase on both Pd(100) and Pd(111) may be the TiO2(B) phase.

  4. Fermi Surface and Quasiparticle Excitations of Sr2RhO4

    SciTech Connect

    Baumberger, F.; Ingle, N. J. C.; Meevasana, W.; Lu, D. H.; Perry, R. S.; Mackenzie, A. P.; Hussain, Z; Singh, David J; Shen, Z. X.

    2006-01-01

    The electronic structure of the layered 4d transition metal oxide Sr2RhO4 is investigated by angle resolved photoemission. We find well-defined quasiparticle excitations with a highly anisotropic dispersion, suggesting a quasi-two-dimensional Fermi-liquid-like ground state. Markedly different from the isostructural Sr2RuO4, only two bands with dominant Rh 4dxz;zy character contribute to the Fermi surface. A quantitative analysis of the photoemission quasiparticle band structure is in excellent agreement with bulk data. In contrast, it is found that state-of-the-art density functional calculations in the local density approximation differ significantly from the experimental findings.

  5. Field-orientation dependence of low-energy quasiparticle excitations in the heavy-electron superconductor UBe(13).

    PubMed

    Shimizu, Yusei; Kittaka, Shunichiro; Sakakibara, Toshiro; Haga, Yoshinori; Yamamoto, Etsuji; Amitsuka, Hiroshi; Tsutsumi, Yasumasa; Machida, Kazushige

    2015-04-10

    Low-energy quasiparticle excitations in the superconducting (SC) state of UBe_{13} were studied by means of specific-heat (C) measurements in a rotating field. Quite unexpectedly, the magnetic-field dependence of C(H) is linear in H with no angular dependence at low fields in the SC state, implying that the gap is fully open over the Fermi surfaces, in stark contrast to previous expectations. In addition, a characteristic cubic anisotropy of C(H) was observed above 2 T with a maximum (minimum) for H∥[001] ([111]) within the (11[over ¯]0) plane, in the normal as well as in the SC states. This oscillation possibly originates from the anisotropic response of the heavy quasiparticle bands, and might be a key to understand the unusual properties of UBe_{13}. PMID:25910153

  6. Origin of the quasiparticle dispersion kinks in Bi-2212 determined from angle-resolved inelastic electron scattering

    NASA Astrophysics Data System (ADS)

    Vig, Sean; Kogar, Anshul; Mishra, Vivek; Norman, Mike; Gu, Genda; Abbamonte, Peter

    2015-03-01

    The kink features in the low energy quasiparticle dispersion in cuprate superconductors have been extensively studied using angle-resolved photoemission spectroscopy (ARPES). The existence of these kinks is a signature of a renormalization of the fermionic quasiparticles due to coupling to some bosonic collective mode at a scale related to the kink energy. In this talk, I will present angle-resolved inelastic electron scattering studies of the bosonic collective excitations in optimally doped Bi2Sr2CaCu2O8+δ. Performing a 2D momentum parameterization of these modes, we reconstruct the complete dynamical susceptibility, χ (q , ω) , which we use to perform a one-loop self energy correction to the quasiparticle dispersion. The result reproduces well the dispersion observed with ARPES, indicating that these excitations are the origin of the observed kinks. I will discuss the implications of our study for phonon vs. spin fluctuation interpretation of these effects. This work was supported as part of the Center for Emergent Superconductivity, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science.

  7. Quasiparticle band structures and thermoelectric transport properties of p-type SnSe

    SciTech Connect

    Shi, Guangsha; Kioupakis, Emmanouil

    2015-02-14

    We used density functional and many-body perturbation theory to calculate the quasiparticle band structures and electronic transport parameters of p-type SnSe both for the low-temperature Pnma and high-temperature Cmcm phases. The Pnma phase has an indirect band gap of 0.829 eV, while the Cmcm has a direct band gap of 0.464 eV. Both phases exhibit multiple local band extrema within an energy range comparable to the thermal energy of carriers from the global extrema. We calculated the electronic transport coefficients as a function of doping concentration and temperature for single-crystal and polycrystalline materials to understand the previous experimental measurements. The electronic transport coefficients are highly anisotropic and are strongly affected by bipolar transport effects at high temperature. Our results indicate that SnSe exhibits optimal thermoelectric performance at high temperature when doped in the 10{sup 19}–10{sup 20 }cm{sup −3} range.

  8. Direct Observation of a Majorana Quasiparticle Heat Capacity in 3He

    NASA Astrophysics Data System (ADS)

    Bunkov, Y. M.

    2014-04-01

    The Majorana fermion, which acts as its own antiparticle, was suggested by Majorana in 1937 (Nuovo Cimento 14:171). While no stable particle with Majorana properties has yet been observed, Majorana quasiparticles (QP) may exist at the boundaries of topological insulators. Here we report the preliminary results of direct observation of Majorana QPs by a precise measurements of superfluid 3He heat capacity. The bulk superfluid 3He heat capacity falls exponentially with cooling at the temperatures significantly below the energy gap. Owing to the zero energy gap mode the Majorana heat capacity falls in a power law. The Majorana heat capacity can be larger than bulk one at some temperature, which depends on surface to volume ratio of the experimental cell. Some times ago we developed the Dark matter particles detector (DMD) on a basis of superfluid 3He which is working at the frontier of extremely low temperatures (Winkelmann et al., Nucl. Instrum. Meth. A 559:384-386, 2006). Here we report the observation of zero gap mode of Majorana, follows from the new analyses of DMD heat capacity, published early. We have found a 10 % deviation from the bulk superfluid 3He heat capacity at the temperature of 135 μK. This deviation corresponds well to the theoretical value for Majorana heat capacity at such low temperature. (Note, there were no fitting parameters).

  9. Bose glass and Mott glass of quasiparticles in a doped quantum magnet.

    PubMed

    Yu, Rong; Yin, Liang; Sullivan, Neil S; Xia, J S; Huan, Chao; Paduan-Filho, Armando; Oliveira, Nei F; Haas, Stephan; Steppke, Alexander; Miclea, Corneliu F; Weickert, Franziska; Movshovich, Roman; Mun, Eun-Deok; Scott, Brian L; Zapf, Vivien S; Roscilde, Tommaso

    2012-09-20

    The low-temperature states of bosonic fluids exhibit fundamental quantum effects at the macroscopic scale: the best-known examples are Bose-Einstein condensation and superfluidity, which have been tested experimentally in a variety of different systems. When bosons interact, disorder can destroy condensation, leading to a 'Bose glass'. This phase has been very elusive in experiments owing to the absence of any broken symmetry and to the simultaneous absence of a finite energy gap in the spectrum. Here we report the observation of a Bose glass of field-induced magnetic quasiparticles in a doped quantum magnet (bromine-doped dichloro-tetrakis-thiourea-nickel, DTN). The physics of DTN in a magnetic field is equivalent to that of a lattice gas of bosons in the grand canonical ensemble; bromine doping introduces disorder into the hopping and interaction strength of the bosons, leading to their localization into a Bose glass down to zero field, where it becomes an incompressible Mott glass. The transition from the Bose glass (corresponding to a gapless spin liquid) to the Bose-Einstein condensate (corresponding to a magnetically ordered phase) is marked by a universal exponent that governs the scaling of the critical temperature with the applied field, in excellent agreement with theoretical predictions. Our study represents a quantitative experimental account of the universal features of disordered bosons in the grand canonical ensemble. PMID:22996552

  10. Landau quantization and quasiparticle interference in the three-dimensional Dirac semimetal Cd3As2

    NASA Astrophysics Data System (ADS)

    Jeon, Sangjun; Zhou, Brian B.; Gyenis, Andras; Feldman, Benjamin E.; Kimchi, Itamar; Potter, Andrew C.; Gibson, Quinn D.; Cava, Robert J.; Vishwanath, Ashvin; Yazdani, Ali

    2014-09-01

    Condensed-matter systems provide a rich setting to realize Dirac and Majorana fermionic excitations as well as the possibility to manipulate them for potential applications. It has recently been proposed that chiral, massless particles known as Weyl fermions can emerge in certain bulk materials or in topological insulator multilayers and give rise to unusual transport properties, such as charge pumping driven by a chiral anomaly. A pair of Weyl fermions protected by crystalline symmetry effectively forming a massless Dirac fermion has been predicted to appear as low-energy excitations in a number of materials termed three-dimensional Dirac semimetals. Here we report scanning tunnelling microscopy measurements at sub-kelvin temperatures and high magnetic fields on the II-V semiconductor Cd3As2. We probe this system down to atomic length scales, and show that defects mostly influence the valence band, consistent with the observation of ultrahigh-mobility carriers in the conduction band. By combining Landau level spectroscopy and quasiparticle interference, we distinguish a large spin-splitting of the conduction band in a magnetic field and its extended Dirac-like dispersion above the expected regime. A model band structure consistent with our experimental findings suggests that for a magnetic field applied along the axis of the Dirac points, Weyl fermions are the low-energy excitations in Cd3As2.

  11. Quasiparticle lifetime broadening in resonant x-ray scattering of NH4NO3

    NASA Astrophysics Data System (ADS)

    Vinson, John; Jach, Terrence; Müller, Matthias; Unterumsberger, Rainer; Beckhoff, Burkhard

    2016-07-01

    It has been previously shown that two effects cause dramatic changes in the x-ray absorption and emission spectra from the N K edge of the insulating crystal ammonium nitrate. First, vibrational disorder causes major changes in the absorption spectrum, originating not only from the thermal population of phonons, but, significantly, from zero-point motion as well. Second, the anomalously large broadening (˜4 eV) of the emission originating from nitrate σ states is due to the unusually short lifetimes of quasiparticles in an otherwise extremely narrow band. In this work, we investigate the coupling of these effects to core and valence excitons that are created as the initial x-ray excitation energy is progressively reduced toward the N edge. Using a G W /Bethe-Salpeter approach, we show the extent to which this anomalous broadening is captured by the G W approximation. The data and calculations demonstrate the importance that the complex self-energies (finite lifetimes) of the valence bands have on the interpretation of emission spectra. We produce a scheme to explain why extreme lifetimes should appear in σ states of other similar compounds.

  12. Quasiparticle breakdown in the quasi-one-dimensional Ising ferromagnet CoNb2O6

    NASA Astrophysics Data System (ADS)

    Robinson, Neil J.; Essler, Fabian H. L.; Cabrera, Ivelisse; Coldea, Radu

    2014-11-01

    We present experimental and theoretical evidence that an interesting quantum many-body effect—quasiparticle breakdown—occurs in the quasi-one-dimensional spin-1/2 Ising-like ferromagnet CoNb2O6 in its paramagnetic phase at high transverse field as a result of explicit breaking of spin inversion symmetry. We propose a quantum spin Hamiltonian capturing the essential one-dimensional physics of CoNb2O6 and determine the exchange parameters of this model by fitting the calculated single-particle dispersion to the one observed experimentally in applied transverse magnetic fields [1]. We present high-resolution inelastic neutron scattering measurements of the single-particle dispersion which observe "anomalous broadening" effects over a narrow energy range at intermediate energies. We propose that this effect originates from the decay of the one particle mode into two-particle states. This decay arises from (i) a finite overlap between the one-particle dispersion and the two-particle continuum in a narrow energy-momentum range and (ii) a small misalignment of the applied field away from the direction perpendicular to the Ising axis in the experiments, which allows for nonzero matrix elements for decay by breaking the Z2 spin inversion symmetry of the Hamiltonian.

  13. Self-energies, renormalization factor, Luttinger sum rule and quasiparticle structure of the Hubbard systems

    SciTech Connect

    Lopez-Aguilar, F.; Costa-Quintana, J. )

    1992-07-10

    In this paper, the authors give a method for obtaining the renormalized electronic structure of the Hubbard systems. The first step is the determination of the self-energy beyond the Hartree-Fock approximation. This self-energy is constructed from several dielectric response functions. The second step is the determination of the quasiparticle band structure calculation which is performed from an appropriate modification of the augmented plane wave method. The third step consists in the determination of the renormalized density of states deduced from the spectral functions. The analysis of the renormalized density of states of the strongly correlated systems leads to the conclusion that there exist three types of resonances in their electronic structures, the lower energy resonances (LER), the middle energy resonances (MER) and the upper energy resonances (UER). In addition, the authors analyze the conditions for which the Luttinger theorem is satisfied. All of these questions are determined in a characteristic example which allows to test the theoretical method.

  14. Spin-Orbit Effects in the Quasiparticle Bandstructure of Noble Metals

    NASA Astrophysics Data System (ADS)

    Mustafa, Jamal; Louie, Steven

    2014-03-01

    Applications of the GW approximation to the electron self-energy have proven quite successful for calculating the quasiparticle properties of materials. We find that for the noble metals, in line with previous work in such calculations, the semicore states need to be taken into account. We show that, with these semicore states, a large cutoff must be used to describe the screening and, in turn, a large number of empty states must be included. Taking all of this into account, and carefully checking convergence, shows G0W0 can describe experimental results from angle-resolved photoemission spectroscopy quite well when the effects of spin-orbit coupling is also included. We compare our results to recent self-consistent GW calculations on gold. This work was supported by NSF grant No. DMR10-1006184 and U.S. DOE under Contract No. DE-AC02-05CH11231. Computational resources have been provided by DOE at LBNL's NERSC facility.

  15. Calculation of the spectrum of quasiparticle electron excitations in organic molecular semiconductors

    SciTech Connect

    Tikhonov, E. V.; Uspenskii, Yu. A.; Khokhlov, D. R.

    2015-06-15

    A quasiparticle electronic spectrum belongs to the characteristics of nanoobjects that are most important for applications. The following methods of calculating the electronic spectrum are analyzed: the Kohn-Sham equations of the density functional theory (DFT), the hybrid functional method, the GW approximation, and the Lehmann approximation used in the spectral representation of one-electron Green’s function. The results of these approaches are compared with the data of photoemission measurements of benzene, PTCDA, and phthalocyanine (CuPc, H{sub 2}Pc, FePc, PtPc) molecules, which are typical representatives of organic molecular semiconductors (OMS). This comparison demonstrates that the Kohn-Sham equations of DFT incorrectly reproduce the electronic spectrum of OMS. The hybrid functional method correctly describes the spectrum of the valence and conduction bands; however, the HOMO-LUMO gap width is significantly underestimated. The correct gap width is obtained in both the GW approximation and the Lehmann approach, and the total energy in this approach can be calculated in the local density approximation of DFT.

  16. Self-Localized Quasi-Particle Excitation in Quantum Electrodynamics and Its Physical Interpretation

    NASA Astrophysics Data System (ADS)

    Feranchuk, Ilya D.; Feranchuk, Sergey I.

    2007-12-01

    The self-localized quasi-particle excitation of the electron-positron field (EPF) is found for the first time in the framework of a standard form of the quantum electrodynamics. This state is interpreted as the ''physical'' electron (positron) and it allows one to solve the following problems: i) to express the ''primary'' charge e0 and the mass m0 of the ''bare'' electron in terms of the observed values of e and m of the ''physical'' electron without any infinite parameters and by essentially nonperturbative way; ii) to consider μ-meson as another self-localized EPF state and to estimate the ratio mμ/m; iii) to prove that the self-localized state is Lorentz-invariant and its energy spectrum corresponds to the relativistic free particle with the observed mass m; iv) to show that the expansion in a power of the observed charge e << 1 corresponds to the strong coupling e! xpansion in a power of the ''primary'' charge e-10 ~ e when the interaction between the ``physical'' electron and the transverse electromagnetic field is considered by means of the perturbation theory and all terms of this series are free from the ultraviolet divergence.

  17. Characterizing Featureless Mott Insulating State by Quasiparticle Interferences - A DMFT Prospect

    NASA Astrophysics Data System (ADS)

    Mukherjee, Shantanu; Lee, Wei-Cheng

    In this talk we discuss the quasiparticle interferences (QPIs) of a Mott insulator using a T-matrix formalism implemented with the dynamical mean-field theory (T-DMFT). In the Mott insulating state, the DMFT predicts a singularity in the real part of electron self energy s (w) at low frequencies, which completely washes out the QPI at small bias voltage. However, the QPI patterns produced by the non-interacting Fermi surfaces can appear at a critical bias voltage in Mott insulating state. The existence of this non-zero critical bias voltage is a direct consequence of the singular behavior of Re[s (w)] /sim n/w with n behaving as the 'order parameter' of Mott insulating state. We propose that this reentry of non-interacting QPI patterns could serve as an experimental signature of Mott insulating state, and the 'order parameter' can be experimentally measured W.C.L acknowledges financial support from start up fund from Binghamton University.

  18. Flux Pinning and Quasi-particle Scattering in Charge- Doped Iron-Based Superconductors

    NASA Astrophysics Data System (ADS)

    van der Beek, Kees; Demirdis, S.; Konczykowski, M.; Kasahara, S.; Terashima, T.; Okazaki, R.; Shibauchi, T.; Matsuda, Yuji

    2011-03-01

    Whereas isovalently doped iron-based superconductors, such as BaFe 2 (As 1-x Px)2 and Ba(Fe 1-x Ru x)2 As 2 show only strong, ''individual-defect'' vortex pinning due to nanometer-sized defects, charge-doped iron-pnictide superconductors show a low-field, field-independent contribution to the critical current density jc that is well described by the collective pinning theory. Quantitative analysis of the magnitude, temperature, and field-dependence of jc in the PrFeAs O1 - y compound shows that the behavior of jc can be fully explained, if one assumes the oxygen vacancies in this material to be responsible for quasi-particle scattering in the vortex cores. Analysis of jc of this and other charge-doped compounds such as NdFeAs(O,F), (Ba,K) Fe 2 As 2 , and Ba(Fe,Co)2 As 2 yields estimates for the transport scattering cross-section of the dopant impurities in all these materials. We find scattering to be in the Born limit, with a scattering phase angle δ0 such that sinδ0 ~ 0.2 - 0.3 .

  19. Interpretation of Scanning Tunneling Quasiparticle Interference and Impurity States in Cuprates

    SciTech Connect

    Kreisel, A.; Choubey, P.; Berlijn, T.; Ku, W.; Andersen, B. M.; Hirschfeld, P. J.

    2015-05-27

    We apply a recently developed method combining first principles based Wannier functions with solutions to the Bogoliubov-de Gennes equations to the problem of interpreting STM data in cuprate superconductors. We show that the observed images of Zn on the surface of Bi2Sr2CaCu2O8 can only be understood by accounting for the tails of the Cu Wannier functions, which include significant weight on apical O sites in neighboring unit cells. This calculation thus puts earlier crude “filter” theories on a microscopic foundation and solves a long standing puzzle. We then study quasiparticle interference (QPI) phenomena induced by out-of-plane weak potential scatterers, and show how patterns long observed in cuprates can be understood in terms of the interference of Wannier functions above the surface. Our results show excellent agreement with experiment and enable a better understanding of novel phenomena in the cuprates via STM imaging.

  20. Interpretation of scanning tunneling quasiparticle interference and impurity states in cuprates

    SciTech Connect

    Kreisel, Andreas; Choubey, Peayush; Berlijn, Tom; Ku, W.; Andersen, Brian M.; Hirschfeld, Peter J.

    2015-05-27

    We apply a recently developed method combining first principles based Wannier functions with solutions to the Bogoliubov–de Gennes equations to the problem of interpreting STM data in cuprate superconductors. We show that the observed images of Zn on the surface of Bi2Sr2CaCu2O8 can only be understood by accounting for the tails of the Cu Wannier functions, which include significant weight on apical O sites in neighboring unit cells. This calculation thus puts earlier crude “filter” theories on a microscopic foundation and solves a long-standing puzzle. We then study quasiparticle interference phenomena induced by out-of-plane weak potential scatterers, and show how patterns long observed in cuprates can be understood in terms of the interference of Wannier functions above the surface. Furthermore, our results show excellent agreement with experiment and enable a better understanding of novel phenomena in the cuprates via STM imaging.

  1. Interpretation of Scanning Tunneling Quasiparticle Interference and Impurity States in Cuprates

    DOE PAGESBeta

    Kreisel, A.; Choubey, P.; Berlijn, T.; Ku, W.; Andersen, B. M.; Hirschfeld, P. J.

    2015-05-27

    We apply a recently developed method combining first principles based Wannier functions with solutions to the Bogoliubov-de Gennes equations to the problem of interpreting STM data in cuprate superconductors. We show that the observed images of Zn on the surface of Bi2Sr2CaCu2O8 can only be understood by accounting for the tails of the Cu Wannier functions, which include significant weight on apical O sites in neighboring unit cells. This calculation thus puts earlier crude “filter” theories on a microscopic foundation and solves a long standing puzzle. We then study quasiparticle interference (QPI) phenomena induced by out-of-plane weak potential scatterers, andmore » show how patterns long observed in cuprates can be understood in terms of the interference of Wannier functions above the surface. Our results show excellent agreement with experiment and enable a better understanding of novel phenomena in the cuprates via STM imaging.« less

  2. Interpretation of scanning tunneling quasiparticle interference and impurity states in cuprates

    DOE PAGESBeta

    Kreisel, Andreas; Choubey, Peayush; Berlijn, Tom; Ku, W.; Andersen, Brian M.; Hirschfeld, Peter J.

    2015-05-27

    We apply a recently developed method combining first principles based Wannier functions with solutions to the Bogoliubov–de Gennes equations to the problem of interpreting STM data in cuprate superconductors. We show that the observed images of Zn on the surface of Bi2Sr2CaCu2O8 can only be understood by accounting for the tails of the Cu Wannier functions, which include significant weight on apical O sites in neighboring unit cells. This calculation thus puts earlier crude “filter” theories on a microscopic foundation and solves a long-standing puzzle. We then study quasiparticle interference phenomena induced by out-of-plane weak potential scatterers, and show howmore » patterns long observed in cuprates can be understood in terms of the interference of Wannier functions above the surface. Furthermore, our results show excellent agreement with experiment and enable a better understanding of novel phenomena in the cuprates via STM imaging.« less

  3. Quasiparticle Spectra from a Nonempirical Optimally Tuned Range-Separated Hybrid Density Functional

    NASA Astrophysics Data System (ADS)

    Refaely-Abramson, Sivan; Sharifzadeh, Sahar; Govind, Niranjan; Autschbach, Jochen; Neaton, Jeffrey B.; Baer, Roi; Kronik, Leeor

    2012-11-01

    We present a method for obtaining outer-valence quasiparticle excitation energies from a density-functional-theory-based calculation, with an accuracy that is comparable to that of many-body perturbation theory within the GW approximation. The approach uses a range-separated hybrid density functional, with an asymptotically exact and short-range fractional Fock exchange. The functional contains two parameters, the range separation and the short-range Fock fraction. Both are determined nonempirically, per system, on the basis of the satisfaction of exact physical constraints for the ionization potential and frontier-orbital many-electron self-interaction, respectively. The accuracy of the method is demonstrated on four important benchmark organic molecules: perylene, pentacene, 3,4,9,10-perylene-tetracarboxylic-dianydride (PTCDA), and 1,4,5,8-naphthalene-tetracarboxylic-dianhydride (NTCDA). We envision that for the outer-valence excitation spectra of finite systems the approach could provide an inexpensive alternative to GW, opening the door to the study of presently out of reach large-scale systems.

  4. Calculation of the spectrum of quasiparticle electron excitations in organic molecular semiconductors

    NASA Astrophysics Data System (ADS)

    Tikhonov, E. V.; Uspenskii, Yu. A.; Khokhlov, D. R.

    2015-06-01

    A quasiparticle electronic spectrum belongs to the characteristics of nanoobjects that are most important for applications. The following methods of calculating the electronic spectrum are analyzed: the Kohn-Sham equations of the density functional theory (DFT), the hybrid functional method, the GW approximation, and the Lehmann approximation used in the spectral representation of one-electron Green's function. The results of these approaches are compared with the data of photoemission measurements of benzene, PTCDA, and phthalocyanine (CuPc, H2Pc, FePc, PtPc) molecules, which are typical representatives of organic molecular semiconductors (OMS). This comparison demonstrates that the Kohn-Sham equations of DFT incorrectly reproduce the electronic spectrum of OMS. The hybrid functional method correctly describes the spectrum of the valence and conduction bands; however, the HOMO-LUMO gap width is significantly underestimated. The correct gap width is obtained in both the GW approximation and the Lehmann approach, and the total energy in this approach can be calculated in the local density approximation of DFT.

  5. Quasiparticle Spectra from a Nonempirical Optimally Tuned Range-Separated Hybrid Density Functional

    NASA Astrophysics Data System (ADS)

    Refaely-Abramson, Sivan; Sharifzadeh, Sahar; Govind, Niranjan; Autschbach, Jochen; Neaton, Jeffrey B.; Baer, Roi; Kronik, Leeor

    2013-03-01

    We present a method for obtaining outer-valence quasiparticle excitation energies from a density-functional-theory-based calculation, with an accuracy that is comparable to that of many-body perturbation theory within the GW approximation. The approach uses a range-separated hybrid density functional, with an asymptotically exact and short-range fractional Fock exchange. The functional contains two parameters, the range separation and the short-range Fock fraction. Both are determined nonempirically, per system, on the basis of the satisfaction of exact physical constraints for the ionization potential and many-electron self-interaction, respectively. The accuracy of the method is demonstrated on four important benchmark organic molecules: perylene, pentacene, 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA), and 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA). We envision that for finite systems the approach could provide an inexpensive alternative to GW, opening the door to the study of presently out of reach large-scale systems (Phys. Rev. Lett., in press).

  6. Quasiparticle spectra from a nonempirical optimally tuned range-separated hybrid density functional.

    PubMed

    Refaely-Abramson, Sivan; Sharifzadeh, Sahar; Govind, Niranjan; Autschbach, Jochen; Neaton, Jeffrey B; Baer, Roi; Kronik, Leeor

    2012-11-30

    We present a method for obtaining outer-valence quasiparticle excitation energies from a density-functional-theory-based calculation, with an accuracy that is comparable to that of many-body perturbation theory within the GW approximation. The approach uses a range-separated hybrid density functional, with an asymptotically exact and short-range fractional Fock exchange. The functional contains two parameters, the range separation and the short-range Fock fraction. Both are determined nonempirically, per system, on the basis of the satisfaction of exact physical constraints for the ionization potential and frontier-orbital many-electron self-interaction, respectively. The accuracy of the method is demonstrated on four important benchmark organic molecules: perylene, pentacene, 3,4,9,10-perylene-tetracarboxylic-dianydride (PTCDA), and 1,4,5,8-naphthalene-tetracarboxylic-dianhydride (NTCDA). We envision that for the outer-valence excitation spectra of finite systems the approach could provide an inexpensive alternative to GW, opening the door to the study of presently out of reach large-scale systems. PMID:23368141

  7. Quantum effects and the dissipation by quasiparticle tunneling in arrays of Josephson junctions

    SciTech Connect

    Kampf, A.; Schoen, G.

    1987-09-01

    We investigate the influence of dissipative quasiparticle tunneling currents on quantum effects and phase transitions in d-dimensional arrays of Josephson junctions. We show how the dissipative phase transition, which is known from single junctions at zero temperature, is modified due to the multidimensional coupling. The transition depends on the strength of the dissipation but also on the ratio of Josephson coupling energy to the capacitive charging energy e/sup 2//2C. It separates an ordered (superconducting) regime from a disordered (resistive) regime where fluctuations prevent phase coherence. In arrays with small capacitance junctions and weak dissipation, the disordered phase persists down to zero temperature. Finite temperatures modify the phase diagram significantly. A reentrant transition between a resistive and a superconducting state is found for weak dissipation. We also make contact with the familiar phase transitions of d-dimensional XY models and show how the charging energy and dissipation in Josephson-junction arrays influence these transitions. The results are of relevance for granular superconductors.

  8. Normal and anomalous K-hindered decays from four-quasiparticle isomers in 176Lu

    NASA Astrophysics Data System (ADS)

    McGoram, T. R.; Dracoulis, G. D.; Kibédi, T.; Byrne, A. P.; Bark, R. A.; Baxter, A. M.; Mullins, S. M.

    2000-09-01

    Two four-quasiparticle isomers, with Kπ=12+ and (14+) and mean lives of 450(100) ns and 58(5) μs, have been identified in 176Lu, at excitation energies of 1515 and 1588 keV, respectively. The 12+ isomer exhibits a large number of K-forbidden decay branches, populating the rotational sequences based on the Kπ=7- ground state, two Kπ=8+ states, and a Kπ=4+ state from the ν\\{7/2-[514]\\}⊗π\\{1/2-[541]\\} configuration. Most branches have decay rates that are consistent with normal K-hindrances except for the branch to the Kπ=4+ band. It has an anomalously low hindrance factor, which is attributed to two-state mixing due to a near-degeneracy between the 12+ isomer and the 12+ member of this band. The implied mixing matrix element has a value of only 5 eV, showing explicitly that very small mixing matrix elements may be responsible for anomalous K-hindered decays.

  9. Hanbury-Brown Twiss noise correlation with time controlled quasi-particles in ballistic quantum conductors

    NASA Astrophysics Data System (ADS)

    Glattli, D. C.; Roulleau, P.

    2016-02-01

    We study the Hanbury Brown and Twiss correlation of electronic quasi-particles injected in a quantum conductor using current noise correlations and we experimentally address the effect of finite temperature. By controlling the relative time of injection of two streams of electrons it is possible to probe the fermionic antibunching, performing the electron analog of the optical Hong Ou Mandel (HOM) experiment. The electrons are injected using voltage pulses with either sine-wave or Lorentzian shape. In the latter case, we propose a set of orthogonal wavefunctions, describing periodic trains of multiply charged electron pulses, which give a simple interpretation to the HOM shot noise. The effect of temperature is then discussed and experimentally investigated. We observe a perfect electron anti-bunching for a large range of temperature, showing that, as recently predicted, thermal mixing of the states does not affect anti-bunching properties, a feature qualitatively different from dephasing. For single charge Lorentzian pulses, we provide experimental evidence of the prediction that the HOM shot noise variation versus the emission time delay is remarkably independent of the temperature.

  10. Inverse correlation between quasiparticle mass and Tc in a cuprate high-Tc superconductor

    PubMed Central

    Putzke, Carsten; Malone, Liam; Badoux, Sven; Vignolle, Baptiste; Vignolles, David; Tabis, Wojciech; Walmsley, Philip; Bird, Matthew; Hussey, Nigel E.; Proust, Cyril; Carrington, Antony

    2016-01-01

    Close to a zero-temperature transition between ordered and disordered electronic phases, quantum fluctuations can lead to a strong enhancement of electron mass and to the emergence of competing phases such as superconductivity. A correlation between the existence of such a quantum phase transition and superconductivity is quite well established in some heavy fermion and iron-based superconductors, and there have been suggestions that high-temperature superconductivity in copper-oxide materials (cuprates) may also be driven by the same mechanism. Close to optimal doping, where the superconducting transition temperature Tc is maximal in cuprates, two different phases are known to compete with superconductivity: a poorly understood pseudogap phase and a charge-ordered phase. Recent experiments have shown a strong increase in quasiparticle mass m* in the cuprate YBa2Cu3O7-δ as optimal doping is approached, suggesting that quantum fluctuations of the charge-ordered phase may be responsible for the high-Tc superconductivity. We have tested the robustness of this correlation between m* and Tc by performing quantum oscillation studies on the stoichiometric compound YBa2Cu4O8 under hydrostatic pressure. In contrast to the results for YBa2Cu3O7-δ, we find that in YBa2Cu4O8, the mass decreases as Tc increases under pressure. This inverse correlation between m* and Tc suggests that quantum fluctuations of the charge order enhance m* but do not enhance Tc. PMID:27034989

  11. Inverse correlation between quasiparticle mass and T c in a cuprate high-T c superconductor.

    PubMed

    Putzke, Carsten; Malone, Liam; Badoux, Sven; Vignolle, Baptiste; Vignolles, David; Tabis, Wojciech; Walmsley, Philip; Bird, Matthew; Hussey, Nigel E; Proust, Cyril; Carrington, Antony

    2016-03-01

    Close to a zero-temperature transition between ordered and disordered electronic phases, quantum fluctuations can lead to a strong enhancement of electron mass and to the emergence of competing phases such as superconductivity. A correlation between the existence of such a quantum phase transition and superconductivity is quite well established in some heavy fermion and iron-based superconductors, and there have been suggestions that high-temperature superconductivity in copper-oxide materials (cuprates) may also be driven by the same mechanism. Close to optimal doping, where the superconducting transition temperature T c is maximal in cuprates, two different phases are known to compete with superconductivity: a poorly understood pseudogap phase and a charge-ordered phase. Recent experiments have shown a strong increase in quasiparticle mass m* in the cuprate YBa2Cu3O7-δ as optimal doping is approached, suggesting that quantum fluctuations of the charge-ordered phase may be responsible for the high-T c superconductivity. We have tested the robustness of this correlation between m* and T c by performing quantum oscillation studies on the stoichiometric compound YBa2Cu4O8 under hydrostatic pressure. In contrast to the results for YBa2Cu3O7-δ, we find that in YBa2Cu4O8, the mass decreases as T c increases under pressure. This inverse correlation between m* and T c suggests that quantum fluctuations of the charge order enhance m* but do not enhance T c. PMID:27034989

  12. Search for a 2-quasiparticle high-K isomer in {sup 256}Rf

    SciTech Connect

    Robinson, A. P.; Jenkins, D. G.; Marley, P.; Khoo, T. L.; Seweryniak, D.; Ahmad, I.; Back, B. B.; Carpenter, M. P.; Davids, C. N.; Greene, J.; Janssens, R. V. F.; Kondev, F. G.; Lauritsen, T.; Lister, C. J.; McCutchan, E.; Peterson, D.; Stefanescu, I.; Zhu, S.; Asai, M.; Chowdhury, P.

    2011-06-15

    The energies of 2-quasiparticle (2-qp) states in heavy shell-stabilized nuclei provide information on the single-particle states that are responsible for the stability of superheavy nuclei. We have calculated the energies of 2-qp states in {sup 256}Rf, which suggest that a long-lived, low-energy 8{sup -} isomer should exist. A search was conducted for this isomer through a calorimetric conversion electron signal, sandwiched in time between implantation of a {sup 256}Rf nucleus and its fission decay, all within the same pixel of a double-sided Si strip detector. A 17(5)-{mu}s isomer was identified. However, its low population, {approx}5(2)% that of the ground state instead of the expected {approx}30%, suggests that it is more likely a 4-qp isomer. Possible reasons for the absence of an electromagnetic signature of a 2-qp isomer decay are discussed. These include the favored possibility that the isomer decays by fission, with a half-life indistinguishably close to that of the ground state. Another possibility, that there is no 2-qp isomer at all, would imply an abrupt termination of axially symmetric deformed shapes at Z=104, which describes nuclei with Z=92-103 very well.

  13. Search for a 2-quasiparticle high-K isomer in {sup 256}Rf.

    SciTech Connect

    Robinson, A. P.; Khoo, T. L.; Seweryniak, D.; Ahmad, I.; Asai, M.; Back, B. B.; Carpenter, M. P.; Davids, C. N.; Greene, J.; Janssens, R. V. F.; Kondev, F. G.; Lauritsen, T.; Lister, C. J.; McCutchan, E.; Peterson, D.; Zhu, S.

    2011-06-13

    The energies of 2-quasiparticle (2-qp) states in heavy shell-stabilized nuclei provide information on the single-particle states that are responsible for the stability of superheavy nuclei. We have calculated the energies of 2-qp states in {sup 256}Rf, which suggest that a long-lived, low-energy 8{sup -} isomer should exist. A search was conducted for this isomer through a calorimetric conversion electron signal, sandwiched in time between implantation of a {sup 256}Rf nucleus and its fission decay, all within the same pixel of a double-sided Si strip detector. A 17(5)-{micro}s isomer was identified. However, its low population, {approx}5(2)% that of the ground state instead of the expected {approx}30%, suggests that it is more likely a 4-qp isomer. Possible reasons for the absence of an electromagnetic signature of a 2-qp isomer decay are discussed. These include the favored possibility that the isomer decays by fission, with a half-life indistinguishably close to that of the ground state. Another possibility, that there is no 2-qp isomer at all, would imply an abrupt termination of axially symmetric deformed shapes at Z = 104, which describes nuclei with Z = 92-103 very well.

  14. Random thoughts

    NASA Astrophysics Data System (ADS)

    ajansen; kwhitefoot; panteltje1; edprochak; sudhakar, the

    2014-07-01

    In reply to the physicsworld.com news story “How to make a quantum random-number generator from a mobile phone” (16 May, http://ow.ly/xFiYc, see also p5), which describes a way of delivering random numbers by counting the number of photons that impinge on each of the individual pixels in the camera of a Nokia N9 smartphone.

  15. A Comprehensive Search for Stable Pt-Pd Nanoalloy Configurations and Their Use as Tunable Catalysts

    SciTech Connect

    Tan, Teck L.; Wang, Lin-Lin; Johnson, Duane D.; Bai, Kewu

    2012-08-15

    Using density-functional theory, we predict stable alloy configurations (ground states) for a 1 nm Pt–Pd cuboctahedral nanoparticle across the entire composition range and demonstrate their use as tunable alloy catalysts via hydrogen-adsorption studies. Unlike previous works, we use simulated annealing with a cluster expansion Hamiltonian to perform a rapid and comprehensive search that encompasses both high and low-symmetry configurations. The ground states show Pt(core)–Pd(shell) type configurations across all compositions but with specific Pd patterns. For catalysis studies at room temperatures, the ground states are more realistic structural models than the commonly assumed random alloy configurations. Using the ground states, we reveal that the hydrogen adsorption energy increases (decreases) monotonically with at. % Pt for the {111} hollow ({100} bridge) adsorption site. Such trends are useful for designing tunable Pd–Pt nanocatalysts for the hydrogen evolution reaction.

  16. The Pyrite Structure of PdS2 and PdSe2 Monolayers

    NASA Astrophysics Data System (ADS)

    Singh, Arunima K.; Hennig, Richard G.; National Institute of Standards; Technology Collaboration; University of Florida Collaboration

    There has been a rising interest in two-dimensional (2D) materials due to a range of extraordinary electronic, optical and mechanical properties which are different from their bulk counterparts. The structure, stability and electronic properties of 2D PdS2 and PdSe2 have been investigated in the past in the well-known hexagonal 1T and 2H structures. However, bulk PdS2 and PdSe2 are layered compounds with individual rhombohedral pyrite-type monolayers vertically stacked with van-der Waals forces. Using density functional theory simulations, and five different functionals, we compare the energetic stability of 2D PdS2 and PdSe2 pyrite structure with the 1T and 2H structures. We find that the PdS2 is most stable in the pyrite structure, whereas the PdSe2 is most stable in the 1T structure with the pyrite structure closely competing in energy. The fundamental band gap of these compounds as a function of the structure, number of layers, the stacking arrangement and in-layer strain has been investigated. The pyrite structures of PdS2 and PdSe2 are found to be semi-conducting with indirect band gaps, and effective masses comparable to that of monolayer MoS2; thus are potential candidates for nano-electronic applications.

  17. Parental education and the WHO neonatal G-6-PD screening program: a quarter century later.

    PubMed

    Kaplan, M; Hammerman, C; Bhutani, V K

    2015-10-01

    Neonatal screening for glucose-6-phosphate dehydrogenase (G-6-PD) deficiency in any population with a male frequency >3-5%, combined with parental education regarding the dietary, environmental and sepsis-related triggers for hemolysis was recommended by the WHO (World Health Organization) Working Group in 1989. As the aim of identifying G-6-PD deficiency in the newborn period is to avert or detect extreme hyperbilirubinemia developing at home, before the development of kernicterus, the parental role in identifying evolving icterus was considered integral to any screening program. Now, a quarter century after publication of this report, severe bilirubin neurotoxicity associated with G-6-PD deficiency continues to be encountered worldwide. Screening programs have not been universally introduced but several national or regional maternal child health programs have implemented neonatal G-6-PD screening. Some reports detail the role of parental education, based on the above mentioned principles, through a variety of audio-visual materials. The paucity of randomized controlled trials or validated evidence to demonstrate the effectiveness of the contribution of parental education fails to meet the ideal testable evidence-based approach. However, our review of the cumulative experience and evidence currently available does supply certain information reflecting a positive impact of screening programs combined with parental input. We propose that the current information is sufficient to continue to support and apply the Working Group's recommendations. In order not to waste unnecessary time available, data may be used in lieu of randomized trials to continue to recommend screening programs, as suggested, in high-risk regions. If the incidence of kernicterus associated with G-6-PD deficiency is to be diminished, G-6-PD screening in combination with parental explanation may be one instance in which the consensus approach suggested by the WHO Working Group, rather than reliance

  18. Hydrogen solubility in inhomogeneous Pd alloys

    SciTech Connect

    Flanagan, T.B.; Wang, D.; Clewley, J.D.

    1998-12-31

    As-cast, arc-melted Pd-Ni alloys are inhomogeneous and the H{sub 2} isotherms for these differ from their homogeneous counterparts in the two phase, (dilute + hydride), regions but not in the dilute phase regions. Pd-Ni alloys, which become inhomogeneous via a ternary (Pd + Ni + H) equilibrium phase change, have H{sub 2} isotherms which differ from those of the homogeneous alloy in both the two-phase and the dilute phase regions. These results are discussed with respect to the expected type of inhomogeneities.

  19. Randomized controlled trials for Alzheimer disease and Parkinson disease.

    PubMed

    Lauretani, Fulvio; Ticinesi, Andrea; Meschi, Tiziana; Teresi, Giulio; Ceda, Gian Paolo; Maggio, Marcello

    2016-01-01

    The continuous increase in elderly and oldest-old population, and subsequent rise in prevalence of chronic neurological diseases like Alzheimer's disease (AD) and Parkinson's disease (PD), are a major challenge for healthcare systems. These two conditions are the most prevalent neurodegenerative diseases in older persons and physicians should engage treatment for these patients. In this field, Randomized Clinical Trials (RCTs) specifically focused on elderly populations are still lacking. The aim of this study was to identify RCTs conducted among AD and PD and to examine the difference between mean age of enrollment and incidence of these two neurodegenerative diseases. We found that the scenario is different between PD and AD. In particular, the enrollment for PD trials seems to include younger persons than AD, although the incidence of both diseases is similar and highest after 80 years old. The consequence of these results could influence conclusive guidelines of treatment in older parkinsonian patients. PMID:27100346

  20. Asymmetric magnetic proximity effect in a Pd/Co/Pd trilayer system

    DOE PAGESBeta

    Kim, Dong -Ok; Song, Kyung Mee; Choi, Yongseong; Min, Byoung -Chul; Kim, Jae -Sung; Choi, Jun Woo; Lee, Dong Ryeol

    2016-05-06

    In spintronic devices consisting of ferromagnetic/nonmagnetic systems, the ferromagnet-induced magnetic moment in the adjacent nonmagnetic material significantly influences the spin transport properties. In this study, such magnetic proximity effect in a Pd/Co/Pd trilayer system is investigated by x-ray magnetic circular dichroism and x-ray resonant magnetic reflectivity, which enables magnetic characterizations with element and depth resolution. We observe that the total Pd magnetic moments induced at the top Co/Pd interface are significantly larger than the Pd moments at the bottom Pd/Co interface, whereas transmission electron microscopy and reflectivity analysis indicate the two interfaces are nearly identical structurally. Furthermore, such asymmetry inmore » magnetic proximity effects could be important for understanding spin transport characteristics in ferromagnetic/nonmagnetic systems and its potential application to spin devices.« less

  1. Asymmetric magnetic proximity effect in a Pd/Co/Pd trilayer system.

    PubMed

    Kim, Dong-Ok; Song, Kyung Mee; Choi, Yongseong; Min, Byoung-Chul; Kim, Jae-Sung; Choi, Jun Woo; Lee, Dong Ryeol

    2016-01-01

    In spintronic devices consisting of ferromagnetic/nonmagnetic systems, the ferromagnet-induced magnetic moment in the adjacent nonmagnetic material significantly influences the spin transport properties. In this study, such magnetic proximity effect in a Pd/Co/Pd trilayer system is investigated by x-ray magnetic circular dichroism and x-ray resonant magnetic reflectivity, which enables magnetic characterizations with element and depth resolution. We observe that the total Pd magnetic moments induced at the top Co/Pd interface are significantly larger than the Pd moments at the bottom Pd/Co interface, whereas transmission electron microscopy and reflectivity analysis indicate the two interfaces are nearly identical structurally. Such asymmetry in magnetic proximity effects could be important for understanding spin transport characteristics in ferromagnetic/nonmagnetic systems and its potential application to spin devices. PMID:27151368

  2. Asymmetric magnetic proximity effect in a Pd/Co/Pd trilayer system

    NASA Astrophysics Data System (ADS)

    Kim, Dong-Ok; Song, Kyung Mee; Choi, Yongseong; Min, Byoung-Chul; Kim, Jae-Sung; Choi, Jun Woo; Lee, Dong Ryeol

    2016-05-01

    In spintronic devices consisting of ferromagnetic/nonmagnetic systems, the ferromagnet-induced magnetic moment in the adjacent nonmagnetic material significantly influences the spin transport properties. In this study, such magnetic proximity effect in a Pd/Co/Pd trilayer system is investigated by x-ray magnetic circular dichroism and x-ray resonant magnetic reflectivity, which enables magnetic characterizations with element and depth resolution. We observe that the total Pd magnetic moments induced at the top Co/Pd interface are significantly larger than the Pd moments at the bottom Pd/Co interface, whereas transmission electron microscopy and reflectivity analysis indicate the two interfaces are nearly identical structurally. Such asymmetry in magnetic proximity effects could be important for understanding spin transport characteristics in ferromagnetic/nonmagnetic systems and its potential application to spin devices.

  3. Toxicities of the anti-PD-1 and anti-PD-L1 immune checkpoint antibodies.

    PubMed

    Naidoo, J; Page, D B; Li, B T; Connell, L C; Schindler, K; Lacouture, M E; Postow, M A; Wolchok, J D

    2015-12-01

    Immune checkpoint antibodies that augment the programmed cell death protein 1 (PD-1)/PD-L1 pathway have demonstrated antitumor activity across multiple malignancies, and gained recent regulatory approval as single-agent therapy for the treatment of metastatic malignant melanoma and nonsmall-cell lung cancer. Knowledge of toxicities associated with PD-1/PD-L1 blockade, as well as effective management algorithms for these toxicities, is pivotal in order to optimize clinical efficacy and safety. In this article, we review selected published and presented clinical studies investigating single-agent anti-PD-1/PD-L1 therapy and trials of combination approaches with other standard anticancer therapies, in multiple tumor types. We summarize the key adverse events reported in these studies and their management algorithms. PMID:26371282

  4. Asymmetric magnetic proximity effect in a Pd/Co/Pd trilayer system

    PubMed Central

    Kim, Dong-Ok; Song, Kyung Mee; Choi, Yongseong; Min, Byoung-Chul; Kim, Jae-Sung; Choi, Jun Woo; Lee, Dong Ryeol

    2016-01-01

    In spintronic devices consisting of ferromagnetic/nonmagnetic systems, the ferromagnet-induced magnetic moment in the adjacent nonmagnetic material significantly influences the spin transport properties. In this study, such magnetic proximity effect in a Pd/Co/Pd trilayer system is investigated by x-ray magnetic circular dichroism and x-ray resonant magnetic reflectivity, which enables magnetic characterizations with element and depth resolution. We observe that the total Pd magnetic moments induced at the top Co/Pd interface are significantly larger than the Pd moments at the bottom Pd/Co interface, whereas transmission electron microscopy and reflectivity analysis indicate the two interfaces are nearly identical structurally. Such asymmetry in magnetic proximity effects could be important for understanding spin transport characteristics in ferromagnetic/nonmagnetic systems and its potential application to spin devices. PMID:27151368

  5. NADP(+) binding effects tryptophan accessibility, folding and stability of recombinant B. malayi G6PD.

    PubMed

    Verma, Anita; Chandra, Sharat; Suthar, Manish Kumar; Doharey, Pawan Kumar; Siddiqi, Mohammad Imran; Saxena, Jitendra Kumar

    2016-04-01

    Brugia malayi Glucose 6-phosphate dehydrogenase apoenzyme (BmG6PD) was expressed and purified by affinity chromatography to study the differences in kinetic properties of enzyme and the effect of the cofactor NADP(+) binding on enzyme stability. The presence of cofactor NADP(+) influenced the tertiary structure of enzyme due to significant differences in the tryptophan microenvironment. However, NADP(+) binding have no effect on secondary structure of the enzyme. Quenching with acrylamide indicated that two or more tryptophan residues became accessible upon cofactor binding. Unfolding and cross linking study of BmG6PD showed that NADP(+) stabilized the protein in presence of high concentration of urea/GdmCl. A homology model of BmG6PD constructed using human G6PD (PDB id: 2BH9) as a template indicated 34% α-helix, 19% β-sheet and 47% random coil conformations in the predicted model of the enzyme. In the predicted model binding of NADP(+) to BmG6PD was less tight with the structural sites (-10.96kJ/mol binding score) as compared with the coenzyme site (-15.47kJ/mol binding score). PMID:26763177

  6. Validation of G6PD Point-of-Care Tests among Healthy Volunteers in Yangon, Myanmar

    PubMed Central

    Maw, Lwin Zar; Chowwiwat, Nongnud; Bansil, Pooja; Domingo, Gonzalo J.; Htun, Moh Moh; Thant, Kyaw Zin; Htut, Ye; Nosten, Francois

    2016-01-01

    Primaquine and other 8-amnoquinoline based anti-malarials can cause haemolysis in subjects with glucose-6-phosphate dehydrogenase (G6PD) deficiency. Correct diagnosis of G6PD status in patients is crucial for safe treatment of both relapsing stages of Plasmodium vivax and transmitting forms of Plasmodium falciparum. Lack of suitable point-of-care tests has hampered a much needed wide use of primaquine for malaria elimination. In this study we have assessed the performances of two qualitative tests, the fluorescent spot test (FST) and the G6PD CareStart test (CST), against the gold standard quantitative spectrophotometric assay in a population of 1000 random adult healthy volunteers living in Yangon, Myanmar. The prevalence of G6PD deficiency in the Bamar, Karen and in the whole sample set was 6.6% (10.1% in males), 9.2% (21.0% in males) and 6.8% (11.1% in males) respectively. The FST and CST showed comparable performances with sensitivity over 95% and specificity over 90%, however for cases with severe G6PD activity the FTS had improved performance. If used with a conservative interpretation of the signal, the CareStart test has the potential to be used in the field and, by allowing a wider use of primaquine, to help malaria elimination. PMID:27035821

  7. Validation of G6PD Point-of-Care Tests among Healthy Volunteers in Yangon, Myanmar.

    PubMed

    Oo, Nwe Nwe; Bancone, Germana; Maw, Lwin Zar; Chowwiwat, Nongnud; Bansil, Pooja; Domingo, Gonzalo J; Htun, Moh Moh; Thant, Kyaw Zin; Htut, Ye; Nosten, Francois

    2016-01-01

    Primaquine and other 8-amnoquinoline based anti-malarials can cause haemolysis in subjects with glucose-6-phosphate dehydrogenase (G6PD) deficiency. Correct diagnosis of G6PD status in patients is crucial for safe treatment of both relapsing stages of Plasmodium vivax and transmitting forms of Plasmodium falciparum. Lack of suitable point-of-care tests has hampered a much needed wide use of primaquine for malaria elimination. In this study we have assessed the performances of two qualitative tests, the fluorescent spot test (FST) and the G6PD CareStart test (CST), against the gold standard quantitative spectrophotometric assay in a population of 1000 random adult healthy volunteers living in Yangon, Myanmar. The prevalence of G6PD deficiency in the Bamar, Karen and in the whole sample set was 6.6% (10.1% in males), 9.2% (21.0% in males) and 6.8% (11.1% in males) respectively. The FST and CST showed comparable performances with sensitivity over 95% and specificity over 90%, however for cases with severe G6PD activity the FTS had improved performance. If used with a conservative interpretation of the signal, the CareStart test has the potential to be used in the field and, by allowing a wider use of primaquine, to help malaria elimination. PMID:27035821

  8. Thermodynamic and kinetic characterization of H-D exchange in Pd and Pd alloys.

    SciTech Connect

    Luo, Weifang

    2010-09-01

    A Sieverts apparatus coupled with an RGA is an effective method to detect composition variations during isotopic exchange. This experimental setup provides a powerful tool for the thermodynamic and kinetic characterization of H-D isotope exchange on metals and alloys. H-D exchange behavior during absorption and desorption in the plateau region in Pd have been investigated and reported here. It was found that in the plateau region of H-D-Pd system the equilibrium pressures are between those of H2-Pd and D2-Pd for both absorption and desorption and the equilibrium pressures are higher when the fractions of D in the Pd are higher. Adding a dose of gas H2 (or D2) to Pd-D (or Pd-H) system results in releasing of gas D2 and HD (or H2 and HD) in {beta}-phase of Pd-D (or {beta}-phase of Pd-H), but this does not happen in the plateau region. The equilibrium constants have been determined during exchange and it was found that they agree well with the calculated values reported in literature. The separation factor {alpha} values during exchange have been measured and compared with the literature values. The exchange rates have been determined from the exchange profiles and a first order kinetic model for the exchange of H-D-Pd systems has been employed for the analysis. The exchange activation energies for both directions, H2+PdD and D2+PdH, have been determined.

  9. Initial growth process of Co (Pd) layers on a Pd (Co) surface

    SciTech Connect

    Nishizawa, N. Porquez, J. G.; Munekata, H.; Kitamoto, Y.

    2015-05-07

    The deposition process of ultra-thin Co and Pd layers is studied using DC magnetron sputtering and ex situ atomic force microscopy (AFM). It is found that observation with AFM in the air atmosphere is reliable to discuss nucleation of Co and Pd crystallites. It is discussed that a Co ultra-thin layer is formed primarily through the process of two-dimensional island formation, whereas a Pd ultra-thin layer is formed through the process of mixed two- and three-dimensional island formation. On the basis of those results, Co/Pd multilayers having a flat top surface are prepared successfully.

  10. Spatiotemporal dynamics of photoexcited quasiparticles in two-dimensional crystals studied by ultrafast laser techniques

    NASA Astrophysics Data System (ADS)

    Kumar, Nardeep

    Layered materials in which atomic sheets are stacked together by weak van der Waals forces can be used to fabricate two-dimensional systems. They represent a diverse and rich, but largely unexplored, source of materials. Atomically-thin structures derived from these materials possess a number of interesting electrical, optical, and mechanical properties, and are attractive for new nanodevices. For their applications in semiconductor industry, it is necessary to understand the dynamics of photoexcited quasiparticles that occur on ultrafast time scales of less than one nanosecond. In this dissertation, I discuss ultrafast optical experimental techniques and results from various two-dimensional materials, which provide information about electronic dynamics. First, a second harmonic generation technique that can be used to find the crystalline orientation, thickness uniformity, layer stacking, and single-crystal domain size is discussed, with results presented on exfoliated and chemical vapor deposition MoS2 samples. Second, a third harmonic generation technique is discussed, which can be used to explore nonlinear optical properties of materials, and results are presented on graphene and few-layer graphite films. Third, a spatially resolved femtosecond pump-probe is described, which can be used to study hot carrier and photoexcited phonon dynamics and results are presented on Bi2 Se3 sample. Then, exciton dynamics in MoS2 and MoSe2 are explored by using transient absorption microscopy with a high spatiotemporal resolution. Finally, a polarization-resolved femtosecond transient absorption spectroscopy that can be used to study valley and spin dynamics is discussed, with results presented on monolayer, few-layer, and bulk MoSe2 samples.

  11. Quasiparticle and optical spectroscopy of the organic semiconductors pentacene and PTCDA from first principles

    NASA Astrophysics Data System (ADS)

    Sharifzadeh, Sahar; Biller, Ariel; Kronik, Leeor; Neaton, Jeffrey B.

    2012-03-01

    The broad use of organic semiconductors for optoelectronic applications relies on quantitative understanding and control of their spectroscopic properties. Of paramount importance are the transport gap—the difference between ionization potential and electron affinity—and the exciton binding energy—inferred from the difference between the transport and optical absorption gaps. Transport gaps are commonly established via photoemission and inverse photoemission spectroscopy (PES/IPES). However, PES and IPES are surface-sensitive, average over a dynamic lattice, and are subject to extrinsic effects, leading to significant uncertainty in gaps. Here, we use density functional theory and many-body perturbation theory to calculate the spectroscopic properties of two prototypical organic semiconductors, pentacene, and 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA), quantitatively comparing with measured PES, IPES, and optical absorption spectra. For bulk pentacene and PTCDA, the computed transport gaps are 2.4 and 3.0 eV, and optical gaps are 1.7 and 2.1 eV, respectively. Computed bulk quasiparticle spectra are in excellent agreement with surface-sensitive photoemission measurements over several eV only if the measured gap is reduced by 0.6 eV for pentacene and 0.6-0.9 eV for PTCDA. We attribute this redshift to several physical effects, including incomplete charge screening at the surface, static and dynamical disorder, and experimental resolution. Optical gaps are in excellent agreement with experiment with solid-state exciton binding energies of ˜0.5 eV for both systems; for pentacene the exciton is delocalized over several molecules and exhibits significant charge transfer character. Our parameter-free calculations provide new interpretation of spectroscopic properties of organic semiconductors critical to optoelectronics.

  12. Quasiparticle energies and excitonic effects in dense solid hydrogen near metallization

    NASA Astrophysics Data System (ADS)

    Dvorak, Marc; Chen, Xiao-Jia; Wu, Zhigang

    2014-07-01

    We investigate the crucial metallization pressure of the Cmca-12 phase of solid hydrogen (H) using many-body perturbation theory within the GW approximation. We consider the effects of self-consistency, plasmon-pole models, and the vertex correction on the quasiparticle band gap (Eg). Our calculations show that self-consistency leads to an increase in Eg by 0.33 eV over the one-shot G0W0 approach. Because of error cancellation between the effects of self-consistency and the vertex correction, the simplest G0W0 method underestimates Eg by only 0.16 eV compared with the prediction of the more accurate GWΓ approach. Employing the plasmon-pole models underestimates Eg by 0.1-0.2 eV compared to the full-frequency numerical integration results. We thus predict a metallization pressure around 280 GPa, instead of 260 GPa predicted previously. Furthermore, we compute the optical absorption including the electron-hole interaction by solving the Bethe-Salpeter equation (BSE). The resulting absorption spectra demonstrate substantial redshifts and enhancement of absorption peaks compared to the calculated spectra neglecting excitonic effects. We find that the exciton binding energy decreases with increasing pressure from 66 meV at 100 GPa to 12 meV at 200 GPa due to the enhanced electronic screening as solid H approaches metallization. Because optical measurements are so important in identifying the structure of solid H, our BSE results should improve agreement between theory and experiment.

  13. Condensates and quasiparticles in inflationary cosmology: Mass generation and decay widths

    NASA Astrophysics Data System (ADS)

    Boyanovsky, Daniel

    2012-06-01

    During de Sitter inflation massless particles of minimally coupled scalar fields acquire a mass and a decay width thereby becoming quasiparticles. For bare massless particles nonperturbative infrared radiative corrections lead to a self-consistent generation of mass, for a quartic self-interaction M∝λ1/4H, and for a cubic self-interaction the mass is induced by the formation of a nonperturbative condensate leading to M∝λ1/3H2/3. These radiatively generated masses restore de Sitter invariance and result in anomalous scaling dimensions of superhorizon fluctuations. We introduce a generalization of the nonperturbative Wigner-Weisskopf method to obtain the time evolution of quantum states that include the self-consistent generation of mass and regulate the infrared behavior. The infrared divergences are manifest as poles in Δ=M2/3H2 in the single particle self-energies, leading to a rearrangement of the perturbative series nonanalytic in the couplings. A set of simple rules that yield the leading order infrared contributions to the decay width are obtained and implemented. The lack of kinematic thresholds entail that all particle states acquire a decay width, dominated by the emission and absorption of superhorizon quanta ∝(λ/H)4/3[H/kph(η)]6; λ[H/kph(η)]6 for cubic and quartic couplings respectively to leading order in M/H. The decay of single particle quantum states hastens as their wave vectors cross the Hubble radius and their width is related to the highly squeezed limit of the bi- or trispectrum of scalar fluctuations respectively.

  14. Fabrication of Pd-Cr wire

    NASA Technical Reports Server (NTRS)

    Diamond, Sidney; Leach, Dennen M.

    1989-01-01

    Fabrication of Pd-13 percent Cr alloy wires is described. Melting, casting, swaging and annealing processes are discussed. Drawing to reach two diameters (0.003 inch and 0.00176 inch) of wire is described. Representative micrographs of the Pd-Cr alloy at selected stages during wire fabrication are included. The resistance of the wire was somewhat lower, by about 15 to 20 percent, than comparable wire of other alloys used for strain gages.

  15. Potential of Diffusion Tensor Imaging and Relaxometry for the Detection of Specific Pathological Alterations in Parkinson's Disease (PD)

    PubMed Central

    Esterhammer, Regina; Seppi, Klaus; Reiter, Eva; Pinter, Bernadette; Mueller, Christoph; Kremser, Christian; Zitzelsberger, Tanja; Nocker, Michael; Scherfler, Christoph; Poewe, Werner; Schocke, Michael

    2015-01-01

    The purpose of the present study was to evaluate the potential of multimodal MR imaging including mean diffusivity (MD), fractional anisotropy (FA), relaxation rates R2 and R2* to detect disease specific alterations in Parkinson's Disease (PD). We enrolled 82 PD patients (PD-all) with varying disease durations (≤5 years: PD≤5, n = 43; >5 years: PD>5, n = 39) and 38 matched healthy controls (HC), receiving diffusion tensor imaging as well as R2 and R2* relaxometry calculated from multi-echo T2*-weighted and dual-echo TSE imaging, respectively. ROIs were drawn to delineate caudate nucleus (CN), putamen (PU), globus pallidus (GP) and substantia nigra (SN) on the co-registered maps. The SN was divided in 3 descending levels (SL 1–3). The most significant parameters were used for a flexible discrimination analysis (FDA) in a training collective consisting of 25 randomized subjects from each group in order to predict the classification of remaining subjects. PD-all showed significant increases in MD, R2 and R2* within SN and its subregions as well as in MD and R2* within different basal ganglia regions. Compared to the HC group, the PD≤5 and the PD>5 group showed significant MD increases within the SN and its lower two subregions, while the PD≤5 group exhibited significant increases in R2 and R2* within SN and its subregions, and tended to elevation within the basal ganglia. The PD>5 group had significantly increased MD in PU and GP, whereas the PD≤5 group presented normal MD within the basal ganglia. FDA achieved right classification in 84% of study participants. Micro-structural damage affects primarily the SN of PD patients and in later disease stages the basal ganglia. Iron contents of PU, GP and SN are increased at early disease stages of PD. PMID:26713760

  16. Potential of Diffusion Tensor Imaging and Relaxometry for the Detection of Specific Pathological Alterations in Parkinson's Disease (PD).

    PubMed

    Esterhammer, Regina; Seppi, Klaus; Reiter, Eva; Pinter, Bernadette; Mueller, Christoph; Kremser, Christian; Zitzelsberger, Tanja; Nocker, Michael; Scherfler, Christoph; Poewe, Werner; Schocke, Michael

    2015-01-01

    The purpose of the present study was to evaluate the potential of multimodal MR imaging including mean diffusivity (MD), fractional anisotropy (FA), relaxation rates R2 and R2* to detect disease specific alterations in Parkinson's Disease (PD). We enrolled 82 PD patients (PD-all) with varying disease durations (≤5 years: PD≤5, n = 43; >5 years: PD>5, n = 39) and 38 matched healthy controls (HC), receiving diffusion tensor imaging as well as R2 and R2* relaxometry calculated from multi-echo T2*-weighted and dual-echo TSE imaging, respectively. ROIs were drawn to delineate caudate nucleus (CN), putamen (PU), globus pallidus (GP) and substantia nigra (SN) on the co-registered maps. The SN was divided in 3 descending levels (SL 1-3). The most significant parameters were used for a flexible discrimination analysis (FDA) in a training collective consisting of 25 randomized subjects from each group in order to predict the classification of remaining subjects. PD-all showed significant increases in MD, R2 and R2* within SN and its subregions as well as in MD and R2* within different basal ganglia regions. Compared to the HC group, the PD≤5 and the PD>5 group showed significant MD increases within the SN and its lower two subregions, while the PD≤5 group exhibited significant increases in R2 and R2* within SN and its subregions, and tended to elevation within the basal ganglia. The PD>5 group had significantly increased MD in PU and GP, whereas the PD≤5 group presented normal MD within the basal ganglia. FDA achieved right classification in 84% of study participants. Micro-structural damage affects primarily the SN of PD patients and in later disease stages the basal ganglia. Iron contents of PU, GP and SN are increased at early disease stages of PD. PMID:26713760

  17. A Randomized Controlled Trial of Professional Development for Interdisciplinary Civic Education: Impacts on Humanities Teachers and Their Students

    ERIC Educational Resources Information Center

    Barr, Dennis J.; Boulay, Beth; Selman, Robert L.; McCormick, Rachel; Lowenstein, Ethan; Gamse, Beth; Fine, Melinda; Leonard, M. Brielle

    2015-01-01

    Background/Context: Billions of dollars are spent annually on professional development (PD) for educators, yet few randomized controlled trials (RCT) have demonstrated the ultimate impact PD has on student learning. Further, while policymakers and others speak to the role schools should play in developing students' civic awareness, RCTs of PD…

  18. Two-dimensional growth of Pd on a thin FeO(111) film: a physical manifestation of strong metal-support interaction [rapid communication

    NASA Astrophysics Data System (ADS)

    Meyer, R.; Bäumer, M.; Shaikhutdinov, Sh. K.; Freund, H.-J.

    2003-12-01

    Nucleation and growth of palladium vapor deposited on a thin FeO(1 1 1) film grown on a Pt(1 1 1) have been studied by scanning tunneling microscopy (STM). STM data shows that Pd randomly nucleates on the oxide surface and forms two-dimensional islands at sub-monolayer coverages. Annealing to 600 K results in strong metal sintering, thus forming extended Pd(1 1 1) monolayer islands at low coverage, and a thick Pd(1 1 1) film wetting the FeO substrate, at higher Pd coverage. Our data is in agreement with theoretical predictions which indicates this wetting behavior arises from a strong metal-support interaction between Pd and the FeO(1 1 1) film.

  19. The hydrogen permeability of Pd{sub 4}S

    SciTech Connect

    O'Brien, Casey; Miller, James; Gellman, Andrew; Morreale, Bryan

    2011-04-01

    Hydrogen permeates rapidly through pure Pd membranes, but H{sub 2}S, a common minor component in hydrogen-containing streams, produces a Pd{sub 4}S film on the Pd surface that severely retards hydrogen permeation. Hydrogen still permeates through the bi-layered Pd{sub 4}S/Pd structure, indicating that the Pd{sub 4}S surface is active for H{sub 2} dissociation; the low hydrogen permeability of the Pd4S film is responsible for the decreased rate of hydrogen transport. In this work, the hydrogen permeability of Pd{sub 4}S was determined experimentally in the 623-773 K temperature range. Bi-layered Pd{sub 4}S/Pd foils were produced by exposing pure Pd foils to H{sub 2}S. H{sub 2} fluxes through the bi-layered Pd{sub 4}S/Pd foils were measured during exposure to both pure H{sub 2} and a 1000 ppm H{sub 2}S in H{sub 2} gas mixture. Our results show that H{sub 2}S slows hydrogen permeation through Pd mainly by producing a Pd{sub 4}S film on the Pd surface that is roughly an order-of-magnitude less permeable to hydrogen (k{sub Pd{sub 4}S} = 10{sup −7.5} exp(−0.22 eV/k{sub B}T) molH{sub 2}/m/s/Pa{sup 1/2}) than pure Pd. The presence of H{sub 2}S in the gas stream results in greater inhibition of hydrogen transport than can be explained by the very low permeability of Pd{sub 4}S. H{sub 2}S may block H2 dissociation sites at the Pd{sub 4}S surface.

  20. Random Vibrations

    NASA Technical Reports Server (NTRS)

    Messaro. Semma; Harrison, Phillip

    2010-01-01

    Ares I Zonal Random vibration environments due to acoustic impingement and combustion processes are develop for liftoff, ascent and reentry. Random Vibration test criteria for Ares I Upper Stage pyrotechnic components are developed by enveloping the applicable zonal environments where each component is located. Random vibration tests will be conducted to assure that these components will survive and function appropriately after exposure to the expected vibration environments. Methodology: Random Vibration test criteria for Ares I Upper Stage pyrotechnic components were desired that would envelope all the applicable environments where each component was located. Applicable Ares I Vehicle drawings and design information needed to be assessed to determine the location(s) for each component on the Ares I Upper Stage. Design and test criteria needed to be developed by plotting and enveloping the applicable environments using Microsoft Excel Spreadsheet Software and documenting them in a report Using Microsoft Word Processing Software. Conclusion: Random vibration liftoff, ascent, and green run design & test criteria for the Upper Stage Pyrotechnic Components were developed by using Microsoft Excel to envelope zonal environments applicable to each component. Results were transferred from Excel into a report using Microsoft Word. After the report is reviewed and edited by my mentor it will be submitted for publication as an attachment to a memorandum. Pyrotechnic component designers will extract criteria from my report for incorporation into the design and test specifications for components. Eventually the hardware will be tested to the environments I developed to assure that the components will survive and function appropriately after exposure to the expected vibration environments.

  1. Enhanced hydrogenation and reduced lattice distortion in size selected Pd-Ag and Pd-Cu alloy nanoparticles

    SciTech Connect

    Sengar, Saurabh K.; Mehta, B. R.; Kulriya, P. K.; Khan, S. A.

    2013-10-21

    Important correlation between valence band spectra and hydrogenation properties in Pd alloy nanoparticles is established by studying the properties of size selected and monocrystalline Pd, Ag, Cu, Pd-Ag, and Pd-Cu nanoparticles. The X-ray photoelectron spectroscopy and elastic recoil detection analysis show that size induced Pd4d centroid shift is related to enhanced hydrogenation with H/Pd ratio of 0.57 and 0.49 in Pd-Ag and Pd-Cu nanoparticles in comparison to reported bulk values of 0.2 and 0.1, respectively. Pd-alloy nanoparticles show lower hydrogen induced lattice distortion. The reduced distortion and higher hydrogen reactivity of Pd-alloy nanoparticles is important for numerous hydrogen related applications.

  2. Normal state bottleneck and nematic fluctuations from femtosecond quasiparticle relaxation dynamics in Sm(Fe,Co)AsO

    NASA Astrophysics Data System (ADS)

    Mertelj, T.; Stojchevska, L.; Zhigadlo, N. D.; Karpinski, J.; Mihailovic, D.

    2013-05-01

    We investigate temperature and fluence dependent dynamics of the photoexcited quasiparticle relaxation and low-energy electronic structure in electron-doped 1111-structure Sm(Fe0.93Co0.07)AsO single crystal. We find that the behavior is qualitatively identical to the 122-structure Ba(Fe,Co)2As2 including the presence of a normal state pseudogap and a marked twofold symmetry breaking in the tetragonal phase that we relate to the electronic nematicity. The twofold symmetry breaking appears to be a general feature of the electron-doped iron pnictides.

  3. Immune escape to PD-L1/PD-1 blockade: seven steps to success (or failure).

    PubMed

    Kim, J M; Chen, D S

    2016-08-01

    The emergence of programmed death-ligand 1 (PD-L1)/programmed death-1 (PD-1)-targeted therapy has demonstrated the importance of the PD-L1 : PD-1 interaction in inhibiting anticancer T-cell immunity in multiple human cancers, generating durable responses and extended overall survival. However, not all patients treated with PD-L1/PD-1-targeted therapy experience tumor shrinkage, durable responses, or prolonged survival. To extend such benefits to more cancer patients, it is necessary to understand why some patients experience primary or secondary immune escape, in which the immune response is incapable of eradicating all cancer cells. Understanding immune escape from PD-L1/PD-1-targeted therapy will be important to the development of rational immune-combination therapy and predictive diagnostics and to the identification of novel immune targets. Factors that likely relate to immune escape include the lack of strong cancer antigens or epitopes recognized by T cells, minimal activation of cancer-specific T cells, poor infiltration of T cells into tumors, downregulation of the major histocompatibility complex on cancer cells, and immunosuppressive factors and cells in the tumor microenvironment. Precisely identifying and understanding these mechanisms of immune escape in individual cancer patients will allow for personalized cancer immunotherapy, in which monotherapy and combination immunotherapy are chosen based on the presence of specific immune biology. This approach may enable treatment with immunotherapy without inducing immune escape, resulting in a larger proportion of patients obtaining clinical benefit. PMID:27207108

  4. Differential control of CD4+ T cell subsets by the PD-1/PD-L1 axis in allergic asthma

    PubMed Central

    McAlees, Jaclyn W.; Lajoie, Stephane; Dienger, Krista; Sproles, Alyssa A.; Richgels, Phoebe K.; Yang, Yanfen; Khodoun, Marat; Azuma, Miyuki; Yagita, Hideo; Fulkerson, Patricia C.; Wills-Karp, Marsha; Lewkowich, Ian P.

    2015-01-01

    Studies examining the role of PD-1 family members in allergic asthma have yielded conflicting results. Using a mouse model of allergic asthma, we find that blockade of PD-1/PD-L1 has distinct influences on different CD4+ T cell subsets. PD-1/PD-L1 blockade enhances AHR not by altering the magnitude of the underlying Th2 immune response, but by allowing the development of a concomitant Th17 immune response. Supporting differential CD4+ T cell responsiveness to PD-1-mediated inhibition, naïve PD-1−/− mice displayed elevated Th1 and Th17 levels, but diminished Th2 cytokine levels, ligation of PD-1 limited cytokine production by in vitro-polarized Th1 and Th17 cells, but slightly enhanced cytokine production by in vitro-polarized Th2 cells, and PD-1 ligation enhanced Th2 cytokine production by naïve T cells cultured under non-polarizing conditions. These data demonstrate that different CD4+ T cell subsets respond differentially to PD-1 ligation and may explain some of the variable results observed in control of allergic asthma by the PD-1 family members. As the PD-1/PD-L1 axis limits asthma severity by constraining Th17 cell activity, this suggests that severe allergic asthma may be associated with a defective PD-1/PD-L1 regulatory axis in some individuals. PMID:25630305

  5. Crystal Structure of the Complex Between Programmed Death-1 (PD-1) and its Ligand PD-L2

    SciTech Connect

    Lazar-Molnar,E.; Yan, Q.; Cao, E.; Ramagopal, U.; Nathenson, S.; Almo, S.

    2008-01-01

    Programmed death-1 (PD-1) is a member of the CD28/B7 superfamily that delivers negative signals upon interaction with its two ligands, PD-L1 or PD-L2. The high-resolution crystal structure of the complex formed by the complete ectodomains of murine PD-1 and PD-L2 revealed a 1:1 receptor:ligand stoichiometry and displayed a binding interface and overall molecular organization distinct from that observed in the CTLA-4/B7 inhibitory complexes. Furthermore, our structure also provides insights into the association between PD-1 and PD-L1 and highlights differences in the interfaces formed by the two PD-1 ligands (PD-Ls) Mutagenesis studies confirmed the details of the proposed PD-1/PD-L binding interfaces and allowed for the design of a mutant PD-1 receptor with enhanced affinity. These studies define spatial and organizational constraints that control the localization and signaling of PD-1/PD-L complexes within the immunological synapse and provide a basis for manipulating the PD-1 pathways for immunotherapy.

  6. Modification of local order in FePd films by low energy He{sup +} irradiation

    SciTech Connect

    Merkel, D. G.; Tancziko, F.; Sajti, Sz.; Major, M.; Nemeth, A.; Bottyan, L.; Horvath, Z. E.; Waizinger, J.; Stankov, S.; Kovacs, A.

    2008-07-01

    Owing to their strong perpendicular magnetic anisotropy, FePd, CoPd, and their Co(Fe)Pt counterparts are candidate materials for ultrahigh density magnetic recording. The stability and magnetic properties of such films are largely dependent on the orientation and local distribution of the L1{sub 0} FePd phase fraction. Therefore, the formation and transformation of the L1{sub 0} phase in such thin films have been the subject of continued interest. Highly ordered epitaxial FePd(001) thin films (with an L1{sub 0} phase fraction of 0.81) were prepared by molecular-beam epitaxy on a MgO(001) substrate. The effect of postgrown room temperature, 130 keV He{sup +} irradiation was investigated at fluences up to 14.9x10{sup 15} ions/cm{sup 2}. X-ray diffraction and conversion electron Moessbauer spectroscopy revealed that with increasing fluence, the L1{sub 0} FePd phase decomposes into the face centered cubic phase with random Fe and Pd occupation of the sites. A partially ordered local environment exhibiting a large hyperfine magnetic field also develops. Upon He{sup +} irradiation, the lattice parameter c of the FePd L1{sub 0} structure increases and the long range order parameter S steeply decreases. The Fe-Fe nearest-neighbor coordination in the Fe-containing environments increases on average from Fe{sub 47}Pd{sub 53} to Fe{sub 54}Pd{sub 46}, indicating a tendency of formation iron-rich clusters. The equilibrium parameters corresponding to the equiatomic L1{sub 0} phase were found at different fluences by conversion electron Moessbauer spectroscopy and by x-ray diffraction a difference, from which a plane-perpendicular compressive stress and a corresponding in-plane tensile stress are conjectured. The steep increase in the interface roughness above 7.4x10{sup 15} ions/cm{sup 2} is interpreted as a percolation-type behavior related to the high diffusion anisotropy in the L1{sub 0} phase.

  7. RANDOM LASSO.

    PubMed

    Wang, Sijian; Nan, Bin; Rosset, Saharon; Zhu, Ji

    2011-03-01

    We propose a computationally intensive method, the random lasso method, for variable selection in linear models. The method consists of two major steps. In step 1, the lasso method is applied to many bootstrap samples, each using a set of randomly selected covariates. A measure of importance is yielded from this step for each covariate. In step 2, a similar procedure to the first step is implemented with the exception that for each bootstrap sample, a subset of covariates is randomly selected with unequal selection probabilities determined by the covariates' importance. Adaptive lasso may be used in the second step with weights determined by the importance measures. The final set of covariates and their coefficients are determined by averaging bootstrap results obtained from step 2. The proposed method alleviates some of the limitations of lasso, elastic-net and related methods noted especially in the context of microarray data analysis: it tends to remove highly correlated variables altogether or select them all, and maintains maximal flexibility in estimating their coefficients, particularly with different signs; the number of selected variables is no longer limited by the sample size; and the resulting prediction accuracy is competitive or superior compared to the alternatives. We illustrate the proposed method by extensive simulation studies. The proposed method is also applied to a Glioblastoma microarray data analysis. PMID:22997542

  8. Domain structures and magnetization reversal in Co/Pd and CoFeB/Pd multilayers

    SciTech Connect

    Sbiaa, R.; Ranjbar, M.; Åkerman, J.

    2015-05-07

    Domain structures and magnetization reversal of (Co/Pd) and (CoFeB/Pd) multilayers with 7 and 14 repeats were investigated. The Co-based multilayers show much larger coercivities, a better squareness, and a sharper magnetization switching than CoFeB-based multilayers. From magnetic force microscopy observations, both structures show strong reduction in domains size as the number of repeats increases but the magnetic domains for Co-based multilayers are more than one order of magnitude larger than for CoFeB-based multilayers. By imaging domains at different times, breaks in the (CoFeB/Pd) multilayer stripes were observed within only few hours, while no change could be seen for (Co/Pd) multilayers. Although CoFeB single layers are suitable for magnetoresistive devices due to their large spin polarization and low damping constants, their lamination with Pd suffers mainly from thermal instability.

  9. Josephson and Quasiparticle Tunneling Studies of LITHIUM-TITANIUM(2)-OXYGEN(4)

    NASA Astrophysics Data System (ADS)

    Ng, Kwok-Wai

    Josephson and quasiparticle tunneling measurements have been performed on superconducting LiTi(,2)O(,4). High quality, dense samples were made by arc melting LiTi(,2)O(,4) pellets produced by sintering con- stituent powders of Li(,2)CO(,3), Ti(,2)O(,3) and TiO(,2). The conductive spinel phase was recovered by annealing the ingot for about two months. The sample was characterized by X-ray diffraction and a.c. suscepti- bility, and it was shown to be in the correct crystal structure with only a slight amount of impurity and have a proper superconducting criti- cal temperature of 11.3 K. The measured density was about 99.3% of the single crystal value, hence the sample was dense and suitable for the tunneling experiment. Josephson point contact tunneling between LiTi(,2)O(,4) and Nb reveals, under K-band microwave radiation of frequency (nu) = 25.2 GHz, Shapiro steps of spacing approximately h(nu)/2e. Assuming the validity of the analysis of Pals and van Haeringen, we were led to the conclusion that the pairing in superconducting LiTi(,2)O(,4) was of the s-wave type, as in Nb. The "squeezable junction" method of Moreland and Hansma has been applied to study the superconducting energy gap of an arc melted bulk LiTi(,2)O(,4) sample and also of co-sputtered MoRe films. The MoRe film was estimated to have an energy gap of 1.05 mV, corre- sponding to a Re concentration of 17%. The energy gap of LiTi(,2)O(,4) is determined to be 1.95 (+OR-) 0.03 mV corresponding to 2(DELTA)/k(,B)T(,c) = 4.00 (+OR-) 0.06, making this material a conventional, electron-phonon strong coupled superconductor. The new results for LiTi(,2)O(,4) rule out the recent suggestion of Alexandrov and Ranninger that this material. might exhibit a bipolaronic form superconductivity, for such a form would be gapless, contrary to our results. *DOE Report IS-T-1245. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.

  10. Detection of a Pd-Ni interlayer at the Pd/Ni interface of an epitaxial Pd film on cube textured nickel ( 0 0 1 )

    NASA Astrophysics Data System (ADS)

    Je, J. H.; You, H.; Cullen, W. G.; Maroni, V. A.; Ma, B.; Koritala, R. E.; Thieme, C.

    2002-12-01

    We studied the microstructure of a Pd overlayer deposited on a cube textured Ni(0 0 1) substrate using synchrotron X-ray scattering. We find the existence of an epitaxial Pd-Ni interlayer between the epitaxial Pd layer and the Ni substrate. The Pd-Ni interlayer, which is compressively strained in a manner similar to the Pd overlayer, seemingly acts to relieve the strain at the Pd/Ni interface caused by the Pd-Ni lattice mismatch. The Ni mosaic distribution of our samples is multiply spiked with a rocking angle spread of ∼16°, which reconciles the previously reported observation of saw tooth peaks on top of a Gaussian distribution for a similarly prepared Pd on Ni specimen. The observed sharpening of the mosaic distributions for the Pd(0 0 2) grains (full-width at half-maximum (FWHM)=1.95°) and for the (0 0 2) grains of Pd-Ni interlayer (FWHM=3.0°) indicates that the Pd and Pd-Ni(0 0 2) layers conform to the surface morphology instead of to the (0 0 1) crystallographic planes of Ni-substrate grains.

  11. Nanocrystalline Pd alloy films coated by electroless deposition.

    PubMed

    Strukov, G V; Strukova, G K; Batov, I E; Sakharov, M K; Kudrenko, E A; Mazilkin, A A

    2011-10-01

    The structures of palladium and palladium alloys thin films deposited from organic electrolytes onto metallic substrates by electroless plating method have been investigated. The coatings are dense, pore-free 0.005-1 microm thick films with high adhesive strength to the substrate surface. EDX, XRD, SEM and TEM methods were used to determine the composition and structure of alloy coatings of the following binary systems: Pd-Au, Pd-Ag, Pd-Ni, Pd-Pb, and ternary system Pd-Au-Ni. The coatings of Pd-Au, Pd-Ag and Pd-Ni have a solid solution structure, whereas Pd-Pb is intermetallic compound. It has been found that the deposited films consist of nanocrystalline grains with sizes in the range of 11-35 nm. Scanning and transmission electron microscopy investigations reveal the existence of clusters formed by nanocrystalline grains. The origin for the formation of nanocrystalline structures of coating films is discussed. PMID:22400291

  12. Charge Qubit Coupled to an Intense Microwave Electromagnetic Field in a Superconducting Nb Device: Evidence for Photon-Assisted Quasiparticle Tunneling

    NASA Astrophysics Data System (ADS)

    de Graaf, S. E.; Leppäkangas, J.; Adamyan, A.; Danilov, A. V.; Lindström, T.; Fogelström, M.; Bauch, T.; Johansson, G.; Kubatkin, S. E.

    2013-09-01

    We study a superconducting charge qubit coupled to an intensive electromagnetic field and probe changes in the resonance frequency of the formed dressed states. At large driving strengths, exceeding the qubit energy-level splitting, this reveals the well known Landau-Zener-Stückelberg interference structure of a longitudinally driven two-level system. For even stronger drives, we observe a significant change in the Landau-Zener-Stückelberg pattern and contrast. We attribute this to photon-assisted quasiparticle tunneling in the qubit. This results in the recovery of the qubit parity, eliminating effects of quasiparticle poisoning, and leads to an enhanced interferometric response. The interference pattern becomes robust to quasiparticle poisoning and has a good potential for accurate charge sensing.

  13. Quasiparticle injection effect of a YBa{sub 2}Cu{sub 3}O{sub 7{minus}y} film with double injector geometry

    SciTech Connect

    Arie, H.; Kume, E.; Iguchi, I.

    1997-08-01

    We present measurements on quasiparticle injection into a YBa{sub 2}Cu{sub 3}O{sub 7{minus}y} (YBCO) film, with double injector-junction geometry free from the parallel overlapping effect of the currents, fabricated by electron-beam coevaporation and photolithographic lift off. The observed injection characteristics are quite symmetric with respect to the relative flow direction between the injection current and the film current, in contrast to previous reports. The film critical current decreases almost linearly with the injection current. The critical current density J{sub c} can be controlled by injection current density much smaller than J{sub c}, indicating that quasiparticle injection is dominant. The estimated effective quasiparticle recombination time at the critical injection is about 2 ns, consistent with previous reports of optical excitation. {copyright} {ital 1997} {ital The American Physical Society}

  14. Heat capacity measurements on UBe13 in rotated magnetic fields: Anisotropic response in the normal state and absence of nodal quasiparticles

    NASA Astrophysics Data System (ADS)

    Shimizu, Yusei; Kittaka, Shunichiro; Sakakibara, Toshiro; Haga, Yoshinori; Yamamoto, Etsuji; Amitsuka, Hiroshi; Tsutsumi, Yasumasa; Machida, Kazushige

    2016-02-01

    In order to gain insight into the superconducting (SC) gap of UBe13, we studied its quasiparticle excitations by means of heat-capacity measurements. Quite unexpectedly, we found the isotropic C(H) ∝ H behavior in low fields at low temperatures, implying the absence of nodal quasiparticle excitations. This result indicates that the SC gap in UBe13 is fully open over the Fermi surfaces. Furthermore, we observed a characteristic oscillation of heat capacity both in the SC and non-Fermi-liquid normal states above ∼2 T, and the angular variation of heat capacity possibly originates from anisotropic magnetic response of the heavy-electron state. Our result regarding the low-energy quasiparticle excitations in the SC and normal states will be a clue to understand the unusual nature of UBe13.

  15. Charge qubit coupled to an intense microwave electromagnetic field in a superconducting Nb device: evidence for photon-assisted quasiparticle tunneling.

    PubMed

    de Graaf, S E; Leppäkangas, J; Adamyan, A; Danilov, A V; Lindström, T; Fogelström, M; Bauch, T; Johansson, G; Kubatkin, S E

    2013-09-27

    We study a superconducting charge qubit coupled to an intensive electromagnetic field and probe changes in the resonance frequency of the formed dressed states. At large driving strengths, exceeding the qubit energy-level splitting, this reveals the well known Landau-Zener-Stückelberg interference structure of a longitudinally driven two-level system. For even stronger drives, we observe a significant change in the Landau-Zener-Stückelberg pattern and contrast. We attribute this to photon-assisted quasiparticle tunneling in the qubit. This results in the recovery of the qubit parity, eliminating effects of quasiparticle poisoning, and leads to an enhanced interferometric response. The interference pattern becomes robust to quasiparticle poisoning and has a good potential for accurate charge sensing. PMID:24116809

  16. Investigation of the two-quasiparticle bands in the doubly-odd nucleus 166Ta using a particle-number conserving cranked shell model

    NASA Astrophysics Data System (ADS)

    Zhang, ZhenHua

    2016-07-01

    The high-spin rotational properties of two-quasiparticle bands in the doubly-odd 166Ta are analyzed using the cranked shell model with pairing correlations treated by a particle-number conserving method, in which the blocking effects are taken into account exactly. The experimental moments of inertia and alignments and their variations with the rotational frequency hω are reproduced very well by the particle-number conserving calculations, which provides a reliable support to the configuration assignments in previous works for these bands. The backbendings in these two-quasiparticle bands are analyzed by the calculated occupation probabilities and the contributions of each orbital to the total angular momentum alignments. The moments of inertia and alignments for the Gallagher-Moszkowski partners of these observed two-quasiparticle rotational bands are also predicted.

  17. CTLA-4 and PD-1 Pathways

    PubMed Central

    Desai, Anupam

    2016-01-01

    The cytotoxic T-lymphocyte–associated antigen 4 (CTLA-4) and programmed death 1 (PD-1) immune checkpoints are negative regulators of T-cell immune function. Inhibition of these targets, resulting in increased activation of the immune system, has led to new immunotherapies for melanoma, non–small cell lung cancer, and other cancers. Ipilimumab, an inhibitor of CTLA-4, is approved for the treatment of advanced or unresectable melanoma. Nivolumab and pembrolizumab, both PD-1 inhibitors, are approved to treat patients with advanced or metastatic melanoma and patients with metastatic, refractory non-small cell lung cancer. In addition the combination of ipilimumab and nivolumab has been approved in patients with BRAF WT metastatic or unresectable melanoma. The roles of CTLA-4 and PD-1 in inhibiting immune responses, including antitumor responses, are largely distinct. CTLA-4 is thought to regulate T-cell proliferation early in an immune response, primarily in lymph nodes, whereas PD-1 suppresses T cells later in an immune response, primarily in peripheral tissues. The clinical profiles of immuno-oncology agents inhibiting these 2 checkpoints may vary based on their mechanistic differences. This article provides an overview of the CTLA-4 and PD-1 pathways and implications of their inhibition in cancer therapy. PMID:26558876

  18. Understanding Physical Developer (PD): Part II--Is PD targeting eccrine constituents?

    PubMed

    de la Hunty, Mackenzie; Moret, Sébastien; Chadwick, Scott; Lennard, Chris; Spindler, Xanthe; Roux, Claude

    2015-12-01

    Physical developer (PD) is a fingermark development technique that deposits silver onto fingermark ridges. It is the only technique currently in routine operational use that gives results on porous substrates that have been wet. There is a reasonable understanding of the working solution chemistry, but the chemical constituent(s) contained in fingermark residue that are specifically targeted by PD are largely unknown. A better understanding of the PD technique will permit a more informed selection of alternative or complementary detection methods, and greater usage in operational laboratories. Recent research by our group has shown that PD does not selectively target the lipids present in the residue. This research investigated the hypothesis that PD targets the eccrine constituents in fingermark residue. This was tested by comparison of PD and indanedione-zinc (Ind-Zn) treated natural fingermarks that had been deposited successively, and marks that had been deposited with a ten second interval in between depositions. Such an interval allows for the regeneration of secretions from the pores located on the ridges of the fingers. On fingermark depletions with no time interval between depositions, PD and Ind-Zn treated depletions successively (and comparatively) decreased in development intensity as the amount of residue diminished. Short time intervals in between successive depletions resulted in additional secretions from the pores intermittently occurring, the increased development of which was visualised by treatment with both PD and Ind-Zn. The changes in development intensity were seen with both techniques on the same split depletions in a series, comparably and proportionately. These results indicate that the components targeted by PD are contained in the material excreted by the friction ridge pores through its mirrored development with Ind-Zn. Repetition of the experiments on marks that only contained eccrine material showed good Ind-Zn development but poor

  19. Magnetic characteristics of CoPd and FePd antidot arrays on nanoperforated Al2O3 templates

    NASA Astrophysics Data System (ADS)

    Maximenko, A.; Fedotova, J.; Marszałek, M.; Zarzycki, A.; Zabila, Y.

    2016-02-01

    Hard magnetic antidot arrays show promising results in context of designing of percolated perpendicular media. In this work the technology of magnetic FePd and CoPd antidot arrays fabrication is presented and correlation between surface morphology, structure and magnetic properties is discussed. CoPd and FePd antidot arrays were fabricated by deposition of Co/Pd and Fe/Pd multilayers (MLs) on porous anodic aluminum oxide templates with bowl-shape cell structure with inclined intercellular regions. FePd ordered L10 structure was obtained by successive vacuum annealing at elevated temperatures (530 °C) and confirmed by XRD analysis. Systematic analysis of magnetization curves evidenced perpendicular magnetic anisotropy of CoPd antidot arrays, while FePd antidot arrays revealed isotropic magnetic anisotropy with increased out-of-plane magnetic contribution. MFM images of antidots showed more complicated contrast, with alternating magnetic dots oriented parallel and antiparallel to tip magnetization moment.

  20. High-Resolution PET Imaging with Therapeutic Antibody-based PD-1/PD-L1 Checkpoint Tracers

    PubMed Central

    Hettich, Michael; Braun, Friederike; Bartholomä, Mark D.; Schirmbeck, Reinhold; Niedermann, Gabriele

    2016-01-01

    Checkpoint-blocking antibodies like those targeting the PD-1/PD-L1 pathway have revolutionized oncology. We developed radiotracers based on therapeutic checkpoint-blocking antibodies permitting sensitive and high-resolution PET imaging of both PD-1 and PD-L1 in immunocompetent mice. ImmunoPET of naive mice revealed similar overall expression patterns for PD-1 and PD-L1 in secondary lymphoid organs (spleen and lymph nodes). Interestingly, PD-L1 was also detected in brown adipose tissue (BAT), confirming the notion that BAT is immunologically relevant. Under pathophysiological conditions, strong expression of the receptor/ligand pair was also found in non-lymphoid tissues. Both were specifically detected in malignant tumors. PD-1 was readily detected after combined immunoradiotherapy causing massive tumor infiltration by PD-1+ lymphocytes. PD-L1 tracer uptake was reduced in PD-L1 knockout tumors. Moreover, monitoring the expression changes of PD-L1 in response to its main inducer, the effector T cell cytokine IFN-γ, revealed robust upregulation in the lung. This suggests that T cell responses in the lung, a vital organ continuously exposed to a variety of antigens, are strongly restrained by the PD-1 checkpoint. In turn, this could explain the association of PD-1 checkpoint inhibition with potentially fatal immune-mediated pneumonitis and partially also its efficacy in lung cancer. PMID:27446497

  1. Injection of nonequilibrium quasiparticles into Zeeman-split superconductors: A way to create long-range spin imbalance

    NASA Astrophysics Data System (ADS)

    Bobkova, I. V.; Bobkov, A. M.

    2016-01-01

    A theory of spin transport and spin detection in Zeeman-split superconducting films at low temperatures is developed. It is shown that an injection of spin-unpolarized quasiparticles into a Zeeman-split superconductor gives rise to a spin imbalance. The relaxation length of such a spin signal is determined by the energy relaxation length and can be extremely large as compared to the usual spin relaxation length. There can exist two types of signals: due to nonthermalized quasiparticle distribution and due to thermalized overheated electron distribution. They have different decay lengths and can be distinguished by their different dependencies on the applied voltage. The decay length of the nonthermalized signal is determined by the electron-electron scattering rate, renormalized due to superconductivity. The decay length of the thermalized signal is determined by the length on which energy leaves the electronic subsystem and can be very large under special conditions. Applications of the theory to recent experimental data on spin relaxation in Zeeman-split and exchange-split superconductors are discussed. In particular, it can explain the extremely high spin relaxation lengths, experimentally observed in Zeeman-split superconductors, and their growth with the magnetic field and with the applied voltage.

  2. Observation of van Hove singularity and quasiparticle interference in KFe2 As2 superconductors revealed by STM/STS measurements

    NASA Astrophysics Data System (ADS)

    Wen, Hai-Hu; Fang, Delong; Du, Zengyi; Wang, Zhenyu; Yang, Huan; Ding, Xiaxin

    2015-03-01

    We have conducted STM/STS investigations on the KFe2As2 superconducting single crystals down to 0.45 K under magnetic field. Clear electronic standing waves have been observed allowing us to investigate the quasiparticle interference (QPI). Interestingly we observed a sharp peak of local density of states (LDOS) near the Fermi energy showing evidence of strongly enhanced DOS both below and above Tc. We demonstrate that this is induced by a van Hove singularity with the saddle point locating only 4 meV below the Fermi energy. Below Tc it is found that only 20% of the normal state DOS is gapped away by superconductivity, with the major part of DOS due to VHS ungapped. Combing with the ARPES data, we find that the VHS points locate on the (π,0) point, which gives strong constraint on the gap function and pairing mechanism. In the mixed state we clearly observed the mixture of vortices and the standing waves due to quasiparticle interference, giving support to above picture. In collaboration with X. Shi, P. Richard, T. Qian and H. Ding et al. in Institute of Physics, CAS.

  3. Evolution of quasiparticle excitations with enhanced electron correlations in superconducting A Fe2As2 (A =K , Rb, and Cs)

    NASA Astrophysics Data System (ADS)

    Mizukami, Y.; Kawamoto, Y.; Shimoyama, Y.; Kurata, S.; Ikeda, H.; Wolf, T.; Zocco, D. A.; Grube, K.; Löhneysen, H. v.; Matsuda, Y.; Shibauchi, T.

    2016-07-01

    In the heavily hole-doped iron-based superconductors A Fe2As2 (A =K , Rb, and Cs), the electron effective mass increases rapidly with alkali-ion radius. To study the superconducting gap structure in this series, we measure the in-plane London penetration depth λa b(T ) in clean crystals of A Fe2As2 down to low temperature T ˜0.1 K. In KFe2As2 , the superfluid stiffness ρsa b(T ) =λab 2(0 ) /λab 2(T ) at low temperatures can be accounted for by the strongly band-dependent multiple gaps reported recently. Although the λa b(T ) in all systems exhibits similar nonexponential temperature dependence indicating nodes or small minima in the gap, we find that the quasiparticle excitations at low temperatures show a systematic suppression with increasing alkali-ion radius. A possible origin of such evolution of low-energy excitations is discussed in terms of the momentum-dependent effect of enhanced quasiparticle mass near a quantum critical point.

  4. Q-balls of quasi-particles in a (2, 0)-theory model of the fractional quantum Hall effect

    NASA Astrophysics Data System (ADS)

    Ganor, Ori J.; Hong, Yoon Pyo; Moore, Nathan; Sun, Hao-Yu; Tan, Hai Siong; Torres-Chicon, Nesty R.

    2015-09-01

    A toy model of the fractional quantum Hall effect appears as part of the low-energy description of the Coulomb branch of the A 1 (2 , 0)-theory formulated on ({S}^1× {{R}}^2)/{{Z}}_k , where the generator of {{Z}}_k acts as a combination of translation on S 1 and rotation by 2 π/k on {{R}}^2 . At low energy the configuration is described in terms of a 4+1D Super-Yang-Mills theory on a cone ({{R}}^2/{{Z}}_k) with additional 2+1D degrees of freedom at the tip of the cone that include fractionally charged particles. These fractionally charged "quasi-particles" are BPS strings of the (2 , 0)-theory wrapped on short cycles. We analyze the large k limit, where a smooth cigar-geometry provides an alternative description. In this framework a W-boson can be modeled as a bound state of k quasi-particles. The W-boson becomes a Q-ball, and it can be described as a soliton solution of Bogomolnyi monopole equations on a certain auxiliary curved space. We show that axisymmetric solutions of these equations correspond to singular maps from AdS 3 to AdS 2, and we present some numerical results and an asymptotic expansion.

  5. The role of engineered materials in superconducting tunnel junction X-ray detectors - Suppression of quasiparticle recombination losses via a phononic band gap

    NASA Technical Reports Server (NTRS)

    Rippert, Edward D.; Ketterson, John B.; Chen, Jun; Song, Shenian; Lomatch, Susanne; Maglic, Stevan R.; Thomas, Christopher; Cheida, M. A.; Ulmer, Melville P.

    1992-01-01

    An engineered structure is proposed that can alleviate quasi-particle recombination losses via the existence of a phononic band gap that overlaps the 2-Delta energy of phonons produced during recombination of quasi-particles. Attention is given to a 1D Kronig-Penny model for phonons normally incident to the layers of a multilayered superconducting tunnel junction as an idealized example. A device with a high density of Bragg resonances is identified as desirable; both Nb/Si and NbN/SiN superlattices have been produced, with the latter having generally superior performance.

  6. Decomposition of ethylene on small Pd particles

    NASA Technical Reports Server (NTRS)

    Durrer, W. G.; Poppa, H.; Dickinson, J. T.; Park, C.

    1985-01-01

    New results have been obtained which contribute to the understanding of hydrocarbon reactions on the surface of highly dispersed metal systems. Small particle of Pd were grown by electron beam evaporation on cleavage planes of high purity natural mica under ultrahigh vacuum conditions. Samples were subsequently characterized by transmission electron microscopy. Average particle sizes ranged from about 1 to 10 nm diameter. The chemisoption and decomposition of C2H4 on the Pd particles was studied using Auger electron spectroscopy and flash thermal desorption. It is shown that (a) C2H4 decomposes on Pd particles at room temperature, (b) specific surface sites are causing decomposition, and (c) the proportion of such active sites is significantly greater for the smaller metal particles. This enhanced reactivity may be due to an increase in the density of step, corner, and edge sites with a decrease in particle size.

  7. Plunger Lifetime Measurements in 102Pd

    SciTech Connect

    Kalyva, G.; Spyrou, A.; Axiotis, M.; Harissopulos, S.; Dewald, A.; Fitzler, A.; Saha, B.; Liennemann, A.; Vlastou, R.; Napoli, D. R.; Marginean, N.; Rusu, C.; De Angelis, G.; Ur, C.; Bazzacco, D.; Farnea, E.; Balabanski, D. L.; Julin, R.

    2006-04-26

    Recently, an intense experimental effort has been devoted to the search of empirical proofs of critical-point symmetries in nuclear structure. These symmetries describe shape-phase transitions and provide parameter-free predictions (up to over-all scale factors) for excitation spectra and B(E2) values. This contribution reports on recent plunger-lifetime measurements ON 102Pd carried out at LNL, Legnaro, with the Cologne plunger apparatus coupled to the GASP spectrometer and using the 92Zr(13C,3n)102Pd reaction at 48 MeV. According to the results of our measurements, 102Pd is so far the best known paradigm of the E(5) critical-point symmetry.

  8. Nitrite reduction mechanism on a Pd surface.

    PubMed

    Shin, Hyeyoung; Jung, Sungyoon; Bae, Sungjun; Lee, Woojin; Kim, Hyungjun

    2014-11-01

    Nitrate (NO3-) is one of the most harmful contaminants in the groundwater, and it causes various health problems. Bimetallic catalysts, usually palladium (Pd) coupled with secondary metallic catalyst, are found to properly treat nitrate-containing wastewaters; however, the selectivity toward N2 production over ammonia (NH3) production still requires further improvement. Because the N2 selectivity is determined at the nitrite (NO2-) reduction step on the Pd surface, which occurs after NO3- is decomposed into NO2- on the secondary metallic catalyst, we here performed density functional theory (DFT) calculations and experiments to investigate the NO2- reduction pathway on the Pd surface activated by hydrogen. Based on extensive DFT calculations on the relative energetics among ∼100 possible intermediates, we found that NO2- is easily reduced to NO* on the Pd surface, followed by either sequential hydrogenation steps to yield NH3 or a decomposition step to N* and O* (an adsorbate on Pd is denoted using an asterisk). Based on the calculated high migration barrier of N*, we further discussed that the direct combination of two N* to yield N2 is kinetically less favorable than the combination of a highly mobile H* with N* to yield NH3. Instead, the reduction of NO2- in the vicinity of the N* can yield N2O* that can be preferentially transformed into N2 via diverse reaction pathways. Our DFT results suggest that enhancing the likelihood of N* encountering NO2- in the solution phase before combination with surface H* is important for maximizing the N2 selectivity. This is further supported by our experiments on NO2- reduction by Pd/TiO2, showing that both a decreased H2 flow rate and an increased NO2- concentration increased the N2 selectivity (78.6-93.6% and 57.8-90.9%, respectively). PMID:25280017

  9. Anti-PD-1/PD-L1 therapy of human cancer: past, present, and future.

    PubMed

    Chen, Lieping; Han, Xue

    2015-09-01

    Major progress has been made toward our understanding of the programmed death-1/programmed death ligand-1 (PD-1/PD-L1) pathway (referred to as the PD pathway). mAbs are already being used to block the PD pathway to treat human cancers (anti-PD therapy), especially advanced solid tumors. This therapy is based on principles that were discovered through basic research more than a decade ago, but the great potential of this pathway to treat a broad spectrum of advanced human cancers is just now becoming apparent. In this Review, we will briefly review the history and development of anti-PD therapy, from the original benchwork to the most up-to-date clinical results. We will then focus the discussion on three basic principles that define this unique therapeutic approach and highlight how anti-PD therapy is distinct from other immunotherapeutic approaches, namely tumor site immune modulation, targeting tumor-induced immune defects, and repairing ongoing (rather than generating de novo) tumor immunity. We believe that these fundamental principles set the standard for future immunotherapies and will guide our efforts to develop more efficacious and less toxic immune therapeutics to treat human cancers. PMID:26325035

  10. Magnetic properties of Mn2PdSn and Mn2PdIn

    NASA Astrophysics Data System (ADS)

    Xu, Xiao; Kanomata, Takeshi; Hayasaka, Masanobu; Umino, Ryosuke; Endo, Keita; Nishihara, Hironori; Adachi, Yoshiya; Kainuma, Ryosuke; Ziebeck, Kurt R. A.

    2016-03-01

    New Mn2PdZ (Z=In, Sn) alloys have been synthesized. Both alloys crystallize in a Heusler-type cubic structure. The lattice parameters of solution-treated Mn2PdSn and Mn2PdIn were found to be 6.351 Å and 6.399 Å, respectively. Magnetization measurements were carried out under magnetic fields up to 68 kOe. Both the solution-treated alloys have spontaneous magnetizations. The magnetic moment at 6 K and the Curie temperature of solution-treated Mn2PdSn were estimated to be 1.70 μB / f . u . and 411 K, respectively. The magnetic moment at 6 K of solution-treated Mn2PdIn was found to be 0.59 μB / f . u .. Ageing heat treatments at 673 K on these alloy, instead of an increase of degree of atomic order, resulted in phase decomposition. Thin-plate precipitates and a very fine Widmanstätten morphology were found for the aged Mn2PdSn and Mn2PdIn alloys, respectively.

  11. PD-L1 Expression in Triple Negative Breast Cancer

    PubMed Central

    Mittendorf, Elizabeth A.; Philips, Anne V.; Meric-Bernstam, Funda; Qiao, Na; Wu, Yun; Harrington, Susan; Su, Xiaoping; Wang, Ying; Gonzalez-Angulo, Ana M.; Akcakanat, Argun; Chawla, Akhil; Curran, Michael; Hwu, Patrick; Sharma, Padmanee; Litton, Jennifer K.; Molldrem, Jeffrey J.; Alatrash, Gheath

    2014-01-01

    Early phase trials targeting the T-cell inhibitory molecule PD-L1 have shown clinical efficacy in cancer. This study was undertaken to determine whether PD-L1 is overexpressed in triple-negative breast cancer (TNBC) and to investigate the loss of the phosphatase and tensin homolog (PTEN) as a mechanism of PD-L1 regulation. The Cancer Genome Atlas (TCGA) RNA sequencing data showed significantly greater expression of the PD-L1 gene in TNBC (n=120) compared to non-TNBC (n=716) (P<0.001). Breast tumor tissue microarrays were evaluated for PD-L1 expression which was present in 19% (20 of 105) TNBC specimens. PD-L1+ tumors had greater CD8+ T-cell infiltrate than PD-L1− tumors (688 cells/mm versus 263 cells/mm; P<0.0001). To determine the effect of PTEN loss on PD-L1 expression, stable cell lines were generated using PTEN shRNA. PTEN knockdown led to significantly higher cell-surface PD-L1 expression and PD-L1 transcripts, suggesting transcriptional regulation. Moreover, PI3K pathway inhibition using the AKT inhibitor MK-2206 or rapamycin resulted in decreased PD-L1 expression, further linking PTEN and PI3K signaling to PD-L1 regulation. Co-culture experiments were performed to determine the functional effect of altered PD-L1 expression. Increased PD-L1 cell surface expression by tumor cells induced by PTEN loss led to decreased T cell proliferation and increased apoptosis. PD-L1 is expressed in 20% of TNBC, suggesting PD-L1 as a therapeutic target in TNBC. Since PTEN loss is one mechanism regulating PD-L1 expression, agents targeting the PI3K pathway may increase the antitumor adaptive immune responses. PMID:24764583

  12. The clinical utility of PD-L1 testing in selecting non-small cell lung cancer patients for PD1/PD-L1-directed therapy.

    PubMed

    Villaruz, L C; Socinski, M A

    2016-09-01

    Lung cancer is the leading cause of cancer mortality in the United States and worldwide. Long thought to be nonimmunogenic, immunotherapy in lung cancer has historically been met with disappointing results. Programmed death-1 (PD-1), and the PD-1 ligand, PD-L1, are immune checkpoint proteins that fine-tune the antigen-specific T-cell response after stimulation of the T-cell receptor and are crucial for self-tolerance. This pathway in particular is co-opted by tumors through expression of PD-L1 on the tumor cell surface and within the tumor microenvironment, allowing for direct suppression of antitumor cytolytic T-cell activity by the tumor. Indeed, induction of the PD1/PD-L1 pathway represents an adaptive immune resistance mechanism exerted by tumor cells in response to endogenous antitumor activity. In 2015, the US Food and Drug Administration (FDA) approved two immuno-oncology agents, the PD-1 inhibitors nivolumab and pembrolizumab, for the treatment of previously treated advanced non-small cell lung cancer (NSCLC). Coincident with the clinical trials that led to these regulatory approvals has been the development of several immunohistochemistry (IHC) tests of PD-L1 expression, which may serve to select patients who will derive the most benefit from PD1- or PD-L1-directed therapy. The PD-L1 IHC assays are distinct in their methods and interpretation, which poses a challenge to clinicians selecting patients for these therapies. PMID:27090296

  13. THE EFFECT OF CO ON HYDROGEN PERMEATION THROUGH PD AND INTERNALLY OXIDIZED AND UN-OXIDIZED PD ALLOY MEMBRANES

    SciTech Connect

    Shanahan, K.; Flanagan, T.; Wang, D.

    2010-10-20

    The H permeation of internally oxidized Pd alloy membranes such as Pd-Al and Pd-Fe, but not Pd-Y alloys, is shown to be more resistant to inhibition by CO(g) as compared to Pd or un-oxidized Pd alloy membranes. The increased resistance to CO is found to be greater at 423 K than at 473 K or 523 K. In these experiments CO was pre-adsorbed onto the membranes and then CO-free H{sub 2} was introduced to initiate the H permeation.

  14. Is random access memory random?

    NASA Technical Reports Server (NTRS)

    Denning, P. J.

    1986-01-01

    Most software is contructed on the assumption that the programs and data are stored in random access memory (RAM). Physical limitations on the relative speeds of processor and memory elements lead to a variety of memory organizations that match processor addressing rate with memory service rate. These include interleaved and cached memory. A very high fraction of a processor's address requests can be satified from the cache without reference to the main memory. The cache requests information from main memory in blocks that can be transferred at the full memory speed. Programmers who organize algorithms for locality can realize the highest performance from these computers.

  15. Perpendicular magnetic tunnel junction with thin CoFeB/Ta/Co/Pd/Co reference layer

    SciTech Connect

    Gan, Huadong Malmhall, Roger; Wang, Zihui; Yen, Bing K; Zhang, Jing; Wang, Xiaobin; Zhou, Yuchen; Hao, Xiaojie; Jung, Dongha; Satoh, Kimihiro; Huai, Yiming

    2014-11-10

    Integration of high density spin transfer torque magnetoresistance random access memory requires a thin stack (less than 15 nm) of perpendicular magnetic tunnel junction (p-MTJ). We propose an innovative approach to solve this challenging problem by reducing the thickness and/or moment of the reference layer. A thin reference layer structure of CoFeB/Ta/Co/Pd/Co has 60% magnetic moment of the conventional thick structure including [Co/Pd] multilayers. We demonstrate that the perpendicular magnetization of the CoFeB/Ta/Co/Pd/Co structure can be realized by anti-ferromagnetically coupling to a pinned layer with strong perpendicular anisotropy via Ruderman-Kittel-Kasuya-Yosida exchange interaction. The pMTJ with thin CoFeB/Ta/Co/Pd/Co reference layer has a comparable TMR ratio (near 80%) as that with thick reference layer after annealing at 280 °C. The pMTJ with thin reference layer has a total thickness less than 15 nm, thereby significantly increasing the etching margin required for integration of high density pMTJ array on wafers with form factor of 300 mm and beyond.

  16. Perpendicular magnetic tunnel junction with thin CoFeB/Ta/Co/Pd/Co reference layer

    NASA Astrophysics Data System (ADS)

    Gan, Huadong; Malmhall, Roger; Wang, Zihui; Yen, Bing K.; Zhang, Jing; Wang, Xiaobin; Zhou, Yuchen; Hao, Xiaojie; Jung, Dongha; Satoh, Kimihiro; Huai, Yiming

    2014-11-01

    Integration of high density spin transfer torque magnetoresistance random access memory requires a thin stack (less than 15 nm) of perpendicular magnetic tunnel junction (p-MTJ). We propose an innovative approach to solve this challenging problem by reducing the thickness and/or moment of the reference layer. A thin reference layer structure of CoFeB/Ta/Co/Pd/Co has 60% magnetic moment of the conventional thick structure including [Co/Pd] multilayers. We demonstrate that the perpendicular magnetization of the CoFeB/Ta/Co/Pd/Co structure can be realized by anti-ferromagnetically coupling to a pinned layer with strong perpendicular anisotropy via Ruderman-Kittel-Kasuya-Yosida exchange interaction. The pMTJ with thin CoFeB/Ta/Co/Pd/Co reference layer has a comparable TMR ratio (near 80%) as that with thick reference layer after annealing at 280 °C. The pMTJ with thin reference layer has a total thickness less than 15 nm, thereby significantly increasing the etching margin required for integration of high density pMTJ array on wafers with form factor of 300 mm and beyond.

  17. Investigation of magnetic order in SmTr2Zn20 (Tr = Fe, Co, Ru) and SmTr2Cd20 (Tr = Ni, Pd)

    NASA Astrophysics Data System (ADS)

    Yazici, Duygu; White, B. D.; Ho, P.-C.; Kanchanavatee, N.; Huang, K.; Dilley, N. R.; Maple, M. B.

    2015-03-01

    Single crystals of the cage compounds Sm Tr 2Zn20 (Tr = Fe, Co, Ru) and Sm Tr 2Cd20 (Tr = Ni, Pd) have been investigated by means of electrical resistivity, magnetization, and specific heat measurements. The compounds SmFe2Zn20, SmRu2Zn20,andSmNi2Cd20 exhibit ferromagnetic order with Curie temperatures of TC = 47.4 K, 7.6 K, and 7.5 K, respectively, whereas SmPd2Cd20 is an antiferromagnet with a Néel temperature of TN = 3.4 K. No evidence for magnetic order is observed in SmCo2Zn20 down to 110 mK. The Sommerfeld coefficients γ are found to be 57 mJ/mol-K2 for SmFe2Zn20, 79.5 mJ/mol-K2 for SmCo2Zn20, 258 mJ/mol-K2 for SmRu2Zn20, 165 mJ/mol-K2 for SmNi2Cd20, and 208 mJ/mol-K2 for SmPd2Cd20. Enhanced values of Sommerfeld coefficients γ and a quadratic temperature dependence of the electrical resistivity at low temperature for SmRu2Zn20andSmPd2Cd20 suggest an enhancement of the quasiparticle masses due to hybridization between localized 4 f and conduction electron states. Research at UCSD was supported by the U.S. DOE under Grant No. DE-FG02-04-ER46105 and the U.S. NSF under Award Grant No. DMR 1206553. Research at California State University, Fresno was supported by the U.S. NSF under Grant No. DMR 1104544.

  18. G6PD Deficiency (Glucose-6-Phosphate Dehydrogenase) (For Parents)

    MedlinePlus

    ... are high-risk areas for the infectious disease malaria . Researchers have found evidence that the parasite that ... deficiency may have developed as a protection against malaria. continue G6PD Deficiency Symptom Triggers Kids with G6PD ...

  19. Structure of quenched alloys of the Ti-Pd system

    NASA Astrophysics Data System (ADS)

    Dobromyslov, A. V.; Taluts, N. I.

    2016-07-01

    The quenched alloys of the Ti-Pd system containing 2-15 at % Pd have been studied using X-ray diffraction analysis, optical metallography, transmission electron microscopy, and measurements of the microhardness. It has been found that, in the course of quenching, epy alloys containing 2, 3, and 5 at % Pd undergo a eutectoid decomposition into the α phase and Ti2Pd intermetallic compound, and the Ti-7 at % Pd and Ti-9 at % Pd alloys undergo a β → α' martensitic transformation. In the alloys with Pd contents of more than 9 at %, the β phase is fixed in the metastable state. The complete stabilization of the β phase takes place in the alloys containing 11 at % Pd and more. It has been found that the formation of the orthorhombic α" phase and metastable ω phase in the quenched alloys of this system does not occur.

  20. How Does Your Doctor Make a PD Diagnosis?

    MedlinePlus

    ... More > Español In Your Area NPF Shop How Does Your Doctor Make a PD Diagnosis Make Text ... and possible falls, also called postural instability How does your doctor make a PD diagnosis? The bedside ...

  1. State of Supported Pd during Catalysis in Water

    SciTech Connect

    Chase, Zizwe; Fulton, John L.; Camaioni, Donald M.; Mei, Donghai; Balasubramanian, Mahalingam; Pham, Van Thai; Zhao, Chen; Weber, Robert S.; Wang, Yong; Lercher, Johannes A.

    2013-08-29

    In operando X-ray absorption was used to measure the structure and chemical state of supported Pd nanoparticles with 3 -10 nm diameter in contact with H2 saturated water at 298-473 K. The Pd-Pd distances determined were consistent with the presence of subsurface hydrogen, i.e., longer than those measured by others for bare, reduced Pd particles, and within the range of distances for Pd hydrides. During the Pd-catalyzed hydrogenation of phenol, cyclohexanone, cyclohexanol or cyclohexene in the presence of water, the Pd nanoparticles exhibited a lengthening of the Pd-Pd bond that we attribute to a change in the concentration of sorbed H related to the steady state of H at the surface of the Pd particles. This steady state is established by all reactions involving H2, i.e., the sorption/desorption into the bulk, the sorption at the surface, and the reaction with adsorbed unsaturated reactants. Thus, first insight into the chemical state of Pd and the H/Pd ratio during catalysis in water is provided. The Pd particles did not change upon their exposure to water or reactants; nor did the spectra show any effect from the interaction of the Pd particles with various supports. The experimental results are consistent with ab initio molecular dynamic simulations, which indicate that Pd-water interactions are relatively weak for Pd metal and that these interactions become even weaker, when hydrogen is incorporated into the metal particles. This work was supported by the US Department of Energy (DOE), Office of Basic Energy Sciences (BES), Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory is a multi-program national laboratory operated for DOE by Battelle through Contract DE-AC05-76RL01830.

  2. The Next Immune-Checkpoint Inhibitors: PD-1/PD-L1 Blockade in Melanoma

    PubMed Central

    Mahoney, Kathleen M.; Freeman, Gordon J.; McDermott, David F.

    2015-01-01

    Purpose Blocking the interaction between the programmed cell death (PD)-1 protein and one of its ligands, PD-L1, has been reported to have impressive antitumor responses. Therapeutics targeting this pathway are currently in clinical trials. Pembrolizumab and nivolumab are the first of this anti-PD-1 pathway family of checkpoint inhibitors to gain accelerated approval from the US Food and Drug Administration (FDA) for the treatment of ipilimumab-refractory melanoma. Nivolumab has been associated with improved overall survival compared with dacarbazine in patients with previously untreated wild-type serine/threonine-protein kinase B-raf proto-oncogene BRAF melanoma. Although the most mature data are in the treatment of melanoma, the FDA has granted approval of nivolumab for squamous cell lung cancer and the breakthrough therapy designation to immune-checkpoint inhibitors for use in other cancers: nivolumab, an anti-PD-1 monoclonal antibody, for Hodgkin lymphoma, and MPDL-3280A, an anti-PD-L1 monoclonal antibody, for bladder cancer and non–small cell lung cancer. Here we review the literature on PD-1 and PD-L1 blockade and focus on the reported clinical studies that have included patients with melanoma. Methods PubMed was searched to identify relevant clinical studies of PD-1/PD-L1–targeted therapies in melanoma. A review of data from the current trials on clinicaltrial.gov was incorporated, as well as data presented in abstracts at the 2014 annual meeting of the American Society of Clinical Oncology, given the limited number of published clinical trials on this topic. Findings The anti-PD-1 and anti-PD-L1 agents have been reported to have impressive antitumor effects in several malignancies, including melanoma. The greatest clinical activity in unselected patients has been seen in melanoma. Tumor expression of PD-L1 is a suggestive, but inadequate, biomarker predictive of response to immune-checkpoint blockade. However, tumors expressing little or no PD-L1 are

  3. Expression of PD-1, PD-L1 and PD-L2 is associated with differentiation status and histological type of endometrial cancer

    PubMed Central

    Mo, Zhongfu; Liu, Jing; Zhang, Qiuyang; Chen, Zhiquan; Mei, Jiandong; Liu, Lunxu; Yang, Shijie; Li, Huina; Zhou, Lifei; You, Zongbing

    2016-01-01

    Endometrial cancer (EC) is the most frequent gynecological malignancy and a major cause of morbidity and mortality for women worldwide. Programmed cell death protein 1 (PD-1) and its ligands programmed death ligand 1 (PD-L1) and programmed death ligand 2 (PD-L2) have been well studied in lung cancer, melanoma and renal-cell cancer. However, few studies have been performed in EC. The purpose of the present study was to assess the expression of PD-1, PD-L1 and PD-L2 in 35 human normal endometrial tissue samples and 75 human EC tissue samples using immunohistochemical staining. It was found that 61.3% of ECs were positive for PD-1 staining, which was almost exclusively found in the tumor-infiltrating immune cells. By contrast, PD-1 was not expressed in the tumor cells or normal endometrial tissues. It was also found that 14.3% of normal endometria and 17.3% of EC tissues were positive for PD-L1 expression, while 20.0% of normal endometrium and 37.3% of EC tissues were positive for PD-L2 expression; however, there was no statistically significant difference between the normal endometrium and EC tissues. PD-1 expression in the tumor-infiltrating immune cells was more frequently found in the moderately and poorly-differentiated ECs and non-endometrioid (type II) ECs than in the well-differentiated ECs and endometrioid (type I) ECs. Similarly, PD-L1 and PD-L2 expression in the tumor-infiltrating immune cells was more frequently found in the moderately and poorly-differentiated ECs and type II ECs than in the type I ECs. The present findings indicate a possible better outcome for future treatment with anti-PD-1 or anti-PD-L1 antibody-based therapies against these subgroups of endometrial cancers with frequent expression of the PD-1/PD-L1/PD-L2 axis. PMID:27446374

  4. The anticancer immune response of anti-PD-1/PD-L1 and the genetic determinants of response to anti-PD-1/PD-L1 antibodies in cancer patients

    PubMed Central

    Han, Weidong; Wang, Xian; Fang, Yong; Li, Da; Pan, Hongming; Zhang, Li

    2015-01-01

    The programmed death-1 (PD-1), a coinhibitory receptor expressed on activated T cells and B cells, is demonstrated to induce an immune-mediated response and play a critical role in tumor initiation and development. The cancer patients harboring PD-1 or PD ligand 1 (PD-L1) protein expression have often a poor prognosis and clinical outcome. Currently, targeting PD-1 pathway as a potential new anticancer strategy is attracting more and more attention in cancer treatment. Several monoclonal antibodies against PD-1 or PD-L1 have been reported to enhance anticancer immune responses and induce tumor cell death. Nonetheless, the precise molecular mechanisms by which PD-1 affects various cancers remain elusive. Moreover, this therapy is not effective for all the cancer patients and only a fraction of patients respond to the antibodies targeting PD-1 or PD-L1, indicating these antibodies may only works in a subset of certain cancers. Thus, understanding the novel function of PD-1 and genetic determinants of response to anti-PD-1 therapy will allow us to develop a more effective and individualized immunotherapeutic strategy for cancer. PMID:26305724

  5. Characterization and functionalities of Pd/hydrotalcite catalysts

    NASA Astrophysics Data System (ADS)

    Naresh, Dhachapally; Kumar, Vanama Pavan; Harisekhar, Mitta; Nagaraju, Nekkala; Putrakumar, Balla; Chary, Komandur V. R.

    2014-09-01

    A series of palladium supported on calcined hydrotalcite (CHT) catalysts with varying palladium (Pd) loadings (1.0-8.0 wt%) were prepared by impregnation method. Their catalytic performance was evaluated for the reductive amination of phenol to aniline that showed a tremendous interest in the chemical industry. The catalysts were characterized by BET surface area, XRD, TEM, XPS, TPR of H2, TPD of CO2 and CO chemisorption. BET surface area decreased continuously with increase in Pd content. XRD results confirmed the changes in the crystalline phases with altering Pd content. TEM results showed the formation of fine particles at lower loadings and agglomerates at higher loadings. TPR profiles revealed that the reducibility increases with increase of Pd loading. CO2 TPD results illustrate the catalysts basicity increases with increase of Pd loading up to 4.0 wt% and decreases at higher loadings. Pd dispersion, metal area and crystallite sizes were determined by CO chemisorption method. Pd dispersion and metal area decreases with increase of Pd content and crystallite sizes. The results demonstrated that the Pd dispersion and basic properties are depending on the Pd loading. The catalytic performance clearly showed that the increase Pd loading the conversion of phenol increased up to 2.0 wt% and level off beyond the loading. The catalytic properties are well correlated with the active Pd sites determined by CO chemisorption, dispersion and basicity.

  6. In situ encapsulation of Pd inside the MCM-41 channel.

    PubMed

    Lin, Xi-Jie; Zhong, Ai-Zhi; Sun, Yong-Bin; Zhang, Xing; Song, Wei-Guo; Lu, Rong-Wen; Cao, An-Min; Wan, Li-Jun

    2015-05-01

    Pd nanoparticles were successfully introduced into the channels of mesoporous silica MCM-41 with their dispersion well-tuned. We identified the dual role played by CTAB, which was critical for both the micelle template and Pd grafting, leading to the formation of a highly active Pd-MCM-41 nanocomposite for catalysing the Suzuki reaction. PMID:25827909

  7. Theoretical investigation of superconductivity in SrPd2Ge2 , SrPd2As2 , and CaPd2As2

    NASA Astrophysics Data System (ADS)

    Karaca, Ertuǧrul; Tütüncü, H. M.; Uzunok, H. Y.; Srivastava, G. P.; Uǧur, Ş.

    2016-02-01

    Ab initio pseudopotential calculations have been performed to investigate the structural, electronic, and vibrational properties of SrPd2Ge2 , SrPd2As2 , and CaPd2As2 crystallizing in the ThCr2Si2 -type body-centered tetragonal structure. Our electronic results show that the density of states at the Fermi level is mainly dominated by the strong hybridization of Pd d states and Ge (or As) p states. The linear response method and the Migdal-Eliashberg approach have been used to calculate the Eliashberg spectral function for all these compounds. By integrating the Eliashberg spectral function, the average electron-phonon coupling parameter (λ ) is found to be 0.74 for SrPd2Ge2 , 0.66 for SrPd2As2 , and 0.72 for CaPd2As2 . Using the calculated values of λ and the logarithmically averaged phonon frequency ωln the superconducting critical temperature (Tc) values for SrPd2Ge2 , SrPd2As2 , and CaPd2As2 are found to be 3.20, 2.05, and 2.48 K, respectively, which are in acceptable agreement with the corresponding experimental values. The relative differences in the Tc values between the Ge and As compounds have been explained in terms of some key physical parameters.

  8. The Pd2Si - /Pd/ - Ni - solder plated metallization system for silicon solar cells

    NASA Technical Reports Server (NTRS)

    Coleman, M. G.; Pryor, R. A.; Sparks, T. G.

    1978-01-01

    The rationale and application of a plated metal system, Pd2Si Pd - Ni - solder, is presented. This metallization system is particularly useful on shallow p-n junction solar cells. The advantages of such plated solar cell contacts are discussed. A process sequence for applying the metallization system is outlined. A specific example is presented, including chemical plating solution formulations and detailed process step descriptions. Electrical test data for solar cells metallized with the palladium-nickel-solder system are provided.

  9. Synthesis of Fe-Pd and Fe-Pd/Ta magnetic nanocomposites by severe plastic deformation

    SciTech Connect

    Saha, S.; Kulovits, A.; Soffa, W.A.; Barnard, J.A.

    2005-05-15

    Severe plastic deformation (SPD) and cyclic codeformation were used to prepare bulk magnetic nanocomposite of ordered L1{sub 0} Fe-Pd phase and soft {alpha}-Fe following an atomic ordering and precipitation reaction. Enhanced coercivity and remanence have been achieved with this method. Layering of Ta foils with the Fe-34 at. %Pd foils was explored in an effort to minimize nanocomposite grain size by confinement. Faster kinetics and improvement in the remanence resulted from Ta layering.

  10. Predictive Markers for the Efficacy of Anti-PD-1/PD-L1 Antibodies in Lung Cancer.

    PubMed

    Shukuya, Takehito; Carbone, David P

    2016-07-01

    Blockade of the programmed death protein 1 (PD-1)/programmed death ligand 1 (PD-L1) axis using antibodies against the associated receptors and ligands has yielded good clinical responses and improved overall survival in patients with non-small cell lung cancer (NSCLC). Once patients show a response to anti-PD-1/PD-L1 antibody, the median duration of response is often longer than that achieved using existing cytotoxic agents and even some molecular targeted agents. However, the response rates to these antibodies are only 15% to 20% in unselected patients with NSCLC and the cost of this therapy is high. Therefore, there is an urgent need for effective predictive biomarkers to identify patients likely to benefit. PD-L1 expression, which can be detected by immunohistochemical analysis, is a rational biomarker for selecting responders to anti-PD-1/PD-L1 antibody treatments, and this selection method has been introduced into clinical practice. However, the response rate to anti-PD-1/PD-L1 antibody in PD-L1-expressing patients with NSCLC is only 15% to 45%, response can occur in PD-L1-negative patients, and predictability based on PD-L1 expression may differ between nonsquamous NSCLC and squamous cell NSCLC. In addition, the methods of immunohistochemical analysis and evaluation of its results differ for different anti-PD-1/PD-L1 agents. This article reviews the existing data on predictive markers for the efficacy of anti-PD-1/PD-L1 antibodies in NSCLC. PMID:26944305

  11. PD-1 and PD-L1 expression in molecularly selected non-small-cell lung cancer patients

    PubMed Central

    D'Incecco, A; Andreozzi, M; Ludovini, V; Rossi, E; Capodanno, A; Landi, L; Tibaldi, C; Minuti, G; Salvini, J; Coppi, E; Chella, A; Fontanini, G; Filice, M E; Tornillo, L; Incensati, R M; Sani, S; Crinò, L; Terracciano, L; Cappuzzo, F

    2015-01-01

    Background: Agents targeting programmed death-1 receptor (PD-1) and its ligand (PD-L1) are showing promising results in non-small-cell lung cancer (NSCLC). It is unknown whether PD-1/PD-L1 are differently expressed in oncogene-addicted NSCLC. Methods: We analysed a cohort of 125 NSCLC patients, including 56 EGFR mutated, 29 KRAS mutated, 10 ALK translocated and 30 EGFR/KRAS/ALK wild type. PD-L1 and PD-1 expression were assessed by immunohistochemistry. All cases with moderate or strong staining (2+/3+) in >5% of tumour cells were considered as positive. Results: PD-1 positive (+) was significantly associated with current smoking status (P=0.02) and with the presence of KRAS mutations (P=0.006), whereas PD-L1+ was significantly associated to adenocarcinoma histology (P=0.005) and with presence of EGFR mutations (P=0.001). In patients treated with EGFR tyrosine kinase inhibitors (N=95), sensitivity to gefitinib or erlotinib was higher in PD-L1+ vs PD-L1 negative in terms of the response rate (RR: P=0.01) time to progression (TTP: P<0.0001) and survival (OS: P=0.09), with no difference in PD1+ vs PD-1 negative. In the subset of 54 EGFR mutated patients, TTP was significantly longer in PD-L1+ than in PD-L1 negative (P=0.01). Conclusions: PD-1 and PD-L1 are differentially expressed in oncogene-addicted NSCLC supporting further investigation of specific checkpoint inhibitors in combination with targeted therapies. PMID:25349974

  12. Development of membranes for hydrogen separation: Pd-coated V-10Pd

    SciTech Connect

    Paglieri, Stephen N; Wermer, Joseph R; Buxbaum, Robert E; Ciocco, Michael V; Howard, Bret H; Morreale, Bryan D

    2009-01-01

    Numerous Group IVB and VB alloys were prepared and tested as potential membrane materials but most of these materials were brittle or exhibited cracking during hydrogen exposure. One of the more ductile alloys, V-10Pd (at. %), was fabricated into a thin (107-{micro}m thick) composite membrane coated with 100 nm of Pd on each side. The material was tested for hydrogen permeability, resistance to hydrogen embrittlement, and long term hydrogen flux stability. The hydrogen permeability, {phi}, of the V-10Pd membrane was 3.86 x 10{sup -8} mol H{sub 2} m{sup -1} s{sup -1} Pa{sup -0.5} (avg. of three different samples) at 400 C, which is slightly higher than the permeability of Pd-23Ag at that temperature. A 1400 h hydrogen flux test at 400 C demonstrated that the rate of metallic interdiffusion was slow between the V-10Pd foil and the 100-nm-thick Pd coating on the surface. However, at the end of testing the membrane cracked at 118 C because of hydrogen embrittlement.

  13. Targeting PD-1/PD-L1 in the treatment of metastatic renal cell carcinoma

    PubMed Central

    Weinstock, Matthew; McDermott, David

    2015-01-01

    Immunostimulatory therapies have been a cornerstone of treatment for metastatic renal cell carcinoma (RCC) since the 1990s. However, the use of traditional immunotherapeutic approaches for RCC, such as high-dose interleukin-2 and interferon-α, has been limited by significant systemic toxicities and the need to deliver these therapies at centers of expertise. Furthermore, in spite of the success of these immunostimulatory therapies for some patients with RCC, it is clear that most patients fail to respond to cytokine therapy. More effective immune therapy for RCC has therefore been necessary. The interaction between programmed death-1 (PD-1, present on T cells), and one of its ligands (PD-L1, present on antigen-presenting cells and tumor cells) constitutes an immune checkpoint through which tumors can induce T-cell tolerance and avoid immune destruction. Monoclonal antibodies that disrupt the PD-1/PD-L1 interaction serve as inhibitors of this immune checkpoint, and have demonstrated favorable activity in RCC as monotherapy and in combination with other active agents. This review summarizes the current landscape of anti-PD-1/PD-L1 therapy for RCC, and highlights challenges for the future development of this promising approach. PMID:26622321

  14. Pd surface and Pt subsurface segregation in Pt1-c Pd c nanoalloys.

    PubMed

    De Clercq, A; Giorgio, S; Mottet, C

    2016-02-17

    The structure and chemical arrangement of Pt1-c Pd c nanoalloys with the icosahedral and face centered cubic symmetry are studied using Monte Carlo simulations with a tight binding interatomic potential fitted to density-functional theory calculations. Pd surface segregation from the lowest to the highest coordinated sites is predicted by the theory together with a Pt enrichment at the subsurface, whatever the structure and the size of the nanoparticles, and which subsists when increasing the temperature. The onion-shell chemical configuration is found for both symmetries and is initiated from the Pd surface segregation. It is amplified in the icosahedral symmetry and small sizes but when considering larger sizes, the oscillating segregation profile occurs near the surface on about three to four shells whatever the structure. Pd segregation results from the significant lower cohesive energy of Pd as compared to Pt and the weak ordering tendency leads to the Pt subsurface segregation. The very weak size mismatch does not prevent the bigger atoms (Pt) from occupying subsurface sites which are in compression whereas the smaller ones (Pd) occupy the central site of the icosahedra where the compression is an order of magnitude higher. PMID:26795206

  15. Pd surface and Pt subsurface segregation in Pt1-c Pd c nanoalloys

    NASA Astrophysics Data System (ADS)

    De Clercq, A.; Giorgio, S.; Mottet, C.

    2016-02-01

    The structure and chemical arrangement of Pt1-c Pd c nanoalloys with the icosahedral and face centered cubic symmetry are studied using Monte Carlo simulations with a tight binding interatomic potential fitted to density-functional theory calculations. Pd surface segregation from the lowest to the highest coordinated sites is predicted by the theory together with a Pt enrichment at the subsurface, whatever the structure and the size of the nanoparticles, and which subsists when increasing the temperature. The onion-shell chemical configuration is found for both symmetries and is initiated from the Pd surface segregation. It is amplified in the icosahedral symmetry and small sizes but when considering larger sizes, the oscillating segregation profile occurs near the surface on about three to four shells whatever the structure. Pd segregation results from the significant lower cohesive energy of Pd as compared to Pt and the weak ordering tendency leads to the Pt subsurface segregation. The very weak size mismatch does not prevent the bigger atoms (Pt) from occupying subsurface sites which are in compression whereas the smaller ones (Pd) occupy the central site of the icosahedra where the compression is an order of magnitude higher.

  16. Herbal Medicines for Parkinson's Disease: A Systematic Review of Randomized Controlled Trials

    PubMed Central

    Kim, Tae-Hun; Cho, Ki-Ho; Jung, Woo-Sang; Lee, Myeong Soo

    2012-01-01

    Objective We conducted systematic review to evaluate current evidence of herbal medicines (HMs) for Parkinson's disease (PD). Methods Along with hand searches, relevant literatures were located from the electronic databases including CENTRAL, MEDLINE, EMBASE, CINAHL, AMED, PsycInfo, CNKI, 7 Korean Medical Databases and J-East until August, 2010 without language and publication status. Randomized controlled trials (RCTs), quasi-randomized controlled trials and randomized crossover trials, which evaluate HMs for idiopathic PD were selected for this review. Two independent authors extracted data from the relevant literatures and any disagreement was solved by discussion. Results From the 3432 of relevant literatures, 64 were included. We failed to suggest overall estimates of treatment effects on PD because of the wide heterogeneity of used herbal recipes and study designs in the included studies. When compared with placebo, specific effects were not observed in favor of HMs definitely. Direct comparison with conventional drugs suggested that there was no evidence of better effect for HMs. Many studies compared combination therapy with single active drugs and combination therapy showed significant improvement in PD related outcomes and decrease in the dose of anti-Parkinson's drugs with low adverse events rate. Conclusion Currently, there is no conclusive evidence about the effectiveness and efficacy of HMs on PD. For establishing clinical evidence of HMs on PD, rigorous RCTs with sufficient statistical power should be promoted in future. PMID:22615738

  17. Ultrafast dynamics of quasiparticles and coherent acoustic phonons in slightly underdoped (BaK)Fe2As2

    NASA Astrophysics Data System (ADS)

    Lin, Kung-Hsuan; Wang, Kuan-Jen; Chang, Chung-Chieh; Wen, Yu-Chieh; Lv, Bing; Chu, Ching-Wu; Wu, Maw-Kuen

    2016-05-01

    We have utilized ultrafast optical spectroscopy to study carrier dynamics in slightly underdoped (BaK)Fe2As2 crystals without magnetic transition. The photoelastic signals due to coherent acoustic phonons have been quantitatively investigated. According to our temperature-dependent results, we found that the relaxation component of superconducting quasiparticles persisted from the superconducting state up to at least 70 K in the normal state. Our findings suggest that the pseudogaplike feature in the normal state is possibly the precursor of superconductivity. We also highlight that the pseudogap feature of K-doped BaFe2As2 is different from that of other iron-based superconductors, including Co-doped or P-doped BaFe2As2.

  18. Quasiparticle self-consistent GW study of cuprates: electronic structure, model parameters, and the two-band theory for Tc

    PubMed Central

    Jang, Seung Woo; Kotani, Takao; Kino, Hiori; Kuroki, Kazuhiko; Han, Myung Joon

    2015-01-01

    Despite decades of progress, an understanding of unconventional superconductivity still remains elusive. An important open question is about the material dependence of the superconducting properties. Using the quasiparticle self-consistent GW method, we re-examine the electronic structure of copper oxide high-Tc materials. We show that QSGW captures several important features, distinctive from the conventional LDA results. The energy level splitting between and is significantly enlarged and the van Hove singularity point is lowered. The calculated results compare better than LDA with recent experimental results from resonant inelastic xray scattering and angle resolved photoemission experiments. This agreement with the experiments supports the previously suggested two-band theory for the material dependence of the superconducting transition temperature, Tc. PMID:26206417

  19. Ultrafast dynamics of quasiparticles and coherent acoustic phonons in slightly underdoped (BaK)Fe2As2

    PubMed Central

    Lin, Kung-Hsuan; Wang, Kuan-Jen; Chang, Chung-Chieh; Wen, Yu-Chieh; Lv, Bing; Chu, Ching-Wu; Wu, Maw-Kuen

    2016-01-01

    We have utilized ultrafast optical spectroscopy to study carrier dynamics in slightly underdoped (BaK)Fe2As2 crystals without magnetic transition. The photoelastic signals due to coherent acoustic phonons have been quantitatively investigated. According to our temperature-dependent results, we found that the relaxation component of superconducting quasiparticles persisted from the superconducting state up to at least 70 K in the normal state. Our findings suggest that the pseudogaplike feature in the normal state is possibly the precursor of superconductivity. We also highlight that the pseudogap feature of K-doped BaFe2As2 is different from that of other iron-based superconductors, including Co-doped or P-doped BaFe2As2. PMID:27180873

  20. Ultrafast dynamics of quasiparticles and coherent acoustic phonons in slightly underdoped (BaK)Fe2As2.

    PubMed

    Lin, Kung-Hsuan; Wang, Kuan-Jen; Chang, Chung-Chieh; Wen, Yu-Chieh; Lv, Bing; Chu, Ching-Wu; Wu, Maw-Kuen

    2016-01-01

    We have utilized ultrafast optical spectroscopy to study carrier dynamics in slightly underdoped (BaK)Fe2As2 crystals without magnetic transition. The photoelastic signals due to coherent acoustic phonons have been quantitatively investigated. According to our temperature-dependent results, we found that the relaxation component of superconducting quasiparticles persisted from the superconducting state up to at least 70 K in the normal state. Our findings suggest that the pseudogaplike feature in the normal state is possibly the precursor of superconductivity. We also highlight that the pseudogap feature of K-doped BaFe2As2 is different from that of other iron-based superconductors, including Co-doped or P-doped BaFe2As2. PMID:27180873

  1. Quasi-particle band structure of potassium-doped few-layer black phosphorus with GW approximation

    NASA Astrophysics Data System (ADS)

    Kim, Han-Gyu; Baik, Seung Su; Choi, Hyoung Joon

    We calculate the quasi-particle band structure of pristine and potassium-doped black phosphorus (BP) by using the GW approximation. We obtain band gaps of pristine bulk and few-layer BP and compare them with the result of the density functional calculations and experimental measurements. For potassium-doped cases, we calculate the electronic band structure of potassium-doped few-layer BPs with various doping densities. We obtain the critical doping density for the band-gap closing, and the energy-band dispersions when the band gap is inverted. We discuss Dirac semimetal properties of doped few-layer BPs obtained by the GW approximation. This work was supported by NRF of Korea (Grant No. 2011-0018306) and KISTI supercomputing center (Project No. KSC-2015-C3-039).

  2. Thermal and electrochemically assisted Pd-Cl bond cleavage in the d9-d9 Pd2dppm2Cl2 complex by Pd3 dppm3COn+ clusters (n = 2, 1, 0).

    PubMed

    Cugnet, Cyril; Mugnier, Yves; Dal Molin, Sophie; Brevet, David; Lucas, Dominique; Harvey, Pierre D

    2007-04-16

    A new aspect of reactivity of the cluster [Pd3(dppm)3(micro3-CO)]n+, ([Pd3]n+, n = 2, 1, 0) with the low-valent metal-metal-bonded Pd2(dppm)2Cl2 dimer (Pd2Cl2) was observed using electrochemical techniques. The direct reaction between [Pd3]2+ and Pd2Cl2 in THF at room temperature leads to the known [Pd3(dppm)3(micro3-CO)(Cl)]+ ([Pd3(Cl)]+) adduct and the monocationic species Pd2(dppm)2Cl+ (very likely as Pd2(dppm)2(Cl)(THF)+, [Pd2Cl]+) as unambiguously demonstrated by UV-vis and 31P NMR spectroscopy. In this case, [Pd3]2+ acts as a strong Lewis acid toward the labile Cl- ion, which weakly dissociates from Pd2Cl2 (i.e., dissociative mechanism). Host-guest interactions between [Pd3]2+ and Pd2Cl2 seem unlikely on the basis of computer modeling because of the strong screening of the Pd-Cl fragment by the Ph-dppm groups in Pd2Cl2. The electrogenerated clusters [Pd3]+ and [Pd3]0 also react with Pd2Cl2 to unexpectedly form the same oxidized adduct, [Pd3(Cl)]+, despite the known very low affinity of [Pd3]+ and [Pd3]0 toward Cl- ions. The reduced biproduct in this case is the highly reactive zerovalent species "Pd2(dppm)2" or "Pd(dppm)" as demonstrated by quenching with CDCl3 (forming the well-known complex Pd(dppm)Cl2) or in presence of dppm (forming the known Pd2(dppm)3 d10-d10 dimer). To bring these halide-electron exchange reactions to completion for [Pd3]+ and [Pd3]0, 0.5 and 1.0 equiv of Pd2Cl2 are necessary, respectively, accounting perfectly for the number of exchanged electrons. The presence of a partial dissociation of Pd2Cl2 into the Cl- ion and the monocation [Pd2Cl]+, which is easier to reduce than Pd2Cl2, is suggested to explain the overall electrochemical results. It is possible to regulate the nature of the species formed from Pd2Cl2 by changing the state of charge of the title cluster. PMID:17371010

  3. Fabrication of Pd/Pd-Alloy Films by Surfactant Induced Electroless Plating for Hydrogen Separation from Advanced Coal Gasification Processes

    SciTech Connect

    Ilias, Shamsuddin; Kumar, Dhananjay

    2012-07-31

    Dense Pd, Pd-Cu and Pd-Ag composite membranes on microporous stainless steel substrate (MPSS) were fabricated by a novel electroless plating (EP) process. In the conventional Pd-EP process, the oxidation-reduction reactions between Pd-complex and hydrazine result in an evolution of NH{sub 3} and N{sub 2} gas bubbles. When adhered to the substrate surface and in the pores, these gas bubbles hinder uniform Pd-film deposition which results in dendrite growth leading to poor film formation. This problem was addressed by introducing cationic surfactant in the electroless plating process known as surfactant induced electroless plating (SIEP). The unique features of this innovation provide control of Pd-deposition rate, and Pd-grain size distribution. The surfactant molecules play an important role in the EP process by tailoring grain size and the process of agglomeration by removing tiny gas bubbles through adsorption at the gas-liquid interface. As a result surfactant can tailor a nanocrystalline Pd, Cu and Ag deposition in the film resulting in reduced membrane film thickness. Also, it produces a uniform, agglomerated film structure. The Pd-Cu and Pd-Ag membranes on MPSS support were fabricated by sequential deposition using SIEP method. The pre- and post-annealing characterizations of these membranes (Pd, Pd-Cu and Pd-Ag on MPSS substrate) were carried out by SEM, EDX, XRD, and AFM studies. The SEM images show significant improvement of the membrane surface morphology, in terms of metal grain structures and grain agglomeration compared to the membranes fabricated by conventional EP process. The SEM images and helium gas-tightness studies indicate that dense and thinner films of Pd, Pd-Cu and Pd-Ag membranes can be produced with shorter deposition time using surfactant. H{sub 2} Flux through the membranes fabricated by SIEP shows large improvement compared to those by CEP with comparable permselectivity. Pd-MPSS composite membrane was subjected to test for long term

  4. Improved quasiparticle wave functions and mean field for G0W0 calculations: Initialization with the COHSEX operator

    NASA Astrophysics Data System (ADS)

    Jain, Manish; Deslippe, Jack; Samsonidze, Georgy; Cohen, Marvin L.; Chelikowsky, James R.; Louie, Steven G.

    2014-09-01

    The GW approximation to the electron self-energy has become a standard method for ab initio calculation of excited-state properties of condensed-matter systems. In many calculations, the GW self-energy operator, Σ, is taken to be diagonal in the density functional theory (DFT) Kohn-Sham basis within the G0W0 scheme. However, there are known situations in which this diagonal G0W0 approximation starting from DFT is inadequate. We present two schemes to resolve such problems. The first, which we called sc -COHSEX+GW, involves construction of an improved mean field using the static limit of GW, known as COHSEX (Coulomb hole and screened exchange), which is significantly simpler to treat than GW. In this scheme, frequency-dependent self energy Σ (ω), is constructed and taken to be diagonal in the COHSEX orbitals after the system is solved self-consistently within this formalism. The second method is called off diagonal-COHSEX GW (od -COHSEX+GW). In this method, one does not self-consistently change the mean-field starting point but diagonalizes the COHSEX Hamiltonian within the Kohn-Sham basis to obtain quasiparticle wave functions and uses the resulting orbitals to construct the GW Σ in the diagonal form. We apply both methods to a molecular system, silane, and to two bulk systems, Si and Ge under pressure. For silane, both methods give good quasiparticle wave functions and energies. Both methods give good band gaps for bulk silicon and maintain good agreement with experiment. Further, the sc -COHSEX+GW method solves the qualitatively incorrect DFT mean-field starting point (having a band overlap) in bulk Ge under pressure.

  5. Kinetics of monolayer graphene growth by segregation on Pd(111)

    SciTech Connect

    Mok, H. S.; Murata, Y.; Kodambaka, S.; Ebnonnasir, A.; Ciobanu, C. V.; Nie, S.; McCarty, K. F.

    2014-03-10

    Using in situ low-energy electron microscopy and density functional theory calculations, we follow the growth of monolayer graphene on Pd(111) via surface segregation of bulk-dissolved carbon. Upon lowering the substrate temperature, nucleation of graphene begins on graphene-free Pd surface and continues to occur during graphene growth. Measurements of graphene growth rates and Pd surface work functions establish that this continued nucleation is due to increasing C adatom concentration on the Pd surface with time. We attribute this anomalous phenomenon to a large barrier for attachment of C adatoms to graphene coupled with a strong binding of the non-graphitic C to the Pd surface.

  6. Magnetic properties of metastable Fe Pd alloys by mechanical alloying

    NASA Astrophysics Data System (ADS)

    Yabe, Hiromasa; O'Handley, Robert C.; Kuji, Toshiro

    2007-03-01

    Metastable Fe-Pd powder samples with various Pd content were synthesized by mechanical alloying. Their fundamental properties, i.e., structure, magnetization and coercive fore are discussed. The saturation magnetizations of the metastable Fe-Pd powders gradually decreases with increasing Pd content. The coercive forces observed in as-milled samples are all less than 40 Oe. However, some of the heat-treated samples, notably, Pd content around 55 at% with L1 0 structure, shows Hc up to 1589 Oe.

  7. Two Year Exercise Program Improves Physical Function in Parkinson’s Disease: the PRET-PD Study

    PubMed Central

    Prodoehl, Janey; Rafferty, Miriam; David, Fabian J.; Poon, Cynthia; Vaillancourt, David E.; Comella, Cynthia L.; Leurgans, Sue; Kohrt, Wendy M.; Corcos, Daniel M.; Robichaud, Julie A.

    2014-01-01

    Background The progressive resistance exercise (PRE) in Parkinson’s disease trial (PRET-PD) showed that PRE improved the motor signs of PD compared to a modified Fitness Counts (mFC) program. It is unclear how long-term exercise affects physical function in these individuals. Objective To examine the effects of long-term PRE and mFC on physical function outcome measures in individuals with PD. Methods A preplanned secondary analysis was conducted using data from the 38 patients with idiopathic PD who completed the PRET-PD trial. Participants were randomized into PRE or mFC groups and exercised 2 days/week up to 24 months. Blinded assessors obtained functional outcomes on and off medication at baseline, 6 and 24 months with the Modified Physical Performance Test (mPPT), five times sit to stand test (STS), Functional Reach Test (FRT), Timed Up and Go (TUG), Berg Balance Scale (BBS), 6 minute walk test (6MWT), and 50ft walking speed (walk speed). Results The groups did not differ on any physical function measure at 6 or 24 months (p’s > 0.1). Across time, all physical function measures improved from baseline to 24 months when tested on medication (p’s < .0001), except for 6MWT(p = .068). Off medication results were similar except that the 6MWT was now significant. Conclusions 24 months of supervised and structured exercise (either PRE or mFC) is effective at improving functional performance outcomes in individuals with moderate PD. Clinicians should strive to include structured and supervised exercise in the long-term plan of care for individuals with PD. PMID:24961994

  8. Prognostic significance of PD-L1 expression in patients with gastric cancer in East Asia: a meta-analysis

    PubMed Central

    Liu, Yong-Xuan; Wang, Xin-Shuai; Wang, Yu-Feng; Hu, Xiao-Chen; Yan, Jun-Qiang; Zhang, Ya-Li; Wang, Wei; Yang, Rui-Jie; Feng, Ying-Ying; Gao, She-Gan; Feng, Xiao-Shan

    2016-01-01

    The overexpression of programmed cell death-ligand 1(PD-L1) has been observed in gastric cancer (GC). However, whether the expression of PD-L1 in tumor cells or blood serum is associated with the prognosis of patients with GC remains unclear. Therefore, we performed a meta-analysis to evaluate the prognostic significance of PD-L1 expression in GC. Electronic databases were searched systematically. Studies that met the inclusion criteria were included in the meta-analysis. Data concerning the hazard ratio (HR) for overall survival and disease-free survival with a 95% confidence interval (CI) according to the expression status of PD-L1 evaluated by immunohistochemistry or enzyme-linked immunosorbent assay were extracted. The data were analyzed using a random effects model. Subgroup analyses were proposed. Our results showed that eight studies with 950 patients met the inclusion criteria and were included in the meta-analysis. The pooled HR for overall survival indicated that patients with PD-L1-positive expression had significantly shorter survival time compared with the PD-L1-negative group (HR 1.60, 95% CI 1.09–2.36, P=0.012). The pooled HR for disease-free survival demonstrated that the difference between the two groups was not statistically significant (HR 1.02, 95% CI 0.32–3.20, P=0.98). In conclusion, our results indicate that the evaluation of PD-L1 overexpression in GC tissue or blood serum may be useful in the future as a novel prognostic factor. PMID:27226727

  9. PD-1 on Immature and PD-1 Ligands on Migratory Human Langerhans Cells Regulate Antigen-Presenting Cell Activity

    PubMed Central

    Peña-Cruz, Victor; McDonough, Sean M.; Diaz-Griffero, Felipe; Crum, Christopher P.; Carrasco, Ruben D.; Freeman, Gordon J.

    2010-01-01

    Langerhans cells (LCs) are known as “sentinels” of the immune system that function as professional antigen-presenting cells (APCs) after migration to draining lymph node. LCs are proposed to have a role in tolerance and the resolution of cutaneous immune responses. The Programmed Death-1 (PD-1) receptor and its ligands, PD-L1 and PD-L2, are a co-inhibitory pathway that contributes to the negative regulation of T-lymphocyte activation and peripheral tolerance. Surprisingly, we found PD-1 to be expressed on immature LCs (iLCs) in situ. PD-1 engagement on iLCs reduced IL-6 and macrophage inflammatory protein (MIP)-1α cytokine production in response to TLR2 signals but had no effect on LC maturation. PD-L1 and PD-L2 were expressed at very low levels on iLCs. Maturation of LCs upon migration from epidermis led to loss of PD-l expression and gain of high expression of PD-L1 and PD-L2 as well as co-stimulatory molecules. Blockade of PD-L1 and/or PD-L2 on migratory LCs (mLCs) and DDCs enhanced T-cell activation, as has been reported for other APCs. Thus the PD-1 pathway is active in iLCs and inhibits iLC activities, but expression of receptor and ligands reverses upon maturation and PD-L1 and PD-L2 on mLC function to inhibit T-cell responses. PMID:20445553

  10. Activation of the PD-1/PD-L1 immune checkpoint confers tumor cell chemoresistance associated with increased metastasis

    PubMed Central

    Black, Madison; Barsoum, Ivraym B.; Truesdell, Peter; Cotechini, Tiziana; Macdonald-Goodfellow, Shannyn K.; Petroff, Margaret; Siemens, D. Robert; Koti, Madhuri; Craig, Andrew W.B.; Graham, Charles H.

    2016-01-01

    The ability of tumor cells to avoid immune destruction (immune escape) as well as their acquired resistance to anti-cancer drugs constitute important barriers to the successful management of cancer. Interaction between the Programmed Death Ligand 1 (PD-L1) on the surface of tumor cells with the Programmed Death-1 (PD-1) receptor on cytotoxic T lymphocytes leads to inactivation of these immune effectors and, consequently, immune escape. Here we show that the PD-1/PD-L1 axis also leads to tumor cell resistance to conventional chemotherapeutic agents. Using a panel of PD-L1-expressing human and mouse breast and prostate cancer cell lines, we found that incubation of breast and prostate cancer cells in the presence of purified recombinant PD-1 resulted in resistance to doxorubicin and docetaxel as determined using clonogenic survival assays. Co-culture with PD-1-expressing Jurkat T cells also promoted chemoresistance and this was prevented by antibody blockade of either PD-L1 or PD-1 or by silencing of the PD-L1 gene. Moreover, inhibition of the PD-1/PD-L1 axis using anti-PD-1 antibody enhanced doxorubicin chemotherapy to inhibit metastasis in a syngeneic mammary orthotopic mouse model of metastatic breast cancer. To further investigate the mechanism of tumor cell survival advantage upon PD-L1 ligation, we show that exposure to rPD-1 promoted ERK and mTOR growth and survival pathways leading to increased cell proliferation. Overall, the findings of this study indicate that combinations of chemotherapy and immune checkpoint blockade may limit chemoresistance and progression to metastatic disease. PMID:26859684

  11. 102Pd(n, {gamma}) Cross Section Measurement Using DANCE

    SciTech Connect

    Hatarik, R.; Alpizar-Vicente, A. M.; Bredeweg, T. A.; Esch, E.-I.; Haight, R. C.; O'Donnell, J. M.; Reifarth, R.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Wouters, J. M.; Greife, U.

    2006-03-13

    The neutron capture cross section of the proton rich nucleus 102Pd was measured with the Detector for Advanced Neutron Capture Experiments (DANCE) at the Los Alamos Neutron Science Center. The target was a 2 mg Pd foil with 78% enriched 102Pd. It was held by a 0.9 {mu}m thick Mylar bag which was selected after comparing different thicknesses of Kapton and Mylar for their scattering background. To identify the contribution of the other Pd isotopes the data of a natural Pd sample was compared to the data of the 102Pd enriched sample. A 12C sample was used to determine the scattering background. The 102Pd(n, {gamma}) rate is of importance for the p-process nucleosynthesis.

  12. High-spin structure of 95Pd

    NASA Astrophysics Data System (ADS)

    Mărginean, R.; Rusu, C.; Mărginean, N.; Bucurescu, D.; Ur, C. A.; de Angelis, G.; Axiotis, M.; Bazzacco, D.; Farnea, E.; Gadea, A.; Ionescu-Bujor, M.; Iordăchescu, A.; Krolas, W.; Kröll, Th.; Lenzi, S. M.; Lunardi, S.; Napoli, D. R.; Alvarez, C. Rossi; Wrzesinski, J.

    2012-09-01

    The level scheme of the neutron-deficient nucleus 95Pd has been studied with the 58Ni + 40Ca fusion-evaporation reaction at 135 MeV with the GASP γ-ray array, the ISIS silicon ball, and the N-ring neutron detector. Excited levels with spins at least up to (45)/(2)ℏ are reported for both parities. The observed experimental data are compared to large-scale shell-model calculations.

  13. Emotional manifestations of PD: Neurobiological basis.

    PubMed

    Castrioto, Anna; Thobois, Stéphane; Carnicella, Sebastien; Maillet, Audrey; Krack, Paul

    2016-08-01

    Neuropsychiatric symptoms are common and disabling in PD. Their neurobiological bases are complex, partly because of the disease itself and partly because of the dopaminergic treatment. The aim of this review is to focus on the emotional manifestations stemming from the neurodegenerative process itself. We focus on depression, anxiety, apathy, and fatigue, which can all be part of the clinical spectrum of premotor disease and may be improved or masked by medications targeting parkinsonian motor signs or psychiatric symptoms as the disease progresses. Findings from clinical, neuroimaging, and animal studies are reviewed, showing a major contribution of the dopaminergic system to the pathophysiology of these disabling symptoms. Degeneration of noradrenergic and serotonergic projection systems also has an impact on psychiatric symptoms of PD. The available literature is reviewed, but at present there is a lack of studies that would allow disentangling the separate contribution of each of the monoaminergic systems. The use of a pragmatic classification of all these symptoms under the umbrella of hypodopaminergic behavioral syndrome seems clinically useful, as it emphasizes the crucial, although not exclusive, nature of their dopaminergic neurobiological basis, which has important implications in the clinical management of PD. © 2016 International Parkinson and Movement Disorder Society. PMID:27041545

  14. Autoimmune Bullous Skin Disorders with Immune Checkpoint Inhibitors Targeting PD-1 and PD-L1.

    PubMed

    Naidoo, Jarushka; Schindler, Katja; Querfeld, Christiane; Busam, Klaus; Cunningham, Jane; Page, David B; Postow, Michael A; Weinstein, Alyona; Lucas, Anna Skripnik; Ciccolini, Kathryn T; Quigley, Elizabeth A; Lesokhin, Alexander M; Paik, Paul K; Chaft, Jamie E; Segal, Neil H; D'Angelo, Sandra P; Dickson, Mark A; Wolchok, Jedd D; Lacouture, Mario E

    2016-05-01

    Monoclonal antibodies (mAb) targeting immune checkpoint pathways such as cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed death 1 (PD-1) may confer durable disease control in several malignancies. In some patients, immune checkpoint mAbs cause cutaneous immune-related adverse events. Although the most commonly reported cutaneous toxicities are mild, a subset may persist despite therapy and can lead to severe or life-threatening toxicity. Autoimmune blistering disorders are not commonly associated with immune checkpoint mAb therapy. We report a case series of patients who developed bullous pemphigoid (BP), an autoimmune process classically attributed to pathologic autoantibody formation and complement deposition. Three patients were identified. Two patients developed BP while receiving the anti-PD-1 mAb nivolumab, and one while receiving the anti-PD-L1 mAb durvalumab. The clinicopathologic features of each patient and rash, and corresponding radiologic findings at the development of the rash and after its treatment, are described. Patients receiving an anti-PD-1/PD-L1 mAb may develop immune-related BP. This may be related to both T-cell- and B-cell-mediated responses. Referral to a dermatologist for accurate diagnosis and management is recommended. Cancer Immunol Res; 4(5); 383-9. ©2016 AACR. PMID:26928461

  15. A Mini-Review for Cancer Immunotherapy: Molecular Understanding of PD-1/PD-L1 Pathway & Translational Blockade of Immune Checkpoints.

    PubMed

    Li, Yongshu; Li, Fangfei; Jiang, Feng; Lv, Xiaoqing; Zhang, Rongjiang; Lu, Aiping; Zhang, Ge

    2016-01-01

    Interference of the binding of programmed cell death protein 1 (PD-1) and programmed death-ligand 1 (PD-L1) has become a new inspiring immunotherapy for resisting cancers. To date, the FDA has approved two PD-1 monoclonal antibody drugs against cancer as well as a monoclonal antibody for PD-L1. More PD-1 and PD-L1 monoclonal antibody drugs are on their way in clinical trials. In this review, we focused on the mechanism of the PD-1/PD-L1 signaling pathway and the monoclonal antibodies (mAbs) against PD-1 and PD-L1, which were approved by the FDA or are still in clinical trials. And also presented is the prospect of the PD-1/PD-L1 immune checkpoint blockade in the next generation of immunotherapy. PMID:27438833

  16. A Mini-Review for Cancer Immunotherapy: Molecular Understanding of PD-1/PD-L1 Pathway & Translational Blockade of Immune Checkpoints

    PubMed Central

    Li, Yongshu; Li, Fangfei; Jiang, Feng; Lv, Xiaoqing; Zhang, Rongjiang; Lu, Aiping; Zhang, Ge

    2016-01-01

    Interference of the binding of programmed cell death protein 1 (PD-1) and programmed death-ligand 1 (PD-L1) has become a new inspiring immunotherapy for resisting cancers. To date, the FDA has approved two PD-1 monoclonal antibody drugs against cancer as well as a monoclonal antibody for PD-L1. More PD-1 and PD-L1 monoclonal antibody drugs are on their way in clinical trials. In this review, we focused on the mechanism of the PD-1/PD-L1 signaling pathway and the monoclonal antibodies (mAbs) against PD-1 and PD-L1, which were approved by the FDA or are still in clinical trials. And also presented is the prospect of the PD-1/PD-L1 immune checkpoint blockade in the next generation of immunotherapy. PMID:27438833

  17. Cancer Treatment with Anti-PD-1/PD-L1 Agents: Is PD-L1 Expression a Biomarker for Patient Selection?

    PubMed

    Festino, Lucia; Botti, Gerardo; Lorigan, Paul; Masucci, Giuseppe V; Hipp, Jason D; Horak, Christine E; Melero, Ignacio; Ascierto, Paolo A

    2016-06-01

    Strategies to help improve the efficacy of the immune system against cancer represent an important innovation, with recent attention having focused on anti-programmed death (PD)-1/PD-ligand 1 (L1) monoclonal antibodies. Clinical trials have shown objective clinical activity of these agents (e.g., nivolumab, pembrolizumab) in several malignancies, including melanoma, non-small-cell lung cancer, bladder cancer, squamous head and neck cancer, renal cell cancer, ovarian cancer, microsatellite-unstable colorectal cancer, and Hodgkin's lymphoma. Expression of PD-L1 in the tumor microenvironment appears to be crucial for therapeutic activity, and initial trials suggested positive PD-L1 tumor expression was associated with higher response rates. However, subsequent observations have questioned the prospect of using PD-L1 expression as a biomarker for selecting patients for therapy, especially since many patients considered PD-L1-negative experience a benefit from treatment. Importantly, there is not yet a definitive test for determination of PD-L1 and a cut-off reference for PD-L1-positive status has not been established. Immunohistochemistry with different antibodies and different thresholds has been used to define PD-L1 positivity (1-50 %), with no clear superiority of one threshold over another for identifying which patients respond. Moreover, the type of cells on which PD-L1 expression is most relevant is not yet clear, with immune infiltrate cells and tumor cells both being used. In conclusion, while PD-L1 expression is often a predictive factor for treatment response, it must be complemented by other biomarkers or histopathologic features, such as the composition and amount of inflammatory cells in the tumor microenvironment and their functional status. Multi-parameter quantitative or semi-quantitative algorithms may become useful and reliable tools to guide patient selection. PMID:27229745

  18. PD-1 Restrains Radiotherapy-Induced Abscopal Effect.

    PubMed

    Park, Sean S; Dong, Haidong; Liu, Xin; Harrington, Susan M; Krco, Christopher J; Grams, Michael P; Mansfield, Aaron S; Furutani, Keith M; Olivier, Kenneth R; Kwon, Eugene D

    2015-06-01

    We investigated the influence of PD-1 expression on the systemic antitumor response (abscopal effect) induced by stereotactic ablative radiotherapy (SABR) in preclinical melanoma and renal cell carcinoma models. We compared the SABR-induced antitumor response in PD-1-expressing wild-type (WT) and PD-1-deficient knockout (KO) mice and found that PD-1 expression compromises the survival of tumor-bearing mice treated with SABR. None of the PD-1 WT mice survived beyond 25 days, whereas 20% of the PD-1 KO mice survived beyond 40 days. Similarly, PD-1-blocking antibody in WT mice was able to recapitulate SABR-induced antitumor responses observed in PD-1 KO mice and led to increased survival. The combination of SABR plus PD-1 blockade induced near complete regression of the irradiated primary tumor (synergistic effect), as opposed to SABR alone or SABR plus control antibody. The combination of SABR plus PD-1 blockade therapy elicited a 66% reduction in size of nonirradiated, secondary tumors outside the SABR radiation field (abscopal effect). The observed abscopal effect was tumor specific and was not dependent on tumor histology or host genetic background. The CD11a(high) CD8(+) T-cell phenotype identifies a tumor-reactive population, which was associated in frequency and function with a SABR-induced antitumor immune response in PD-1 KO mice. We conclude that SABR induces an abscopal tumor-specific immune response in both the irradiated and nonirradiated tumors, which is potentiated by PD-1 blockade. The combination of SABR and PD-1 blockade has the potential to translate into a potent immunotherapy strategy in the management of patients with metastatic cancer. PMID:25701325

  19. Serum Iron Levels and the Risk of Parkinson Disease: A Mendelian Randomization Study

    PubMed Central

    Gögele, Martin; Lill, Christina M.; Bertram, Lars; Do, Chuong B.; Eriksson, Nicholas; Foroud, Tatiana; Myers, Richard H.; Nalls, Michael; Keller, Margaux F.; Benyamin, Beben; Whitfield, John B.; Pramstaller, Peter P.; Hicks, Andrew A.; Thompson, John R.; Minelli, Cosetta

    2013-01-01

    Background Although levels of iron are known to be increased in the brains of patients with Parkinson disease (PD), epidemiological evidence on a possible effect of iron blood levels on PD risk is inconclusive, with effects reported in opposite directions. Epidemiological studies suffer from problems of confounding and reverse causation, and mendelian randomization (MR) represents an alternative approach to provide unconfounded estimates of the effects of biomarkers on disease. We performed a MR study where genes known to modify iron levels were used as instruments to estimate the effect of iron on PD risk, based on estimates of the genetic effects on both iron and PD obtained from the largest sample meta-analyzed to date. Methods and Findings We used as instrumental variables three genetic variants influencing iron levels, HFE rs1800562, HFE rs1799945, and TMPRSS6 rs855791. Estimates of their effect on serum iron were based on a recent genome-wide meta-analysis of 21,567 individuals, while estimates of their effect on PD risk were obtained through meta-analysis of genome-wide and candidate gene studies with 20,809 PD cases and 88,892 controls. Separate MR estimates of the effect of iron on PD were obtained for each variant and pooled by meta-analysis. We investigated heterogeneity across the three estimates as an indication of possible pleiotropy and found no evidence of it. The combined MR estimate showed a statistically significant protective effect of iron, with a relative risk reduction for PD of 3% (95% CI 1%–6%; p = 0.001) per 10 µg/dl increase in serum iron. Conclusions Our study suggests that increased iron levels are causally associated with a decreased risk of developing PD. Further studies are needed to understand the pathophysiological mechanism of action of serum iron on PD risk before recommendations can be made. Please see later in the article for the Editors' Summary PMID:23750121

  20. Prognostic impact of programmed cell death-1 (PD-1) and PD-ligand 1 (PD-L1) expression in cancer cells and tumor-infiltrating lymphocytes in ovarian high grade serous carcinoma

    PubMed Central

    Kulbe, Hagen; Sehouli, Jalid; Wienert, Stephan; Lindner, Judith; Budczies, Jan; Bockmayr, Michael; Dietel, Manfred; Denkert, Carsten; Braicu, Ioana; Jöhrens, Korinna

    2016-01-01

    Aims Antibodies targeting the checkpoint molecules programmed cell death 1 (PD-1) and its ligand PD-L1 are emerging cancer therapeutics. We systematically investigated PD-1 and PD-L1 expression patterns in the poor-prognosis tumor entity high-grade serous ovarian carcinoma. Methods PD-1 and PD-L1 protein expression was determined by immunohistochemistry on tissue microarrays from 215 primary cancers both in cancer cells and in tumor-infiltrating lymphocytes (TILs). mRNA expression was measured by quantitative reverse transcription PCR. An in silico validation of mRNA data was performed in The Cancer Genome Atlas (TCGA) dataset. Results PD-1 and PD-L1 expression in cancer cells, CD3+, PD-1+, and PD-L1+ TILs densities as well as PD-1 and PD-L1 mRNA levels were positive prognostic factors for progression-free (PFS) and overall survival (OS), with all factors being significant for PFS (p < 0.035 each), and most being significant for OS. Most factors also had prognostic value that was independent from age, stage, and residual tumor. Moreover, high PD-1+ TILs as well as PD-L1+ TILs densities added prognostic value to CD3+TILs (PD-1+: p = 0.002,; PD-L1+: p = 0.002). The significant positive prognostic impact of PD-1 and PD-L1 mRNA expression could be reproduced in the TCGA gene expression datasets (p = 0.02 and p < 0.0001, respectively). Conclusions Despite their reported immune-modulatory function, high PD-1 and PD-L1 levels are indicators of a favorable prognosis in ovarian cancer. Our data indicate that PD-1 and PD-L1 molecules are biologically relevant regulators of the immune response in high-grade serous ovarian carcinoma, which is an argument for the evaluation of immune checkpoint inhibiting drugs in this tumor entity. PMID:26625204

  1. Molecular characterization of immunoinhibitory factors PD-1/PD-L1 in chickens infected with Marek’s disease virus

    PubMed Central

    2012-01-01

    Background An immunoinhibitory receptor, programmed death-1 (PD-1), and its ligand, programmed death-ligand 1 (PD-L1), are involved in immune evasion mechanisms for several pathogens causing chronic infections and for neoplastic diseases. However, little has been reported for the functions of these molecules in chickens. Thus, in this study, their expressions and roles were analyzed in chickens infected with Marek’s disease virus (MDV), which induces immunosuppression in infected chickens. Results A chicken T cell line, Lee1, which constitutively produces IFN-γ was co-cultured with DF-1 cells, which is a spontaneously immortalized chicken fibroblast cell line, transiently expressing PD-L1, and the IFN-γ expression level was analyzed in the cell line by real-time RT-PCR. The IFN-γ expression was significantly decreased in Lee1 cells co-cultured with DF-1 cells expressing PD-L1. The expression level of PD-1 was increased in chickens at the early cytolytic phase of the MDV infection, while the PD-L1 expression level was increased at the latent phase. In addition, the expression levels of PD-1 and PD-L1 were increased at tumor lesions found in MDV-challenged chickens. The expressions levels of PD-1 and PD-L1 were also increased in the spleens and tumors derived from MDV-infected chickens in the field. Conclusions We demonstrated that the chicken PD-1/PD-L1 pathway has immunoinhibitory functions, and PD-1 may be involved in MD pathogenesis at the early cytolytic phase of the MDV infection, whereas PD-L1 could contribute to the establishment and maintenance of MDV latency. We also observed the increased expressions of PD-1 and PD-L1 in tumors from MDV-infected chickens, suggesting that tumor cells transformed by MDV highly express PD-1 and PD-L1 and thereby could evade from immune responses of the host. PMID:22612856

  2. Synthesis of bimetallic Pt-Pd core-shell nanocrystals and their high electrocatalytic activity modulated by Pd shell thickness.

    PubMed

    Li, Yujing; Wang, Zhi Wei; Chiu, Chin-Yi; Ruan, Lingyan; Yang, Wenbing; Yang, Yang; Palmer, Richard E; Huang, Yu

    2012-02-01

    Bimetallic Pt-Pd core-shell nanocrystals (NCs) are synthesized through a two-step process with controlled Pd thickness from sub-monolayer to multiple atomic layers. The oxygen reduction reaction (ORR) catalytic activity and methanol oxidation reactivity of the core-shell NCs for fuel cell applications in alkaline solution are systematically studied and compared based on different Pd thickness. It is found that the Pd shell helps to reduce the over-potential of ORR by up to 50 mV when compared to commercial Pd black, while generating up to 3-fold higher kinetic current density. The carbon monoxide poisoning test shows that the bimetallic NCs are more resistant to the CO poisoning than Pt NCs and Pt black. It is also demonstrated that the bimetallic Pt-Pd core-shell NCs can enhance the current density of the methanol oxidation reaction, lowering the over-potential by 35 mV with respect to the Pt core NCs. Further investigation reveals that the Pd/Pt ratio of 1/3, which corresponds to nearly monolayer Pd deposition on Pt core NCs, gives the highest oxidation current density and lowest over-potential. This study shows for the first time the systematic investigation of effects of Pd atomic shells on Pt-Pd bimetallic nanocatalysts, providing valuable guidelines for designing high-performance catalysts for fuel cell applications. PMID:22159178

  3. From monoclonal antibodies to small molecules: the development of inhibitors targeting the PD-1/PD-L1 pathway.

    PubMed

    Zhan, Mei-Miao; Hu, Xue-Qin; Liu, Xiu-Xiu; Ruan, Ban-Feng; Xu, Jun; Liao, Chenzhong

    2016-06-01

    Cancer immunotherapy has made an extraordinary journey from bench to bedside. Blocking the interactions between programmed cell death protein 1 (PD-1) and its ligand, PD-L1, has emerged as a promising immunotherapy for treating cancer. Here, we review the development of drugs targeting the PD-1/PD-L1 pathway. We discuss the monoclonal antibodies (mAbs) approved or in clinical trials, peptides and patented small molecules developed against this pathway. Such compounds have the potential to treat cancer as well as chronic virological diseases. We also detail PD-1/PD-L1 interactions, an understanding of which will be useful for the rational design of small-molecule therapeutics that disrupt the PD-1/PD-L1 pathway. It is likely that more mAbs targeting the PD-1/PD-L1 pathway will be approved for the treatment of a range of cancers. By contrast, it is likely to be more difficult to successfully develop small molecules or peptides and for them to reach the clinic. PMID:27094104

  4. Polarization corrections to single-particle energies studied within the energy-density-functional and quasiparticle random-phase approximation approaches

    NASA Astrophysics Data System (ADS)

    Tarpanov, D.; Toivanen, J.; Dobaczewski, J.; Carlsson, B. G.

    2014-01-01

    Background: Models based on using perturbative polarization corrections and mean-field blocking approximation give conflicting results for masses of odd nuclei. Purpose: We systematically investigate the polarization and mean-field models, implemented within self-consistent approaches that use identical interactions and model spaces, to find reasons for the conflicts between them. Methods: For density-dependent interactions and with pairing correlations included, we derive and study links between the mean-field and polarization results obtained for energies of odd nuclei. We also identify and discuss differences between the polarization-correction and full particle-vibration-coupling (PVC) models. Numerical calculations are performed for the mean-field ground-state properties of deformed odd nuclei and then compared to the polarization corrections determined using the approach that conserves spherical symmetry. Results: We have identified and numerically evaluated self-interaction (SI) energies that are at the origin of different results obtained within the mean-field and polarization-correction approaches. Conclusions: Mean-field energies of odd nuclei are polluted by the SI energies, and this makes them different from those obtained using polarization-correction methods. A comparison of both approaches allows for the identification and determination of the SI terms, which then can be calculated and removed from the mean-field results, giving the self-interaction-free energies. The simplest deformed mean-field approach that does not break parity symmetry is unable to reproduce full PVC effects.

  5. Running sums for 2{nu}{beta}{beta}-decay matrix elements within the quasiparticle random-phase approximation with account for deformation

    SciTech Connect

    Fang Dongliang; Faessler, Amand; Rodin, Vadim; Simkovic, Fedor; Yousef, Mohamed Saleh

    2010-03-15

    The 2{nu}{beta}{beta}-decay running sums for {sup 76}Ge and {sup 150}Nd nuclei are calculated within a QRPA approach with account for deformation. A realistic nucleon-nucleon residual interaction based on the Brueckner G matrix (for the Bonn CD force) is used. The influence of different model parameters on the functional behavior of the running sums is studied. It is found that the parameter g{sub pp} renormalizing the G matrix in the QRPA particle-particle channel is responsible for a qualitative change in behavior of the running sums at higher excitation energies. For realistic values of g{sub pp} a significant negative contribution to the total 2{nu}{beta}{beta}-decay matrix element is found to come from the energy region of the giant Gamow-Teller resonance. This behavior agrees with results of other authors.

  6. Elevated Cellular PD1/PD-L1 Expression Confers Acquired Resistance to Cisplatin in Small Cell Lung Cancer Cells.

    PubMed

    Yan, Fei; Pang, Jiuxia; Peng, Yong; Molina, Julian R; Yang, Ping; Liu, Shujun

    2016-01-01

    Although small cell lung cancer (SCLC) is highly responsive to chemotherapies (e.g., cisplatin-etoposide doublet), virtually almost all responsive SCLC patients experience disease recurrence characterized by drug resistance. The mechanisms underlying cisplatin resistance remain elusive. Here we report that cell-intrinsic expression of PD1 and PD-L1, two immune checkpoints, is required for sustained expansion of SCLC cells under cisplatin selection. Indeed, PD1 and PD-L1 were expressed at a higher level in lung cancer cell lines, tumor tissues, and importantly, in SCLC cells resistant to cisplatin (H69R, H82R), when compared to respective controls. Genetic abrogation of PD1 and PD-L1 in H69R and H82R cells decreased their proliferation rate, and restored their sensitivity to cisplatin. Mechanistically, PD-L1 upregulation in H69R and H82R cells was attributed to the overexpression of DNA methyltransferase 1 (DNMT1) or receptor tyrosine kinase KIT, as knockdown of DNMT1 or KIT in H69R and H82R cells led to PD-L1 downregulation. Consequently, combined knockdown of PD-L1 with KIT or DNMT1 resulted in more pronounced inhibition of H69R and H82R cell growth. Thus, cell intrinsic PD1/PD-L1 signaling may be a predictor for poor efficacy of cisplatin treatment, and targeting the cellular PD1/PD-L1 axis may improve chemosensitization of aggressive SCLC. PMID:27610620

  7. G6PD Deficiency and Hemoglobinopathies: Molecular Epidemiological Characteristics and Healthy Effects on Malaria Endemic Bioko Island, Equatorial Guinea

    PubMed Central

    Lin, Min; Yang, Li Ye; Xie, Dong De; Chen, Jiang Tao; Nguba, Santiago-m Monte; Ehapo, Carlos Sala; Zhan, Xiao Fen; Eyi, Juan Urbano Monsuy; Matesa, Rocio Apicante; Obono, Maximo Miko Ondo; Yang, Hui; Yang, Hui Tian; Cheng, Ji Dong

    2015-01-01

    Background Glucose-6-phosphate dehydrogenase (G6PD) deficiency and hemoglobinopathies were the inherited conditions found mostly in African. However, few epidemiological data of these disorders was reported in Equatorial Guinea (EQG). This study aimed to assess the prevalence and healthy effects of G6PD deficiency and hemoglobinopathies among the people on malaria endemic Bioko Island, EQG. Materials and Methods Blood samples from 4,144 unrelated subjects were analyzed for G6PD deficieny by fluorescence spot test (FST), high-resolution melting assay and PCR-DNA sequencing. In addition, 1,186 samples were randomly selected from the 4,144 subjects for detection of hemoglobin S (HbS), HbC, and α-thalassemia deletion by complete blood count, PCR-DNA sequencing and reverse dot blot (RDB). Results The prevalence of malaria and anemia was 12.6% (522/4,144) and 32.8% (389/1,186), respectively. Overall, 8.7% subjects (359/4,144) were G6PD-deficient by FST, including 9.0% (249/2,758) males and 7.9% (110/1,386) females. Among the 359 G6PD-deficient individuals molecularly studied, the G6PD A- (G202A/A376G) were detected in 356 cases (99.2%), G6PD Betica (T968C/A376G) in 3 cases. Among the 1,186 subjects, 201 cases were HbS heterozygotes, 35 cases were HbC heterozygotes, and 2 cases were HbCS double heterozygotes; 452 cases showed heterozygous α-thalassemia 3.7 kb deletion (-α3.7 kb deletion) and 85 homozygous - α3.7 kb deletion. The overall allele frequencies were HbS 17.1% (203/1186); HbC, 3.1% (37/1186); and –α3.7 kb deletion 52.4% (622/1186), respectively. Conclusions High G6PD deficiency in this population indicate that diagnosis and management of G6PD deficiency is necessary on Bioko Island. Obligatory newborn screening, prenatal screening and counseling for these genetic disorders, especially HbS, are needed on the island. PMID:25915902

  8. Quasiparticle and Optical Properties of Mono- and Bi-layer SnS2: A First-Principles GW and GW +BSE Study

    NASA Astrophysics Data System (ADS)

    Wu, Meng; Qiu, Diana; Louie, Steven G.

    2015-03-01

    Unlike most semiconducting transition metal dichalcogenides, SnS2, another layered metal dichalcogenide, is calculated within density functional theory to be an indirect bandgap semiconductor in both its bulk and monolayer forms. Experimental characterization of mono- and bi-layer SnS2 has been performed, but the details of its quasiparticle and excitonic properties remain unclear. Thus, we employ ab initio GW and GW +BSE calculations to study the quasiparticle band structure and optical absorption spectrum, respectively, of mono- and bi-layer SnS2 with spin-orbit coupling included throughout the calculations. We further investigate the character of excitonic states contributing to the optical spectrum. This work was supported by NSF Grant No. DMR10-1006184 and the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Computational resources have been provided by DOE at Lawrence Berkeley National Laboratory's NERSC facility.

  9. On the combined use of GW approximation and cumulant expansion in the calculations of quasiparticle spectra: The paradigm of Si valence bands

    NASA Astrophysics Data System (ADS)

    Gumhalter, Branko; Kovač, Vjekoslav; Caruso, Fabio; Lambert, Henry; Giustino, Feliciano

    2016-07-01

    Since the earliest implementations of the various GW approximations and cumulant expansion in the calculations of quasiparticle propagators and spectra, several attempts have been made to combine the advantageous properties and results of these two theoretical approaches. While the GW-plus-cumulant approach has proven successful in interpreting photoemission spectroscopy data in solids, the formal connection between the two methods has not been investigated in detail. By introducing a general bijective integral representation of the cumulants, we can rigorously identify at which point these two approximations can be connected for the paradigmatic model of quasiparticle interaction with the dielectric response of the system that has been extensively exploited in recent interpretations of the satellite structures in photoelectron spectra. We establish a protocol for consistent practical implementation of the thus established GW +cumulant scheme and illustrate it by comprehensive state-of-the-art first-principles calculations of intrinsic angle-resolved photoemission spectra from Si valence bands.

  10. Superfluid density and microwave conductivity of FeSe superconductor: ultra-long-lived quasiparticles and extended s-wave energy gap

    NASA Astrophysics Data System (ADS)

    Li, Meng; Lee-Hone, N. R.; Chi, Shun; Liang, Ruixing; Hardy, W. N.; Bonn, D. A.; Girt, E.; Broun, D. M.

    2016-08-01

    FeSe is an iron-based superconductor of immense current interest due to the large enhancements of T c that occur when it is pressurised or grown as a single layer on an insulating substrate. Here we report precision measurements of its superconducting electrodynamics, at frequencies of 202 and 658 MHz and at temperatures down to 0.1 K. The quasiparticle conductivity reveals a rapid collapse in scattering on entering the superconducting state that is strongly reminiscent of unconventional superconductors such as cuprates, organics and the heavy fermion material CeCoIn5. At the lowest temperatures the quasiparticle mean free path exceeds 50 μm, a record for a compound superconductor. From the superfluid response we confirm the importance of multiband superconductivity and reveal strong evidence for a non-zero energy-gap minimum.

  11. Treadmill Training Improves Overground Walking Economy in Parkinson’s Disease: A Randomized, Controlled Pilot Study

    PubMed Central

    Fernández-del-Olmo, Miguel Angel; Sanchez, Jose Andres; Bello, Olalla; Lopez-Alonso, Virginia; Márquez, Gonzalo; Morenilla, Luis; Castro, Xabier; Giraldez, Manolo; Santos-García, Diego

    2014-01-01

    Gait disturbances are one of the principal and most incapacitating symptoms of Parkinson’s disease (PD). In addition, walking economy is impaired in PD patients and could contribute to excess fatigue in this population. An important number of studies have shown that treadmill training can improve kinematic parameters in PD patients. However, the effects of treadmill and overground walking on the walking economy remain unknown. The goal of this study was to explore the walking economy changes in response to a treadmill and an overground training program, as well as the differences in the walking economy during treadmill and overground walking. Twenty-two mild PD patients were randomly assigned to a treadmill or overground training group. The training program consisted of 5 weeks (3 sessions/week). We evaluated the energy expenditure of overground walking, before and after each of the training programs. The energy expenditure of treadmill walking (before the program) was also evaluated. The treadmill, but not the overground training program, lead to an improvement in the walking economy (the rate of oxygen consumed per distance during overground walking at a preferred speed) in PD patients. In addition, walking on a treadmill required more energy expenditure compared with overground walking at the same speed. This study provides evidence that in mild PD patients, treadmill training is more beneficial compared with that of walking overground, leading to a greater improvement in the walking economy. This finding is of clinical importance for the therapeutic administration of exercise in PD. PMID:25309510

  12. PD-1 as a potential target in cancer therapy

    PubMed Central

    McDermott, David F; Atkins, Michael B

    2013-01-01

    Recently, an improved understanding of the molecular mechanisms governing the host response to tumors has led to the identification of checkpoint signaling pathways involved in limiting the anticancer immune response. One of the most critical checkpoint pathways responsible for mediating tumor-induced immune suppression is the programmed death-1 (PD-1) pathway, normally involved in promoting tolerance and preventing tissue damage in settings of chronic inflammation. Many human solid tumors express PD ligand 1 (PD-L1), and this is often associated with a worse prognosis. Tumor-infiltrating lymphocytes from patients with cancer typically express PD-1 and have impaired antitumor functionality. Proof-of-concept has come from several preclinical studies in which blockade of PD-1 or PD-L1 enhanced T-cell function and tumor cell lysis. Three monoclonal antibodies against PD-1, and one against PD-L1, have reported phase 1 data. All four agents have shown encouraging preliminary activity, and those that have been evaluated in larger patient populations appear to have encouraging safety profiles. Additional data are eagerly awaited. This review summarizes emerging clinical data and potential of PD-1 pathway–targeted antibodies in development. If subsequent investigations confirm the initial results, it is conceivable that agents blocking the PD-1/PD-L1 pathway will prove valuable additions to the growing armamentarium of targeted immunotherapeutic agents. Next-generation immunotherapy agents that target the PD-1 checkpoint pathway are demonstrating antitumor activity and encouraging safety profiles in early clinical trials. Current and future clinical trials will provide new insights, and the evaluation of biomarkers and rational combination therapies is ongoing. PMID:24403232

  13. Pd doped reduced graphene oxide for hydrogen storage

    SciTech Connect

    Das, Tapas; Banerjee, Seemita; Sudarsan, V.

    2015-06-24

    Pd nanoparticles dispersed reduced graphene oxide sample has been prepared by a simple chemical method using hydrazine as the reducing agent. Based on XRD and {sup 13}C MAS NMR studies it is confirmed that, Pd nanoparticles are effectively mixed with the reduced graphene oxide sample. Maximum hydrogen storage capacity has been estimated to be ∼1.36 wt % at 123K. Improved hydrogen storage capacity of Pd incorporated sample can be explained based on the phenomenon of spillover of atomic hydrogen.

  14. Magnetic hysteresis in small-grained CoxPd1-x nanowire arrays

    NASA Astrophysics Data System (ADS)

    Viqueira, M. S.; Pozo-López, G.; Urreta, S. E.; Condó, A. M.; Cornejo, D. R.; Fabietti, L. M.

    2015-11-01

    Co-Pd nanowires with small grain size are fabricated by AC electrodeposition into hexagonally ordered alumina pores, 20-35 nm in diameter and about 1 μm long. The effects of the alloy composition, the nanowire diameter and the grain size on the hysteresis properties are considered. X-ray diffraction indicates that the nanowires are single phase, a fcc Co-Pd solid solution; electron microscopy results show that they are polycrystalline, with randomly oriented grains (7-12 nm), smaller than the wire diameter. Nanowire arrays are ferromagnetic, with an easy magnetization axis parallel to the nanowire long axis. Both, the coercive field and the loop squareness monotonously increase with the Co content and with the grain size, but no clear correlation with the wire diameter is found. The Co and Co-rich nanowire arrays exhibit coercive fields and reduced remanence values quite insensitive to temperature in the range 4 K-300 K; on the contrary, in Pd-rich nanowires both magnitudes are smaller and they largely increase during cooling below 100 K. These behaviors are systematized by considering the strong dependences displayed by the magneto-crystalline anisotropy and the saturation magnetostriction on composition and temperature. At low temperatures the effective anisotropy value and the domain-wall width to grain size ratio drastically change, promoting less cooperative and harder nucleation modes.

  15. Bulk metallic glass formation in the Pd-Ni-P and Pd-Cu-P alloy systems

    SciTech Connect

    Schwarz, R.B.; He, Y.

    1996-12-11

    Bulk metallic glasses were prepared in the Pd-Ni-P and Pd-Cu-P systems using a fluxing technique. The formation of bulk amorphous Pd-Cu-P alloys was reported here for the first time. For both alloy systems, bulk glass formation requires maintaining the phosphorus content near 20 at.%. In the Pd-Ni-P system, 10-mm diameter amorphous Pd{sub x}Ni{sub 80{minus}x}P{sub 20} rods can be formed for 25 {le} x {le} 60. In the Pd-Cu-P system, 7-mm diameter amorphous Pd{sub x}Cu{sub 80{minus}x}P{sub 20} rods can be produced for 40 {le} x {le} 60. From all the ternary alloys studied, Pd{sub 40}Ni{sub 40}P{sub 20} has the highest glass formability, and 25-mm diameter amorphous cylinders, 50 mm in length, can be easily fabricated. The glass stability of the Pd-Ni-P system is wider than that of the Pd-Cu-P system. For most bulk Pd-Ni-P glasses, {Delta}T > 90 K. The {Delta}T values of bulk amorphous Pd-Cu-P alloys are considerably smaller, ranging from 27 to 73 K. The elastic constants of bulk amorphous Pd-Ni-P and Pd-Cu-P alloys were determined using a resonant ultrasound spectroscopy technique. The Pd-Ni-P glasses are slightly stiffer than the Pd-Cu-P glasses. Within each alloy system, the Young`s modulus and the bulk modulus show little change with alloy composition. Of all the bulk glass forming systems so far investigated, the ternary Pd-Ni-P system has the best glass formability. This alloy was one of the first bulk glasses discovered, yet it still remains the best in terms of glass formability. Upon replacing part of Ni by Cu, the critical cooling rates are expected to be further reduced.

  16. Deep Brain Stimulation in Early Stage Parkinson’s Disease: Operative Experience from a Prospective, Randomized Clinical Trial

    PubMed Central

    Kahn, Elyne; D'Haese, Pierre-Francois; Dawant, Benoit; Allen, Laura; Kao, Chris; Charles, P. David; Konrad, Peter

    2013-01-01

    Background Recent evidence suggests that STN-DBS may have a disease-modifying effect in early PD. A randomized, prospective study is underway to determine whether STN-DBS in early PD is safe and tolerable. Objectives / Methods Fifteen of thirty early PD patients were randomized to receive STN-DBS implants in an IRB-approved protocol. Operative technique, location of DBS leads, and perioperative adverse events are reported. Active contact used for stimulation in these patients were compared with 47 advanced PD patients undergoing an identical procedure by the same surgeon. Results Fourteen of the 15 patients did not sustain any long-term (> 3 months) complications from the surgery. One subject suffered a stroke resulting in mild cognitive changes and slight right arm and face weakness. The average optimal contact used in symptomatic treatment of early PD patients was: anterior −1.1±1.7mm, lateral 10.7±1.7mm, superior −3.3±2.5mm (AC-PC coordinates). This location is statistically no different (0.77mm, p> 0.05) than the optimal contact used in treatment of 47 advanced PD patients. Conclusions The perioperative adverse events in this trial of subjects with early stage PD are comparable to that reported for STN-DBS in advanced PD. The active contact position used in early PD is not significantly different from that used in late stage disease. This is the first report of the operative experience from a randomized, surgical-versus-best-medical-therapy trial for the early treatment of Parkinson’s disease. PMID:21890575

  17. Self-consistent quasiparticle formulation of a multiphonon method and its application to the neutron-rich O20 nucleus

    NASA Astrophysics Data System (ADS)

    De Gregorio, G.; Knapp, F.; Lo Iudice, N.; Vesely, P.

    2016-04-01

    A Bogoliubov quasiparticle formulation of an equation-of-motion phonon method, suited for open-shell nuclei, is derived. Like its particle-hole version, it consists of deriving a set of equations of motions whose iterative solution generates an orthonormal basis of n -phonon states (n =0 ,1 ,2 ,... ), built of quasiparticle Tamm-Dancoff phonons, which simplifies the solution of the eigenvalue problem. The method is applied to the open-shell neutron-rich O20 for illustrative purposes. A Hartree-Fock-Bogoliubov canonical basis, derived from an intrinsic two-body optimized chiral Hamiltonian, is used to derive and solve the eigenvalue equations in a space encompassing a truncated two-phonon basis. The spurious admixtures induced by the violation of the particle number and the center-of-mass motion are eliminated to a large extent by a Gram-Schmidt orthogonalization procedure. The calculation takes into account the Pauli principle, is self-consistent, and is parameter free except for the energy cutoff used to truncate the two-phonon basis, which induces an increasing depression of the ground state through its strong coupling to the quasiparticle vacuum. Such a cutoff is fixed so as to reproduce the first 1- level. The two-phonon states are shown to enhance the level density of the low-energy spectrum, consistently with the data, and to induce a fragmentation of the E 1 strength which, while accounting for the very low E 1 transitions, is not sufficient to reproduce the experimental cross section in the intermediate energy region. This and other discrepancies suggest the need of including the three-phonon states. These are also expected to offset the action of the two phonons on the quasiparticle vacuum and, therefore, free the calculation from any parameter.

  18. Synthesis and Catalytic Properties of Au Pd Nanoflowers

    SciTech Connect

    Xu, Jianguang; Wilson, Adria; Howe, Jane Y; Chi, Miaofang; Wiley, Benjamin J

    2011-01-01

    Reduction of Pd ions by hydroquinone in the presence of gold nanoparticles and polyvinylpyrrolidone resulted in the formation of nanoflowers with a Au core and Pd petals. Addition of HCl to the synthesis halted the reduction by hydroquinone and enabled the acquisition of snapshots of the nanoflowers at different stages of growth. TEM images of the reaction after 10 s show that the nanoflower morphology resulted from the homogeneous nucleation of Pd clusters in solution and their subsequent attachment to gold seeds coated with a thin (0.8 0.1 nm) shell of Pd. UV visible spectra also indicate Pd clusters formed in the early stages of the reaction and disappeared as the nanoflowers grew. The speed at which this reaction can be halted is useful not only for producing a variety of bimetallic nanostructures with precisely controlled dimensions and morphologies but also for understanding the growth mechanism of these structures. The ability of the AuPd core shell structure to catalyze the Suzuki coupling reaction of iodobenzene to phenylboronic acid was probed and compared against the activity of Pd nanocubes and thin-shelled AuPd core shell nanoparticles. The results of this study suggest that Suzuki coupling was not affected by the surface structure or subsurface composition of the nanoparticles, but instead was primarily catalyzed by molecular Pd species that leached from the nanostructures.

  19. Synthesis of Au-Pd Nanoflowers Through Nanocluster Assembly

    SciTech Connect

    Xu, Jianguang; Howe, Jane Y; Chi, Miaofang; Wilson, Adria; Rathmall, Aaron; Wiley, Benjamin J

    2011-01-01

    Reduction of Pd ions by hydroquinone in the presence of gold nanoparticles and polyvinylpyrrolidone resulted in the formation of nanoflowers with a Au core and Pd petals. Addition of HCl to the synthesis halted the reduction by hydroquinone and enabled the acquisition of snapshots of the nanoflowers at different stages of growth. TEM images of the reaction after 10 s show that the nanoflower morphology resulted from the homogeneous nucleation of Pd clusters in solution and their subsequent attachment to gold seeds coated with a thin (0.8 {+-} 0.1 nm) shell of Pd. UV-visible spectra also indicate Pd clusters formed in the early stages of the reaction and disappeared as the nanoflowers grew. The speed at which this reaction can be halted is useful not only for producing a variety of bimetallic nanostructures with precisely controlled dimensions and morphologies but also for understanding the growth mechanism of these structures. The ability of the AuPd core-shell structure to catalyze the Suzuki coupling reaction of iodobenzene to phenylboronic acid was probed and compared against the activity of Pd nanocubes and thin-shelled AuPd core-shell nanoparticles. The results of this study suggest that Suzuki coupling was not affected by the surface structure or subsurface composition of the nanoparticles, but instead was primarily catalyzed by molecular Pd species that leached from the nanostructures.

  20. A photoemission study of Pd ultrathin films on Pt(111)

    SciTech Connect

    Mun, Bongjin Simon; Lee, Choongman; Stamenkovic, Vojislav; Markovic, Nenad M.; Ross Jr., Philip N.

    2005-05-11

    The origin of surface core-level shift (SCLS) of Pd thin films on Pt(111) substrate is investigated. At sub-monolayer coverage of Pd thin films, the splitting of Pd 3d core level peaks indicate the contribution of both initial and final-state of photo-ionization processes while there is almost no change on valence band (VB) spectra. When the coverage of Pd reaches to single monolayer, the final-state relaxation effect on the Pd 3d vanishes and only the initial-state effect, a negative SCLS, is present. Also, the VB spectrum at Pd monolayer films shows a clear band narrowing, that is the origin of the negative SCLS at monolayer coverage. As the Pd coverage is increased to more than monolayer thickness, the Pd 3d peaks start to show the surface layer contribution from second and third layers, positive SCLS, and the VB spectrum shows even narrower band width, possibly due to the formation of surface states and strained effect of Pd adlayers on top of the first pseudomorphic layer.

  1. Structural characterization of bimetallic Pd-Cu vapor derived catalysts

    NASA Astrophysics Data System (ADS)

    Balerna, Antonella; Evangelisti, Claudio; Psaro, Rinaldo; Fusini, Graziano; Carpita, Adriano

    2016-05-01

    Pd-Cu bimetallic Solvated Metal Atoms (SMA) were synthesized by metal vapor synthesis technique and supported on PVPy resin. Since the catalytic activity, of the Pd-Cu system turned out to be quite high also compared to the corresponding monometallic system, a structural characterization, using electron microscopy techniques and X-ray Absorption Fine Structure spectroscopy, was performed. HRTEM analysis showed the presence of Pd particles distributed in a narrow range with a mean diameter of about 2.5 nm while the XAFS analysis, confirmed the presence of the Pd nanoparticles but revealed also some alloying with Cu atoms.

  2. Orientations to Professional Development Design and Implementation: Understanding Their Relationship to PD Outcomes across Multiple Projects

    ERIC Educational Resources Information Center

    Marra, Rose M.; Arbaugh, Fran; Lannin, John; Abell, Sandra; Ehlert, Mark; Smith, Rena; Merle-Johnson, Dominike; Rogers, Meredith Park

    2011-01-01

    Given the large investment in teacher professional development (PD), further understanding of the factors that impact PD success is needed. In a previous study, the authors established a framework for categorizing PD projects using the notion of orientations. A PD orientation is comprised of project characteristics that drive the PD design and…

  3. Size and alloying induced shift in core and valence bands of Pd-Ag and Pd-Cu nanoparticles

    SciTech Connect

    Sengar, Saurabh K.; Mehta, B. R.; Govind

    2014-03-28

    In this report, X-ray photoelectron spectroscopy studies have been carried out on Pd, Ag, Cu, Pd-Ag, and Pd-Cu nanoparticles having identical sizes corresponding to mobility equivalent diameters of 60, 40, and 20 nm. The nanoparticles were prepared by the gas phase synthesis method. The effect of size on valence and core levels in metal and alloy nanoparticles has been studied by comparing the values to those with the 60 nm nanoparticles. The effect of alloying has been investigated by comparing the valence and core level binding energies of Pd-Cu and Pd-Ag alloy nanoparticles with the corresponding values for Pd, Ag, and Cu nanoparticles of identical sizes. These effects have been explained in terms of size induced lattice contractions, alloying induced charge transfer, and hybridization effects. The observation of alloying and size induced binding energy shifts in bimetallic nanoparticles is important from the point of view of hydrogen reactivity.

  4. Superconductivity in Ta3Pd3Te14 with quasi-one-dimensional PdTe2 chains

    PubMed Central

    Jiao, Wen-He; He, Lan-Po; Liu, Yi; Xu, Xiao-Feng; Li, Yu-Ke; Zhang, Chu-Hang; Zhou, Nan; Xu, Zhu-An; Li, Shi-Yan; Cao, Guang-Han

    2016-01-01

    We report bulk superconductivity at 1.0 K in a low-dimensional ternary telluride Ta3Pd3Te14 containing edge-sharing PdTe2 chains along crystallographic b axis, similar to the recently discovered superconductor Ta4Pd3Te16. The electronic heat capacity data show an obvious anomaly at the transition temperature, which indicates bulk superconductivity. The specific-heat jump is ΔC/(γnTc) ≈ 1.35, suggesting a weak coupling scenario. By measuring the low-temperature thermal conductivity, we conclude that Ta3Pd3Te14 is very likely a dirty s-wave superconductor. The emergence of superconductivity in Ta3Pd3Te14 with a lower Tc, compared to that of Ta4Pd3Te16, may be attributed to the lower density of states. PMID:26876362

  5. Anti-PD-L1/PD-1 immune therapies in ovarian cancer: basic mechanism and future clinical application.

    PubMed

    Mandai, Masaki; Hamanishi, Junzo; Abiko, Kaoru; Matsumura, Noriomi; Baba, Tsukasa; Konishi, Ikuo

    2016-06-01

    Tumor immune therapy, especially anti-programmed cell death ligand-1/programmed cell death-1 (PD-L1/PD-1) treatment, is currently the focus of substantial attention. Ovarian cancer is the leading cause of mortality from gynecological malignancies, and novel treatment modalities, including immune therapy, are needed. However, a basic understanding of tumor immunity associated with the PD-L1/PD-1 signal has only recently emerged. In this review, we first discuss the importance of local tumor immunity, which affects the clinical outcome of ovarian cancer. We subsequently provide an overview of the basic findings regarding how the PD-L1/PD-1 signal influences local tumor immunity in ovarian cancer. Finally, we discuss what is needed to apply immune therapy in future clinical medicine. PMID:26968587

  6. Heterostructured Au/Pd-M (M = Au, Pd, Pt) nanoparticles with compartmentalized composition, morphology, and electrocatalytic activity.

    PubMed

    Lutz, Patrick S; Bae, In-Tae; Maye, Mathew M

    2015-10-14

    The synthesis, processing, and galvanic exchange of three heterostructured nanoparticle systems is described. The surface accessibility and redox potential of a Au/Pd-Ag dumbbell nanoparticle, where a Au/Pd core/shell region, and a silver region make up the domains, was used to prepare the new nanostructures with controlled composition, morphology, and microstructure. Results indicate that the silver domain was particularly susceptible to galvanic displacement, and was exchanged to Au/Pd-M (M = Au, Pd, Pt). Interestingly, the dumbbell morphology remained after exchange, and the silver region was transformed to hollow, parachute, or concentric domains respectively. The morphology and microstructure change was visualized via TEM and HRTEM, and the composition changes were probed via STEM-EDS imaging and XPS. The electrocatalytic activity of the Au/Pd-M towards methanol oxidation was studied, with results indicating that the Au/Pd-Pt nanoparticles had high activity attributed to the porous nature of the platinum domains. PMID:26351824

  7. Breaking of Cooper pairs in 108Pd

    NASA Astrophysics Data System (ADS)

    Rahmatinejad, A.; Kakavand, T.; Razavi, R.

    2016-04-01

    In this paper, breaking of Cooper pairs in 108Pd is investigated within the canonical ensemble framework and the BCS model. Our results show an evidence of two phase transitions, which are related to neutron and proton systems. Also, with consideration of pairing interaction, the role of neutron and proton systems in entropy, spin cutoff parameter and as a result in the moment of inertia are investigated. The results show minor role for the proton system at low temperatures and approximately equal roles for both neutron and proton systems after the critical temperature. Good agreement was observed between obtained results and the experimental data.

  8. Hallucinations and sleep disorders in PD

    PubMed Central

    Goetz, Christopher G.; Ouyang, Bichun; Negron, Alice; Stebbins, Glenn T.

    2010-01-01

    Objective: To assess prospectively progression and relationship of hallucinations and sleep disorders over a 10-year longitudinal study of patients with Parkinson disease (PD). Methods: Eighty-nine patients with PD were recruited to fill cells of normal sleep without hallucinations (n = 20), sleep fragmentation only (n = 20), vivid dreams/nightmares (n = 20), hallucinations with insight (n = 20), and hallucinations without insight (n = 9). At baseline, 0.5, 1.5, 4, 6, and 10 years, sleep disorders and hallucinations were assessed by standardized scales with the longitudinal data analyzed by generalized estimating equations with assumptions of linearity in time. Results: At 10 years, we could account for all subjects (27 interviewed, 61 deceased, and 1 too ill for interview). Hallucination prevalence and severity increased over time (p < 0.0001, p = 0.0001). Acting out dreams also increased over time (p = 0.001). In contrast, presence of vivid dreams/nightmares or sleep fragmentation did not increase over time. For all visits, the prevalence of sleep fragmentation did not differ between subjects with vs without hallucinations (odds ratio [OR] = 1.50, p = 0.09). However, severe sleep fragmentation was associated with concurrent hallucinations (OR 2.01, p = 0.006). The presence of hallucinations was also highly associated with concurrent vivid dreams/nightmares (OR = 2.60, p < 0.0001) and with concurrent acting out dreams (OR = 2.38, p = 0.0004). Among the baseline nonhallucinators, no sleep abnormalities at study entry predicted future development of hallucinations. Conclusions: Hallucinations and sleep abnormalities follow very different patterns of progression in PD over 10 years. Whereas patients with hallucinations often have concurrent sleep aberrations, no sleep problem is predictive of future hallucinations. GLOSSARY CI = confidence interval; GEE = generalized estimating equation; MMSE = Mini-Mental State Examination; OR = odds ratio; PD = Parkinson disease

  9. Superconductivity in Pd, Ir, and Pt chalcogenide

    NASA Astrophysics Data System (ADS)

    Oh, Yoon Seok; Yang, Junjie; Choi, Y. J.; Hogan, A.; Horibe, Y.; Cheong, S.-W.

    2012-02-01

    Large spin-orbit coupling in materials with heavy chalcogens can result in unique quantum states or functional properties such as topological insulator, giant thermoelectric power, and superconductivity. When materials contain heavy cations in addition to heavy chalcogens, spin-orbit coupling can be further enhanced. For these reasons, we have studied the superconductivity of Pd, Ir, and Pt tellurides and selenides. In the exploration of these chalcogenides, we have focused on the competition between superconductivity and charge density wave that is associated with superlattice reflections.

  10. The quasiparticle spectrum in Sr{sub 2}CuO{sub 2}Cl{sub 2}

    SciTech Connect

    Ovchinnikov, S.G.

    1996-12-31

    The electronic structure in antiferromagnetic insulator Sr{sub 2}CuO{sub 2}Cl{sub 2} is calculated in the multi band p-d model of CuO{sub 2} layer with account for strong electron correlations. The results are in good agreement with recent ARPES data and are compared with the results of the t-J model. Spin fluctuations result in the anisotropy of the effective mass at the top of the valence band.

  11. Middle School Mathematics PD Study: Description of the PD Intervention. Paper #2

    ERIC Educational Resources Information Center

    Walters, Kirk; Garet, Michael; Leinwand, Steve

    2010-01-01

    This paper describes the PD program that was delivered during the first year of the study. The main goal of the intervention was to increase teachers' capability to teach positive rational number topics effectively. The program included a 3-day summer institute (18 hours per teacher), five 1-day seminars held during the school year (30 hours per…

  12. Low-energy electron diffraction investigation of epitaxial growth: Pt and Pd on Pd(100)

    SciTech Connect

    Flynn-Sanders, D.

    1990-09-21

    We investigate the epitaxial growth of Pt and Pd and Pd(100) via spot profile analysis using conventional low-energy electron diffraction (LEED). We resolve a central-spike and diffuse component in the spot profiles, reflecting the layer-occupations and pair-correlations, respectively. Kinetic limitations inhibit layer-by-layer growth at low temperatures. Our data suggest diffusion switches on at ca. 150 K for Pt and ca. 170 K for Pd indicating activation barriers to surface diffusion of ca. 10 and ca. 13 kcal/mol, respectively. To clarify the role of diffusion in determining the resulting film morphology, we develop a growth model that incorporates the adsorption-site requirement and predicts intensity oscillations. We present a new procedure to experimentally determine out-of-phase scattering conditions. At these energies, ring-structure is evident in the profiles during Pd growth between ca. 200 and 400 K. We report ring intensity oscillations as a function of coverage, which demonstrate the filling of individual layers.

  13. Crystal structure and hydrogenation properties of pseudo-binary Mg 6Pd 0.5Ni 0.5 complex metallic alloy

    NASA Astrophysics Data System (ADS)

    Cuevas, F.; Fernández, J. F.; Ares, J. R.; Leardini, F.; Latroche, M.

    2009-10-01

    The crystal structure of the Ni-substituted Mg 6.10(2)Pd 0.52(2)Ni 0.41(2) complex metallic alloy has been determined by X-ray and neutron powder diffraction. The reaction of this compound at 573 K towards deuterium absorption for pressures up to 23 bar has also been studied. The crystal structure of Mg 6.10(2)Pd 0.52(2)Ni 0.41(2) compound was determined in the light of Samson's [Acta Crystallogr. B 28 (1972) 936) and Makongo's (Philos. Mag. 86 (2006) 427] models for the binary Mg 6Pd compound. It crystallizes in F4¯3m space group with lattice parameter 20.13331(7) Å. The refined unit-cell composition is Mg 342(1)Pd 29(1)Ni 23(1) with Z=56. Nickel by palladium substitution is not fully random. Nickel atoms preferentially locate on Pd sites with low coordination number due to steric effects. Deuterium uptake is 9.6 D/f.u. under the given conditions of pressure and temperature. Upon absorption, the intermetallic compound disproportionates into MgD 2, Mg 5Pd 2 and Mg 2NiD 4 phases. The Mg 2NiD 4 phase is observed to crystallize in the orthorhombic LT2 modification for which an averaged crystal structure in the Pcc2 space group is proposed.

  14. An efficient photochemical route to Pd nanoparticles; application to the one-step synthesis of Pd@polymer nanocomposite films.

    PubMed

    Wolak, Séverine; Vidal, Loïc; Becht, Jean-Michel; Michelin, Laure; Balan, Lavinia

    2016-08-26

    We have developed a facile, efficient, low cost and 'green' photochemical approach to preparing surfactant-free Pd nanoparticles and Pd-immobilized@acrylate photo-polymer films at room temperature, under air and without any additional treatment. The reaction system only includes a photo-initiator used as a generator of free radicals and a Pd(II) salt. In ethanol solution, the photochemical reduction of Pd(II) to Pd(0) generates very small metal particles with a narrow size distribution (2-4 nm). Furthermore, we have shown that the formation of Pd nanoparticles from a Pd(II) salt can be reversible thus allowing easy handling and safe storage with the possibility of generating the nanoparticles just before use. In the presence of an acrylate bifunctional monomer, Pd@polymer film was obtained through a 'one-pot, one-step' process resulting from a simultaneous photo-reduction of Pd(II) and photo-polymerization of acrylate units. The simultaneous generation of a 3D polymer network and of metal particles leads to a homogeneous distribution of Pd nanoparticles in the photo-polymer matrix with an average diameter of approximately 3.7 ± 1.1 nm. Such as-prepared Pd@polymer films were found to efficiently catalyze the Mizoroki-Heck reaction in the presence of only 0.9 mequiv. of supported palladium. The major interest of this arrangement is its recoverability and reusability, which makes it very attractive both from a practical and economical viewpoint. Finally, it is worth noting that this innovation offers a great advantage over concurrent methods in that it is simply generated within minutes, it is highly stable, and there is sharp monodispersity in the size of the Pd nanoparticles that can be stored for months without alteration of their physico-chemical properties and catalytic activity. PMID:27418591

  15. An efficient photochemical route to Pd nanoparticles; application to the one-step synthesis of Pd@polymer nanocomposite films

    NASA Astrophysics Data System (ADS)

    Wolak, Séverine; Vidal, Loïc; Becht, Jean-Michel; Michelin, Laure; Balan, Lavinia

    2016-08-01

    We have developed a facile, efficient, low cost and ‘green’ photochemical approach to preparing surfactant-free Pd nanoparticles and Pd-immobilized@acrylate photo-polymer films at room temperature, under air and without any additional treatment. The reaction system only includes a photo-initiator used as a generator of free radicals and a Pd(II) salt. In ethanol solution, the photochemical reduction of Pd(II) to Pd(0) generates very small metal particles with a narrow size distribution (2–4 nm). Furthermore, we have shown that the formation of Pd nanoparticles from a Pd(II) salt can be reversible thus allowing easy handling and safe storage with the possibility of generating the nanoparticles just before use. In the presence of an acrylate bifunctional monomer, Pd@polymer film was obtained through a ‘one-pot, one-step’ process resulting from a simultaneous photo-reduction of Pd(II) and photo-polymerization of acrylate units. The simultaneous generation of a 3D polymer network and of metal particles leads to a homogeneous distribution of Pd nanoparticles in the photo-polymer matrix with an average diameter of approximately 3.7 ± 1.1 nm. Such as-prepared Pd@polymer films were found to efficiently catalyze the Mizoroki–Heck reaction in the presence of only 0.9 mequiv. of supported palladium. The major interest of this arrangement is its recoverability and reusability, which makes it very attractive both from a practical and economical viewpoint. Finally, it is worth noting that this innovation offers a great advantage over concurrent methods in that it is simply generated within minutes, it is highly stable, and there is sharp monodispersity in the size of the Pd nanoparticles that can be stored for months without alteration of their physico-chemical properties and catalytic activity.

  16. Accurate all-electron G0W0 quasiparticle energies employing the full-potential augmented plane-wave method

    NASA Astrophysics Data System (ADS)

    Nabok, Dmitrii; Gulans, Andris; Draxl, Claudia

    2016-07-01

    The G W approach of many-body perturbation theory has become a common tool for calculating the electronic structure of materials. However, with increasing number of published results, discrepancies between the values obtained by different methods and codes become more and more apparent. For a test set of small- and wide-gap semiconductors, we demonstrate how to reach the numerically best electronic structure within the framework of the full-potential linearized augmented plane-wave (FLAPW) method. We first evaluate the impact of local orbitals in the Kohn-Sham eigenvalue spectrum of the underlying starting point. The role of the basis-set quality is then further analyzed when calculating the G0W0 quasiparticle energies. Our results, computed with the exciting code, are compared to those obtained using the projector-augmented plane-wave formalism, finding overall good agreement between both methods. We also provide data produced with a typical FLAPW basis set as a benchmark for other G0W0 implementations.

  17. Structural, vibrational, and quasiparticle band structure of 1,1-diamino-2,2-dinitroethelene from ab initio calculations

    SciTech Connect

    Appalakondaiah, S.; Vaitheeswaran, G.; Lebègue, S.

    2014-01-07

    The effects of pressure on the structural and vibrational properties of the layered molecular crystal 1,1-diamino-2,2-dinitroethelene (FOX-7) are explored by first principles calculations. We observe significant changes in the calculated structural properties with different corrections for treating van der Waals interactions to Density Functional Theory (DFT), as compared with standard DFT functionals. In particular, the calculated ground state lattice parameters, volume and bulk modulus obtained with Grimme's scheme, are found to agree well with experiments. The calculated vibrational frequencies demonstrate the dependence of the intra and inter-molecular interactions on FOX-7 under pressure. In addition, we also found a significant increment in the N–H...O hydrogen bond strength under compression. This is explained by the change in bond lengths between nitrogen, hydrogen, and oxygen atoms, as well as calculated IR spectra under pressure. Finally, the computed band gap is about 2.3 eV with generalized gradient approximation, and is enhanced to 5.1 eV with the GW approximation, which reveals the importance of performing quasiparticle calculations in high energy density materials.

  18. Quasiparticle dynamics and spin-orbital texture of the SrTiO3 two-dimensional electron gas.

    PubMed

    King, P D C; McKeown Walker, S; Tamai, A; de la Torre, A; Eknapakul, T; Buaphet, P; Mo, S-K; Meevasana, W; Bahramy, M S; Baumberger, F

    2014-01-01

    Two-dimensional electron gases (2DEGs) in SrTiO3 have become model systems for engineering emergent behaviour in complex transition metal oxides. Understanding the collective interactions that enable this, however, has thus far proved elusive. Here we demonstrate that angle-resolved photoemission can directly image the quasiparticle dynamics of the d-electron subband ladder of this complex-oxide 2DEG. Combined with realistic tight-binding supercell calculations, we uncover how quantum confinement and inversion symmetry breaking collectively tune the delicate interplay of charge, spin, orbital and lattice degrees of freedom in this system. We reveal how they lead to pronounced orbital ordering, mediate an orbitally enhanced Rashba splitting with complex subband-dependent spin-orbital textures and markedly change the character of electron-phonon coupling, co-operatively shaping the low-energy electronic structure of the 2DEG. Our results allow for a unified understanding of spectroscopic and transport measurements across different classes of SrTiO3-based 2DEGs, and yield new microscopic insights on their functional properties. PMID:24572991

  19. Full self-consistency versus quasiparticle self-consistency in diagrammatic approaches: Exactly solvable two-site Hubbard model

    SciTech Connect

    Kutepov, A. L.

    2015-07-22

    Self-consistent solutions of Hedin's equations (HE) for the two-site Hubbard model (HM) have been studied. They have been found for three-point vertices of increasing complexity (Γ = 1 (GW approximation), Γ₁ from the first-order perturbation theory, and the exact vertex ΓE). Comparison is made between the cases when an additional quasiparticle (QP) approximation for Green's functions is applied during the self-consistent iterative solving of HE and when QP approximation is not applied. Results obtained with the exact vertex are directly related to the present open question—which approximation is more advantageous for future implementations, GW + DMFT or QPGW + DMFT. It is shown that in a regime of strong correlations only the originally proposed GW + DMFT scheme is able to provide reliable results. Vertex corrections based on Perturbation Theory systematically improve the GW results when full self-consistency is applied. The application of QP self-consistency combined with PT vertex corrections shows similar problems to the case when the exact vertex is applied combined with QP sc. An analysis of Ward Identity violation is performed for all studied in this work's approximations and its relation to the general accuracy of the schemes used is provided.

  20. Signatures of Fermi Arcs in the Quasiparticle Interferences of the Weyl Semimetals TaAs and NbP

    NASA Astrophysics Data System (ADS)

    Chang, Guoqing; Xu, Su-Yang; Zheng, Hao; Lee, Chi-Cheng; Huang, Shin-Ming; Belopolski, Ilya; Sanchez, Daniel S.; Bian, Guang; Alidoust, Nasser; Chang, Tay-Rong; Hsu, Chuang-Han; Jeng, Horng-Tay; Bansil, Arun; Lin, Hsin; Hasan, M. Zahid

    2016-02-01

    The recent discovery of the first Weyl semimetal in TaAs provides the first observation of a Weyl fermion in nature. Such a topological semimetal features a novel type of anomalous surface state, the Fermi arc, which connects a pair of Weyl nodes through the boundary of the crystal. Here, we present theoretical calculations of the quasiparticle interference (QPI) patterns that arise from the surface states including the topological Fermi arcs in the Weyl semimetals TaAs and NbP. Most importantly, we discover that the QPI exhibits termination points that are fingerprints of the Weyl nodes in the interference pattern. Our results, for the first time, propose a universal interference signature of the topological Fermi arcs in TaAs, which is fundamental for scanning tunneling microscope (STM) measurements on this prototypical Weyl semimetal compound. More generally, our work provides critical guideline and methodology for STM studies on new Weyl semimetals. Further, the scattering channels revealed by our QPIs are broadly relevant to surface transport and device applications based on Weyl semimetals.