Effects of structural spin-orbit coupling in two dimensional electron and hole liquids

NASA Astrophysics Data System (ADS)

Chesi, Stefano

The recent interest in spin-dependent phenomena in semiconductor heterostructures motivates our detailed study of the structural spin-orbit coupling present in clean two-dimensional electron and hole liquids. Interesting polarization effects are produced in a system out of equilibrium, as when a finite current flows in the sample. In particular, the consequences of a lateral confinement creating a quasi one-dimensional wire are studied in detail, partially motivated by a recent experimental investigation of the point-contact transmission for two-dimensional holes. We also address the role of the electron-electron interaction in the presence of spin-orbit coupling, which has received little attention in the literature. We discuss the formulation of the Hartree-Fock approximation in the particular case of linear Rashba spin-orbit. We establish the form of the mean-field phase diagram in the homogeneous case, which shows a complex interplay between paramagnetic and ferromagnetic states. The latter can be polarized in the plane or in a transverse direction, and are characterized by a complex spin structure and nontrivial occupation. The generality of the Hartree-Fock method allows a simple treatment of the Pauli spin susceptibility, and the application to different forms of spin-orbit coupling. Correlation corrections can be obtained in an analytic form for particular asymptotic regimes. For linear Rashba spin-orbit we identified the relevance of the large spin-orbit limit, dominated by many-body effects, and explicitly treated the high density limit, in which the system is asymptotically noninteracting. As a special case, we derive a new exact formula for the polarization dependence of the ring-diagram correlation energy.

Thermal properties of spin-S Kitaev-Heisenberg model on a honeycomb lattice

NASA Astrophysics Data System (ADS)

Suzuki, Takafumi; Yamaji, Youhei

2018-05-01

Temperature (T) dependence of heat capacity C (T) in the S = 1 / 2 Kitaev honeycomb model shows a double-peak structure resulting from fractionalization of spins into two kinds of Majorana fermions. Recently it has been discussed that the double-peak structure in C (T) is also observed in magnetic ordered phases of the S = 1 / 2 Kitaev-Heisenberg (KH) model on a honeycomb lattice when the system is located in the vicinity of the Kitaev's spin liquid phase. In addition to the S = 1 / 2 spin case, similar double-peak structure has been confirmed in the KH honeycomb model for classical Heisenberg spins, where spin S is regarded as S → ∞ . We investigate spin-S dependence of C (T) for the KH honeycomb models by using thermal pure quantum state. We also perform classical Monte Carlo calculations to obtain C (T) for the classical KH model. From obtained results, we find that the origin of the high-temperature peak is different between the quantum spin case with small Ss and the classical Heisenberg spin case. Furthermore, the high-temperature peak in the quantum spin case, which is one of the clues for fractionalization of spins, disappears for S > 1 .

Coulombic charge ice

NASA Astrophysics Data System (ADS)

McClarty, P. A.; O'Brien, A.; Pollmann, F.

2014-05-01

We consider a classical model of charges ±q on a pyrochlore lattice in the presence of long-range Coulomb interactions. This model first appeared in the early literature on charge order in magnetite [P. W. Anderson, Phys. Rev. 102, 1008 (1956), 10.1103/PhysRev.102.1008]. In the limit where the interactions become short ranged, the model has a ground state with an extensive entropy and dipolar charge-charge correlations. When long-range interactions are introduced, the exact degeneracy is broken. We study the thermodynamics of the model and show the presence of a correlated charge liquid within a temperature window in which the physics is well described as a liquid of screened charged defects. The structure factor in this phase, which has smeared pinch points at the reciprocal lattice points, may be used to detect charge ice experimentally. In addition, the model exhibits fractionally charged excitations ±q/2 which are shown to interact via a 1/r potential. At lower temperatures, the model exhibits a transition to a long-range ordered phase. We are able to treat the Coulombic charge ice model and the dipolar spin ice model on an equal footing by mapping both to a constrained charge model on the diamond lattice. We find that states of the two ice models are related by a staggering field which is reflected in the energetics of these two models. From this perspective, we can understand the origin of the spin ice and charge ice ground states as coming from a dipolar model on a diamond lattice. We study the properties of charge ice in an external electric field, finding that the correlated liquid is robust to the presence of a field in contrast to the case of spin ice in a magnetic field. Finally, we comment on the transport properties of Coulombic charge ice in the correlated liquid phase.

Anomalous transport phenomena in Weyl metal beyond the Drude model for Landau's Fermi liquids.

PubMed

Kim, Ki-Seok; Kim, Heon-Jung; Sasaki, M; Wang, J-F; Li, L

2014-12-01

Landau's Fermi-liquid theory is the standard model for metals, characterized by the existence of electron quasiparticles near a Fermi surface as long as Landau's interaction parameters lie below critical values for instabilities. Recently this fundamental paradigm has been challenged by the physics of strong spin-orbit coupling, although the concept of electron quasiparticles remains valid near the Fermi surface, where Landau's Fermi-liquid theory fails to describe the electromagnetic properties of this novel metallic state, referred to as Weyl metal. A novel ingredient is that such a Fermi surface encloses a Weyl point with definite chirality, referred to as a chiral Fermi surface, which can arise from breaking of either time reversal or inversion symmetry in systems with strong spin-orbit coupling, responsible for both the Berry curvature and the chiral anomaly. As a result, electromagnetic properties of the Weyl metallic state are described not by conventional Maxwell equations but by axion electrodynamics, where Maxwell equations are modified with a topological-in-origin spatially modulated [Formula: see text] term. This novel metallic state was realized recently in Bi[Formula: see text]Sb x around [Formula: see text] under magnetic fields, where the Dirac spectrum appears around the critical point between the normal semiconducting ([Formula: see text]) and topological semiconducting phases ([Formula: see text]) and the time reversal symmetry breaking perturbation causes the Dirac point to split into a pair of Weyl points along the direction of the applied magnetic field for a very strong spin-orbit coupled system. In this review article, we discuss how the topological structure of both the Berry curvature and the chiral anomaly (axion electrodynamics) gives rise to anomalous transport phenomena in [Formula: see text]Sb x around [Formula: see text] under magnetic fields, thus modifying the Drude model of Landau's Fermi liquids.

Slosh dynamics of a spin-stabilized spacecraft comprising off-axis tanks filled partially with liquid propellant

NASA Technical Reports Server (NTRS)

Fontenot, L. L.

1981-01-01

The fundamental nonlinear equations of motion were derived and the specialized to a steady-state rotation of the vehicle about a given axis of rotation. A thrust about the spin axis was introduced. A perturbation solution was derived which linearizes the problem. The effect of the centrifugal and coriolis accelerations together with vorticity are implicitly taken into consideration in the formulation. A variational formulation of the associated boundary conditions is presented. For practical cases it is shown that the simple classical pendulum representation for slosh is not very appealing for a spinning spacecraft unless severe restrictions are allowed.

Ising antiferromagnet on the Archimedean lattices.

PubMed

Yu, Unjong

2015-06-01

Geometric frustration effects were studied systematically with the Ising antiferromagnet on the 11 Archimedean lattices using the Monte Carlo methods. The Wang-Landau algorithm for static properties (specific heat and residual entropy) and the Metropolis algorithm for a freezing order parameter were adopted. The exact residual entropy was also found. Based on the degree of frustration and dynamic properties, ground states of them were determined. The Shastry-Sutherland lattice and the trellis lattice are weakly frustrated and have two- and one-dimensional long-range-ordered ground states, respectively. The bounce, maple-leaf, and star lattices have the spin ice phase. The spin liquid phase appears in the triangular and kagome lattices.

Ising antiferromagnet on the Archimedean lattices

NASA Astrophysics Data System (ADS)

Yu, Unjong

2015-06-01

Geometric frustration effects were studied systematically with the Ising antiferromagnet on the 11 Archimedean lattices using the Monte Carlo methods. The Wang-Landau algorithm for static properties (specific heat and residual entropy) and the Metropolis algorithm for a freezing order parameter were adopted. The exact residual entropy was also found. Based on the degree of frustration and dynamic properties, ground states of them were determined. The Shastry-Sutherland lattice and the trellis lattice are weakly frustrated and have two- and one-dimensional long-range-ordered ground states, respectively. The bounce, maple-leaf, and star lattices have the spin ice phase. The spin liquid phase appears in the triangular and kagome lattices.

Neutron polarization analysis study of the frustrated magnetic ground state of β-Mn1-xAlx

NASA Astrophysics Data System (ADS)

Stewart, J. R.; Andersen, K. H.; Cywinski, R.

2008-07-01

We have performed a neutron polarization analysis study of the short-range nuclear and magnetic correlations present in the dilute alloy, β-Mn1-xAlx with 0.03≤x≤0.16 , in order to study the evolution of the magnetic ground state of this system as it achieves static spin-glass order at concentrations x>0.09 . To this end we have developed a reverse-Monte Carlo algorithm which has enabled us to extract Warren-Cowley nuclear short-range order parameters and magnetic spin correlations. Using conventional neutron powder diffraction, we show that the nonmagnetic Al substituents preferentially occupy the magnetic site II Wyckoff positions in the β-Mn structure—resulting in a reduction of the magnetic topological frustration of the Mn atoms. These Al impurities are found to display strong anticlustering behavior. The magnetic spin correlations are predominantly antiferromagnetic, persisting over a short range which is similar for all the samples studied—above and below the spin-liquid-spin-glass boundary—while the observed static (disordered) moment is shown to increase with increasing Al concentration.

Weyl magnons in noncoplanar stacked kagome antiferromagnets

NASA Astrophysics Data System (ADS)

Owerre, S. A.

2018-03-01

Weyl nodes have been experimentally realized in photonic, electronic, and phononic crystals. However, magnonic Weyl nodes are yet to be seen experimentally. In this paper, we propose Weyl magnon nodes in noncoplanar stacked frustrated kagome antiferromagnets, naturally available in various real materials. Most crucially, the Weyl nodes in the current system occur at the lowest excitation and possess a topological thermal Hall effect, therefore they are experimentally accessible at low temperatures due to the population effect of bosonic quasiparticles. In stark contrast to other magnetic systems, the current Weyl nodes do not rely on time-reversal symmetry breaking by the magnetic order. Rather, they result from explicit macroscopically broken time reversal symmetry by the scalar spin chirality of noncoplanar spin textures and can be generalized to chiral spin liquid states. Moreover, the scalar spin chirality gives a real space Berry curvature which is not available in previously studied magnetic Weyl systems. We show the existence of magnon arc surface states connecting projected Weyl magnon nodes on the surface Brillouin zone. We also uncover the first realization of triply-degenerate nodal magnon point in the noncollinear regime with zero scalar spin chirality.

Statistics of Fractionalized Excitations through Threshold Spectroscopy.

PubMed

Morampudi, Siddhardh C; Turner, Ari M; Pollmann, Frank; Wilczek, Frank

2017-06-02

We show that neutral anyonic excitations have a signature in spectroscopic measurements of materials: The low-energy onset of spectral functions near the threshold follows universal power laws with an exponent that depends only on the statistics of the anyons. This provides a route, using experimental techniques such as neutron scattering and tunneling spectroscopy, for detecting anyonic statistics in topologically ordered states such as gapped quantum spin liquids and hypothesized fractional Chern insulators. Our calculations also explain some recent theoretical results in spin systems.

Fractionalized Fermi liquids and exotic superconductivity in the Kitaev-Kondo lattice

NASA Astrophysics Data System (ADS)

Seifert, Urban F. P.; Meng, Tobias; Vojta, Matthias

2018-02-01

Fractionalized Fermi liquids (FL*) have been introduced as non-Fermi-liquid metallic phases, characterized by coexisting electron-like charge carriers and local moments which form a fractionalized spin liquid. Here we investigate a Kondo lattice model on the honeycomb lattice with Kitaev interactions among the local moments, a concrete model hosting FL* phases based on Kitaev's Z2 spin liquid. We characterize the FL* phases via perturbation theory, and we employ a Majorana-fermion mean-field theory to map out the full phase diagram. Most remarkably we find nematic triplet superconducting phases which mask the quantum phase transition between fractionalized and conventional Fermi liquid phases. Their pairing structure is inherited from the Kitaev spin liquid; i.e., superconductivity is driven by Majorana glue.

Frustrated spin chains in strong magnetic field: Dilute two-component Bose gas regime

NASA Astrophysics Data System (ADS)

Kolezhuk, A. K.; Heidrich-Meisner, F.; Greschner, S.; Vekua, T.

2012-02-01

We study the ground state of frustrated spin-S chains in a strong magnetic field in the immediate vicinity of saturation. In strongly frustrated chains, the magnon dispersion has two degenerate minima at inequivalent momenta ±Q, and just below the saturation field the system can be effectively represented as a dilute one-dimensional lattice gas of two species of bosons that correspond to magnons with momenta around ±Q. We present a theory of effective interactions in such a dilute magnon gas that allows us to make quantitative predictions for arbitrary values of the spin. With the help of this method, we are able to establish the magnetic phase diagram of frustrated chains close to saturation and study phase transitions between several nontrivial states, including a two-component Luttinger liquid, a vector chiral phase, and phases with bound magnons. We study those phase transitions numerically and find a good agreement with our analytical predictions.

Construction and 13C NMR signal-amplification efficiency of a dynamic nuclear polarizer at 6.4 T and 1.4 K

NASA Astrophysics Data System (ADS)

Kiswandhi, Andhika; Niedbalski, Peter; Parish, Christopher; Ferguson, Sarah; Taylor, David; McDonald, George; Lumata, Lloyd

Dissolution dynamic nuclear polarization (DNP) is a rapidly emerging technique in biomedical and metabolic imaging since it amplifies the liquid-state nuclear magnetic resonance (NMR) and imaging (MRI) signals by >10,000-fold. Originally used in nuclear scattering experiments, DNP works by creating a non-Boltzmann nuclear spin distribution by transferring the high electron (γ = 28,000 MHz/T) thermal polarization to the nuclear spins via microwave irradiation of the sample at high magnetic field and low temperature. A dissolution device is used to rapidly dissolve the frozen sample and consequently produces an injectable ``hyperpolarized'' liquid at physiologically-tolerable temperature. Here we report the construction and performance evaluation of a dissolution DNP hyperpolarizer at 6.4 T and 1.4 K using a continuous-flow cryostat. The solid and liquid-state 13C NMR signal enhancement levels of 13C acetate samples doped with trityl OX063 and 4-oxo-TEMPO free radicals will be discussed and compared with the results from the 3.35 T commercial hyperpolarizer. This work is supported by US Dept of Defense Award No. W81XWH-14-1-0048 and Robert A. Welch Foundation Grant No. AT-1877.

Angle-resolved molecular beam scattering of NO at the gas-liquid interface.

PubMed

Zutz, Amelia; Nesbitt, David J

2017-08-07

This study presents first results on angle-resolved, inelastic collision dynamics of thermal and hyperthermal molecular beams of NO at gas-liquid interfaces. Specifically, a collimated incident beam of supersonically cooled NO ( 2 Π 1/2 , J = 0.5) is directed toward a series of low vapor pressure liquid surfaces ([bmim][Tf 2 N], squalane, and PFPE) at θ inc = 45(1)°, with the scattered molecules detected with quantum state resolution over a series of final angles (θ s = -60°, -30°, 0°, 30°, 45°, and 60°) via spatially filtered laser induced fluorescence. At low collision energies [E inc = 2.7(9) kcal/mol], the angle-resolved quantum state distributions reveal (i) cos(θ s ) probabilities for the scattered NO and (ii) electronic/rotational temperatures independent of final angle (θ s ), in support of a simple physical picture of angle independent sticking coefficients and all incident NO thermally accommodating on the surface. However, the observed electronic/rotational temperatures for NO scattering reveal cooling below the surface temperature (T elec < T rot < T S ) for all three liquids, indicating a significant dependence of the sticking coefficient on NO internal quantum state. Angle-resolved scattering at high collision energies [E inc = 20(2) kcal/mol] has also been explored, for which the NO scattering populations reveal angle-dependent dynamical branching between thermal desorption and impulsive scattering (IS) pathways that depend strongly on θ s . Characterization of the data in terms of the final angle, rotational state, spin-orbit electronic state, collision energy, and liquid permit new correlations to be revealed and investigated in detail. For example, the IS rotational distributions reveal an enhanced propensity for higher J/spin-orbit excited states scattered into near specular angles and thus hotter rotational/electronic distributions measured in the forward scattering direction. Even more surprisingly, the average NO scattering angle (⟨θ s ⟩) exhibits a remarkably strong correlation with final angular momentum, N, which implies a linear scaling between net forward scattering propensity and torque delivered to the NO projectile by the gas-liquid interface.

Angle-resolved molecular beam scattering of NO at the gas-liquid interface

NASA Astrophysics Data System (ADS)

Zutz, Amelia; Nesbitt, David J.

2017-08-01

This study presents first results on angle-resolved, inelastic collision dynamics of thermal and hyperthermal molecular beams of NO at gas-liquid interfaces. Specifically, a collimated incident beam of supersonically cooled NO (2 Π 1/2, J = 0.5) is directed toward a series of low vapor pressure liquid surfaces ([bmim][Tf2N], squalane, and PFPE) at θinc = 45(1)°, with the scattered molecules detected with quantum state resolution over a series of final angles (θs = -60°, -30°, 0°, 30°, 45°, and 60°) via spatially filtered laser induced fluorescence. At low collision energies [Einc = 2.7(9) kcal/mol], the angle-resolved quantum state distributions reveal (i) cos(θs) probabilities for the scattered NO and (ii) electronic/rotational temperatures independent of final angle (θs), in support of a simple physical picture of angle independent sticking coefficients and all incident NO thermally accommodating on the surface. However, the observed electronic/rotational temperatures for NO scattering reveal cooling below the surface temperature (Telec < Trot < TS) for all three liquids, indicating a significant dependence of the sticking coefficient on NO internal quantum state. Angle-resolved scattering at high collision energies [Einc = 20(2) kcal/mol] has also been explored, for which the NO scattering populations reveal angle-dependent dynamical branching between thermal desorption and impulsive scattering (IS) pathways that depend strongly on θs. Characterization of the data in terms of the final angle, rotational state, spin-orbit electronic state, collision energy, and liquid permit new correlations to be revealed and investigated in detail. For example, the IS rotational distributions reveal an enhanced propensity for higher J/spin-orbit excited states scattered into near specular angles and thus hotter rotational/electronic distributions measured in the forward scattering direction. Even more surprisingly, the average NO scattering angle (⟨θs⟩) exhibits a remarkably strong correlation with final angular momentum, N, which implies a linear scaling between net forward scattering propensity and torque delivered to the NO projectile by the gas-liquid interface.

Solid-state NMR adiabatic TOBSY sequences provide enhanced sensitivity for multidimensional high-resolution magic-angle-spinning 1H MR spectroscopy

NASA Astrophysics Data System (ADS)

Andronesi, Ovidiu C.; Mintzopoulos, Dionyssios; Struppe, Jochem; Black, Peter M.; Tzika, A. Aria

2008-08-01

We propose a solid-state NMR method that maximizes the advantages of high-resolution magic-angle-spinning (HRMAS) applied to intact biopsies when compared to more conventional liquid-state NMR approaches. Theoretical treatment, numerical simulations and experimental results on intact human brain biopsies are presented. Experimentally, it is proven that an optimized adiabatic TOBSY (TOtal through Bond correlation SpectroscopY) solid-state NMR pulse sequence for two-dimensional 1H- 1H homonuclear scalar-coupling longitudinal isotropic mixing provides a 20%-50% improvement in signal-to-noise ratio relative to its liquid-state analogue TOCSY (TOtal Correlation SpectroscopY). For this purpose we have refined the C9151 symmetry-based 13C TOBSY pulse sequence for 1H MRS use and compared it to MLEV-16 TOCSY sequence. Both sequences were rotor-synchronized and implemented using WURST-8 adiabatic inversion pulses. As discussed theoretically and shown in simulations, the improved magnetization-transfer comes from actively removing residual dipolar couplings from the average Hamiltonian. Importantly, the solid-state NMR techniques are tailored to perform measurements at low temperatures where sample degradation is reduced. This is the first demonstration of such a concept for HRMAS metabolic profiling of disease processes, including cancer, from biopsies requiring reduced sample degradation for further genomic analysis.

Incoherent vs. coherent behavior in the normal state of copper oxide superconductors

NASA Technical Reports Server (NTRS)

Tesanovic, Zlatko

1991-01-01

The self-consistent quantum fluctuations around the mean-field Hartree-Fock state of the Hubbard model provide a very good description of the ground state and low temperature properties of a 2-D itinerant antiferromagnet. Very good agreement with numerical calculations and experimental data is obtained by including the one- and two-loop spin wave corrections to various physical quantities. In particular, the destruction of the long-range order above the Neel temperature can be understood as a spontaneous generation of a length-scale epsilon(T), which should be identified as the spin correlation length. For finite doping, the question of the Hartree-Fock starting point becomes a more complex one since an extra hole tends to self-trap in antiferromagnetic background. Such quantum defects in an underlying antiferromagnetic state can be spin-bags or vortex-like structures and tend to suppress the long-range order. If motion of the holes occurs on a time-scale shorter than the one associated with the motion of these quantum defects of a spin background, one obtains several important empirical features of the normal state of CuO superconductors like linear T-dependence of resistivity, the cusp in the tunneling density of states, etc. As opposed to a familiar Fermi-liquid behavior, the phenomenology of the above system is dominated by a large incoherent piece of a single hole propagator, resulting in many unusual normal state properties.

Sensitizing solid state nuclear magnetic resonance of dilute nuclei by spin-diffusion assisted polarization transfers.

PubMed

Lupulescu, Adonis; Frydman, Lucio

2011-10-07

Recent years have witnessed efforts geared at increasing the sensitivity of NMR experiments, by relying on the suitable tailoring and exploitation of relaxation phenomena. These efforts have included the use of paramagnetic agents, enhanced (1)H-(1)H incoherent and coherent transfers processes in 2D liquid state spectroscopy, and homonuclear (13)C-(13)C spin diffusion effects in labeled solids. The present study examines some of the opportunities that could open when exploiting spontaneous (1)H-(1)H spin-diffusion processes, to enhance relaxation and to improve the sensitivity of dilute nuclei in solid state NMR measurements. It is shown that polarization transfer experiments executed under sufficiently fast magic-angle-spinning conditions, enable a selective polarization of the dilute low-γ spins by their immediate neighboring protons. Repolarization of the latter can then occur during the time involved in monitoring the signal emitted by the low-γ nuclei. The basic features involved in the resulting approach, and its potential to improve the effective sensitivity of solid state NMR measurements on dilute nuclei, are analyzed. Experimental tests witness the advantages that could reside from utilizing this kind of approach over conventional cross-polarization processes. These measurements also highlight a number of limitations that will have to be overcome for transforming selective polarization transfers of this kind into analytical methods of choice. © 2011 American Institute of Physics

Neutron scattering in the proximate quantum spin liquid α-RuCl3

NASA Astrophysics Data System (ADS)

Banerjee, Arnab; Yan, Jiaqiang; Knolle, Johannes; Bridges, Craig A.; Stone, Matthew B.; Lumsden, Mark D.; Mandrus, David G.; Tennant, David A.; Moessner, Roderich; Nagler, Stephen E.

2017-06-01

The Kitaev quantum spin liquid (KQSL) is an exotic emergent state of matter exhibiting Majorana fermion and gauge flux excitations. The magnetic insulator α-RuCl3 is thought to realize a proximate KQSL. We used neutron scattering on single crystals of α-RuCl3 to reconstruct dynamical correlations in energy-momentum space. We discovered highly unusual signals, including a column of scattering over a large energy interval around the Brillouin zone center, which is very stable with temperature. This finding is consistent with scattering from the Majorana excitations of a KQSL. Other, more delicate experimental features can be transparently associated with perturbations to an ideal model. Our results encourage further study of this prototypical material and may open a window into investigating emergent magnetic Majorana fermions in correlated materials.

Excitations in the field-induced quantum spin liquid state of α-RuCl3

NASA Astrophysics Data System (ADS)

Banerjee, Arnab; Lampen-Kelley, Paula; Knolle, Johannes; Balz, Christian; Aczel, Adam Anthony; Winn, Barry; Liu, Yaohua; Pajerowski, Daniel; Yan, Jiaqiang; Bridges, Craig A.; Savici, Andrei T.; Chakoumakos, Bryan C.; Lumsden, Mark D.; Tennant, David Alan; Moessner, Roderich; Mandrus, David G.; Nagler, Stephen E.

2018-03-01

The celebrated Kitaev quantum spin liquid (QSL) is the paradigmatic example of a topological magnet with emergent excitations in the form of Majorana Fermions and gauge fluxes. Upon breaking of time-reversal symmetry, for example in an external magnetic field, these fractionalized quasiparticles acquire non-Abelian exchange statistics, an important ingredient for topologically protected quantum computing. Consequently, there has been enormous interest in exploring possible material realizations of Kitaev physics and several candidate materials have been put forward, recently including α-RuCl3. In the absence of a magnetic field this material orders at a finite temperature and exhibits low-energy spin wave excitations. However, at moderate energies, the spectrum is unconventional and the response shows evidence for fractional excitations. Here we use time-of-flight inelastic neutron scattering to show that the application of a sufficiently large magnetic field in the honeycomb plane suppresses the magnetic order and the spin waves, leaving a gapped continuum spectrum of magnetic excitations. Our comparisons of the scattering to the available calculations for a Kitaev QSL show that they are consistent with the magnetic field induced QSL phase.

Excitations in the field-induced quantum spin liquid state of α-RuCl 3

DOE PAGES

Banerjee, Arnab; Kelley, Paula J.; Knolle, Johannes; ...

2018-02-20

The celebrated Kitaev quantum spin liquid (QSL) is the paradigmatic example of a topological magnet with emergent excitations in the form of Majorana Fermions and gauge fluxes. Upon breaking of time-reversal symmetry, for example in an external magnetic field, these fractionalized quasiparticles acquire non-Abelian exchange statistics, an important ingredient for topologically protected quantum computing. Consequently, there has been enormous interest in exploring possible material realizations of Kitaev physics and several candidate materials have been put forward, recently including α-RuCl 3. In the absence of a magnetic field this material orders at a finite temperature and exhibits low-energy spin wave excitations.more » However, at moderate energies, the spectrum is unconventional and the response shows evidence for fractional excitations. Here in this paper, we use time-of-flight inelastic neutron scattering to show that the application of a sufficiently large magnetic field in the honeycomb plane suppresses the magnetic order and the spin waves, leaving a gapped continuum spectrum of magnetic excitations. Our comparisons of the scattering to the available calculations for a Kitaev QSL show that they are consistent with the magnetic field induced QSL phase.« less

Excitations in the field-induced quantum spin liquid state of α-RuCl 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Banerjee, Arnab; Kelley, Paula J.; Knolle, Johannes

The celebrated Kitaev quantum spin liquid (QSL) is the paradigmatic example of a topological magnet with emergent excitations in the form of Majorana Fermions and gauge fluxes. Upon breaking of time-reversal symmetry, for example in an external magnetic field, these fractionalized quasiparticles acquire non-Abelian exchange statistics, an important ingredient for topologically protected quantum computing. Consequently, there has been enormous interest in exploring possible material realizations of Kitaev physics and several candidate materials have been put forward, recently including α-RuCl 3. In the absence of a magnetic field this material orders at a finite temperature and exhibits low-energy spin wave excitations.more » However, at moderate energies, the spectrum is unconventional and the response shows evidence for fractional excitations. Here in this paper, we use time-of-flight inelastic neutron scattering to show that the application of a sufficiently large magnetic field in the honeycomb plane suppresses the magnetic order and the spin waves, leaving a gapped continuum spectrum of magnetic excitations. Our comparisons of the scattering to the available calculations for a Kitaev QSL show that they are consistent with the magnetic field induced QSL phase.« less

Direct experimental observation of the molecular J eff=3/2 ground state in the lacunar spinel GaTa 4Se 8

DOE PAGES

Jeong, Min Yong; Chang, Seo Hyoung; Kim, Beom Hyun; ...

2017-10-04

Strong spin-orbit coupling lifts the degeneracy of t 2g orbitals in 5d transition-metal systems, leaving a Kramers doublet and quartet with effective angular momentum of J eff = 1/2 and 3/2, respectively. These spin-orbit entangled states can host exotic quantum phases such as topological Mott state, unconventional superconductivity, and quantum spin liquid. The lacunar spinel GaTa 4Se 8 was theoretically predicted to form the molecular J eff = 3/2 ground state. Experimental verification of its existence is an important first step to exploring the consequences of the J eff = 3/2 state. Here, we report direct experimental evidence of themore » J eff = 3/2 state in GaTa 4Se 8 by means of excitation spectra of resonant inelastic x-rays scattering at the Ta L 3 and L 2 edges. In conclusion, we found that the excitations involving the J eff = 1/2 molecular orbital were absent only at the Ta L 2 edge, manifesting the realization of the molecular J eff = 3/2 ground state in GaTa 4Se 8.« less

Direct experimental observation of the molecular J eff=3/2 ground state in the lacunar spinel GaTa 4Se 8

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jeong, Min Yong; Chang, Seo Hyoung; Kim, Beom Hyun

Strong spin-orbit coupling lifts the degeneracy of t 2g orbitals in 5d transition-metal systems, leaving a Kramers doublet and quartet with effective angular momentum of J eff = 1/2 and 3/2, respectively. These spin-orbit entangled states can host exotic quantum phases such as topological Mott state, unconventional superconductivity, and quantum spin liquid. The lacunar spinel GaTa 4Se 8 was theoretically predicted to form the molecular J eff = 3/2 ground state. Experimental verification of its existence is an important first step to exploring the consequences of the J eff = 3/2 state. Here, we report direct experimental evidence of themore » J eff = 3/2 state in GaTa 4Se 8 by means of excitation spectra of resonant inelastic x-rays scattering at the Ta L 3 and L 2 edges. In conclusion, we found that the excitations involving the J eff = 1/2 molecular orbital were absent only at the Ta L 2 edge, manifesting the realization of the molecular J eff = 3/2 ground state in GaTa 4Se 8.« less

Optimization of identity operation in NMR spectroscopy via genetic algorithm: Application to the TEDOR experiment

NASA Astrophysics Data System (ADS)

Manu, V. S.; Veglia, Gianluigi

2016-12-01

Identity operation in the form of π pulses is widely used in NMR spectroscopy. For an isolated single spin system, a sequence of even number of π pulses performs an identity operation, leaving the spin state essentially unaltered. For multi-spin systems, trains of π pulses with appropriate phases and time delays modulate the spin Hamiltonian to perform operations such as decoupling and recoupling. However, experimental imperfections often jeopardize the outcome, leading to severe losses in sensitivity. Here, we demonstrate that a newly designed Genetic Algorithm (GA) is able to optimize a train of π pulses, resulting in a robust identity operation. As proof-of-concept, we optimized the recoupling sequence in the transferred-echo double-resonance (TEDOR) pulse sequence, a key experiment in biological magic angle spinning (MAS) solid-state NMR for measuring multiple carbon-nitrogen distances. The GA modified TEDOR (GMO-TEDOR) experiment with improved recoupling efficiency results in a net gain of sensitivity up to 28% as tested on a uniformly 13C, 15N labeled microcrystalline ubiquitin sample. The robust identity operation achieved via GA paves the way for the optimization of several other pulse sequences used for both solid- and liquid-state NMR used for decoupling, recoupling, and relaxation experiments.

Probing α -RuCl3 Beyond Magnetic Order: Effects of Temperature and Magnetic Field

NASA Astrophysics Data System (ADS)

Winter, Stephen M.; Riedl, Kira; Kaib, David; Coldea, Radu; Valentí, Roser

2018-02-01

Recent studies have brought α -RuCl3 to the forefront of experimental searches for materials realizing Kitaev spin-liquid physics. This material exhibits strongly anisotropic exchange interactions afforded by the spin-orbit coupling of the 4 d Ru centers. We investigate the dynamical response at finite temperature and magnetic field for a realistic model of the magnetic interactions in α -RuCl3 . These regimes are thought to host unconventional paramagnetic states that emerge from the suppression of magnetic order. Using exact diagonalization calculations of the quantum model complemented by semiclassical analysis, we find a very rich evolution of the spin dynamics as the applied field suppresses the zigzag order and stabilizes a quantum paramagnetic state that is adiabatically connected to the fully polarized state at high fields. At finite temperature, we observe large redistributions of spectral weight that can be attributed to the anisotropic frustration of the model. These results are compared to recent experiments and provide a road map for further studies of these regimes.

Spin crossover in liquid Fe2SiO4 at high pressures: an ab initio Molecular Dynamics study

NASA Astrophysics Data System (ADS)

Munoz Ramo, D.; Stixrude, L. P.

2010-12-01

Liquid iron silicate (Fe2SiO4) is an important component of natural silicate liquids appearing in Earth’s interior. The effect of iron in the properties of these melts is a crucial issue, as it displays a high-spin to low-spin transition at high pressures which is accompanied by volume reduction and changes in the optical absorption spectrum. This phenomenon has a major influence on properties like the buoyancy or the thermal conductivity of the melt, and ultimately on the chemical and thermal evolution of our planet. Computer simulations using ab initio methods have proven to be a powerful approach to the study of liquid silicate systems[1,2], although not yet including Fe. In this paper, we report ab initio molecular dynamics studies of liquid iron silicate at high pressure (up to 300 GPa) and high temperatures (from 3000K to 6000K) that allow us to predict different properties of the system. We use mainly the GGA density functional for the calculation of the electronic structure. We also perform simulations with the GGA+U formalism to estimate the impact of strong electron correlation effects in the properties of the system at high pressures. The spin-polarized formalism is also used in order to keep track of the evolution of the iron magnetic moments in the system. By means of these simulations we predict the short and medium-range structure and thermodynamic properties of the liquid. We compute the theoretical Hugoniot for the system and find very good agreement between the GGA results and the equation of state values obtained from shock experiments [3], while the GGA+U results overestimate the Hugoniot curve at high pressures. Density crossover with the solid is obtained at about 110 GPa at 3000 K. Our calculations show that the spin crossover in this system takes place at a wide pressure interval, dependent on temperature. At 3000K, the spin transition starts at around 10 GPa and finishes at pressures around 250 Gpa. Increase of the temperature to 6000K reduces the interval of the transition to 180 GPa. [1] N. P. de Koker, L. Stixrude, B. B. Karki, Geochim Cosmochim Acta 2008, 72, 1427. [2] B. B. Karki, D. Bhattarai, L. Stixrude, Phys. Rev. B 2007, 76, 104205. [3] G. Q. Chen, T. J. Ahrens, E. M. Stolper, Phys. Earth Planet. Inter. 2002, 134, 35.

Solitonic Spin-Liquid State Due to the Violation of the Lifshitz Condition in Fe(1+y)Te.

PubMed

Materne, Ph; Koz, C; Rössler, U K; Doerr, M; Goltz, T; Klauss, H H; Schwarz, U; Wirth, S; Rössler, S

2015-10-23

A combination of phenomenological analysis and Mössbauer spectroscopy experiments on the tetragonal Fe(1+y)Te system indicates that the magnetic ordering transition in compounds with higher Fe excess, y≥0.11, is unconventional. Experimentally, a liquidlike magnetic precursor with quasistatic spin order is found from significantly broadened Mössbauer spectra at temperatures above the antiferromagnetic transition. The incommensurate spin-density wave order in Fe(1+y)Te is described by a magnetic free energy that violates the weak Lifshitz condition in the Landau theory of second-order transitions. The presence of multiple Lifshitz invariants provides the mechanism to create multidimensional, twisted, and modulated solitonic phases.

Solitonic Spin-Liquid State Due to the Violation of the Lifshitz Condition in Fe1 +yTe

NASA Astrophysics Data System (ADS)

Materne, Ph.; Koz, C.; Rößler, U. K.; Doerr, M.; Goltz, T.; Klauss, H. H.; Schwarz, U.; Wirth, S.; Rößler, S.

2015-10-01

A combination of phenomenological analysis and Mössbauer spectroscopy experiments on the tetragonal Fe1 +yTe system indicates that the magnetic ordering transition in compounds with higher Fe excess, y ≥0.11 , is unconventional. Experimentally, a liquidlike magnetic precursor with quasistatic spin order is found from significantly broadened Mössbauer spectra at temperatures above the antiferromagnetic transition. The incommensurate spin-density wave order in Fe1 +yTe is described by a magnetic free energy that violates the weak Lifshitz condition in the Landau theory of second-order transitions. The presence of multiple Lifshitz invariants provides the mechanism to create multidimensional, twisted, and modulated solitonic phases.

On the nature of the solvated electron in ice Ih.

PubMed

de Koning, Maurice; Fazzio, Adalberto; da Silva, Antônio José Roque; Antonelli, Alex

2016-02-14

The water-solvated excess electron (EE) is a key chemical agent whose hallmark signature, its asymmetric optical absorption spectrum, continues to be a topic of debate. While nearly all investigation has focused on the liquid-water solvent, the fact that the crystalline-water solvated EE shows a very similar visible absorption pattern has remained largely unexplored. Here, we present spin-polarized density-functional theory calculations subject to periodic boundary conditions of the interplay between an EE and a number of intrinsic lattice defects in ice Ih. Our results show that the optical absorption signatures in the presence of three unsaturated hydrogen bonds (HB) are very similar to those observed experimentally. Its low-energy side can be attributed to transitions between the EE ground state and a single localized excited level, in a picture that is different from that for the liquid solvent, where this portion has been associated with hydrogen-like s → p excitations. The blue tail, on the other hand, relates to transitions between the EE ground state and delocalized excited states, which is in line with the bound-to-continuum transition interpretations for the EE in liquid water. Finally, we find that, depending on the number of dangling HBs participating in the EE trap, its charge density may spontaneously break the spin degeneracy through exchange interactions with the surrounding electrons, displaying the many-electron quantum nature of the EE problem in ice Ih.

Breakdown of Magnetic Order in the Pressurized Kitaev Iridate β -Li2IrO3

NASA Astrophysics Data System (ADS)

Majumder, M.; Manna, R. S.; Simutis, G.; Orain, J. C.; Dey, T.; Freund, F.; Jesche, A.; Khasanov, R.; Biswas, P. K.; Bykova, E.; Dubrovinskaia, N.; Dubrovinsky, L. S.; Yadav, R.; Hozoi, L.; Nishimoto, S.; Tsirlin, A. A.; Gegenwart, P.

2018-06-01

Temperature-pressure phase diagram of the Kitaev hyperhoneycomb iridate β -Li2IrO3 is explored using magnetization, thermal expansion, magnetostriction, and muon spin rotation measurements, as well as single-crystal x-ray diffraction under pressure and ab initio calculations. The Néel temperature of β -Li2IrO3 increases with the slope of 0.9 K /GPa upon initial compression, but the reduction in the polarization field Hc reflects a growing instability of the incommensurate order. At 1.4 GPa, the ordered state breaks down upon a first-order transition, giving way to a new ground state marked by the coexistence of dynamically correlated and frozen spins. This partial freezing in the absence of any conspicuous structural defects may indicate the classical nature of the resulting pressure-induced spin liquid, an observation paralleled to the increase in the nearest-neighbor off-diagonal exchange Γ under pressure.

Hyperpolarized nanodiamond with long spin-relaxation times

NASA Astrophysics Data System (ADS)

Rej, Ewa; Gaebel, Torsten; Boele, Thomas; Waddington, David E. J.; Reilly, David J.

2015-10-01

The use of hyperpolarized agents in magnetic resonance, such as 13C-labelled compounds, enables powerful new imaging and detection modalities that stem from a 10,000-fold boost in signal. A major challenge for the future of the hyperpolarization technique is the inherently short spin-relaxation times, typically <60 s for 13C liquid-state compounds, which limit the time that the signal remains boosted. Here we demonstrate that 1.1% natural abundance 13C spins in synthetic nanodiamond can be hyperpolarized at cryogenic and room temperature without the use of free radicals, and, owing to their solid-state environment, exhibit relaxation times exceeding 1 h. Combined with the already established applications of nanodiamonds in the life sciences as inexpensive fluorescent markers and non-cytotoxic substrates for gene and drug delivery, these results extend the theranostic capabilities of nanoscale diamonds into the domain of hyperpolarized magnetic resonance.

Frustration by design

DOE PAGES

Gilbert, Ian; Nisoli, Cristiano; Schiffer, Peter

2016-07-01

Geometrical frustration is a condition that occurs when a material’s lattice geometry precludes minimizing the energy of all the interactions among pairs of neighbors simultaneously. Moreover, the simplest example is three antiferromagnetically coupled Ising spins, pointing up or down, on the corners of an equilateral triangle: It is also impossible to arrange the spins so that each pair is antiparallel. In more complex magnetic lattices, the frustrated state can arise from the combination of lattice geometry and the strength and sign of the interactions among the magnetic dipole moments.1 (See the article by Roderich Moessner and Art Ramirez, Physics Today,more » February 2006, page 24.) A wide variety of exotic and collective phenomena sometimes arises from the competing interactions. One prime example is spin liquids, materials in which the local atomic moments fluctuate down to the lowest accessible temperatures and never settle into a static ground-state configuration.« less

Long-lived states to sustain SABRE hyperpolarised magnetisation.

PubMed

Roy, Soumya S; Rayner, Peter J; Norcott, Philip; Green, Gary G R; Duckett, Simon B

2016-09-14

The applicability of the magnetic resonance (MR) technique in the liquid phase is limited by poor sensitivity and short nuclear spin coherence times which are insufficient for many potential applications. Here we illustrate how it is possible to address both of these issues simultaneously by harnessing long-lived hyperpolarised spin states that are formed by adapting the Signal Amplification by Reversible Exchange (SABRE) technique. We achieve more than 4% net 1 H-polarisation in a long-lived form that remains detectable for over ninety seconds by reference to proton pairs in the biologically important molecule nicotinamide and a pyrazine derivative whose in vivo imaging will offer a new route to probe disease in the future.

Space Group Symmetry Fractionalization in a Chiral Kagome Heisenberg Antiferromagnet.

PubMed

Zaletel, Michael P; Zhu, Zhenyue; Lu, Yuan-Ming; Vishwanath, Ashvin; White, Steven R

2016-05-13

The anyonic excitations of a spin liquid can feature fractional quantum numbers under space group symmetries. Detecting these fractional quantum numbers, which are analogs of the fractional charge of Laughlin quasiparticles, may prove easier than the direct observation of anyonic braiding and statistics. Motivated by the recent numerical discovery of spin-liquid phases in the kagome Heisenberg antiferromagnet, we theoretically predict the pattern of space group symmetry fractionalization in the kagome lattice SO(3)-symmetric chiral spin liquid. We provide a method to detect these fractional quantum numbers in finite-size numerics which is simple to implement in the density matrix renormalization group. Applying these developments to the chiral spin liquid phase of a kagome Heisenberg model, we find perfect agreement between our theoretical prediction and numerical observations.

Topological Spin Glass in Diluted Spin Ice

NASA Astrophysics Data System (ADS)

Sen, Arnab; Moessner, R.

2015-06-01

It is a salient experimental fact that a large fraction of candidate spin liquid materials freeze as the temperature is lowered. The question naturally arises whether such freezing is intrinsic to the spin liquid ("disorder-free glassiness") or extrinsic, in the sense that a topological phase simply coexists with standard freezing of impurities. Here, we demonstrate a surprising third alternative, namely, that freezing and topological liquidity are inseparably linked. The topological phase reacts to the introduction of disorder by generating degrees of freedom of a new type (along with interactions between them), which in turn undergo a freezing transition while the topological phase supporting them remains intact.

Topological Spin Glass in Diluted Spin Ice.

PubMed

Sen, Arnab; Moessner, R

2015-06-19

It is a salient experimental fact that a large fraction of candidate spin liquid materials freeze as the temperature is lowered. The question naturally arises whether such freezing is intrinsic to the spin liquid ("disorder-free glassiness") or extrinsic, in the sense that a topological phase simply coexists with standard freezing of impurities. Here, we demonstrate a surprising third alternative, namely, that freezing and topological liquidity are inseparably linked. The topological phase reacts to the introduction of disorder by generating degrees of freedom of a new type (along with interactions between them), which in turn undergo a freezing transition while the topological phase supporting them remains intact.

Electron Tunneling in Lithium Ammonia Solutions Probed by Frequency-Dependent Electron-Spin Relaxation Studies

PubMed Central

Maeda, Kiminori; Lodge, Matthew T.J.; Harmer, Jeffrey; Freed, Jack H.; Edwards, Peter P.

2012-01-01

Electron transfer or quantum tunneling dynamics for excess or solvated electrons in dilute lithium-ammonia solutions have been studied by pulse electron paramagnetic resonance (EPR) spectroscopy at both X- (9.7 GHz) and W-band (94 GHz) frequencies. The electron spin-lattice (T1) and spin-spin (T2) relaxation data indicate an extremely fast transfer or quantum tunneling rate of the solvated electron in these solutions which serves to modulate the hyperfine (Fermi-contact) interaction with nitrogen nuclei in the solvation shells of ammonia molecules surrounding the localized, solvated electron. The donor and acceptor states of the solvated electron in these solutions are the initial and final electron solvation sites found before, and after, the transfer or tunneling process. To interpret and model our electron spin relaxation data from the two observation EPR frequencies requires a consideration of a multi-exponential correlation function. The electron transfer or tunneling process that we monitor through the correlation time of the nitrogen Fermi-contact interaction has a time scale of (1–10)×10−12 s over a temperature range 230–290K in our most dilute solution of lithium in ammonia. Two types of electron-solvent interaction mechanisms are proposed to account for our experimental findings. The dominant electron spin relaxation mechanism results from an electron tunneling process characterized by a variable donor-acceptor distance or range (consistent with such a rapidly fluctuating liquid structure) in which the solvent shell that ultimately accepts the transferring electron is formed from random, thermal fluctuations of the liquid structure in, and around, a natural hole or Bjerrum-like defect vacancy in the liquid. Following transfer and capture of the tunneling electron, further solvent-cage relaxation with a timescale of ca. 10−13 s results in a minor contribution to the electron spin relaxation times. This investigation illustrates the great potential of multi-frequency EPR measurements to interrogate the microscopic nature and dynamics of ultra fast electron transfer or quantum-tunneling processes in liquids. Our results also impact on the universal issue of the role of a host solvent (or host matrix, e.g. a semiconductor) in mediating long-range electron transfer processes and we discuss the implications of our results with a range of other materials and systems exhibiting the phenomenon of electron transfer. PMID:22568866

Unconventional phases in quantum spin and pseudospin systems in two dimensional and three dimensional lattices

NASA Astrophysics Data System (ADS)

Xu, Cenke

Several examples of quantum spin systems and pseudo spin systems have been studied, and unconventional states of matters and phase transitions have been realized in all these systems under consideration. In the p +/- ip superconductor Josephson lattice and the p--band cold atomic system trapped in optical lattices, novel phases which behave similarly to 1+1 dimensional systems are realized, despite the fact that the real physical systems are in two or three dimensional spaces. For instance, by employing a spin-wave analysis together with a new duality transformation, we establish the existence and stability of a novel gapless "critical phase", which we refer to as a "bond algebraic liquid". This novel critical phase is analogous to the 1+1 dimensional algebraic boson liquid phase. The reason for the novel physics is that there is a quasilocal gauge symmetry in the effective low energy Hamiltonian. In a spin-1 system on the kagome lattice, and a hard-core boson system on the honeycomb lattice, the low energy physics is controlled by two components of compact U(1) gauge symmetries that emerge at low energy. Making use of the confinement nature of the 2+1 dimensional compact gauge theories and the powerful duality between gauge theories and height field theories, the crystalline phase diagrams are studied for both systems, and the transitions to other phases are also considered. These phase diagrams might be accessible in strongly correlated materials, or atomic systems in optical lattices. A novel quantum ground state of matter is realized in a bosonic model on three dimensional fcc lattice with emergent low energy excitations. The novel phase obtained is a stable gapless boson liquid phase, with algebraic boson density correlations. The stability of this phase is protected against the instanton effect and superfluidity by self-duality and large gauge symmetries on both sides of the duality. The gapless collective excitations of this phase closely resemble the graviton, although they have a soft w ˜ k2 dispersion relation. The dynamics of this novel phase is described by a new set of Maxwell's equations.

NMR proton spin dynamics in thermotropic liquid crystals subject to multipulse excitation.

PubMed

Acosta, R H; Zamar, R C; Monti, G A

2003-10-01

Previous experiments of NMR spin-lattice relaxation times as a function of the Larmor frequency, as measured with the field-cycling technique (FC), were shown to be very useful to disentangle the various molecular motions, both local and collective, that dominate the relaxation in different time scales in liquid crystals. However, there are many examples where the known theoretical models that represent the molecular relaxation mechanisms cannot be fitted to the experimental trend in the region of low fields, making it difficult to obtain reliable values for the spectral densities involved, especially for the cooperative motions which dominate at low frequencies. In some cases, these anomalies are loosely ascribed to "local-field" effects but, to our knowledge, there is not a detailed explanation about the origin of these problems nor the range of frequencies where they should be expected. With the aim of isolating the dipolar effects from the influence of molecular dynamics, and taking into account the previous results in solids, in this work we investigate the response of the proton spin system of thermotropic liquid crystals 4-pentyl-4'-cyanobiphenyl (5CB) and 4-octyl-4'-cyanobiphenyl (8CB) in nematic and smectic A phases, due to the NMR multipulse sequence 90( composite function )y-(tau-thetax-tau)N. The nuclear magnetization presents an early transient period characterized by strong oscillations, after which a quasistationary state is attained. Subsequently, this state relaxes towards internal equilibrium over a time much longer than the transverse relaxation time T2. As occurs in solids, the decay time of the quasistationary state T2e presents a minimum when the pulse width thetax and the offset of the radiofrequency are set to satisfy resonance conditions (spin-lock). When measured as a function of the pulse spacing tau in "on-resonance" experiments, T2e shows the behavior expected for cross relaxation between the effective Zeeman and dipolar reservoirs, in accordance with the thermodynamic theory previously developed for solids. Particularly, for values of tau comparable with T2, the relaxation rate follows a power law T2e proportional to tau(-2), in all the observed cases, for the resonance conditions thetax=pi/3 and equivalent frequency omegae=pi/3tau. When tau is similar to or greater than typical dipolar periods, the relaxation rate becomes constant and for tau much shorter than T2, the thermodynamic reservoirs get decoupled. These experiments confirm that the thermodynamic picture is valid also in liquid crystals and the cross relaxation between the reservoirs can be detected without interference with spin-lattice relaxation effects. Accordingly, this technique can be used to estimate the frequency range, where cross-relaxation effects can be expected when Zeeman and dipolar reservoirs are put in thermal contact with each other and with the lattice, as in FC experiments. In particular, the present results allow us to associate the anomalies observed in low-field spin-lattice relaxation with nonadiabatic energy exchange between the reservoirs.

Functional renormalization group approach to SU(N ) Heisenberg models: Real-space renormalization group at arbitrary N

NASA Astrophysics Data System (ADS)

Buessen, Finn Lasse; Roscher, Dietrich; Diehl, Sebastian; Trebst, Simon

2018-02-01

The pseudofermion functional renormalization group (pf-FRG) is one of the few numerical approaches that has been demonstrated to quantitatively determine the ordering tendencies of frustrated quantum magnets in two and three spatial dimensions. The approach, however, relies on a number of presumptions and approximations, in particular the choice of pseudofermion decomposition and the truncation of an infinite number of flow equations to a finite set. Here we generalize the pf-FRG approach to SU (N )-spin systems with arbitrary N and demonstrate that the scheme becomes exact in the large-N limit. Numerically solving the generalized real-space renormalization group equations for arbitrary N , we can make a stringent connection between the physically most significant case of SU(2) spins and more accessible SU (N ) models. In a case study of the square-lattice SU (N ) Heisenberg antiferromagnet, we explicitly demonstrate that the generalized pf-FRG approach is capable of identifying the instability indicating the transition into a staggered flux spin liquid ground state in these models for large, but finite, values of N . In a companion paper [Roscher et al., Phys. Rev. B 97, 064416 (2018), 10.1103/PhysRevB.97.064416] we formulate a momentum-space pf-FRG approach for SU (N ) spin models that allows us to explicitly study the large-N limit and access the low-temperature spin liquid phase.

Anisotropic breakdown of Fermi liquid quasiparticle excitations in overdoped La₂-xSrxCuO₄.

PubMed

Chang, J; Månsson, M; Pailhès, S; Claesson, T; Lipscombe, O J; Hayden, S M; Patthey, L; Tjernberg, O; Mesot, J

2013-01-01

High-temperature superconductivity emerges from an un-conventional metallic state. This has stimulated strong efforts to understand exactly how Fermi liquids breakdown and evolve into an un-conventional metal. A fundamental question is how Fermi liquid quasiparticle excitations break down in momentum space. Here we show, using angle-resolved photoemission spectroscopy, that the Fermi liquid quasiparticle excitations of the overdoped superconducting cuprate La1.77Sr0.23CuO4 is highly anisotropic in momentum space. The quasiparticle scattering and residue behave differently along the Fermi surface and hence the Kadowaki-Wood's relation is not obeyed. This kind of Fermi liquid breakdown may apply to a wide range of strongly correlated metal systems where spin fluctuations are present.

Effects of nuclear spins on the transport properties of the edge of two-dimensional topological insulators

NASA Astrophysics Data System (ADS)

Hsu, Chen-Hsuan; Stano, Peter; Klinovaja, Jelena; Loss, Daniel

2018-03-01

The electrons in the edge channels of two-dimensional topological insulators can be described as a helical Tomonaga-Luttinger liquid. They couple to nuclear spins embedded in the host materials through the hyperfine interaction, and are therefore subject to elastic spin-flip backscattering on the nuclear spins. We investigate the nuclear-spin-induced edge resistance due to such backscattering by performing a renormalization-group analysis. Remarkably, the effect of this backscattering mechanism is stronger in a helical edge than in nonhelical channels, which are believed to be present in the trivial regime of InAs/GaSb quantum wells. In a system with sufficiently long edges, the disordered nuclear spins lead to an edge resistance which grows exponentially upon lowering the temperature. On the other hand, electrons from the edge states mediate an anisotropic Ruderman-Kittel-Kasuya-Yosida nuclear spin-spin interaction, which induces a spiral nuclear spin order below the transition temperature. We discuss the features of the spiral order, as well as its experimental signatures. In the ordered phase, we identify two backscattering mechanisms, due to charge impurities and magnons. The backscattering on charge impurities is allowed by the internally generated magnetic field, and leads to an Anderson-type localization of the edge states. The magnon-mediated backscattering results in a power-law resistance, which is suppressed at zero temperature. Overall, we find that in a sufficiently long edge the nuclear spins, whether ordered or not, suppress the edge conductance to zero as the temperature approaches zero.

Tunable Quantum Spin Liquidity in the 1 /6 th-Filled Breathing Kagome Lattice

NASA Astrophysics Data System (ADS)

Akbari-Sharbaf, A.; Sinclair, R.; Verrier, A.; Ziat, D.; Zhou, H. D.; Sun, X. F.; Quilliam, J. A.

2018-06-01

We present measurements on a series of materials, Li2 In1 -xScx Mo3 O8 , that can be described as a 1 /6 th-filled breathing kagome lattice. Substituting Sc for In generates chemical pressure which alters the breathing parameter nonmonotonically. Muon spin rotation experiments show that this chemical pressure tunes the system from antiferromagnetic long range order to a quantum spin liquid phase. A strong correlation with the breathing parameter implies that it is the dominant parameter controlling the level of magnetic frustration, with increased kagome symmetry generating the quantum spin liquid phase. Magnetic susceptibility measurements suggest that this is related to distinct types of charge order induced by changes in lattice symmetry, in line with the theory of Chen et al. [Phys. Rev. B 93, 245134 (2016), 10.1103/PhysRevB.93.245134]. The specific heat for samples at intermediate Sc concentration, which have the minimum breathing parameter, show consistency with the predicted U (1 ) quantum spin liquid.

A spin filter transistor made of topological Weyl semimetal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shi, Zhangsheng; Wang, Maoji; Wu, Jiansheng, E-mail: wujs@sustc.edu.cn

2015-09-07

Topological boundary states (TBSs) in Weyl semimetal (WSM) thin film can induce tunneling. Such TBSs are spin polarized inducing spin-polarized current, which can be used to build a spin-filter transistor (SFT) in spintronics. The WSM thin film can be viewed as a series of decoupled quantum anomalous Hall insulator (QAHI) wires connected in parallel, so compared with the proposed SFT made of QAHI nanowire, this SFT has a broader working energy region and easier to be manipulated. And within a narrow region outside this energy domain, the 2D WSM is with very low conductance, so it makes a good on/offmore » switch device with controllable chemical potential induced by liquid ion gate. We also construct a loop device made of 2D WSM with inserted controllable flux to control the polarized current.« less

Topological phase in a two-dimensional metallic heavy-fermion system

NASA Astrophysics Data System (ADS)

Yoshida, Tsuneya; Peters, Robert; Fujimoto, Satoshi; Kawakami, Norio

2013-04-01

We report on a topological insulating state in a heavy-fermion system away from half filling, which is hidden within a ferromagnetic metallic phase. In this phase, the cooperation of the RKKY interaction and the Kondo effect, together with the spin-orbit coupling, induces a spin-selective gap, bringing about topologically nontrivial properties. This topological phase is robust against a change in the chemical potential in a much wider range than the gap size. We analyze these remarkable properties by using dynamical mean field theory and the numerical renormalization group. Its topological properties support a gapless chiral edge mode, which exhibits a non-Tomonaga-Luttinger liquid behavior due to the coupling with bulk ferromagnetic spin fluctuations. We also propose that the effects of the spin fluctuations on the edge mode can be detected via the NMR relaxation time measurement.

Ultra-robust high-field magnetization plateau and supersolidity in bond-frustrated MnCr2S4

PubMed Central

Tsurkan, Vladimir; Zherlitsyn, Sergei; Prodan, Lilian; Felea, Viorel; Cong, Pham Thanh; Skourski, Yurii; Wang, Zhe; Deisenhofer, Joachim; von Nidda, Hans-Albrecht Krug; Wosnitza, Joahim; Loidl, Alois

2017-01-01

Frustrated magnets provide a promising avenue for realizing exotic quantum states of matter, such as spin liquids and spin ice or complex spin molecules. Under an external magnetic field, frustrated magnets can exhibit fractional magnetization plateaus related to definite spin patterns stabilized by field-induced lattice distortions. Magnetization and ultrasound experiments in MnCr2S4 up to 60 T reveal two fascinating features: (i) an extremely robust magnetization plateau with an unusual spin structure and (ii) two intermediate phases, indicating possible realizations of supersolid phases. The magnetization plateau characterizes fully polarized chromium moments, without any contributions from manganese spins. At 40 T, the middle of the plateau, a regime evolves, where sound waves propagate almost without dissipation. The external magnetic field exactly compensates the Cr–Mn exchange field and decouples Mn and Cr sublattices. In analogy to predictions of quantum lattice-gas models, the changes of the spin order of the manganese ions at the phase boundaries of the magnetization plateau are interpreted as transitions to supersolid phases. PMID:28345038

Spin re-orientation in heavy fermion system α - YbAl1 - x FexB4

NASA Astrophysics Data System (ADS)

Wu, Shan; Broholm, C.; Kuga, K.; Suzuki, Shintaro; Nakatsuji, S.; Mourigal, M.; Stone, M.; Tian, Wei; Qiu, Y.; Rodriguez-Rivera, Jose

Non centro-symmetric α - YbAlB4 has a heavy Fermi liquid ground state and shares many characteristics with centro-symmetric β - YbAlB4 . Both isomorphs display intermediate valence, associated with a fluctuation scale of T0 = 200 K and a Kondo lattice scale of T* = 8 K. Unlike β - YbAlB4 , α - YbAlB4 is at the boundary of a transition from a Fermi liquid metallic state to an antiferromagnetic (AFM) insulating state, driven by Fe substitution of Al. Magnetization and specific heat measurements reveal two different antiferromagnetic phases with TN = 9 K and TN = 2 K for Fe concentration above and below x =0.07. We report single crystal neutron scattering experiments on Fe doped YbAlB4 with x =0.035 and x =0.125. While the ordering wave vector is identical, k -> = (1 , 0 , 0) , the spin orientation switches from c to a with increasing Fe concentration. This suggests different anisotropic hybridization between 4f and conduction electrons that we confirmed by determining the crystal field levels. Supported by DOE, BES through DE-FG02-08ER46544.

Exact results for the star lattice chiral spin liquid

NASA Astrophysics Data System (ADS)

Kells, G.; Mehta, D.; Slingerland, J. K.; Vala, J.

2010-03-01

We examine the star lattice Kitaev model whose ground state is a chiral spin liquid. We fermionize the model such that the fermionic vacua are toric-code states on an effective Kagome lattice. This implies that the Abelian phase of the system is inherited from the fermionic vacua and that time-reversal symmetry is spontaneously broken at the level of the vacuum. In terms of these fermions we derive the Bloch-matrix Hamiltonians for the vortex-free sector and its time-reversed counterpart and illuminate the relationships between the sectors. The phase diagram for the model is shown to be a sphere in the space of coupling parameters around the triangles of the lattices. The Abelian phase lies inside the sphere and the critical boundary between topologically distinct Abelian and non-Abelian phases lies on the surface. Outside the sphere the system is generically gapped except in the planes where the coupling parameters between the vertices on triangles are zero. These cases correspond to bipartite lattice structures and the dispersion relations are similar to that of the original Kitaev honeycomb model. In a further analysis we demonstrate the threefold non-Abelian ground-state degeneracy on a torus by explicit calculation.

Tunnel transport and interlayer excitons in bilayer fractional quantum Hall systems

NASA Astrophysics Data System (ADS)

Zhang, Yuhe; Jain, J. K.; Eisenstein, J. P.

2017-05-01

In a bilayer system consisting of a composite-fermion (CF) Fermi sea in each layer, the tunnel current is exponentially suppressed at zero bias, followed by a strong peak at a finite-bias voltage Vmax. This behavior, which is qualitatively different from that observed for the electron Fermi sea, provides fundamental insight into the strongly correlated non-Fermi-liquid nature of the CF Fermi sea and, in particular, offers a window into the short-distance high-energy physics of this highly nontrivial state. We identify the exciton responsible for the peak current and provide a quantitative account of the value of Vmax. The excitonic attraction is shown to be quantitatively significant, and its variation accounts for the increase of Vmax with the application of an in-plane magnetic field. We also estimate the critical Zeeman energy where transition occurs from a fully spin-polarized composite-fermion Fermi sea to a partially spin-polarized one, carefully incorporating corrections due to finite width and Landau level mixing, and find it to be in satisfactory agreement with the Zeeman energy where a qualitative change has been observed for the onset bias voltage [J. P. Eisenstein et al., Phys. Rev. B 94, 125409 (2016), 10.1103/PhysRevB.94.125409]. For fractional quantum Hall states, we predict a substantial discontinuous jump in Vmax when the system undergoes a transition from a fully spin-polarized state to a spin singlet or a partially spin-polarized state.

Resonance-inclined optical nuclear spin polarization of liquids in diamond structures

NASA Astrophysics Data System (ADS)

Chen, Q.; Schwarz, I.; Jelezko, F.; Retzker, A.; Plenio, M. B.

2016-02-01

Dynamic nuclear polarization (DNP) of molecules in a solution at room temperature has the potential to revolutionize nuclear magnetic resonance spectroscopy and imaging. The prevalent methods for achieving DNP in solutions are typically most effective in the regime of small interaction correlation times between the electron and nuclear spins, limiting the size of accessible molecules. To solve this limitation, we design a mechanism for DNP in the liquid phase that is applicable for large interaction correlation times. Importantly, while this mechanism makes use of a resonance condition similar to solid-state DNP, the polarization transfer is robust to a relatively large detuning from the resonance due to molecular motion. We combine this scheme with optically polarized nitrogen-vacancy (NV) center spins in nanodiamonds to design a setup that employs optical pumping and is therefore not limited by room temperature electron thermal polarization. We illustrate numerically the effectiveness of the model in a flow cell containing nanodiamonds immobilized in a hydrogel, polarizing flowing water molecules 4700-fold above thermal polarization in a magnetic field of 0.35 T, in volumes detectable by current NMR scanners.

Quantum spin ices and magnetic states from dipolar-octupolar doublets on the pyrochlore lattice

NASA Astrophysics Data System (ADS)

Chen, Gang

We consider a class of electron systems in which dipolar-octupolar Kramers doublets arise on the pyrochlore lattice. In the localized limit, the Kramers doublets are described by the effective spin 1/2 pseudospins. The most general nearest-neighbor exchange model between these pseudospins is the XYZ model. In additional to dipolar ordered and octupolar ordered magnetic states, we show that this XYZ model exhibits two distinct quantum spin ice (QSI) phases, that we dub dipolar QSI and octupolar QSI. These two QSIs are distinct symmetry enriched U(1) quantum spin liquids, enriched by the lattice symmetry. Moreover, the XYZ model is absent from the notorious sign problem for a quantum Monte Carlo simulation in a large parameter space. We discuss the potential relevance to real material systems such as Dy2Ti2O7, Nd2Zr2O7, Nd2Hf2O7, Nd2Ir2O7, Nd2Sn2O7 and Ce2Sn2O7. chggst@gmail.com, Refs: Y-P Huang, G Chen, M Hermele, Phys. Rev. Lett. 112, 167203 (2014).

Direct experimental observation of the molecular J eff = 3/2 ground state in the lacunar spinel GaTa4Se8.

PubMed

Jeong, Min Yong; Chang, Seo Hyoung; Kim, Beom Hyun; Sim, Jae-Hoon; Said, Ayman; Casa, Diego; Gog, Thomas; Janod, Etienne; Cario, Laurent; Yunoki, Seiji; Han, Myung Joon; Kim, Jungho

2017-10-04

Strong spin-orbit coupling lifts the degeneracy of t 2g orbitals in 5d transition-metal systems, leaving a Kramers doublet and quartet with effective angular momentum of J eff  = 1/2 and 3/2, respectively. These spin-orbit entangled states can host exotic quantum phases such as topological Mott state, unconventional superconductivity, and quantum spin liquid. The lacunar spinel GaTa 4 Se 8 was theoretically predicted to form the molecular J eff  = 3/2 ground state. Experimental verification of its existence is an important first step to exploring the consequences of the J eff  = 3/2 state. Here, we report direct experimental evidence of the J eff  = 3/2 state in GaTa 4 Se 8 by means of excitation spectra of resonant inelastic X-ray scattering at the Ta L 3 and L 2 edges. We find that the excitations involving the J eff  = 1/2 molecular orbital are absent only at the Ta L 2 edge, manifesting the realization of the molecular J eff  = 3/2 ground state in GaTa 4 Se 8 .The strong interaction between electron spin and orbital degrees of freedom in 5d oxides can lead to exotic electronic ground states. Here the authors use resonant inelastic X-ray scattering to demonstrate that the theoretically proposed J eff  = 3/2 state is realised in GaTa 4 Se 8 .

Spin-orbit optomechanics of optically levitated chiral Bragg microspheres

NASA Astrophysics Data System (ADS)

Tkachenko, Georgiy; Rafayelyan, Mushegh; Brasselet, Etienne

2017-05-01

We explore the spin-orbit nature of the optical torque exerted on chiral liquid-crystal microspheres exhibiting circular Bragg reflection. Experimental investigation relies on the direct optomechanical observation of spinning liquid-crystal droplets immersed in water and held in a circularly polarized laser levitator. More generally, we anticipate that the total angular momentum transfer per photon may depart from the commonly assumed spin-only ±2 ℏ contribution, when the topological features of the illuminated microsphere are taken into account.

Non-Fermi-liquid and topological states with strong spin-orbit coupling.

PubMed

Moon, Eun-Gook; Xu, Cenke; Kim, Yong Baek; Balents, Leon

2013-11-15

We argue that a class of strongly spin-orbit-coupled materials, including some pyrochlore iridates and the inverted band gap semiconductor HgTe, may be described by a minimal model consisting of the Luttinger Hamiltonian supplemented by Coulomb interactions, a problem studied by Abrikosov and collaborators. It contains twofold degenerate conduction and valence bands touching quadratically at the zone center. Using modern renormalization group methods, we update and extend Abrikosov's classic work and show that interactions induce a quantum critical non-Fermi-liquid phase, stable provided time-reversal and cubic symmetries are maintained. We determine the universal power-law exponents describing various observables in this Luttinger-Abrikosov-Beneslavskii state, which include conductivity, specific heat, nonlinear susceptibility, and the magnetic Gruneisen number. Furthermore, we determine the phase diagram in the presence of cubic and/or time-reversal symmetry breaking perturbations, which includes a topological insulator and Weyl semimetal phases. Many of these phases possess an extraordinarily large anomalous Hall effect, with the Hall conductivity scaling sublinearly with magnetization σ(xy)∼M0.51.

NMR signal analysis to attribute the components to the solid/liquid phases present in mixes and ice creams.

PubMed

Mariette, François; Lucas, Tiphaine

2005-03-09

The NMR relaxation signals from complex products such as ice cream are hard to interpret because of the multiexponential behavior of the relaxation signal and the difficulty of attributing the NMR relaxation components to specific molecule fractions. An attribution of the NMR relaxation parameters is proposed, however, based on an approach that combines quantitative analysis of the spin-spin and spin-lattice relaxation times and the signal intensities with characterization of the ice cream components. We have been able to show that NMR can be used to describe the crystallized and liquid phases separately. The first component of the spin-spin and spin-lattice relaxation describes the behavior of the protons of the crystallized fat in the mix. The amount of fat crystals can then be estimated. In the case of ice cream, only the spin-lattice relaxation signal from the crystallized fraction is relevant. However, it enables the ice protons and the protons of the crystallized fat to be distinguished. The spin-lattice relaxation time can be used to describe the mobility of the protons in the different crystallized phases and also to quantify the amount of ice crystals and fat crystals in the ice cream. The NMR relaxation of the liquid phase of the mix has a biexponential behavior. A first component is attributable to the liquid fraction of the fat and to the sugars, while a second component is attributable to the aqueous phase. Overall, the study shows that despite the complexity of the NMR signal from ice cream, a number of relevant parameters can be extracted to study the influence of the formulation and of the process stages on the ice fraction, the crystallized fat fraction, and the liquid aqueous fraction.

Correlation between non-Fermi-liquid behavior and superconductivity in (Ca, La)(Fe,Co)As2 iron arsenides: A high-pressure study

NASA Astrophysics Data System (ADS)

Zhou, W.; Ke, F.; Xu, Xiaofeng; Sankar, R.; Xing, X.; Xu, C. Q.; Jiang, X. F.; Qian, B.; Zhou, N.; Zhang, Y.; Xu, M.; Li, B.; Chen, B.; Shi, Z. X.

2017-11-01

Non-Fermi-liquid (NFL) phenomena associated with correlation effects have been widely observed in the phase diagrams of unconventional superconducting families. Exploration of the correlation between the normal state NFL, regardless of its microscopic origins, and the superconductivity has been argued as a key to unveiling the mystery of the high-Tc pairing mechanism. Here we systematically investigate the pressure-dependent in-plane resistivity (ρ ) and Hall coefficient (RH) of a high-quality 112-type Fe-based superconductor Ca1 -xLaxFe1 -yCoyAs2 (x =0.2 ,y =0.02 ). With increasing pressure, the normal-state resistivity of the studied sample exhibits a pronounced crossover from non-Fermi-liquid to Fermi-liquid behaviors. Accompanied with this crossover, Tc is gradually suppressed. In parallel, the extremum in the Hall coefficient RH(T ) curve, possibly due to anisotropic scattering induced by spin fluctuations, is also gradually suppressed. The symbiosis of NFL and superconductivity implies that these two phenomena are intimately related. Further study on the pressure-dependent upper critical field reveals that the two-band effects are also gradually weakened with increasing pressure and reduced to the one-band Werthamer-Helfand-Hohenberg limit in the low-Tc regime. Overall, our paper supports the picture that NFL, multigap, and extreme RH(T ) are all of the same magnetic origin, i.e., the spin fluctuations in the 112 iron arsenide superconductors.

Behavior of Spinning Space Vehicles with Onboard Liquids, 2nd Edition, Technical Report B8030

NASA Technical Reports Server (NTRS)

Hubert, Carl

2008-01-01

Although the fundamental principles of spin stabilization are well established, uncertainty regarding the potential for rapid nutation growth caused by onboard liquids is a continuing concern. NASA and other organizations regularly encounter the issue of rapid nutation growth due to energy dissipation by liquids on spinning vehicles. Of concern is the stability of spinning upper stages and of spacecraft that spin for part or all of their missions. Several missions have required last-minute hardware or operational changes to deal with rapid nutation divergences that were identified late in the program. In some instances, major schedule slips were barely averted. In at least two cases, it was determined that a spinning upper stage was not a viable option. Historically, the "slosh" issue has been addressed by each space vehicle project individually, if it has been addressed at all. Due to budgetary and programmatic constraints, individual projects are unable to address the problem globally. Hence, there has been little effort to collect available test and flight data and use that data to make a coherent, unified picture of the "slosh" effect and how to deal with it. To some extent, each project has had to "reinvent the wheel", which can be both costly and risky. This study is a step toward correcting the situation. Specifically, the goal was to identify and collect available flight and test data for spinning vehicles with onboard liquid propellants. A total of 149 flight data points and 1,692 test points were collected as part of this study. This data was analyzed, correlated, and is presented here in a normalized form. In most cases, the normalization involves a dimensionless nutation time constant that can be used to predict performance of other vehicles with the same type of tank. For some configurations, it was also possible to identify conditions that can lead to resonance between nutational motion and liquid modes. Gaps in the knowledge base are identified and approaches to filling those gaps are outlined. The data presented here has two different but related uses. First, it can be applied directly to current and future spacecraft programs. Second, it can provide truth models for testing analytical techniques. Experience has shown that purely analytical models of the liquid "slosh" effect on spinning vehicles are unreliable unless they are validated against flight or test data. To the author's knowledge, this report contains the most extensive and varied data set available. As such, it should be a good resource for anyone seeking to develop and validate improved analytical techniques. All of the original digital data sets have been archived on disk, with copies provided to NASA/KSC. With some restrictions, many of these data sets can be made available to researchers within the United States. Whenever possible, spacecraft are identified by name in this report. However, several organizations provided access to data with the explicit proviso that their programs not be identified and that parameters be presented only in normalized form. These constraints have been respected.

The novel metallic states of the cuprates: Topological Fermi liquids and strange metals

NASA Astrophysics Data System (ADS)

Sachdev, Subir; Chowdhury, Debanjan

2016-12-01

We review ideas on the nature of the metallic states of the hole-doped cuprate high temperature superconductors, with an emphasis on the connections between the Luttinger theorem for the size of the Fermi surface, topological quantum field theories (TQFTs), and critical theories involving changes in the size of the Fermi surface. We begin with the derivation of the Luttinger theorem for a Fermi liquid, using momentum balance during a process of flux insertion in a lattice electronic model with toroidal boundary conditions. We then review the TQFT of the ℤ spin liquid, and demonstrate its compatibility with the toroidal momentum balance argument. This discussion leads naturally to a simple construction of "topological" Fermi liquid states: the fractionalized Fermi liquid (FL*) and the algebraic charge liquid (ACL). We present arguments for a description of the pseudogap metal of the cuprates using ℤ-FL* or ℤ-ACL states with Ising-nematic order. These pseudogap metal states are also described as Higgs phases of a SU(2) gauge theory. The Higgs field represents local antiferromagnetism, but the Higgs-condensed phase does not have long-range antiferromagnetic order: the magnitude of the Higgs field determines the pseudogap, the reconstruction of the Fermi surface, and the Ising-nematic order. Finally, we discuss the route to the large Fermi surface Fermi liquid via the critical point where the Higgs condensate and Ising nematic order vanish, and the application of Higgs criticality to the strange metal.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Veiga, L. S. I.; Etter, M.; Glazyrin, K.

Here, we explore the response of Ir 5d orbitals to pressure in β-Li 2IrO 3, a hyperhoneycomb iridate in proximity to a Kitaev quantum spin-liquid (QSL) ground state. X-ray absorption spectroscopy reveals a reconstruction of the electronic ground state below 2 GPa, the same pressure range where x-ray magnetic circular dichroism shows an apparent collapse of magnetic order. The electronic reconstruction, which manifests a reduction in the effective spin-orbit interaction in 5d orbitals, pushes β-Li 2IrO 3 further away from the pure J eff = 1/2 limit. Although lattice symmetry is preserved across the electronic transition, x-ray diffraction shows amore » highly anisotropic compression of the hyperhoneycomb lattice which affects the balance of bond-directional Ir-Ir exchange interactions driven by spin-orbit coupling at Ir sites. An enhancement of symmetric anisotropic exchange over Kitaev and Heisenberg exchange interactions seen in theoretical calculations that use precisely this anisotropic Ir-Ir bond compression provides one possible route to the realization of a QSL state in this hyperhoneycomb iridate at high pressures.« less

Magnetic order in a frustrated two-dimensional atom lattice at a semiconductor surface.

PubMed

Li, Gang; Höpfner, Philipp; Schäfer, Jörg; Blumenstein, Christian; Meyer, Sebastian; Bostwick, Aaron; Rotenberg, Eli; Claessen, Ralph; Hanke, Werner

2013-01-01

Two-dimensional electron systems, as exploited for device applications, can lose their conducting properties because of local Coulomb repulsion, leading to a Mott-insulating state. In triangular geometries, any concomitant antiferromagnetic spin ordering can be prevented by geometric frustration, spurring speculations about 'melted' phases, known as spin liquid. Here we show that for a realization of a triangular electron system by epitaxial atom adsorption on a semiconductor, such spin disorder, however, does not appear. Our study compares the electron excitation spectra obtained from theoretical simulations of the correlated electron lattice with data from high-resolution photoemission. We find that an unusual row-wise antiferromagnetic spin alignment occurs that is reflected in the photoemission spectra as characteristic 'shadow bands' induced by the spin pattern. The magnetic order in a frustrated lattice of otherwise non-magnetic components emerges from longer-range electron hopping between the atoms. This finding can offer new ways of controlling magnetism on surfaces.

Entanglement entropy and fidelity susceptibility in the one-dimensional spin-1 XXZ chains with alternating single-site anisotropy.

PubMed

Ren, Jie; Liu, Guang-Hua; You, Wen-Long

2015-03-18

We study the fidelity susceptibility in an antiferromagnetic spin-1 XXZ chain numerically. By using the density-matrix renormalization group method, the effects of the alternating single-site anisotropy D on fidelity susceptibility are investigated. Its relation with the quantum phase transition is analyzed. It is found that the quantum phase transition from the Haldane spin liquid to periodic Néel spin solid can be well characterized by the fidelity. Finite size scaling of fidelity susceptibility shows a power-law divergence at criticality, which indicates the quantum phase transition is of second order. The results are confirmed by the second derivative of the ground-state energy. We also study the relationship between the entanglement entropy, the Schmidt gap and quantum phase transitions. Conclusions drawn from these quantum information observables agree well with each other.

Quenched crystal-field disorder and magnetic liquid ground states in Tb 2 Sn 2 - x Ti x O 7 [Crystal field disorder in the quantum spin ice ground state of Tb2Sn2-xTixO7

DOE PAGES

Gaulin, B. D.; Kermarrec, E.; Dahlberg, M. L.; ...

2015-06-01

Solid-solutions of the "soft" quantum spin ice pyrochlore magnets Tb 2B 2O 7 with B=Ti and Sn display a novel magnetic ground state in the presence of strong B-site disorder, characterized by a low susceptibility and strong spin fluctuations to temperatures below 0.1 K. These materials have been studied using ac-susceptibility and muSR techniques to very low temperatures, and time-of-flight inelastic neutron scattering techniques to 1.5 K. Remarkably, neutron spectroscopy of the Tb 3+ crystal field levels appropriate to at high B-site mixing (0.5 < x < 1.5 in Tb 2Sn 2-xTi xO 7) reveal that the doublet ground andmore » first excited states present as continua in energy, while transitions to singlet excited states at higher energies simply interpolate between those of the end members of the solid solution. The resulting ground state suggests an extreme version of a random-anisotropy magnet, with many local moments and anisotropies, depending on the precise local configuration of the six B sites neighboring each magnetic Tb 3+ ion.« less

Nobel Lecture: Topological quantum matter*

NASA Astrophysics Data System (ADS)

Haldane, F. Duncan M.

2017-10-01

Nobel Lecture, presented December 8, 2016, Aula Magna, Stockholm University. I will describe the history and background of three discoveries cited in this Nobel Prize: The "TKNN" topological formula for the integer quantum Hall effect found by David Thouless and collaborators, the Chern insulator or quantum anomalous Hall effect, and its role in the later discovery of time-reversal-invariant topological insulators, and the unexpected topological spin-liquid state of the spin-1 quantum antiferromagnetic chain, which provided an initial example of topological quantum matter. I will summarize how these early beginnings have led to the exciting, and currently extremely active, field of "topological matter."

Chiral spin liquids at finite temperature in a three-dimensional Kitaev model

NASA Astrophysics Data System (ADS)

Kato, Yasuyuki; Kamiya, Yoshitomo; Nasu, Joji; Motome, Yukitoshi

2017-11-01

Chiral spin liquids (CSLs) in three dimensions and thermal phase transitions to paramagnet are studied by unbiased Monte Carlo simulations. For an extension of the Kitaev model to a three-dimensional tricoordinate network dubbed the hypernonagon lattice, we derive low-energy effective models in two different anisotropic limits. We show that the effective interactions between the emergent Z2 degrees of freedom called fluxes are unfrustrated in one limit, while highly frustrated in the other. In both cases, we find a first-order phase transition to the CSL, where both time-reversal and parity symmetries are spontaneously broken. In the frustrated case, however, the CSL state is highly exotic—the flux configuration is subextensively degenerate while showing a directional order with broken C3 rotational symmetry. Our results provide two contrasting archetypes of CSLs in three dimensions, both of which allow approximation-free simulation for investigating the thermodynamics.

Neutron scattering in the proximate quantum spin liquid α-RuCl3.

PubMed

Banerjee, Arnab; Yan, Jiaqiang; Knolle, Johannes; Bridges, Craig A; Stone, Matthew B; Lumsden, Mark D; Mandrus, David G; Tennant, David A; Moessner, Roderich; Nagler, Stephen E

2017-06-09

The Kitaev quantum spin liquid (KQSL) is an exotic emergent state of matter exhibiting Majorana fermion and gauge flux excitations. The magnetic insulator α-RuCl 3 is thought to realize a proximate KQSL. We used neutron scattering on single crystals of α-RuCl 3 to reconstruct dynamical correlations in energy-momentum space. We discovered highly unusual signals, including a column of scattering over a large energy interval around the Brillouin zone center, which is very stable with temperature. This finding is consistent with scattering from the Majorana excitations of a KQSL. Other, more delicate experimental features can be transparently associated with perturbations to an ideal model. Our results encourage further study of this prototypical material and may open a window into investigating emergent magnetic Majorana fermions in correlated materials. Copyright © 2017, American Association for the Advancement of Science.

Self-assembled ordered structures in thin films of HAT5 discotic liquid crystal.

PubMed

Morales, Piero; Lagerwall, Jan; Vacca, Paolo; Laschat, Sabine; Scalia, Giusy

2010-05-20

Thin films of the discotic liquid crystal hexapentyloxytriphenylene (HAT5), prepared from solution via casting or spin-coating, were investigated by atomic force microscopy and polarizing optical microscopy, revealing large-scale ordered structures substantially different from those typically observed in standard samples of the same material. Thin and very long fibrils of planar-aligned liquid crystal were found, possibly formed as a result of an intermediate lyotropic nematic state arising during the solvent evaporation process. Moreover, in sufficiently thin films the crystallization seems to be suppressed, extending the uniform order of the liquid crystal phase down to room temperature. This should be compared to the bulk situation, where the same material crystallizes into a polymorphic structure at 68 °C.

Ground-state phases of the spin-1 J1-J2 Heisenberg antiferromagnet on the honeycomb lattice

NASA Astrophysics Data System (ADS)

Li, P. H. Y.; Bishop, R. F.

2016-06-01

We study the zero-temperature quantum phase diagram of a spin-1 Heisenberg antiferromagnet on the honeycomb lattice with both nearest-neighbor exchange coupling J1>0 and frustrating next-nearest-neighbor coupling J2≡κ J1>0 , using the coupled cluster method implemented to high orders of approximation, and based on model states with different forms of classical magnetic order. For each we calculate directly in the bulk thermodynamic limit both ground-state low-energy parameters (including the energy per spin, magnetic order parameter, spin stiffness coefficient, and zero-field uniform transverse magnetic susceptibility) and their generalized susceptibilities to various forms of valence-bond crystalline (VBC) order, as well as the energy gap to the lowest-lying spin-triplet excitation. In the range 0 <κ <1 we find evidence for four distinct phases. Two of these are quasiclassical phases with antiferromagnetic long-range order, one with two-sublattice Néel order for κ <κc1=0.250(5 ) , and another with four-sublattice Néel-II order for κ >κc 2=0.340 (5 ) . Two different paramagnetic phases are found to exist in the intermediate region. Over the range κc1<κ<κci=0.305 (5 ) we find a gapless phase with no discernible magnetic order, which is a strong candidate for being a quantum spin liquid, while over the range κci<κ <κc 2 we find a gapped phase, which is most likely a lattice nematic with staggered dimer VBC order that breaks the lattice rotational symmetry.

Influence of 13C isotopic labeling location of 13C DNP of acetate using TEMPO free radical

NASA Astrophysics Data System (ADS)

Parish, Christopher; Niedbalski, Peter; Lumata, Lloyd

2015-03-01

Dynamic nuclear polarization (DNP) via the dissolution method enhances the liquid-state magnetic resonance (NMR or MRI) signals of insensitive nuclear spins by at least 10,000-fold. The basis for all these signal enhancements at room temperature is the polarization transfer from the electrons to nuclear spins at cryogenic temperature and high magnetic field. In this work, we have studied the influence of the location of 13C isotopic labeling on the DNP of sodium acetate at 3.35 T and 1.4 K using a wide ESR linewidth free radical 4-oxo-TEMPO. The carbonyl [1-13C]acetate spins produced a polarization level that is almost twice that of the methyl [2-13C]acetate spins. On the other hand, the polarization of the methyl 13C spins doubled to reach the level of [1-13C]acetate when the methyl group was deuterated. Meanwhile, the solid-state nuclear relaxation of these samples are the same and do not correlate with the polarization levels. These behavior implies that the nuclear relaxation for these samples is dominated by the contribution from the free radicals and the polarization levels can be explained by a thermodynamic picture of DNP.

Interaction modifiers in artificial spin ices

DOE PAGES

Ostman, Erik; Stopfel, Henry; Chioar, Ioan -Augustin; ...

2018-02-12

The modification of geometry and interactions in two-dimensional magnetic nanosystems has enabled a range of studies addressing the magnetic order, collective low-energy dynamics and emergent magnetic properties in, for example, artificial spin-ice structures. The common denominator of all these investigations is the use of Ising-like mesospins as building blocks, in the form of elongated magnetic islands. Here, we introduce a new approach: single interaction modifiers, using slave mesospins in the form of discs, within which the mesospin is free to rotate in the disc plane1. We show that by placing these on the vertices of square artificial spin-ice arrays andmore » varying their diameter, it is possible to tailor the strength and the ratio of the interaction energies. We demonstrate the existence of degenerate ice-rule-obeying states in square artificial spin-ice structures, enabling the exploration of thermal dynamics in a spin-liquid manifold. Furthermore, we even observe the emergence of flux lattices on larger length scales, when the energy landscape of the vertices is reversed. In conclusion, the work highlights the potential of a design strategy for two-dimensional magnetic nano-architectures, through which mixed dimensionality of mesospins can be used to promote thermally emergent mesoscale magnetic states.« less

Interaction modifiers in artificial spin ices

NASA Astrophysics Data System (ADS)

Ã-stman, Erik; Stopfel, Henry; Chioar, Ioan-Augustin; Arnalds, Unnar B.; Stein, Aaron; Kapaklis, Vassilios; Hjörvarsson, Björgvin

2018-04-01

The modification of geometry and interactions in two-dimensional magnetic nanosystems has enabled a range of studies addressing the magnetic order1-6, collective low-energy dynamics7,8 and emergent magnetic properties5, 9,10 in, for example, artificial spin-ice structures. The common denominator of all these investigations is the use of Ising-like mesospins as building blocks, in the form of elongated magnetic islands. Here, we introduce a new approach: single interaction modifiers, using slave mesospins in the form of discs, within which the mesospin is free to rotate in the disc plane11. We show that by placing these on the vertices of square artificial spin-ice arrays and varying their diameter, it is possible to tailor the strength and the ratio of the interaction energies. We demonstrate the existence of degenerate ice-rule-obeying states in square artificial spin-ice structures, enabling the exploration of thermal dynamics in a spin-liquid manifold. Furthermore, we even observe the emergence of flux lattices on larger length scales, when the energy landscape of the vertices is reversed. The work highlights the potential of a design strategy for two-dimensional magnetic nano-architectures, through which mixed dimensionality of mesospins can be used to promote thermally emergent mesoscale magnetic states.

Interaction modifiers in artificial spin ices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ostman, Erik; Stopfel, Henry; Chioar, Ioan -Augustin

The modification of geometry and interactions in two-dimensional magnetic nanosystems has enabled a range of studies addressing the magnetic order, collective low-energy dynamics and emergent magnetic properties in, for example, artificial spin-ice structures. The common denominator of all these investigations is the use of Ising-like mesospins as building blocks, in the form of elongated magnetic islands. Here, we introduce a new approach: single interaction modifiers, using slave mesospins in the form of discs, within which the mesospin is free to rotate in the disc plane1. We show that by placing these on the vertices of square artificial spin-ice arrays andmore » varying their diameter, it is possible to tailor the strength and the ratio of the interaction energies. We demonstrate the existence of degenerate ice-rule-obeying states in square artificial spin-ice structures, enabling the exploration of thermal dynamics in a spin-liquid manifold. Furthermore, we even observe the emergence of flux lattices on larger length scales, when the energy landscape of the vertices is reversed. In conclusion, the work highlights the potential of a design strategy for two-dimensional magnetic nano-architectures, through which mixed dimensionality of mesospins can be used to promote thermally emergent mesoscale magnetic states.« less

Microscopic evidence for magnetic ordering in NdCu3Ru4O12 : 63,65Cu nuclear quadrupole resonance study

NASA Astrophysics Data System (ADS)

Yogi, M.; Niki, H.; Hedo, M.; Komesu, S.; Nakama, T.

2018-05-01

We have conducted 63,65Cu nuclear quadrupole resonance (NQR) measurements on A-site ordered perovskite compounds LaCu3Ru4O12 and NdCu3Ru4O12 to investigate their ground state and spin fluctuations. While there is only one Cu site in the crystal structure, multiple NQR resonance lines were observed. This is presumed to be due to the presence of slight distortion and lattice defects in the samples. The nuclear spin-lattice relaxation rate divided by temperature, 1 /T1 T , for LaCu3Ru4O12 showed almost constant value indicating the Fermi-liquid state. A remarkable increase in 1 /T1 T due to spin fluctuations was observed in NdCu3Ru4O12 . Furthermore, an evident magnetic phase transition at TM = 0.6 K was revealed from the distinct peak of 1 /T1 T and the broadening of the NQR spectrum.

Absence of giant spin splitting in the two-dimensional electron liquid at the surface of SrTiO3 (001)

NASA Astrophysics Data System (ADS)

McKeown Walker, S.; Riccò, S.; Bruno, F. Y.; de la Torre, A.; Tamai, A.; Golias, E.; Varykhalov, A.; Marchenko, D.; Hoesch, M.; Bahramy, M. S.; King, P. D. C.; Sánchez-Barriga, J.; Baumberger, F.

2016-06-01

We reinvestigate the putative giant spin splitting at the surface of SrTiO3 reported by Santander-Syro et al. [Nat. Mater. 13, 1085 (2014), 10.1038/nmat4107]. Our spin- and angle-resolved photoemission experiments on fractured (001) oriented surfaces supporting a two-dimensional electron liquid with high carrier density show no detectable spin polarization in the photocurrent. We demonstrate that this result excludes a giant spin splitting while it is consistent with the unconventional Rashba-like splitting seen in band structure calculations that reproduce the experimentally observed ladder of quantum confined subbands.

Experimental boundaries of the quantum rotor induced polarization (QRIP) in liquid state NMR.

PubMed

Icker, Maik; Fricke, Pascal; Grell, Toni; Hollenbach, Julia; Auer, Henry; Berger, Stefan

2013-12-01

The Haupt-effect is a rather seldom used hyperpolarization method. It is based on the interdependence between nuclear spin states and rotational states of nearly free rotating methyl groups having C3 symmetry. A sudden change in temperature from 4.2 K to room temperature by fast dissolution yields considerably enhanced (13)C and (1)H resonance signals. This phenomenon is now termed quantum rotor induced polarization. More than 40 substances have been studied by this approach in order to identify them as polarizable by the 'Haupt-effect in the liquid state'. Influencing factors have been analyzed systematically. It could be concluded that substances having a high tunneling frequency, which is due to a small and narrow potential barrier, are most likely to feature quantum rotor induced polarization-enhanced signals. Copyright © 2013 John Wiley & Sons, Ltd.

Absence of Long-Range Order in a Triangular Spin System with Dipolar Interactions

NASA Astrophysics Data System (ADS)

Keleş, Ahmet; Zhao, Erhai

2018-05-01

The antiferromagnetic Heisenberg model on the triangular lattice is perhaps the best known example of frustrated magnets, but it orders at low temperatures. Recent density matrix renormalization group (DMRG) calculations find that the next nearest neighbor interaction J2 enhances the frustration, and it leads to a spin liquid for J2/J1∈(0.08 ,0.15 ). In addition, a DMRG study of a dipolar Heisenberg model with longer range interactions gives evidence for a spin liquid at a small dipole tilting angle θ ∈[0 ,1 0 ° ). In both cases, the putative spin liquid region appears to be small. Here, we show that for the triangular lattice dipolar Heisenberg model, a robust quantum paramagnetic phase exists in a surprisingly wide region, θ ∈[0 ,5 4 ° ) , for dipoles tilted along the lattice diagonal direction. We obtain the phase diagram of the model by functional renormalization group (RG), which treats all magnetic instabilities on equal footing. The quantum paramagnetic phase is characterized by a smooth continuous flow of vertex functions and spin susceptibility down to the lowest RG scale, in contrast to the apparent breakdown of RG flow in phases with stripe or spiral order. Our finding points to a promising direction to search for quantum spin liquids in ultracold dipolar molecules.

Electron spin resonance modes in a strong-leg ladder in the Tomonaga-Luttinger liquid phase

NASA Astrophysics Data System (ADS)

Ozerov, M.; Maksymenko, M.; Wosnitza, J.; Honecker, A.; Landee, C. P.; Turnbull, M. M.; Furuya, S. C.; Giamarchi, T.; Zvyagin, S. A.

2015-12-01

Magnetic excitations in the strong-leg quantum spin ladder compound (C7H10N) 2CuBr4 (known as DIMPY) in the field-induced Tomonaga-Luttinger spin-liquid phase are studied by means of high-field electron spin resonance (ESR) spectroscopy. The presence of a gapped ESR mode with unusual nonlinear frequency-field dependence is revealed experimentally. Using a combination of analytic and exact-diagonalization methods, we compute the dynamical structure factor and identify this mode with longitudinal excitations in the antisymmetric channel. We argue that these excitations constitute a fingerprint of the spin dynamics in a strong-leg spin-1/2 Heisenberg antiferromagnetic ladder and owe their ESR observability to the uniform Dzyaloshinskii-Moriya interaction.

Slowing dynamics in supercooled liquids and other soft materials

NASA Astrophysics Data System (ADS)

Yardimci, Hasan

The slow structural dynamics displayed by supercooled liquids and the transition to an out-of-equilibrium glass state that they engender are among the most challenging issues in condensed matter physics. This thesis reports experimental studies designed to elucidate central aspects of these slow dynamics and the nature of the glass state. The subjects of these studies include glass forming molecular liquids and other soft materials that have been advanced as model glassy systems such as clay suspensions and block copolymer micelle solutions. The main experimental techniques employed in these investigations have been dielectric susceptibility and neutron scattering. In the first half of this thesis, we report frequency-dependent dielectric susceptibility measurements characterizing the evolution in the dynamical properties, or aging, of two supercooled liquids, sorbitol and xylitol, quenched below their calorimetric glass transition temperatures, Tg. In addition to the alpha relaxation that tracks the structural dynamics, the susceptibilities of both liquids possess a secondary Johari-Goldstein relaxation at higher frequencies. Following a quench below Tg, the susceptibility slowly approaches equilibrium behavior. For both liquids features of the Johari-Goldstein relaxation display a dependence on the time since the quench, or aging time, that is very similar to the age dependence of the alpha peak. Implications of these findings for aging in glasses and the nature of Johari-Goldstein relaxation are discussed. Further investigation of the aging in sorbitol reveals that it displays memory strikingly similar to that of a variety of glassy materials, particularly spin glasses. During a temporary stop in cooling, the susceptibility changes with time due to aging. The memory is revealed upon reheating as the susceptibility retraces these changes. To investigate the out-of-equilibrium state of the liquid as it displays this memory, we have employed a set of intricate thermal histories by interrupting the heating stage of the cycle and characterizing the subsequent aging. At temperatures above that of the original cooling stop, the liquid enters a state on heating with an effective age that is proportional to the duration of the stop, while at lower temperatures no effective age can be assigned and subtler behavior emerges. These results, which reveal differences with memory displayed by spin glasses, are discussed in the context of the liquid's energy landscape. In the second half of the thesis, we report neutron scattering measurements and dielectric studies on a set of disordered soft materials. (Abstract shortened by UMI.)

Application of EPR spectroscopy to the examination of pro-oxidant activity of coffee.

PubMed

Krakowian, Daniel; Skiba, Dominik; Kudelski, Adam; Pilawa, Barbara; Ramos, Paweł; Adamczyk, Jakub; Pawłowska-Góral, Katarzyna

2014-05-15

Free radicals present in coffee may be responsible for exerting toxic effects on an organism. The objectives of this work were to compare free radicals properties and concentrations in different commercially available coffees, in solid and liquid states, and to determine the effect of roasting on the formation of free radicals in coffee beans of various origins. The free radicals content of 15 commercially available coffees (solid and liquid) was compared and the impact of processing examined using electron paramagnetic resonance (EPR) spectroscopy at X-band (9.3 GHz). First derivative EPR spectra were measured at microwave power in the range of 0.7-70 mW. The following parameters were calculated for EPR spectra: amplitude (A), integral intensity (I), and line-width (ΔBpp); g-Factor was obtained from resonance condition. Our study showed that free radicals exist in green coffee beans (10(16) spin/g), roasted coffee beans (10(18) spin/g), and in commercially available coffee (10(17)-10(18) spin/g). Free radical concentrations were higher in solid ground coffee than in instant or lyophilised coffee. Continuous microwave saturation indicated homogeneous broadening of EPR lines from solid and liquid commercial coffee samples as well as green and roasted coffee beans. Slow spin-lattice relaxation processes were found to be present in all coffee samples tested, solid and liquid commercial coffees as well as green and roasted coffee beans. Higher free radicals concentrations were obtained for both the green and roasted at 240 °C coffee beans from Peru compared with those originating from Ethiopia, Brazil, India, or Colombia. Moreover, more free radicals occurred in Arabica coffee beans roasted at 240 °C than Robusta. EPR spectroscopy is a useful method of examining free radicals in different types of coffee. Copyright © 2013 Elsevier Ltd. All rights reserved.

Computer Simulations and Theoretical Studies of Complex Systems: from complex fluids to frustrated magnets

NASA Astrophysics Data System (ADS)

Choi, Eunsong

Computer simulations are an integral part of research in modern condensed matter physics; they serve as a direct bridge between theory and experiment by systemactically applying a microscopic model to a collection of particles that effectively imitate a macroscopic system. In this thesis, we study two very differnt condensed systems, namely complex fluids and frustrated magnets, primarily by simulating classical dynamics of each system. In the first part of the thesis, we focus on ionic liquids (ILs) and polymers--the two complementary classes of materials that can be combined to provide various unique properties. The properties of polymers/ILs systems, such as conductivity, viscosity, and miscibility, can be fine tuned by choosing an appropriate combination of cations, anions, and polymers. However, designing a system that meets a specific need requires a concrete understanding of physics and chemistry that dictates a complex interplay between polymers and ionic liquids. In this regard, molecular dynamics (MD) simulation is an efficient tool that provides a molecular level picture of such complex systems. We study the behavior of Poly (ethylene oxide) (PEO) and the imidazolium based ionic liquids, using MD simulations and statistical mechanics. We also discuss our efforts to develop reliable and efficient classical force-fields for PEO and the ionic liquids. The second part is devoted to studies on geometrically frustrated magnets. In particular, a microscopic model, which gives rise to an incommensurate spiral magnetic ordering observed in a pyrochlore antiferromagnet is investigated. The validation of the model is made via a comparison of the spin-wave spectra with the neutron scattering data. Since the standard Holstein-Primakoff method is difficult to employ in such a complex ground state structure with a large unit cell, we carry out classical spin dynamics simulations to compute spin-wave spectra directly from the Fourier transform of spin trajectories. We conclude the study by showing an excellent agreement between the simulation and the experiment.

Thermodynamics of Ising spins on the triangular kagome lattice: Exact analytical method and Monte Carlo simulations

NASA Astrophysics Data System (ADS)

Loh, Y. L.; Yao, D. X.; Carlson, E. W.

2008-04-01

A new class of two-dimensional magnetic materials Cu9X2(cpa)6ṡxH2O ( cpa=2 -carboxypentonic acid; X=F,Cl,Br ) was recently fabricated in which Cu sites form a triangular kagome lattice (TKL). As the simplest model of geometric frustration in such a system, we study the thermodynamics of Ising spins on the TKL using exact analytic method as well as Monte Carlo simulations. We present the free energy, internal energy, specific heat, entropy, sublattice magnetizations, and susceptibility. We describe the rich phase diagram of the model as a function of coupling constants, temperature, and applied magnetic field. For frustrated interactions in the absence of applied field, the ground state is a spin liquid phase with residual entropy per spin s0/kB=(1)/(9)ln72≈0.4752… . In weak applied field, the system maps to the dimer model on a honeycomb lattice, with residual entropy 0.0359 per spin and quasi-long-range order with power-law spin-spin correlations that should be detectable by neutron scattering. The power-law correlations become exponential at finite temperatures, but the correlation length may still be long.

Antiferromagnetic spin fluctuations in the heavy-fermion superconductor Ce2PdIn8

NASA Astrophysics Data System (ADS)

Tran, V. H.; Hillier, A. D.; Adroja, D. T.; Kaczorowski, D.

2012-09-01

Inelastic neutron scattering and muon spin relaxation/rotation (μSR) measurements were performed on the heavy-fermion superconductor Ce2PdIn8. The observed scaling of the imaginary part of the dynamical susceptibility χ''Tα∝f(ℏω/kBT) with α=3/2 revealed a non-Fermi liquid character of the normal state, being due to critical antiferromagnetic fluctuations near a T=0 quantum phase transition. The longitudinal-field μSR measurements indicated that superconductivity and antiferromagnetic spin fluctuations coexist in Ce2PdIn8 on a microscopic scale. The observed power-law temperature dependence of the magnetic penetration depth λ∝T3/2, deduced from the transverse-field μSR data, strongly confirms an unconventional superconductivity in this compound.

ESR studies on the spin-liquid candidate κ-(BEDT-TTF)2Cu2(CN)3: Anomalous response below T=8 K

NASA Astrophysics Data System (ADS)

Padmalekha, K. G.; Blankenhorn, M.; Ivek, T.; Bogani, L.; Schlueter, J. A.; Dressel, M.

2015-03-01

The organic conductor κ-(BEDT-TTF)2Cu2(CN)3 seems to form a quantum spin liquid, although at low temperatures unusual properties are seen in the charge, spin and lattice degrees of freedom. Here we report results of X-band ESR studies of κ-(BEDT-TTF)2Cu2(CN)3 single crystals as a function of temperature and angle. We find indications of two anisotropic relaxation mechanisms at low temperatures and compare them to the spin-liquid behavior observed in other strongly correlated systems. In addition, we can recognize charge inhomogeneities in the copper ions of the anion layer. This disorder might be linked to the dielectric response measured in this compound.

Tunneling spectroscopy of a spiral Luttinger liquid in contact with superconductors

NASA Astrophysics Data System (ADS)

Liu, Dong E.; Levchenko, Alex

2014-03-01

One-dimensional wires with Rashba spin-orbit coupling, magnetic field, and strong electron-electron interactions are described by a spiral Luttinger liquid model. We develop a theory to investigate the tunneling density of states into a spiral Luttinger liquid in contact with superconductors at its two ends. This approach provides a way to disentangle the delicate interplay between superconducting correlations and strong electron interactions. If the wire-superconductor boundary is dominated by Andreev reflection, we find that in the vicinity of the interface the zero-bias tunneling anomaly reveals a power law enhancement with the unusual exponent. This zero-bias due to Andreev reflections may coexist and thus mask possible peak due to Majorana bound states. Far away from the interface strong correlations inherent to the Luttinger liquid prevail and restore conventional suppression of the tunneling density of states at the Fermi level, which acquires a Friedel-like oscillatory envelope with the period renormalized by the strength of the interaction. D.E.L. was supported by Michigan State University and in part by ARO through Contract No. W911NF-12-1-0235. A.L. acknowledges support from NSF under Grant No. PHYS-1066293, and the hospitality of the Aspen Center for Physics.

Chemical pressure effects on magnetism in the quantum spin liquid candidates Yb2X2O7 (X =Sn, Ti, Ge)

NASA Astrophysics Data System (ADS)

Dun, Z. L.; Lee, M.; Choi, E. S.; Hallas, A. M.; Wiebe, C. R.; Gardner, J. S.; Arrighi, E.; Freitas, R. S.; Arevalo-Lopez, A. M.; Attfield, J. P.; Zhou, H. D.; Cheng, J. G.

2014-02-01

The linear and nonlinear ac susceptibility measurements of Yb-pyrochlores, Yb2X2O7 (X =Sn, Ti, and Ge), show transitions with a ferromagnetic nature at 0.13 and 0.25 K for Yb2Sn2O7 and Yb2Ti2O7, respectively, and an antiferromagnetic ordering at 0.62 K for Yb2Ge2O7. These systematical results (i) provided information about the nature of the unconventional magnetic ground state in Yb2Ti2O7; (ii) realized a distinct antiferromagnetic ordering state in Yb2Ge2O7; and (iii) demonstrated that the application of chemical pressure through the series of Yb-pyrochlores can efficiently perturb the fragile quantum spin fluctuations of the Yb3+ ions and lead to very different magnetic ground states.

Correlated impurities and intrinsic spin-liquid physics in the kagome material herbertsmithite

DOE PAGES

Han, Tian-Heng; Norman, M. R.; Wen, J. -J.; ...

2016-08-18

Low energy inelastic neutron scattering on single crystals of the kagome spin-liquid compound ZnCu 3(OD) 6Cl 2 (herbertsmithite) reveals in this paper antiferromagnetic correlations between impurity spins for energy transfers h(with stroke)ω < 0.8 meV (~ J/20). The momentum dependence differs significantly from higher energy scattering which arises from the intrinsic kagome spins. The low energy fluctuations are characterized by diffuse scattering near wave vectors (100) and (00 3/2), which is consistent with antiferromagnetic correlations between pairs of nearest-neighbor Cu impurities on adjacent triangular (Zn) interlayers. The corresponding impurity lattice resembles a simple cubic lattice in the dilute limit belowmore » the percolation threshold. Such an impurity model can describe prior neutron, NMR, and specific heat data. The low energy neutron data are consistent with the presence of a small spin gap (Δ ~ 0.7 meV) in the kagome layers, similar to that recently observed by NMR. Finally, the ability to distinguish the scattering due to Cu impurities from that of the planar kagome Cu spins provides an important avenue for probing intrinsic spin-liquid physics.« less

Magnetic Phase Diagram of α-RuCl3

NASA Astrophysics Data System (ADS)

Sears, Jennifer; Kim, Young-June; Zhao, Yang; Lynn, Jeffrey

The layered honeycomb material α-RuCl3 is thought to possess unusual magnetic interactions including a strong bond-dependent Kitaev term, offering a potential opportunity to study a material near a well understood spin liquid phase. Although this material orders magnetically at low temperatures and is thus not a realization of a Kitaev spin liquid, it does show a broad continuum of magnetic excitations reminiscent of that expected for the spin liquid phase. It has also been proposed that a magnetic field could destabilize the magnetic order in this material and induce a transition into a spin liquid phase. Low temperature magnetization and specific heat measurements in this material have suggested a complex magnetic phase diagram with multiple unidentified magnetic phases present at low temperature. This has provided motivation for our work characterizing the magnetic transitions and phase diagram in α-RuCl3. I will present detailed bulk measurements combined with magnetic neutron diffraction measurements to map out the phase diagram and identify the various phases present.

Isentropic calculation for thermodynamic properties of polarized liquid 3He by considering the effect of spin-dependent correlation function

NASA Astrophysics Data System (ADS)

Bordbar, G. H.; Hosseini, S.; Poostforush, A.

2017-05-01

Correlations in quantum fluids such as liquid 3He continue to be of high interest to scientists. Based on this prospect, the present work is devoted to study the effects of spin-spin correlation function on the thermodynamic properties of polarized liquid 3He such as pressure, velocity of sound, adiabatic index and adiabatic compressibility along different isentropic paths, using the Lennard-Jones potential and employing the variational approach based on cluster expansion of the energy functional. The inclusion of this correlation improves our previous calculations and leads to good agreements with experimental results.

Quasi-continuous transition from a Fermi liquid to a spin liquid in κ-(ET)2Cu2(CN)3.

PubMed

Furukawa, Tetsuya; Kobashi, Kazuhiko; Kurosaki, Yosuke; Miyagawa, Kazuya; Kanoda, Kazushi

2018-01-22

The Mott metal-insulator transition-a manifestation of Coulomb interactions among electrons-is known as a discontinuous transition. Recent theoretical studies, however, suggest that the transition is continuous if the Mott insulator carries a spin liquid with a spinon Fermi surface. Here, we demonstrate the case of a quasi-continuous Mott transition from a Fermi liquid to a spin liquid in an organic triangular-lattice system κ-(ET) 2 Cu 2 (CN) 3 . Transport experiments performed under fine pressure tuning have found that as the Mott transition is approached, the Fermi liquid coherence temperature continuously falls to the scale of kelvins, with a divergent quasi-particle decay rate on the metal side, and the charge gap continuously closes on the insulator side. A Clausius-Clapeyron analysis provides thermodynamic evidence for the extremely weak first-order nature of the transition. These results provide additional support for the existence of a spinon Fermi surface, which becomes an electron Fermi surface when charges are delocalized.

Elucidation of spin echo small angle neutron scattering correlation functions through model studies.

PubMed

Shew, Chwen-Yang; Chen, Wei-Ren

2012-02-14

Several single-modal Debye correlation functions to approximate part of the overall Debey correlation function of liquids are closely examined for elucidating their behavior in the corresponding spin echo small angle neutron scattering (SESANS) correlation functions. We find that the maximum length scale of a Debye correlation function is identical to that of its SESANS correlation function. For discrete Debye correlation functions, the peak of SESANS correlation function emerges at their first discrete point, whereas for continuous Debye correlation functions with greater width, the peak position shifts to a greater value. In both cases, the intensity and shape of the peak of the SESANS correlation function are determined by the width of the Debye correlation functions. Furthermore, we mimic the intramolecular and intermolecular Debye correlation functions of liquids composed of interacting particles based on a simple model to elucidate their competition in the SESANS correlation function. Our calculations show that the first local minimum of a SESANS correlation function can be negative and positive. By adjusting the spatial distribution of the intermolecular Debye function in the model, the calculated SESANS spectra exhibit the profile consistent with that of hard-sphere and sticky-hard-sphere liquids predicted by more sophisticated liquid state theory and computer simulation. © 2012 American Institute of Physics

Dynamical Reduction of the Dimensionality of Exchange Interactions and the "Spin-Liquid" Phase of κ-(BEDT-TTF)_{2}X.

PubMed

Powell, B J; Kenny, E P; Merino, J

2017-08-25

We show that the anisotropy of the effective spin model for the dimer Mott insulator phase of κ-(BEDT-TTF)_{2}X salts is dramatically different from that of the underlying tight-binding model. Intradimer quantum interference results in a model of coupled spin chains, where frustrated interchain interactions suppress long-range magnetic order. Thus, we argue, the "spin liquid" phase observed in some of these materials is a remnant of the Tomonaga-Luttinger physics of a single chain. This is consistent with previous experiments and resolves some outstanding puzzles.

Theory of a quantum spin liquid in the hydrogen-intercalated honeycomb iridate H3LiIr2O6

NASA Astrophysics Data System (ADS)

Slagle, Kevin; Choi, Wonjune; Chern, Li Ern; Kim, Yong Baek

2018-03-01

We propose a theoretical model for a gapless spin liquid phase that may have been observed in a recent experiment on H3LiIr2O6 . Despite the insulating and nonmagnetic nature of the material, the specific heat coefficient C /T ˜1 /√{T } in zero magnetic field and C /T ˜T /B3 /2 with finite magnetic field B have been observed. In addition, the NMR relaxation rate shows 1 /(T1T ) ˜(C/T ) 2 . Motivated by the fact that the interlayer/in-plane lattice parameters are reduced/elongated by the hydrogen intercalation of the parent compound Li2IrO3 , we consider four layers of the Kitaev honeycomb lattice model with additional interlayer exchange interactions. It is shown that the resulting spin liquid excitations reside mostly in the top and bottom layers of such a layered structure and possess a quartic dispersion. In an applied magnetic field, each quartic mode is split into four Majorana cones with the velocity v ˜B3 /4 . We suggest that the spin liquid phase in these "defect" layers, placed between different stacking patterns of the honeycomb layers, can explain the major phenomenology of the experiment, which can be taken as evidence that the Kitaev interaction plays the primary role in the formation of a quantum spin liquid in this material.

Three-Dimensional Non-Fermi-Liquid Behavior from One-Dimensional Quantum Critical Local Moments

NASA Astrophysics Data System (ADS)

Classen, Laura; Zaliznyak, Igor; Tsvelik, Alexei M.

2018-04-01

We study the temperature dependence of the electrical resistivity in a system composed of critical spin chains interacting with three-dimensional conduction electrons and driven to criticality via an external magnetic field. The relevant experimental system is Yb2 Pt2 Pb , a metal where itinerant electrons coexist with localized moments of Yb ions which can be described in terms of effective S =1 /2 spins with a dominantly one-dimensional exchange interaction. The spin subsystem becomes critical in a relatively weak magnetic field, where it behaves like a Luttinger liquid. We theoretically examine a Kondo lattice with different effective space dimensionalities of the two interacting subsystems. We characterize the corresponding non-Fermi liquid behavior due to the spin criticality by calculating the electronic relaxation rate and the dc resistivity and establish its quasilinear temperature dependence.

Spintronic characteristics of self-assembled neurotransmitter acetylcholine molecular complexes enable quantum information processing in neural networks and brain

NASA Astrophysics Data System (ADS)

Tamulis, Arvydas; Majauskaite, Kristina; Kairys, Visvaldas; Zborowski, Krzysztof; Adhikari, Kapil; Krisciukaitis, Sarunas

2016-09-01

Implementation of liquid state quantum information processing based on spatially localized electronic spin in the neurotransmitter stable acetylcholine (ACh) neutral molecular radical is discussed. Using DFT quantum calculations we proved that this molecule possesses stable localized electron spin, which may represent a qubit in quantum information processing. The necessary operating conditions for ACh molecule are formulated in self-assembled dimer and more complex systems. The main quantum mechanical research result of this paper is that the neurotransmitter ACh systems, which were proposed, include the use of quantum molecular spintronics arrays to control the neurotransmission in neural networks.

Fractional and hidden magnetic excitations in f-electron metal Yb2Pt2Pb

NASA Astrophysics Data System (ADS)

Zaliznyak, Igor

Quantum states with fractionalized excitations such as spinons in one-dimensional chains are commonly viewed as belonging to the domain of S=1/2 spin systems. However, recent experiments on the quantum antiferromagnet Yb2Pt2Pb, part of a large family of R2T2X (R=rare earth, T=transition metal, X=main group) materials spectacularly disqualify this opinion. The results show that spinons can also emerge in an f-electron system with strong spin-orbit coupling, where magnetism is mainly associated with large and anisotropic orbital moment. Here, the competition of several high-energy interactions Coulomb repulsion, spin-orbit coupling, crystal field, and the peculiar crystal structure, which combines low dimensionality and geometrical frustration, lead to the emergence, at low energy, of an effective spin-1/2, purely quantum Hamiltonian. Consequently, it produces unusual spin-liquid states and fractional excitations enabled by the inherently quantum mechanical nature of the moments. The emergent quantum spins bear the unique birthmark of their unusual origin in that they only lead to measurable longitudinal magnetic fluctuations, while the transverse excitations such as spin waves remain invisible to scattering experiments. Similarlyhidden would be transverse magnetic ordering, although it would have visible excitations. The rich magnetic phase diagram of Yb2Pt2Pb is suggestive of the existence of hidden-order phases, while the recent experiments indeed reveal the dark magnon, a hidden excitation in the saturated ferromagnetic (FM) phase of Yb2Pt2Pb. Unlike copper-based spin-1/2 chains, where the magnon in the FM state accounts for the full spectral weight of the zero-field spinon continuum, in the spin-orbital chains in Yb2Pt2Pb it is 100 times, or more weaker. It thus presents an example of dark magnon matter\\x9D, whose Hamiltonian is that of the effective spin-1/2 chain, but whose coupling to magnetic field, the physical probe at our disposal, is vanishingly small. The work was supported by the Office of Basic Energy Sciences, U.S. Department of Energy, under Contract No. DE-SC00112704, and by by NSF-DMR-1310008.

COMMODITY SCALE SYNTHESIS OF 1-METHYLIMIDAZOLE BASED IONIC LIQUIDS USING A SPINNING TUBE-IN-TUBE REACTOR

EPA Science Inventory

The continuous large-scale preparation of several 1-methylimidazole based ionic liquids was carried out using a Spinning Tube-in-Tube (STT) reactor (manufactured by Kreido Laboratories). This reactor, which embodies and facilitates the use of Green Chemistry principles and Proce...

Magnetized liquid 3He at finite temperature: A variational calculation approach

NASA Astrophysics Data System (ADS)

Bordbar, Gholam Hossein; Mohammadi Sabet, Mohammad Taghi

2016-08-01

Using the spin-dependent (SD) and spin-independent (SI) correlation functions, we have investigated the properties of liquid 3He in the presence of magnetic field at finite temperature. Our calculations have been done using the variational method based on cluster expansion of the energy functional. Our results show that the low field magnetic susceptibility obeys Curie law at high temperatures. This behavior is in a good agreement with the experimental data as well as the molecular field theory results in which the spin dependency has been introduced in correlation function. Reduced susceptibility as a function of temperature as well as reduced temperature has been also investigated, and again we have seen that the spin-dependent correlation function leads to a good agreement with the experimental data. The Landau parameter, F0a, has been calculated, and for this parameter, a value about - 0.75 has been found in the case of spin-spin correlation. In the case of spin-independent correlation function, this value is about - 0.7. Therefore, inclusion of spin dependency in the correlation function leads to a more compatible value of F0a with experimental data. The magnetization and susceptibility of liquid 3He have also been investigated as a function of magnetic field. Our results show a downward curvature in magnetization of system with spin-dependent correlation for all densities and relevant temperatures. A metamagnetic behavior has been observed as a maximum in susceptibility versus magnetic field, when the spin-spin correlation has been considered. This maximum occurs at 45T ≤ B ≤ 100T for all densities and temperatures. This behavior has not been observed in the case of spin-independent correlation function.

Pressure-tuning of bond-directional exchange interactions and magnetic frustration in hyperhoneycomb iridate β-Li 2IrO 3

DOE PAGES

Veiga, L. S. I.; Etter, M.; Glazyrin, K.; ...

2017-10-10

Here, we explore the response of Ir 5d orbitals to pressure in β-Li 2IrO 3, a hyperhoneycomb iridate in proximity to a Kitaev quantum spin-liquid (QSL) ground state. X-ray absorption spectroscopy reveals a reconstruction of the electronic ground state below 2 GPa, the same pressure range where x-ray magnetic circular dichroism shows an apparent collapse of magnetic order. The electronic reconstruction, which manifests a reduction in the effective spin-orbit interaction in 5d orbitals, pushes β-Li 2IrO 3 further away from the pure J eff = 1/2 limit. Although lattice symmetry is preserved across the electronic transition, x-ray diffraction shows amore » highly anisotropic compression of the hyperhoneycomb lattice which affects the balance of bond-directional Ir-Ir exchange interactions driven by spin-orbit coupling at Ir sites. An enhancement of symmetric anisotropic exchange over Kitaev and Heisenberg exchange interactions seen in theoretical calculations that use precisely this anisotropic Ir-Ir bond compression provides one possible route to the realization of a QSL state in this hyperhoneycomb iridate at high pressures.« less

Pressure tuning of bond-directional exchange interactions and magnetic frustration in the hyperhoneycomb iridate β -Li2IrO3

NASA Astrophysics Data System (ADS)

Veiga, L. S. I.; Etter, M.; Glazyrin, K.; Sun, F.; Escanhoela, C. A.; Fabbris, G.; Mardegan, J. R. L.; Malavi, P. S.; Deng, Y.; Stavropoulos, P. P.; Kee, H.-Y.; Yang, W. G.; van Veenendaal, M.; Schilling, J. S.; Takayama, T.; Takagi, H.; Haskel, D.

2017-10-01

We explore the response of Ir 5 d orbitals to pressure in β -Li2IrO3 , a hyperhoneycomb iridate in proximity to a Kitaev quantum spin-liquid (QSL) ground state. X-ray absorption spectroscopy reveals a reconstruction of the electronic ground state below 2 GPa, the same pressure range where x-ray magnetic circular dichroism shows an apparent collapse of magnetic order. The electronic reconstruction, which manifests a reduction in the effective spin-orbit interaction in 5 d orbitals, pushes β -Li2IrO3 further away from the pure Jeff=1 /2 limit. Although lattice symmetry is preserved across the electronic transition, x-ray diffraction shows a highly anisotropic compression of the hyperhoneycomb lattice which affects the balance of bond-directional Ir-Ir exchange interactions driven by spin-orbit coupling at Ir sites. An enhancement of symmetric anisotropic exchange over Kitaev and Heisenberg exchange interactions seen in theoretical calculations that use precisely this anisotropic Ir-Ir bond compression provides one possible route to the realization of a QSL state in this hyperhoneycomb iridate at high pressures.

Unusual magnetic excitations in the weakly ordered spin- 1 2 chain antiferromagnet Sr 2 CuO 3 : Possible evidence for Goldstone magnon coupled with the amplitude mode

DOE PAGES

Sergeicheva, E. G.; Sosin, S. S.; Prozorova, L. A.; ...

2017-01-18

We report on an electron spin resonance (ESR) study of a nearly one-dimensional (1D) spin-1/2 chain antiferromagnet, Sr 2CuO 3, with extremely weak magnetic ordering. The ESR spectra at T > T N, in the disordered Luttinger-spin-liquid phase, reveal nearly ideal Heisenberg-chain behavior with only a very small, field-independent linewidth, ~1/T. In the ordered state, below T N, we identify field-dependent antiferromagnetic resonance modes, which are well described by pseudo-Goldstone magnons in the model of a collinear biaxial antiferromagnet. Additionally, we observe a major resonant mode with unusual and strongly anisotropic properties, which is not anticipated by the conventional theorymore » of Goldstone spin waves. Lastly, we propose that this unexpected magnetic excitation can be attributed to a field-independent magnon mode renormalized due to its interaction with the high-energy amplitude (Higgs) mode in the regime of weak spontaneous symmetry breaking.« less

Liquid Motion Experiment Flight Test Results

NASA Technical Reports Server (NTRS)

Chato David J.; Dalton, Penni J.; Dodge, Franklin T.; Green, Steve

1998-01-01

The Liquid Motion Experiment (LME), designed to study the effects of liquid motion in rotating tanks, was flown on STS 84. LME was essentially a spin table that created a realistic nutation motion of scale-model tanks containing liquid. TWo spherical and two cylindrical transparent tanks were tested simultaneously, and three sets of such tanks were employed to vary liquid viscosity, fill level, and propellant management device (PMD) design. All the tanks were approximately 4.5 inches diameter. The primary test measurements were the radial and tangential torques exerted on the tanks by the liquid. Resonant frequencies and damping of the liquid oscillations were determined by sine sweep tests. For a given tank shape, the resonant frequency depended on fill level. For the cylindrical tanks, the resonances had somewhat different frequencies for the tangential axis (0.55 to 0.75 times spin rate) and the radial axis (0.73 to 0.78 times spin rate), and the tangential axis resonance agreed more closely with available analytical models. For the spherical tanks, the resonant frequencies were between 0.74 to 0.77 times the spin rate and were the same for the tangential and radial axes. The damping coefficients varied from about I% to 3% of critical, depending on tank shape, fill level, and liquid viscosity. 'Me viscous energy dissipation rates of the liquid oscillations were determined from sine dwell tests. The LME energy dissipation rates varied from 0.3 to 0.5 times the estimates obtained from scaling previous ground tests and spacecraft flight data. The PNDs sometimes enhanced the resonances and energy dissipation rates and sometimes decreased them, which points out the need to understand better the effects of PMD on liquid motion as a function of PMD and tank design.

Time Frequency Analysis of Spacecraft Propellant Tank Spinning Slosh

NASA Technical Reports Server (NTRS)

Green, Steven T.; Burkey, Russell C.; Sudermann, James

2010-01-01

Many spacecraft are designed to spin about an axis along the flight path as a means of stabilizing the attitude of the spacecraft via gyroscopic stiffness. Because of the assembly requirements of the spacecraft and the launch vehicle, these spacecraft often spin about an axis corresponding to a minor moment of inertia. In such a case, any perturbation of the spin axis will cause sloshing motions in the liquid propellant tanks that will eventually dissipate enough kinetic energy to cause the spin axis nutation (wobble) to grow further. This spinning slosh and resultant nutation growth is a primary design problem of spinning spacecraft and one that is not easily solved by analysis or simulation only. Testing remains the surest way to address spacecraft nutation growth. This paper describes a test method and data analysis technique that reveal the resonant frequency and damping behavior of liquid motions in a spinning tank. Slosh resonant frequency and damping characteristics are necessary inputs to any accurate numerical dynamic simulation of the spacecraft.

Biomolecular solid state NMR with magic-angle spinning at 25K.

PubMed

Thurber, Kent R; Tycko, Robert

2008-12-01

A magic-angle spinning (MAS) probe has been constructed which allows the sample to be cooled with helium, while the MAS bearing and drive gases are nitrogen. The sample can be cooled to 25K using roughly 3 L/h of liquid helium, while the 4-mm diameter rotor spins at 6.7 kHz with good stability (+/-5 Hz) for many hours. Proton decoupling fields up to at least 130 kHz can be applied. This helium-cooled MAS probe enables a variety of one-dimensional and two-dimensional NMR experiments on biomolecular solids and other materials at low temperatures, with signal-to-noise proportional to 1/T. We show examples of low-temperature (13)C NMR data for two biomolecular samples, namely the peptide Abeta(14-23) in the form of amyloid fibrils and the protein HP35 in frozen glycerol/water solution. Issues related to temperature calibration, spin-lattice relaxation at low temperatures, paramagnetic doping of frozen solutions, and (13)C MAS NMR linewidths are discussed.

Fingerprints of entangled spin and orbital physics in itinerant ferromagnets via angle-resolved resonant photoemission

NASA Astrophysics Data System (ADS)

Da Pieve, F.

2016-01-01

A method for mapping the local spin and orbital nature of the ground state of a system via corresponding flip excitations is proposed based on angle-resolved resonant photoemission and related diffraction patterns, obtained here via an ab initio modified one-step theory of photoemission. The analysis is done on the paradigmatic weak itinerant ferromagnet bcc Fe, whose magnetism, a correlation phenomenon given by the coexistence of localized moments and itinerant electrons, and the observed non-Fermi-Liquid behavior at extreme conditions both remain unclear. The combined analysis of energy spectra and diffraction patterns offers a mapping of local pure spin-flip, entangled spin-flip-orbital-flip excitations and chiral transitions with vortexlike wave fronts of photoelectrons, depending on the valence orbital symmetry and the direction of the local magnetic moment. Such effects, mediated by the hole polarization, make resonant photoemission a promising tool to perform a full tomography of the local magnetic properties even in itinerant ferromagnets or macroscopically nonmagnetic systems.

Three-Dimensional Non-Fermi-Liquid Behavior from One-Dimensional Quantum Critical Local Moments

DOE PAGES

Classen, Laura; Zaliznyak, Igor; Tsvelik, Alexei M.

2018-04-10

We study the temperature dependence of the electrical resistivity in a system composed of critical spin chains interacting with three dimensional conduction electrons and driven to criticality via an external magnetic field. The relevant experimental system is Yb 2Pt 2Pb, a metal where itinerant electrons coexist with localized moments of Yb-ions which can be described in terms of effective S = 1/2 spins with dominantly one-dimensional exchange interaction. The spin subsystem becomes critical in a relatively weak magnetic field, where it behaves like a Luttinger liquid. We theoretically examine a Kondo lattice with different effective space dimensionalities of the twomore » interacting subsystems. Lastly, we characterize the corresponding non-Fermi liquid behavior due to the spin criticality by calculating the electronic relaxation rate and the dc resistivity and establish its quasi linear temperature dependence.« less

Three-Dimensional Non-Fermi-Liquid Behavior from One-Dimensional Quantum Critical Local Moments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Classen, Laura; Zaliznyak, Igor; Tsvelik, Alexei M.

We study the temperature dependence of the electrical resistivity in a system composed of critical spin chains interacting with three dimensional conduction electrons and driven to criticality via an external magnetic field. The relevant experimental system is Yb 2Pt 2Pb, a metal where itinerant electrons coexist with localized moments of Yb-ions which can be described in terms of effective S = 1/2 spins with dominantly one-dimensional exchange interaction. The spin subsystem becomes critical in a relatively weak magnetic field, where it behaves like a Luttinger liquid. We theoretically examine a Kondo lattice with different effective space dimensionalities of the twomore » interacting subsystems. Lastly, we characterize the corresponding non-Fermi liquid behavior due to the spin criticality by calculating the electronic relaxation rate and the dc resistivity and establish its quasi linear temperature dependence.« less

Constructing a superhydrophobic surface on polydimethylsiloxane via spin coating and vapor-liquid sol-gel process.

PubMed

Peng, Yu-Ting; Lo, Kuo-Feng; Juang, Yi-Je

2010-04-06

In this study, a superhydrophobic surface on polydimethylsiloxane (PDMS) substrate was constructed via the proposed vapor-liquid sol-gel process in conjunction with spin coating of dodecyltrichlorosilane (DTS). Unlike the conventional sol-gel process where the reaction takes place in the liquid phase, layers of silica (SiO(2)) particles were formed through the reaction between the reactant spin-coated on the PDMS surface and vapor of the acid solution. This led to the SiO(2) particles inlaid on the PDMS surface. Followed by subsequent spin coating of DTS solution, the wrinkle-like structure was formed, and the static contact angle of the water droplet on the surface could reach 162 degrees with 2 degrees sliding angle and less than 5 degrees contact angle hysteresis. The effect of layers of SiO(2) particles, concentrations of DTS solution and surface topography on superhydrophobicity of the surface is discussed.

Spin-Orbit Coupled Quantum Magnetism in the 3D-Honeycomb Iridates

NASA Astrophysics Data System (ADS)

Kimchi, Itamar

In this doctoral dissertation, we consider the significance of spin-orbit coupling for the phases of matter which arise for strongly correlated electrons. We explore emergent behavior in quantum many-body systems, including symmetry-breaking orders, quantum spin liquids, and unconventional superconductivity. Our study is cemented by a particular class of Mott-insulating materials, centered around a family of two- and three-dimensional iridium oxides, whose honeycomb-like lattice structure admits peculiar magnetic interactions, the so-called Kitaev exchange. By analyzing recent experiments on these compounds, we show that this unconventional exchange is the key ingredient in describing their magnetism, and then use a combination of numerical and analytical techniques to investigate the implications for the phase diagram as well as the physics of the proximate three-dimensional quantum spin liquid phases. These long-ranged-entangled fractionalized phases should exhibit special features, including finite-temperature stability as well as unconventional high-Tc superconductivity upon charge-doping, which should aid future experimental searches for spin liquid physics. Our study explores the nature of frustration and fractionalization which can arise in quantum systems in the presence of strong spin-orbit coupling.

Resonant x-ray scattering reveals possible disappearance of magnetic order under hydrostatic pressure in the Kitaev candidate γ - Li 2 IrO 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Breznay, Nicholas P.; Ruiz, Alejandro; Frano, Alex

2017-07-05

Honeycomb iridates such as γ-Li 2IrO 3 are argued to realize Kitaev spin-anisotropic magnetic exchange, along with Heisenberg and possibly other couplings. While systems with pure Kitaev interactions are candidates to realize a quantum spin-liquid ground state, in γ-Li 2IrO 3 it has been shown that the presence of competing magnetic interactions leads to an incommensurate spiral spin order at ambient pressure below 38 K. In this paper, we study the pressure sensitivity of this magnetically ordered state in single crystals of γ-Li 2IrO 3 using resonant x-ray scattering (RXS) under applied hydrostatic pressures of up to 3 GPa. Finally,more » RXS is a direct probe of electronic order, and we observe the abrupt disappearance of the q sp = (0.57, 0, 0) spiral order at a critical pressure P c = 1.4 GPa with no accompanying change in the symmetry of the lattice.« less

On Steady-State Tropical Cyclones

DTIC Science & Technology

2014-01-01

components of the velocity vector, specific humidity, suspended liquid water, perturbation Exner function and perturbation density potential...vorticity and spin-up function, respectively. If the flow is symmetrically stable, the partial differential equation (10) is elliptic with a forcing term...Upper-level inflow jets A prominent feature of the radial velocity component shown in Figure 2(c) is the layered structure of inflow and outflow in the

Nonlinear magnetoelectric effect and magnetostriction in piezoelectric CsCuCl{sub 3} in paramagnetic and antiferromagnetic states

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kharkovskiy, A. I., E-mail: akharkovskiy@inbox.ru; L.F. Vereshchagin Institute for High Pressure Physics RAS, 142190 Troitsk, Moscow; Shaldin, Yu. V.

2016-01-07

The direct nonlinear magnetoelectric (ME) effect and the magnetostriction of piezoelectric CsCuCl{sub 3} single crystals were comprehensively studied over a wide temperature range in stationary magnetic fields of up to 14 T. The direct nonlinear ME effect measurements were also performed in pulsed magnetic fields up to 31 T, at liquid helium temperature in the antiferromagnetic (AF) state for the crystallographic direction in which effect has the maximum value. The nonlinear ME effect was quadratic in the paramagnetic state for the whole range of magnetic fields. In the AF state the phase transition between different configurations of spins manifested itself as plateau-likemore » peculiarity on the nonlinear ME effect. The nonlinear ME effect was saturated by the phase transition to the spin-saturated paramagnetic state. Two contributions to the nonlinear ME effects in CsCuCl{sub 3} were extracted from the experimental data: the intrinsic ME effect originated from the magnetoelectric interactions, and the extrinsic one, which resulted from a magnetostriction-induced piezoelectric effect.« less

A spin-liquid with pinch-line singularities on the pyrochlore lattice.

PubMed

Benton, Owen; Jaubert, L D C; Yan, Han; Shannon, Nic

2016-05-26

The mathematics of gauge theories lies behind many of the most profound advances in physics in the past 200 years, from Maxwell's theory of electromagnetism to Einstein's theory of general relativity. More recently it has become clear that gauge theories also emerge in condensed matter, a prime example being the spin-ice materials which host an emergent electromagnetic gauge field. In spin-ice, the underlying gauge structure is revealed by the presence of pinch-point singularities in neutron-scattering measurements. Here we report the discovery of a spin-liquid where the low-temperature physics is naturally described by the fluctuations of a tensor field with a continuous gauge freedom. This gauge structure underpins an unusual form of spin correlations, giving rise to pinch-line singularities: line-like analogues of the pinch points observed in spin-ice. Remarkably, these features may already have been observed in the pyrochlore material Tb2Ti2O7.

A spin-liquid with pinch-line singularities on the pyrochlore lattice

PubMed Central

Benton, Owen; Jaubert, L.D.C.; Yan, Han; Shannon, Nic

2016-01-01

The mathematics of gauge theories lies behind many of the most profound advances in physics in the past 200 years, from Maxwell's theory of electromagnetism to Einstein's theory of general relativity. More recently it has become clear that gauge theories also emerge in condensed matter, a prime example being the spin-ice materials which host an emergent electromagnetic gauge field. In spin-ice, the underlying gauge structure is revealed by the presence of pinch-point singularities in neutron-scattering measurements. Here we report the discovery of a spin-liquid where the low-temperature physics is naturally described by the fluctuations of a tensor field with a continuous gauge freedom. This gauge structure underpins an unusual form of spin correlations, giving rise to pinch-line singularities: line-like analogues of the pinch points observed in spin-ice. Remarkably, these features may already have been observed in the pyrochlore material Tb2Ti2O7. PMID:27225400

Impurity-induced moments in underdoped cuprates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khaliullin, G.; Kilian, R.; Krivenko, S.

1997-11-01

We examine the effect of a nonmagnetic impurity in a two-dimensional spin liquid in the spin-gap phase, employing a drone-fermion representation of spin-1/2 operators. The properties of the local moment induced in the vicinity of the impurity are investigated and an expression for the nuclear-magnetic-resonance Knight shift is derived, which we compare with experimental results. Introducing a second impurity into the spin liquid an antiferromagnetic interaction between the moments is found when the two impurities are located on different sublattices. The presence of many impurities leads to a screening of this interaction as is shown by means of a coherent-potentialmore » approximation. Further, the Kondo screening of an impurity-induced local spin by charge carriers is discussed. {copyright} {ital 1997} {ital The American Physical Society}« less

The resonant state at filling factor ν = 1/2 in chiral fermionic ladders

NASA Astrophysics Data System (ADS)

Haller, Andreas; Rizzi, Matteo; Burrello, Michele

2018-05-01

Helical liquids have been experimentally realized in both nanowires and ultracold atomic chains as the result of strong spin–orbit interactions. In both cases the inner degrees of freedom can be considered as an additional space dimension, providing an interpretation of these systems as chiral synthetic ladders, with artificial magnetic fluxes determined by the spin–orbit terms. In this work, we characterize the helical state which appears at filling ν = 1/2: this state is generated by a gap arising in the spin sector of the corresponding Luttinger liquid and it can be interpreted as the one-dimensional (1D) limit of a fractional quantum Hall state of bosonic pairs of fermions. We study its main features, focusing on entanglement properties and correlation functions. The techniques developed here provide a key example for the study of similar quasi-1D systems beyond the semiclassical approximation commonly adopted in the description of the Laughlin-like states.

Exact Solution of a Two-Species Quantum Dimer Model for Pseudogap Metals

NASA Astrophysics Data System (ADS)

Feldmeier, Johannes; Huber, Sebastian; Punk, Matthias

2018-05-01

We present an exact ground state solution of a quantum dimer model introduced by Punk, Allais, and Sachdev [Quantum dimer model for the pseudogap metal, Proc. Natl. Acad. Sci. U.S.A. 112, 9552 (2015)., 10.1073/pnas.1512206112], which features ordinary bosonic spin-singlet dimers as well as fermionic dimers that can be viewed as bound states of spinons and holons in a hole-doped resonating valence bond liquid. Interestingly, this model captures several essential properties of the metallic pseudogap phase in high-Tc cuprate superconductors. We identify a line in parameter space where the exact ground state wave functions can be constructed at an arbitrary density of fermionic dimers. At this exactly solvable line the ground state has a huge degeneracy, which can be interpreted as a flat band of fermionic excitations. Perturbing around the exactly solvable line, this degeneracy is lifted and the ground state is a fractionalized Fermi liquid with a small pocket Fermi surface in the low doping limit.

On the search for new anticancer drugs 14: the plasma pharmacokinetics and tissue distribution of spin-labeled thio-TEPA (SL-O-TT).

PubMed

Gutierrez, P L; Cohen, B E; Sosnovsky, G; Davis, T A; Egorin, M J

1985-01-01

We defined the plasma and tissue concentrations and pharmacokinetics of SL-O-TT, a spin-labeled analog of thio-TEPA, in 35-44-g male Swiss Webster mice that had received spin-labeled thio-TEPA at a dosage of 10 mg/kg. Concentrations of spin-labeled thio-TEPA in ethyl acetate extracts of tissue and plasma were determined by gas-liquid chromatography and electron spin resonance spectroscopy. Plasma concentrations of spin-labeled thio-TEPA declined in a biexponential fashion that was well described by the equation: Ct = 21.5e-0.276t + 2.30e-0.026t indicating a half-life alpha of 2.5 min and a half-life beta of 26.6 min. After 2 h there was still spin-labeled thio-TE-PA in plasma, but not in tissues. In tissues, no spin-labeled thio-TEPA was detected with gas-liquid chromatography 15 min after injection, but with electron-spin resonance label was found in lung and skeletal muscle. The main metabolite of spin-labeled thio-TEPA is spin-labeled TEPA, where oxidative desulfurization is invoked as the main metabolic mechanism. Reduction of the spin label to the hydroxylamine was also observed with time.

Exotic states of matter with polariton chains

NASA Astrophysics Data System (ADS)

Kalinin, Kirill P.; Lagoudakis, Pavlos G.; Berloff, Natalia G.

2018-04-01

We consider linear periodic chains of exciton-polariton condensates formed by pumping polaritons nonresonantly into a linear network. To the leading order such a sequence of condensates establishes relative phases as to minimize a classical one-dimensional X Y Hamiltonian with nearest and next-to-nearest neighbors. We show that the low-energy states of polaritonic linear chains demonstrate various classical regimes: ferromagnetic, antiferromagnetic, and frustrated spiral phases where quantum or thermal fluctuations are expected to give rise to a spin-liquid state. At the same time nonlinear interactions at higher pumping intensities bring about phase chaos and novel exotic phases.

Gapless Spin Excitations in the Field-Induced Quantum Spin Liquid Phase of α -RuCl3

NASA Astrophysics Data System (ADS)

Zheng, Jiacheng; Ran, Kejing; Li, Tianrun; Wang, Jinghui; Wang, Pengshuai; Liu, Bin; Liu, Zheng-Xin; Normand, B.; Wen, Jinsheng; Yu, Weiqiang

2017-12-01

α -RuCl3 is a leading candidate material for the observation of physics related to the Kitaev quantum spin liquid (QSL). By combined susceptibility, specific-heat, and nuclear-magnetic-resonance measurements, we demonstrate that α -RuCl3 undergoes a quantum phase transition to a QSL in a magnetic field of 7.5 T applied in the a b plane. We show further that this high-field QSL phase has gapless spin excitations over a field range up to 16 T. This highly unconventional result, unknown in either Heisenberg or Kitaev magnets, offers insight essential to establishing the physics of α -RuCl3 .

Extreme Field Sensitivity of Magnetic Tunneling in Fe-Doped Li3 N

NASA Astrophysics Data System (ADS)

Fix, M.; Atkinson, J. H.; Canfield, P. C.; del Barco, E.; Jesche, A.

2018-04-01

The magnetic properties of dilute Li2 (Li1 -xFex )N with x ˜0.001 are dominated by the spin of single, isolated Fe atoms. Below T =10 K the spin-relaxation times become temperature independent indicating a crossover from thermal excitations to the quantum tunneling regime. We report on a strong increase of the spin-flip probability in transverse magnetic fields that proves the resonant character of this tunneling process. Longitudinal fields, on the other hand, lift the ground-state degeneracy and destroy the tunneling condition. An increase of the relaxation time by 4 orders of magnitude in applied fields of only a few milliTesla reveals exceptionally sharp tunneling resonances. Li2 (Li1 -xFex )N represents a comparatively simple and clean model system that opens the possibility to study quantum tunneling of the magnetization at liquid helium temperatures.

Imaging the Formation of High-Energy Dispersion Anomalies in the Actinide UCoGa5

NASA Astrophysics Data System (ADS)

Das, Tanmoy; Durakiewicz, Tomasz; Zhu, Jian-Xin; Joyce, John J.; Sarrao, John L.; Graf, Matthias J.

2012-10-01

We use angle-resolved photoemission spectroscopy to image the emergence of substantial dispersion and spectral-weight anomalies in the electronic renormalization of the actinide compound UCoGa5 that was presumed to belong to a conventional Fermi-liquid family. Kinks or abrupt breaks in the slope of the quasiparticle dispersion are detected both at low (approximately 130 meV) and high (approximately 1 eV) binding energies below the Fermi energy, ruling out any significant contribution of phonons. We perform numerical calculations to demonstrate that the anomalies are adequately described by coupling between itinerant fermions and spin fluctuations arising from the particle-hole continuum of the spin-orbit-split 5f states of uranium. These anomalies resemble the “waterfall” phenomenon of the high-temperature copper-oxide superconductors, suggesting that spin fluctuations are a generic route toward multiform electronic phases in correlated materials as different as high-temperature superconductors and actinides.

Extreme Field Sensitivity of Magnetic Tunneling in Fe-Doped Li 3 N

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fix, M.; Atkinson, J. H.; Canfield, P. C.

Here, the magnetic properties of dilute Li 2(Li 1–xFe x)N with x~0.001 are dominated by the spin of single, isolated Fe atoms. Below T=10 K the spin-relaxation times become temperature independent indicating a crossover from thermal excitations to the quantum tunneling regime. We report on a strong increase of the spin-flip probability in transverse magnetic fields that proves the resonant character of this tunneling process. Longitudinal fields, on the other hand, lift the ground-state degeneracy and destroy the tunneling condition. An increase of the relaxation time by 4 orders of magnitude in applied fields of only a few milliTesla revealsmore » exceptionally sharp tunneling resonances. Li 2(Li 1–xFe x)N represents a comparatively simple and clean model system that opens the possibility to study quantum tunneling of the magnetization at liquid helium temperatures.« less

Extreme Field Sensitivity of Magnetic Tunneling in Fe-Doped Li 3 N

DOE PAGES

Fix, M.; Atkinson, J. H.; Canfield, P. C.; ...

2018-04-04

Here, the magnetic properties of dilute Li 2(Li 1–xFe x)N with x~0.001 are dominated by the spin of single, isolated Fe atoms. Below T=10 K the spin-relaxation times become temperature independent indicating a crossover from thermal excitations to the quantum tunneling regime. We report on a strong increase of the spin-flip probability in transverse magnetic fields that proves the resonant character of this tunneling process. Longitudinal fields, on the other hand, lift the ground-state degeneracy and destroy the tunneling condition. An increase of the relaxation time by 4 orders of magnitude in applied fields of only a few milliTesla revealsmore » exceptionally sharp tunneling resonances. Li 2(Li 1–xFe x)N represents a comparatively simple and clean model system that opens the possibility to study quantum tunneling of the magnetization at liquid helium temperatures.« less

Extreme Field Sensitivity of Magnetic Tunneling in Fe-Doped Li_{3}N.

PubMed

Fix, M; Atkinson, J H; Canfield, P C; Del Barco, E; Jesche, A

2018-04-06

The magnetic properties of dilute Li_{2}(Li_{1-x}Fe_{x})N with x∼0.001 are dominated by the spin of single, isolated Fe atoms. Below T=10  K the spin-relaxation times become temperature independent indicating a crossover from thermal excitations to the quantum tunneling regime. We report on a strong increase of the spin-flip probability in transverse magnetic fields that proves the resonant character of this tunneling process. Longitudinal fields, on the other hand, lift the ground-state degeneracy and destroy the tunneling condition. An increase of the relaxation time by 4 orders of magnitude in applied fields of only a few milliTesla reveals exceptionally sharp tunneling resonances. Li_{2}(Li_{1-x}Fe_{x})N represents a comparatively simple and clean model system that opens the possibility to study quantum tunneling of the magnetization at liquid helium temperatures.

Physical and chemical interactions at the interface between atmospheric pressure plasmas and aqueous solutions

NASA Astrophysics Data System (ADS)

Lindsay, Alexander; Byrns, Brandon; Knappe, Detlef; Graves, David; Shannon, Steven

2014-10-01

Transport and reactions of charged species, neutrals, and photons at the interface between plasmas and liquids must be better quantified. The work presented here combines theoretical and experimental investigations of conditions in the gas and liquid phases in proximity to the interface for various discharges. OES is used to determine rotational and vibrational temperatures of OH, NO, and N2+; the relationship between these temperatures that characterize the distribution of internal energy states and gas and electron kinetic temperatures is considered. The deviation of OH rotational states from equilibrium under high humidity conditions is also presented. In contradiction with findings of other groups, high energy rotational states appear to become underpopulated with increasing humidity. In the aqueous phase, concentrations of longer-lived species such as nitrate, nitrite, hydrogen peroxide, and ozone are determined using ion chromatography and colorimetric methods. Spin-traps and electron paramagnetic resonance (EPR) are investigated for characterization of short-lived aqueous radicals like OH, O2-, NO, and ONOO-. Finally, experimental results are compared to a numerical model which couples transport and reactions within and between the bulk gas and liquid phases.

Spin-polarized Molecular Dynamics simulations of liquid iron silicate at high pressures.

NASA Astrophysics Data System (ADS)

Munoz Ramo, David; Stixrude, Lars

2010-05-01

Liquid iron silicate (Fe2SiO4) is an important component of natural silicate liquids appearing in Earth's interior. The effect of iron in the properties of these melts is a crucial issue, as it displays a high-spin to low-spin transition at high pressures which is accompanied by volume reduction and changes in the optical absorption spectrum. This phenomenon has a major influence on properties like the buoyancy or the thermal conductivity of the melt, and ultimately on the chemical and thermal evolution of our planet. Computer simulations using ab initio methods have proven to be a powerful approach to the study of liquid silicate systems[1,2], although not yet including Fe. In this paper, we report ab initio molecular dynamics studies of liquid iron silicate at high pressure (up to 400 GPa) and high temperatures (from 3000K to 6000K) that allow us to predict different properties of the system. We use the spin-polarized formalism and the GGA+U density functional for a better treatment of the iron magnetic moments in the system. Previous studies in the solid phase have shown that GGA predicts fayalite as a metal, while the introduction of U leads to a correct description of the band gap and the magnetic ordering of the system. We extend this analysis to the liquid phase. By means of these simulations we predict the liquid structure and thermodynamic properties of the liquid. We compute the theoretical Hugoniot for the system and find good agreement with values obtained from shock experiments [3]. Our calculations show large differences in the magnitude and orientation of the magnetic moments depending on the choice of functional; the GGA+U functional consistently provides larger values of the individual moments (about 1 unit larger) and of the total magnetization of the system. The high-spin to low-spin transition is predicted to take place at pressures from around 260GPa at 3000K to around 280GPa at 6000K in this iron-rich system. [1] N. P. de Koker, L. Stixrude, B. B. Karki, Geochim Cosmochim Acta 2008, 72, 1427. [2] B. B. Karki, D. Bhattarai, L. Stixrude, Phys. Rev. B 2007, 76, 104205. [3] G. Q. Chen, T. J. Ahrens, E. M. Stolper, Phys. Earth Planet. Inter. 2002, 134, 35.

Ground and Low-Lying Excited States of Interacting Electron Systems: A Survey and Some Critical Analyses

NASA Astrophysics Data System (ADS)

Farid, Behnam

1999-12-01

In this contribution we deal with a number of theoretical aspects concerning physics of systems of interacting electrons. Our discussions, although amenable to appropriate generalisations, are subject to some limitations. To name, we deal with systems of spin-less fermions — or those of spin-compensated fermions with spin —, with nondegenerate ground states, and those in which relativistic effects are negligible; we disregard ionic motions and deal with "normal" (not superconducting, for instance) systems that are in addition free from randomly distributed impurities. We restrict our considerations to the absolute zero of temperature. The Green and response functions feature in our theoretical considerations. Here we give especial attention to the analytic properties of these functions for complex values of energy. We discuss how, both fundamentally and from the practical viewpoint, ground and low-lying excited-states properties can be obtained from these correlation functions. Characterising low-lying excited states by means of elementary excitations, we deal with both those that are particle-like (the Landau quasi-particles) and those that are collective (plasmons, excitation in the total distribution of electrons). We devote some space to discussions concerning the domain of validity and breakdown of the many-body perturbation theory, specifically that for the single-particle Green function and the self-energy operator. Extensive analysis of the asymptotic behaviour of dynamic correlation functions in the limits of small and large energies reveal the significance of the Kohn-Sham-like Hamiltonians within the context of the many-body perturbation theory. In view of this, at places we pay especial attention to a number of the existing density-functional theories (including the ones for the single-particle reduced density matrix and time-dependent external potentials). We discuss in some detail a number of issues that are specific to the (phenomenological) Landau Fermi-liquid theory and their justification within the framework of the many-body perturbation theory. In doing so we touch upon a number of characteristic features specific to Fermi-liquid (as oppsed to marginal Fermi- and Luttinger-liquid) systems. Finally, we put one particular approximation scheme for the self-energy operator, known as the the GW scheme, under magnifying glass and observe it in many of its facets.

Exotic emergent phenomena in the fractional quantum Hall effect

NASA Astrophysics Data System (ADS)

Coimbatore Balram, Ajit

When two-dimensional electron systems are subjected to a perpendicular magnetic field, they exhibit the marvelous phenomenon known as the fractional quantum Hall effect (FQHE). This arises as a result of the formation of composite fermions (CFs), which are bound states of electrons and an even number of vortices. The FQHE of electrons is understood as arising from the integer QHE (IQHE) of CFs. Alongside superconductivity, Bose-Einstein condensation and spin-liquids, the CF quantum fluid provides a model system for understanding strongly correlated systems and their collective behavior. Although it has been more than three decades since the experimental discovery of FQHE, the field continues to produce profound insights and pose interesting problems some of which have been addressed in this thesis. A major unanswered question in the field of FQHE is the mechanism of FQHE for the 1/3 state in the second Landau level (7/3 state). Numerical studies of this state have brought out the following puzzle: exact diagonalization studies suggest that the ground state and excitations of 1/3 state in the second Landau level are different from its counterpart in the lowest Landau level (LLL), while entanglement spectra of the two states point to the fact that they fall in the same universality class. Using methods from CF theory we show that the excitations of the 7/3 FQHE lie in the same universality class as those of the 1/3 state but are strongly modified due to screening by CF excitons, thereby settling the above discrepancy. Armed with the exciton calculation, we illustrate that by imposing certain exclusion rules for CF excitons one can build the full spectrum of FQHE in the lowest Landau level. Equipped with the techniques to calculate the spectra of FQHE systems, we carry out an extensive study of FQHE of multi-component CFs (systems possessing degrees of freedom for eg: valley and spin degeneracy), which is applicable to FQHE in systems such as graphene, AlAs and GaAs quantum wells. We provide a comprehensive list of the possible fractions, their ground state energies and the critical "Zeeman" energies for the "spin" transitions between the states and compare them with the experimental observations. In the lowest Landau level of graphene, we find an excellent agreement between theory and experiments. However, in the second Landau level of graphene we find an unexpected spontaneous spin polarization of CFs. We predict that there are no spin transitions to be expected in the second Landau level of graphene, a result that could be tested out in experiments. We reanalyzed some old experimental data showing excitation modes below the Zeeman energy in the vicinity of 1/3 filling of the lowest Landau level whose theoretical origin was unexplained. Using methods of exact diagonalization and CF theory we demonstrate that these modes arise as a result of formation of trions of CFs which have sub-Zeeman energy due to skyrmion-like physics. In the past couple of years, the Fermi wave vector of CFs has been measured very accurately in pioneering experiments at Princeton University. Motivated by these experiments we address the issue of the validity of Luttinger's theorem (which is a fundamental tenet of Landau Fermi liquid theory) for the Fermi sea of CFs. Our calculations suggest that the CF Fermi sea may violate Luttinger's theorem slightly. This not only provides a nontrivial example of a non-Fermi liquid, but gives new insight into the nature of the CF Fermi sea state and opens a new line of inquiry in the field of FQHE.

Quantum process tomography with informational incomplete data of two J-coupled heterogeneous spins relaxation in a time window much greater than T1

NASA Astrophysics Data System (ADS)

Maciel, Thiago O.; Vianna, Reinaldo O.; Sarthour, Roberto S.; Oliveira, Ivan S.

2015-11-01

We reconstruct the time dependent quantum map corresponding to the relaxation process of a two-spin system in liquid-state NMR at room temperature. By means of quantum tomography techniques that handle informational incomplete data, we show how to properly post-process and normalize the measurements data for the simulation of quantum information processing, overcoming the unknown number of molecules prepared in a non-equilibrium magnetization state (Nj) by an initial sequence of radiofrequency pulses. From the reconstructed quantum map, we infer both longitudinal (T1) and transversal (T2) relaxation times, and introduce the J-coupling relaxation times ({T}1J,{T}2J), which are relevant for quantum information processing simulations. We show that the map associated to the relaxation process cannot be assumed approximated unital and trace-preserving for times greater than {T}2J.

Long-lived states to sustain SABRE hyperpolarised magnetisation† †Electronic supplementary information (ESI) available: Experimental details, sample specification, substrate characterisation, SABRE studies, pulse sequence details, simulations. See DOI: 10.1039/c6cp02844f Click here for additional data file.

PubMed Central

Roy, Soumya S.; Rayner, Peter J.; Norcott, Philip; Green, Gary G. R.

2016-01-01

The applicability of the magnetic resonance (MR) technique in the liquid phase is limited by poor sensitivity and short nuclear spin coherence times which are insufficient for many potential applications. Here we illustrate how it is possible to address both of these issues simultaneously by harnessing long-lived hyperpolarised spin states that are formed by adapting the Signal Amplification by Reversible Exchange (SABRE) technique. We achieve more than 4% net 1H-polarisation in a long-lived form that remains detectable for over ninety seconds by reference to proton pairs in the biologically important molecule nicotinamide and a pyrazine derivative whose in vivo imaging will offer a new route to probe disease in the future. PMID:27711398

New Forms of Matter in Optical Lattices

DTIC Science & Technology

2016-05-19

Daley, A. M. Läuchli, and P. Zoller Thermal vs. Entanglement Entropy: A Measurement Protocol for Fermionic Atoms with a Quantum Gas Microscope...J. A. Edge, E. Taylor, S. Zhang, S. Trotzky, J. H. Thywissen Transverse Demagnetization Dynamics of a Unitary Fermi Gas Science 344, 722 (2014...Jiang, J Ignacio Cirac, Peter Zoller, Mikhail D Lukin, "Topologically Protected Quantum State Transfer in a Chiral Spin Liquid , "Nature Communications

Spin currents and magnon dynamics in insulating magnets

NASA Astrophysics Data System (ADS)

Nakata, Kouki; Simon, Pascal; Loss, Daniel

2017-03-01

Nambu-Goldstone theorem provides gapless modes to both relativistic and nonrelativistic systems. The Nambu-Goldstone bosons in insulating magnets are called magnons or spin-waves and play a key role in magnetization transport. We review here our past works on magnetization transport in insulating magnets and also add new insights, with a particular focus on magnon transport. We summarize in detail the magnon counterparts of electron transport, such as the Wiedemann-Franz law, the Onsager reciprocal relation between the Seebeck and Peltier coefficients, the Hall effects, the superconducting state, the Josephson effects, and the persistent quantized current in a ring to list a few. Focusing on the electromagnetism of moving magnons, i.e. magnetic dipoles, we theoretically propose a way to directly measure magnon currents. As a consequence of the Mermin-Wagner-Hohenberg theorem, spin transport is drastically altered in one-dimensional antiferromagnetic (AF) spin-1/2 chains; where the Néel order is destroyed by quantum fluctuations and a quasiparticle magnon-like picture breaks down. Instead, the low-energy collective excitations of the AF spin chain are described by a Tomonaga-Luttinger liquid (TLL) which provides the spin transport properties in such antiferromagnets some universal features at low enough temperature. Finally, we enumerate open issues and provide a platform to discuss the future directions of magnonics.

Crystal field excitations from Yb3 + ions at defective sites in highly stuffed Yb2Ti2O7

NASA Astrophysics Data System (ADS)

Sala, G.; Maharaj, D. D.; Stone, M. B.; Dabkowska, H. A.; Gaulin, B. D.

2018-06-01

The pyrochlore magnet Yb2Ti2O7 has been proposed as a quantum spin ice candidate, a spin liquid state expected to display emergent quantum electrodynamics with gauge photons among its elementary excitations. However, Yb2Ti2O7 's ground state is known to be very sensitive to its precise stoichiometry. Powder samples, produced by solid-state synthesis at relatively low temperatures, tend to be stoichiometric, while single crystals grown from the melt tend to display weak "stuffing" wherein ˜2 % of the Yb3 +, normally at the A site of the A2B2O7 pyrochlore structure, reside as well at the B site. In such samples Yb3 + ions should exist in defective environments at low levels and be subjected to crystalline electric fields very different from those at the stoichiometric A sites. Neutron scattering measurements of Yb3 + in four compositions of Yb2 +xTi2 -xO7 -y show the spectroscopic signatures for these defective Yb3 + ions and explicitly demonstrate that the spin anisotropy of the Yb3 + moment changes from X Y -like for stoichiometric Yb3 + to Ising-like for "stuffed" B site Yb3 + or for A site Yb3 + in the presence of oxygen vacancies.

Novel liquid equilibrium valving on centrifugal microfluidic CD platform.

PubMed

Al-Faqheri, Wisam; Ibrahim, Fatimah; Thio, Tzer Hwai Gilbert; Arof, Hamzah; Madou, Marc

2013-01-01

One of the main challenges faced by researchers in the field of microfluidic compact disc (CD) platforms is the control of liquid movement and sequencing during spinning. This paper presents a novel microfluidic valve based on the principle of liquid equilibrium on a rotating CD. The proposed liquid equilibrium valve operates by balancing the pressure produced by the liquids in a source and a venting chamber during spinning. The valve does not require external forces or triggers, and is able to regulate burst frequencies with high accuracy. In this work, we demonstrate that the burst frequency can be significantly raised by making just a small adjustment of the liquid height in the vent chamber. Finally, the proposed valve ng method can be used separately or combined with other valving methods in advance microfluidic processes.

Experimental realization of universal geometric quantum gates with solid-state spins.

PubMed

Zu, C; Wang, W-B; He, L; Zhang, W-G; Dai, C-Y; Wang, F; Duan, L-M

2014-10-02

Experimental realization of a universal set of quantum logic gates is the central requirement for the implementation of a quantum computer. In an 'all-geometric' approach to quantum computation, the quantum gates are implemented using Berry phases and their non-Abelian extensions, holonomies, from geometric transformation of quantum states in the Hilbert space. Apart from its fundamental interest and rich mathematical structure, the geometric approach has some built-in noise-resilience features. On the experimental side, geometric phases and holonomies have been observed in thermal ensembles of liquid molecules using nuclear magnetic resonance; however, such systems are known to be non-scalable for the purposes of quantum computing. There are proposals to implement geometric quantum computation in scalable experimental platforms such as trapped ions, superconducting quantum bits and quantum dots, and a recent experiment has realized geometric single-bit gates in a superconducting system. Here we report the experimental realization of a universal set of geometric quantum gates using the solid-state spins of diamond nitrogen-vacancy centres. These diamond defects provide a scalable experimental platform with the potential for room-temperature quantum computing, which has attracted strong interest in recent years. Our experiment shows that all-geometric and potentially robust quantum computation can be realized with solid-state spin quantum bits, making use of recent advances in the coherent control of this system.

Improving liquid chromatography-mass spectrometry sensitivity using a subambient pressure ionization with nanoelectrospray (SPIN) interface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang, Keqi; Page, Jason S.; Marginean, Ioan

2011-04-22

In this work the Subambient Pressure Ionization with Nanoelectrospray (SPIN) ion source and interface which operates at ~15-30 Torr is demonstrated to be compatible with gradient reversed-phase liquid chromatography-MS applications, exemplified here with the analysis of complex samples (a protein tryptic digest and a whole cell lysate). A low liquid chromatographic flow rate (100-400 nL/min) allowed stable electrospray to be established while avoiding electrical breakdown. Efforts to increase the operating pressure of the SPIN source relative to previously reported designs prevented solvent freezing and enhanced charged cluster/droplet desolvation. A 5-12-fold improvement in sensitivity relative to a conventional atmospheric pressure nanoelectrospraymore » ionization (ESI) source was obtained for detected peptides.« less

Knight shift and spin-echo decay time of YBa{sub 2}Cu{sub 4}O{sub 8} and YBa{sub 2}Cu{sub 3}O{sub 7} in the superconducting state

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pines, D.; Wrobel, P.

1996-03-01

We report on calculations of the Knight shift and spin-echo decay time, {ital T}{sub 2{ital G}}, in the superconducting state which are based on a nearly antiferromagnetic Fermi-liquid description of the spin-fluctuation spectrum, in which a single spin component is responsible for the dynamic spin behavior and the magnetic interaction between the planar quasiparticles brings the system close to antiferromagnetic behavior. The dynamic spin susceptibility is described by a random-phase-approximation-like expression, with a restoring force which is unchanged from the normal state, and an irreducible particle-hole susceptibility which reflects the {ital d}{sub {ital x}{sup 2}{minus}{ital y}{sup 2}} symmetry of themore » gap parameter and a quasiparticle Fermi surface consistent with photoemission experiments. We obtain a quantitative fit to the Knight shift results for YBa{sub 2}Cu{sub 4}O{sub 8} with a {ital d}{sub {ital x}{sup 2}{minus}{ital y}{sup 2}} strong coupling gap of maximum magnitude 2.8{ital k}{sub {ital BT}}{sub {ital c}}, and show that quantitative agreement with the recent measurements of {ital T}{sub 2{ital G}} by Corey {ital et al}. may be obtained with this {ital d}{sub {ital x}{sup 2}-{ital y}{sup 2}} pairing state and a quite substantial antiferromagnetic enhancement ({approximately}140) of the static {open_quote}{open_quote}band structure{close_quote}{close_quote} spin susceptibility at wave vectors in the vicinity of {bold Q}=({pi},{pi}). We demonstrate that the experimental results of Corey {ital et al}. rule out an anisotropic {ital s}-wave state. Analogous calculations for the Knight shift of YBa{sub 2}Cu{sub 3}O{sub 7} suggest that the {ital d}{sub {ital x}{sup 2}-{ital y}{sup 2}} strong coupling gap possesses a maximum magnitude, 2.6{ital k}{sub {ital BT}}{sub {ital c}}, and on this basis, we predict a reduction in {ital T}{sup -1}{sub 2{ital G}} of some 5% for the smaller antiferromagnetic enhancement ({approximately}38) expected for this system.« less

Broadband excitation in nuclear magnetic resonance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tycko, Robert

1984-10-01

Theoretical methods for designing sequences of radio frequency (rf) radiation pulses for broadband excitation of spin systems in nuclear magnetic resonance (NMR) are described. The sequences excite spins uniformly over large ranges of resonant frequencies arising from static magnetic field inhomogeneity, chemical shift differences, or spin couplings, or over large ranges of rf field amplitudes. Specific sequences for creating a population inversion or transverse magnetization are derived and demonstrated experimentally in liquid and solid state NMR. One approach to broadband excitation is based on principles of coherent averaging theory. A general formalism for deriving pulse sequences is given, along withmore » computational methods for specific cases. This approach leads to sequences that produce strictly constant transformations of a spin system. The importance of this feature in NMR applications is discussed. A second approach to broadband excitation makes use of iterative schemes, i.e. sets of operations that are applied repetitively to a given initial pulse sequences, generating a series of increasingly complex sequences with increasingly desirable properties. A general mathematical framework for analyzing iterative schemes is developed. An iterative scheme is treated as a function that acts on a space of operators corresponding to the transformations produced by all possible pulse sequences. The fixed points of the function and the stability of the fixed points are shown to determine the essential behavior of the scheme. Iterative schemes for broadband population inversion are treated in detail. Algebraic and numerical methods for performing the mathematical analysis are presented. Two additional topics are treated. The first is the construction of sequences for uniform excitation of double-quantum coherence and for uniform polarization transfer over a range of spin couplings. Double-quantum excitation sequences are demonstrated in a liquid crystal system. The second additional topic is the construction of iterative schemes for narrowband population inversion. The use of sequences that invert spin populations only over a narrow range of rf field amplitudes to spatially localize NMR signals in an rf field gradient is discussed.« less

Spin coating of electrolytes

DOEpatents

Stetter, Joseph R.; Maclay, G. Jordan

1989-01-01

Methods for spin coating electrolytic materials onto substrates are disclosed. More particularly, methods for depositing solid coatings of ion-conducting material onto planar substrates and onto electrodes are disclosed. These spin coating methods are employed to fabricate electrochemical sensors for use in measuring, detecting and quantifying gases and liquids.

Quantum Coherence and Random Fields at Mesoscopic Scales

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rosenbaum, Thomas F.

2016-03-01

We seek to explore and exploit model, disordered and geometrically frustrated magnets where coherent spin clusters stably detach themselves from their surroundings, leading to extreme sensitivity to finite frequency excitations and the ability to encode information. Global changes in either the spin concentration or the quantum tunneling probability via the application of an external magnetic field can tune the relative weights of quantum entanglement and random field effects on the mesoscopic scale. These same parameters can be harnessed to manipulate domain wall dynamics in the ferromagnetic state, with technological possibilities for magnetic information storage. Finally, extensions from quantum ferromagnets tomore » antiferromagnets promise new insights into the physics of quantum fluctuations and effective dimensional reduction. A combination of ac susceptometry, dc magnetometry, noise measurements, hole burning, non-linear Fano experiments, and neutron diffraction as functions of temperature, magnetic field, frequency, excitation amplitude, dipole concentration, and disorder address issues of stability, overlap, coherence, and control. We have been especially interested in probing the evolution of the local order in the progression from spin liquid to spin glass to long-range-ordered magnet.« less

George E. Valley, Jr. Prize Talk: Quantum Frustrated Magnetism and its Expression in the Ground State Selection of Pyrochlore Magnets

NASA Astrophysics Data System (ADS)

Ross, Kate

In the search for novel quantum states of matter, such as highly entangled Quantum Spin Liquids, ``geometrically frustrated'' magnetic lattices are essential for suppressing conventional magnetic order. In three dimensions, the pyrochlore lattice is the canonical frustrated geometry. Magnetic materials with pyrochlore structures have the potential to realize unusual phases such as ``quantum spin ice'', which is predicted to host emergent magnetic monopoles, electrons, and photons as its fundamental excitations. Even in pyrochlores that form long range ordered phases, this often occurs through unusual routes such as ``order by disorder'', in which the fluctuation spectrum dictates the preferred ordered state. The rare earth-based pyrochlore series R2Ti2O7 provides a fascinating variety of magnetic ground states. I will introduce the general anisotropic interaction Hamiltonian that has been successfully used to describe several materials in this series. Using inelastic neutron scattering, the relevant anisotropic interaction strengths can be extracted quantitatively. I will discuss this approach, and its application to two rare earth pyrochlore materials, Er2Ti2O7 and Yb2Ti<2O7, whose ground state properties have long been enigmatic. From these studies, ErTi2O7 and Yb2Ti2O7 have been suggested to be realizations of "quantum order by disorder" and "quantum spin ice", respectively. This research was supported by NSERC of Canada and the National Science Foundation.

Spin-Ice Thin Films: Large-N Theory and Monte Carlo Simulations

NASA Astrophysics Data System (ADS)

Lantagne-Hurtubise, Étienne; Rau, Jeffrey G.; Gingras, Michel J. P.

2018-04-01

We explore the physics of highly frustrated magnets in confined geometries, focusing on the Coulomb phase of pyrochlore spin ices. As a specific example, we investigate thin films of nearest-neighbor spin ice, using a combination of analytic large-N techniques and Monte Carlo simulations. In the simplest film geometry, with surfaces perpendicular to the [001] crystallographic direction, we observe pinch points in the spin-spin correlations characteristic of a two-dimensional Coulomb phase. We then consider the consequences of crystal symmetry breaking on the surfaces of the film through the inclusion of orphan bonds. We find that when these bonds are ferromagnetic, the Coulomb phase is destroyed by the presence of fluctuating surface magnetic charges, leading to a classical Z2 spin liquid. Building on this understanding, we discuss other film geometries with surfaces perpendicular to the [110] or the [111] direction. We generically predict the appearance of surface magnetic charges and discuss their implications for the physics of such films, including the possibility of an unusual Z3 classical spin liquid. Finally, we comment on open questions and promising avenues for future research.

Observation of Spin-Polarons in a strongly interacting Fermi liquid

NASA Astrophysics Data System (ADS)

Zwierlein, Martin

2009-03-01

We have observed spin-polarons in a highly imbalanced mixture of fermionic atoms using tomographic RF spectroscopy. Feshbach resonances allow to freely tune the interactions between the two spin states involved. A single spin down atom immersed in a Fermi sea of spin up atoms can do one of two things: For strong attraction, it can form a molecule with exactly one spin up partner, but for weaker interaction it will spread its attraction and surround itself with a collection of majority atoms. This spin down atom ``dressed'' with a spin up cloud constitutes the spin-polaron. We have observed a striking spectroscopic signature of this quasi-particle for various interaction strengths, a narrow peak in the spin down spectrum that emerges above a broad background. The narrow width signals a long lifetime of the spin-polaron, much longer than the collision rate with spin up atoms, as it must be for a proper quasi-particle. The peak position allows to directly measure the polaron energy. The broad pedestal at high energies reveals physics at short distances and is thus ``molecule-like'': It is exactly matched by the spin up spectra. The comparison with the area under the polaron peak allows to directly obtain the quasi-particle weight Z. We observe a smooth transition from polarons to molecules. At a critical interaction strength of 1/kFa = 0.7, the polaron peak vanishes and spin up and spin down spectra exactly match, signalling the formation of molecules. This is the same critical interaction strength found earlier to separate a normal Fermi mixture from a superfluid molecular Bose-Einstein condensate. The spin-polarons determine the low-temperature phase diagram of imbalanced Fermi mixtures. In principle, polarons can interact with each other and should, at low enough temperatures, form a superfluid of p-wave pairs. We will present a first indication for interactions between polarons.

Instrumentation for cryogenic magic angle spinning dynamic nuclear polarization using 90 L of liquid nitrogen per day

NASA Astrophysics Data System (ADS)

Albert, Brice J.; Pahng, Seong Ho; Alaniva, Nicholas; Sesti, Erika L.; Rand, Peter W.; Saliba, Edward P.; Scott, Faith J.; Choi, Eric J.; Barnes, Alexander B.

2017-10-01

Cryogenic sample temperatures can enhance NMR sensitivity by extending spin relaxation times to improve dynamic nuclear polarization (DNP) and by increasing Boltzmann spin polarization. We have developed an efficient heat exchanger with a liquid nitrogen consumption rate of only 90 L per day to perform magic-angle spinning (MAS) DNP experiments below 85 K. In this heat exchanger implementation, cold exhaust gas from the NMR probe is returned to the outer portion of a counterflow coil within an intermediate cooling stage to improve cooling efficiency of the spinning and variable temperature gases. The heat exchange within the counterflow coil is calculated with computational fluid dynamics to optimize the heat transfer. Experimental results using the novel counterflow heat exchanger demonstrate MAS DNP signal enhancements of 328 ± 3 at 81 ± 2 K, and 276 ± 4 at 105 ± 2 K.

Electron paramagnetic resonance studies of slowly tumbling vanadyl spin probes in nematic liquid crystals

NASA Technical Reports Server (NTRS)

Bruno, G. V.; Harrington, J. K.; Eastman, M. P.

1978-01-01

The purposes of this vanadyl spin probe study are threefold: (1) to establish when the breakdown of motionally narrowed formulas occurs; (2) to analyze the experimental vanadyl EPR line shapes by the stochastic Lioville method as developed by Polnaszek et al. (1973) for slow tumbling in an anisotropic liquid; and (3) to compare the vanadyl probe study results with those of Polnaszek and Freed (1975). Spectral EPR line shapes are simulated for experimental spectra of vanadyl acetylacetonate (VOAA) in nematic liquid crystal butyl p-(p-ethoxyphenoxycarbonyl) phenyl carbonate (BEPC) and Phase V of EM laboratories. It is shown that the use of typical vanadyl complexes as spin probes for nematic liquid crystals simplifies the theoretical analysis and the subsequent interpretation. Guidelines for the breakdown of motionally narrowed formulas are established. Both the slow tumbling aspects and the effects of non-Brownian rotation should be resolved in order to extract quantitative information about molecular ordering and rotational mobility.

Spin-fluctuation-induced non-Fermi-liquid behavior with suppressed superconductivity in LiFe 1-xCo xAs

DOE PAGES

Y. M. Dai; Miao, H.; Xing, L. Y.; ...

2015-09-15

A series of LiFe 1–xCo xAs compounds with different Co concentrations by transport, optical spectroscopy, angle-resolved photoemission spectroscopy, and nuclear magnetic resonance. We observe a Fermi-liquid to non-Fermi-liquid to Fermi-liquid (FL-NFL-FL) crossover alongside a monotonic suppression of the superconductivity with increasing Co content. In parallel to the FL-NFL-FL crossover, we find that both the low-energy spin fluctuations and Fermi surface nesting are enhanced and then diminished, strongly suggesting that the NFL behavior in LiFe 1–xCo xAs is induced by low-energy spin fluctuations that are very likely tuned by Fermi surface nesting. Our study reveals a unique phase diagram of LiFemore » 1–xCo xAs where the region of NFL is moved to the boundary of the superconducting phase, implying that they are probably governed by different mechanisms.« less

Solid-state 27Al MRI and NMR thermometry for catalytic applications with conventional (liquids) MRI instrumentation and techniques.

PubMed

Koptyug, Igor V; Sagdeev, Dmitry R; Gerkema, Edo; Van As, Henk; Sagdeev, Renad Z

2005-07-01

Multidimensional images of Al2O3 pellets, cordierite monolith, glass tube, polycrystalline V2O5 and other materials have been detected by 27Al, 51V, and 23Na NMR imaging using techniques and instrumentation conventionally employed for imaging of liquids. These results demonstrate that, contrary to the widely accepted opinion, imaging of "rigid" solids does not necessarily require utilization of solid state NMR imaging approaches, pulse sequences and hardware even for quadrupolar nuclei which exhibit line widths in excess of 100 kHz, such as 51V in polycrystalline V2O5. It is further demonstrated that both 27Al NMR signal intensity and spin-lattice relaxation time decrease with increasing temperature and thus can potentially serve as temperature sensitive parameters for spatially resolved NMR thermometry.

Interplay between the Dzyaloshinskii-Moriya term and external fields on spin transport in the spin-1/2 one-dimensional antiferromagnet

NASA Astrophysics Data System (ADS)

Lima, L. S.

2018-05-01

We study the effect of the uniform Dzyaloshinskii-Moriya interaction (symmetric exchange anisotropy) and arbitrary oriented external magnetic fields on spin conductivity in the spin-1/2 one-dimensional Heisenberg antiferromagnet. The spin conductivity is calculated employing abelian bosonization and the Kubo formalism of transport. We investigate the influence of three competing phases at zero-temperature, (Néel phase, dimerized phase and gapless Luttinger liquid phase) on the AC spin conductivity.

Spin-Mechatronics

NASA Astrophysics Data System (ADS)

Matsuo, Mamoru; Saitoh, Eiji; Maekawa, Sadamichi

2017-01-01

We investigate the interconversion phenomena between spin and mechanical angular momentum in moving objects. In particular, the recent results on spin manipulation and spin-current generation by mechanical motion are examined. In accelerating systems, spin-dependent gauge fields emerge, which enable the conversion from mechanical angular momentum into spins. Such a spin-mechanical effect is predicted by quantum theory in a non-inertial frame. Experiments which confirm the effect, i.e., the resonance frequency shift in nuclear magnetic resonance, the stray field measurement of rotating metals, and electric voltage generation in liquid metals, are discussed.

Many-body effects in electron liquids with Rashba spin-orbit coupling

NASA Astrophysics Data System (ADS)

Simion, George E.

The main topic of the present thesis is represented by the many-body effects which characterize the physical behavior of an electron liquid in various realizations. We begin by studying the problem of the response of an otherwise homogeneous electron liquid to the potential of an impurity embedded in its bulk. The most dramatic consequence of this perturbation is the existence of so called Friedel density oscillations. We present calculations of their amplitude valid in two as well as in three dimensions. The second problem we will discuss is that of the correlation effects in a three dimensional electron liquid in the metallic density regime. A number of quasiparticle properties are evaluated: the electron self-energy, the quasiparticle effective mass and the renormalization constant. We also present an analysis of the effective Lande g-factor as well as the compressibility. The effects of the Coulomb interactions beyond the random phase approximation have been treated by means of an approach based on the many-body local field factors theory and by utilizing the latest numerical results of Quantum Monte Carlo numerical simulations. The final chapter includes the results of our extensive work on various aspects regarding the two dimensional Fermi liquid in the presence of linear Rashba spin-orbit coupling. By using a number of many-body techniques, we have studied the interplay between spin-orbit coupling and electron-electron interaction. After proving an extension to the famous Overhauser Hartree-Fock instability theorem, a considerable amount of work will be presented on the problem of the density and spin response functions. For the study of the spin response, we will present the results of extensive numerical calculations based on the time dependent mean field theory approach.

Models and materials for generalized Kitaev magnetism

NASA Astrophysics Data System (ADS)

Winter, Stephen M.; Tsirlin, Alexander A.; Daghofer, Maria; van den Brink, Jeroen; Singh, Yogesh; Gegenwart, Philipp; Valentí, Roser

2017-12-01

The exactly solvable Kitaev model on the honeycomb lattice has recently received enormous attention linked to the hope of achieving novel spin-liquid states with fractionalized Majorana-like excitations. In this review, we analyze the mechanism proposed by Jackeli and Khaliullin to identify Kitaev materials based on spin-orbital dependent bond interactions and provide a comprehensive overview of its implications in real materials. We set the focus on experimental results and current theoretical understanding of planar honeycomb systems (Na2IrO3, α-Li2IrO3, and α-RuCl3), three-dimensional Kitaev materials (β- and γ-Li2IrO3), and other potential candidates, completing the review with the list of open questions awaiting new insights.

Semiclassical theory of the tunneling anomaly in partially spin-polarized compressible quantum Hall states

NASA Astrophysics Data System (ADS)

Chowdhury, Debanjan; Skinner, Brian; Lee, Patrick A.

2018-05-01

Electron tunneling into a system with strong interactions is known to exhibit an anomaly, in which the tunneling conductance vanishes continuously at low energy due to many-body interactions. Recent measurements have probed this anomaly in a quantum Hall bilayer of the half-filled Landau level, and shown that the anomaly apparently gets stronger as the half-filled Landau level is increasingly spin polarized. Motivated by this result, we construct a semiclassical hydrodynamic theory of the tunneling anomaly in terms of the charge-spreading action associated with tunneling between two copies of the Halperin-Lee-Read state with partial spin polarization. This theory is complementary to our recent work (D. Chowdhury, B. Skinner, and P. A. Lee, arXiv:1709.06091) where the electron spectral function was computed directly using an instanton-based approach. Our results show that the experimental observation cannot be understood within conventional theories of the tunneling anomaly, in which the spreading of the injected charge is driven by the mean-field Coulomb energy. However, we identify a qualitatively new regime, in which the mean-field Coulomb energy is effectively quenched and the tunneling anomaly is dominated by the finite compressibility of the composite Fermion liquid.

Dependence of magnetic field and electronic transport of Mn4 Single-molecule magnet in a Single-Electron Transistor

NASA Astrophysics Data System (ADS)

Rodriguez, Alvar; Singh, Simranjeet; Haque, Firoze; Del Barco, Enrique; Nguyen, Tu; Christou, George

2012-02-01

Dependence of magnetic field and electronic transport of Mn4 Single-molecule magnet in a Single-Electron Transistor A. Rodriguez, S. Singh, F. Haque and E. del Barco Department of Physics, University of Central Florida, 4000 Central Florida Blvd., Orlando, Florida 32816 USA T. Nguyen and G. Christou Department of Chemistry, University of Florida, Gainesville, Florida 32611 USA Abstract We have performed single-electron transport measurements on a series of Mn-based low-nuclearity single-molecule magnets (SMM) observing Coulomb blockade. SMMs with well isolated and low ground spin states, i.e. S = 9/2 (Mn4) and S = 6 (Mn3) were chosen for these studies, such that the ground spin multiplet does not mix with levels of other excited spin states for the magnetic fields (H = 0-8 T) employed in the experiments. Different functionalization groups were employed to change the mechanical, geometrical and transport characteristics of the molecules when deposited from liquid solution on the transistors. Electromigration-broken three-terminal single-electron transistors were used. Results obtained at temperatures down to 240 mK and in the presence of high magnetic fields will be shown.

Low-temperature dynamic nuclear polarization with helium-cooled samples and nitrogen-driven magic-angle spinning.

PubMed

Thurber, Kent; Tycko, Robert

2016-03-01

We describe novel instrumentation for low-temperature solid state nuclear magnetic resonance (NMR) with dynamic nuclear polarization (DNP) and magic-angle spinning (MAS), focusing on aspects of this instrumentation that have not been described in detail in previous publications. We characterize the performance of an extended interaction oscillator (EIO) microwave source, operating near 264 GHz with 1.5 W output power, which we use in conjunction with a quasi-optical microwave polarizing system and a MAS NMR probe that employs liquid helium for sample cooling and nitrogen gas for sample spinning. Enhancement factors for cross-polarized (13)C NMR signals in the 100-200 range are demonstrated with DNP at 25K. The dependences of signal amplitudes on sample temperature, as well as microwave power, polarization, and frequency, are presented. We show that sample temperatures below 30K can be achieved with helium consumption rates below 1.3 l/h. To illustrate potential applications of this instrumentation in structural studies of biochemical systems, we compare results from low-temperature DNP experiments on a calmodulin-binding peptide in its free and bound states. Published by Elsevier Inc.

Spin-lattice relaxation of 13C in solid amino acids using the CP-MAS technique

NASA Astrophysics Data System (ADS)

Naito, A.; Ganapathy, S.; Akasaka, K.; McDowell, C. A.

It is shown by a simple application of relaxation theory that the 13C magnetization decays nonexponentially, in principle, in the CP-MAS experiment because of the distribution of the spin-lattice relaxation times; however, the deviation from the exponential decay is quite small. The transient Overhauser effect also contributes appreciably to the nonexponential decay of the 13C magnetization when the protons are not saturated during the 13C T1 measurements and the correlation time of the group rotational motion satisfies the condition, ω2τc2 ≦ 1. It is shown by both experiment and theory that the transient Overhauser effect in the solid state is much smaller than that expected for the liquid state. The 13C spin-lattice relaxation times of L-alanine, deutero- L-alanine, glycine, and L-serine were determined for the individual carbon atoms. The experimentally obtained 13C T1 values agree well with calculated ones, showing that the CH 3 group rotation provides the main source of the relaxation in alanine, while the NH 3+ group motion plays an important role for the relaxation in glycine and serene.

Lattice spin models for non-Abelian chiral spin liquids

DOE PAGES

Lecheminant, P.; Tsvelik, A. M.

2017-04-26

Here, we suggest a class of two-dimensional lattice spin Hamiltonians describing non-Abelian SU(2) chiral spin liquids—spin analogs of fractional non-Abelian quantum Hall states—with gapped bulk and gapless chiral edge excitations described by the SU(2) n Wess-Zumino-Novikov-Witten conformal field theory. The models are constructed from an array of generalized spin-n/2 ladders with multi-spin-exchange interactions which are coupled by isolated spins. Such models allow a controllable analytic treatment starting from the one-dimensional limit and are characterized by a bulk gap and non-Abelian SU(2) n gapless edge excitations.

The SO(3)×SO(3)×U(1) Hubbard model on a square lattice in terms of c and αν fermions and deconfined η-spinons and spinons

NASA Astrophysics Data System (ADS)

Carmelo, J. M. P.

2012-03-01

In this paper, a general description for the Hubbard model with nearest-neighbor transfer integral t and on-site repulsion U on a square lattice with Na2≫1 sites is introduced. It refers to three types of elementary objects whose occupancy configurations generate the state representations of the model extended global SO(3)×SO(3)×U(1) symmetry recently found in Ref. [11] (Carmelo and Östlund, 2010). Such objects emerge from a suitable electron-rotated-electron unitary transformation. It is such that rotated-electron single and double occupancy are good quantum numbers for U≠0. The advantage of the description is that it accounts for the new found hidden U(1) symmetry in SO(3)×SO(3)×U(1)=[SU(2)×SU(2)×U(1)]/Z22 beyond the well-known SO(4)=[SU(2)×SU(2)]/Z2 model (partial) global symmetry. Specifically, the hidden U(1) symmetry state representations store full information on the positions of the spins of the rotated-electron singly occupied sites relative to the remaining sites. Profiting from that complementary information, for the whole U/4t>0 interaction range independent spin state representations are naturally generated in terms of spin-1/2 spinon occupancy configurations in a spin effective lattice. For all states, such an effective lattice has as many sites as spinons. This allows the extension to intermediate U/4t values of the usual large-U/4t descriptions of the spin degrees of freedom of the electrons that singly occupy sites, now in terms of the spins of the singly-occupied sites rotated electrons. The operator description introduced in this paper brings about a more suitable scenario for handling the effects of hole doping. Within this, such effects are accounted for in terms of the residual interactions of the elementary objects whose occupancy configurations generate the state representations of the charge hidden U(1) symmetry and spin SU(2) symmetry, respectively. This problem is investigated elsewhere. The most interesting physical information revealed by the description refers to the model on the subspace generated by the application of one- and two-electron operators onto zero-magnetization ground states. (This is the square-lattice quantum liquid further studied in Ref. [5] (Carmelo, 2010).) However, to access such an information, one must start from the general description introduced in this paper, which refers to the model in the full Hilbert space.

Single-crystal growth of C u4(OH) 6BrF and universal behavior in quantum spin liquid candidates synthetic barlowite and herbertsmithite

NASA Astrophysics Data System (ADS)

Pasco, C. M.; Trump, B. A.; Tran, Thao T.; Kelly, Z. A.; Hoffmann, C.; Heinmaa, I.; Stern, R.; McQueen, T. M.

2018-04-01

Synthetic barlowite, C u4(OH) 6BrF , has emerged as a new quantum spin liquid (QSL) host, containing kagomé layers of S =1 /2 C u2 + ions separated by interlayer C u2 + ions. Similar to synthetic herbertsmithite, ZnC u3(OH) 6C l2 , it has been reported that Z n2 + substitution for the interlayer C u2 + induces a QSL ground state. Here we report a scalable synthesis of single crystals of C u4(OH) 6BrF . Through x-ray, neutron, and electron diffraction measurements coupled with magic angle spinning 19F and 1H NMR spectroscopy, we resolve the previously reported positional disorder of the interlayer C u2 + ions and find that the structure is best described in the orthorhombic space group, Cmcm, with lattice parameters a =6.665 (13 )Å ,b =11.521 (2 )Å ,c =9.256 (18 )Å , and an ordered arrangement of interlayer C u2 + ions. Infrared spectroscopy measurements of the O—H and F—H stretching frequencies demonstrate that the orthorhombic symmetry persists upon substitution of Z n2 + for C u2 + . Specific heat and magnetic susceptibility measurements of Zn-substituted barlowite, Z nxC u4 -x(OH) 6BrF , reveal striking similarities with the behavior of Z nxC u4 -x(OH) 6C l2 . These parallels imply universal behavior of copper kagomé lattices even in the presence of small symmetry-breaking distortions. Thus, synthetic barlowite demonstrates universality of the physics of synthetic C u2 + kagomé minerals and furthers the development of real QSL states.

Neutron Detection with Centrifugally-Tensioned Metastable Fluid Detectors (CMTFD)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Y.; Smagacz, P.; Lapinskas, J.

2006-07-01

Tensioned metastable liquid states at room temperature were utilized to display sensitivity to impinging nuclear radiation, that manifests itself via audio-visual signals that one can see and hear. A centrifugally-tensioned metastable fluid detector (CTMFD), a diamond shaped spinning device rotating about its axis, was used to induce tension states, i.e. negative (sub-vacuum) pressures in liquids. In this device, radiation induced cavitation is audible due to liquid fracture and is visible from formed bubbles, so called hearing and seeing radiation. This type of detectors is selectively insensitive to Gamma rays and associated indication devices could be extremely simple, reliable and inexpensive.more » Furthermore, any liquids with large neutron interaction cross sections could be good candidates. Two liquids, isopentane and methanol, were tested with three neutron sources of Cf-252, PuBe and Pulsed Neutron Generator (PNG) under various configurations of neutron spectra and fluxes. The neutron count rates were measured using a liquid scintillation detector. The CTMFD was operated at preset values of rotating frequency and a response time was recorded when a cavitation occurred. Other parameters, including ambient temperature, ramp rate, delay time between two consecutive cavitations, were kept constant. The distance between the menisci of the liquid in the CTMFD was measured before and after each experiment. In general, the response of liquid molecules in a CTMFD varies with the neutron spectrum and flux. The response time follows an exponential trend with negative pressures for a given neutron count rate and spectra conditions. Isopentane was found to exhibit lower tension thresholds than methanol. On the other hand, methanol offered a larger tension metastability state variation for the various types of neutron sources, indicating the potential for offering significantly better energy resolution abilities for spectroscopic applications. (authors)« less

Quantum spin circulator in Y junctions of Heisenberg chains

NASA Astrophysics Data System (ADS)

Buccheri, Francesco; Egger, Reinhold; Pereira, Rodrigo G.; Ramos, Flávia B.

2018-06-01

We show that a quantum spin circulator, a nonreciprocal device that routes spin currents without any charge transport, can be achieved in Y junctions of identical spin-1 /2 Heisenberg chains coupled by a chiral three-spin interaction. Using bosonization, boundary conformal field theory, and density matrix renormalization group simulations, we find that a chiral fixed point with maximally asymmetric spin conductance arises at a critical point separating a regime of disconnected chains from a spin-only version of the three-channel Kondo effect. We argue that networks of spin-chain Y junctions provide a controllable approach to construct long-sought chiral spin-liquid phases.

Investigation of Liquid Sloshing in Spin-Stabilized Satellites.

DTIC Science & Technology

1993-01-31

deformation of the spinning structure in addition to the rigid body motion . A Lagrangian approach was used to develop the equations of motion which include...nonlinear relationships for the unknown rigid body motions and linear terms for the relatively small elastic deformations of the members. Appendix F...the rigid body motion of the test assembly. A pendulum analogy was used to model the sloshing liquid in that early program. Several numerical

Multiple Locations of Peptides in the Hydrocarbon Core of Gel-Phase Membranes Revealed by Peptide 13C to Lipid 2H Rotational-Echo Double-Resonance Solid-State Nuclear Magnetic Resonance

PubMed Central

2015-01-01

Membrane locations of peptides and proteins are often critical to their functions. Solid-state rotational-echo double-resonance (REDOR) nuclear magnetic resonance is applied to probe the locations of two peptides via peptide 13CO to lipid 2H distance measurements. The peptides are KALP, an α-helical membrane-spanning peptide, and HFP, the β-sheet N-terminal fusion peptide of the HIV gp41 fusion protein that plays an important role in HIV–host cell membrane fusion. Both peptides are shown to have at least two distinct locations within the hydrocarbon core of gel-phase membranes. The multiple locations are attributed to snorkeling of lysine side chains for KALP and to the distribution of antiparallel β-sheet registries for HFP. The relative population of each location is also quantitated. To the best of our knowledge, this is the first clear experimental support of multiple peptide locations within the membrane hydrocarbon core. These data are for gel-phase membranes, but the approach should work for liquid-ordered membranes containing cholesterol and may be applicable to liquid-disordered membranes with appropriate additional analysis to take into account protein and lipid motion. This paper also describes the methodological development of 13CO–2H REDOR using the lyophilized I4 peptide that is α-helical and 13CO-labeled at A9 and 2Hα-labeled at A8. The I4 spins are well-approximated as an ensemble of isolated 13CO–2H spin pairs each separated by 5.0 Å with a 37 Hz dipolar coupling. A pulse sequence with rectangular 100 kHz 2H π pulses results in rapid and extensive buildup of REDOR (ΔS/S0) with a dephasing time (τ). The buildup is well-fit by a simple exponential function with a rate of 24 Hz and an extent close to 1. These parameter values reflect nonradiative transitions between the 2H spin states during the dephasing period. Each spin pair spends approximately two-thirds of its time in the 13CO–2H (m = ±1) states and approximately one-third of its time in the 13CO–2H (m = 0) state and contributes to the ΔS/S0 buildup during the former but not the latter time segments. PMID:25531389

Possible realization of interacting symmetry-protected topological phases in topological crystalline insulators

NASA Astrophysics Data System (ADS)

Isobe, Hiroki; Fu, Liang

2015-03-01

The effects of electron-electron interaction in edge states of mirror-symmetry protected topological crystalline insulators (TCI's) are discussed. The analysis is performed by using bosonized Hamiltonian following the Tomonaga-Luttinger liquid theory. When two pairs of helical edge states exist, electron-electron interaction could gap out one edge mode, which is a possible realization of interacting symmetry-protected topological (SPT) phases. This type of SPT phase is closely related to a Luther-Emery liquid in spinful 1D system. We also propose a method of detecting the SPT phases by STM. The other focus of the study is the classification of SPT phases in mirror-symmetry protected TCI's. By adopting the Chern-Simons theory, we find that electron-electron interaction reduces the classification from Z to Z4. It means that the edge states can be gapped out when four pairs of edge states exist. In other cases, the edge modes cannot be fully gapped. Each of these states corresponds to a different SPT phase depending on the relevant interaction process.

Iron Partitioning in Ferropericlase and Consequences for the Magma Ocean.

NASA Astrophysics Data System (ADS)

Braithwaite, J. W. H.; Stixrude, L. P.; Holmstrom, E.; Pinilla, C.

2016-12-01

The relative buoyancy of crystals and liquid is likely to exert a strong influence on the thermal and chemical evolution of the magma ocean. Theory indicates that liquids approach, but do not exceed the density of iso-chemical crystals in the deep mantle. The partitioning of heavy elements, such as Fe, is therefore likely to control whether crystals sink or float. While some experimental results exist, our knowledge of silicate liquid-crystal element partitioning is still limited in the deep mantle. We have developed a method for computing the Mg-Fe partitioning of Fe in such systems. We have focused initially on ferropericlase, as a relatively simple system where the buoyancy effects of Fe partitioning are likely to be large. The method is based on molecular dynamics driven by density functional theory (spin polarized, PBEsol+U). We compute the free energy of Mg for Fe substitution in simulations of liquid and B1 crystalline phases via adiabatic switching. We investigate the dependence of partitioning on pressure, temperature, and iron concentration. We find that the liquid is denser than the coexisting crystalline phase at all conditions studies. We also find that the high-spin to low-spin transition in the crystal and the liquid, have an important influence on partitioning behavior.

Electrodynamics of quantum spin liquids

NASA Astrophysics Data System (ADS)

Dressel, Martin; Pustogow, Andrej

2018-05-01

Quantum spin liquids attract great interest due to their exceptional magnetic properties characterized by the absence of long-range order down to low temperatures despite the strong magnetic interaction. Commonly, these compounds are strongly correlated electron systems, and their electrodynamic response is governed by the Mott gap in the excitation spectrum. Here we summarize and discuss the optical properties of several two-dimensional quantum spin liquid candidates. First we consider the inorganic material herbertsmithite ZnCu3(OH)6Cl2 and related compounds, which crystallize in a kagome lattice. Then we turn to the organic compounds -EtMe3Sb[Pd(dmit)2]2, κ-(BEDT-TTF)2Ag2(CN)3 and κ-(BEDT-TTF)2Cu2(CN)3, where the spins are arranged in an almost perfect triangular lattice, leading to strong frustration. Due to differences in bandwidth, the effective correlation strength varies over a wide range, leading to a rather distinct behavior as far as the electrodynamic properties are concerned. We discuss the spinon contributions to the optical conductivity in comparison to metallic quantum fluctuations in the vicinity of the Mott transition.

Spray nozzle designs for agricultural aviation applications. [relation of drop size to spray characteristics and nozzle efficiency

NASA Technical Reports Server (NTRS)

Lee, K. W.; Putnam, A. A.; Gieseke, J. A.; Golovin, M. N.; Hale, J. A.

1979-01-01

Techniques of generating monodisperse sprays and information concerning chemical liquids used in agricultural aviation are surveyed. The periodic dispersion of liquid jet, the spinning disk method, and ultrasonic atomization are the techniques discussed. Conceptually designed spray nozzles for generating monodisperse sprays are assessed. These are based on the classification of the drops using centrifugal force, on using two opposing liquid laden air jets, and on operating a spinning disk at an overloaded flow. Performance requirements for the designs are described and estimates of the operational characteristics are presented.

Spin and charge currents and current rectification in Luttinger liquids

NASA Astrophysics Data System (ADS)

Braunecker, B.; Feldman, D. E.; Marston, J. B.

2006-03-01

Asymmetries in spin and charge transport properties are of great interest for spintronic and electronic applications. We show that externally-driven spin and charge currents in a Luttinger liquid model of a one-dimensional quantum wire are strongly modified by the presence of a localized magnetic or nonmagnetic scatterer. A diode effect appears at low voltages when this scatterer is spatially asymmetric, and a non-monotonous dependence of the current on the voltage is possible. D.E. Feldman, S. Scheidl, and V. M. Vinokur, Phys. Rev. Lett. 94, 186809 (2005); B. Braunecker, D. E. Feldman, and J. B. Marston, Phys. Rev. B 72, 125311 (2005)

Fermionic Spinon Theory of Square Lattice Spin Liquids near the Néel State

NASA Astrophysics Data System (ADS)

Thomson, Alex; Sachdev, Subir

2018-01-01

Quantum fluctuations of the Néel state of the square lattice antiferromagnet are usually described by a CP1 theory of bosonic spinons coupled to a U(1) gauge field, and with a global SU(2) spin rotation symmetry. Such a theory also has a confining phase with valence bond solid (VBS) order, and upon including spin-singlet charge-2 Higgs fields, deconfined phases with Z2 topological order possibly intertwined with discrete broken global symmetries. We present dual theories of the same phases starting from a mean-field theory of fermionic spinons moving in π flux in each square lattice plaquette. Fluctuations about this π -flux state are described by (2 +1 )-dimensional quantum chromodynamics (QCD3 ) with a SU(2) gauge group and Nf=2 flavors of massless Dirac fermions. It has recently been argued by Wang et al. [Deconfined Quantum Critical Points: Symmetries and Dualities, Phys. Rev. X 7, 031051 (2017)., 10.1103/PhysRevX.7.031051] that this QCD3 theory describes the Néel-VBS quantum phase transition. We introduce adjoint Higgs fields in QCD3 and obtain fermionic dual descriptions of the phases with Z2 topological order obtained earlier using the bosonic CP1 theory. We also present a fermionic spinon derivation of the monopole Berry phases in the U(1) gauge theory of the VBS state. The global phase diagram of these phases contains multicritical points, and our results imply new boson-fermion dualities between critical gauge theories of these points.

Quantum phase diagram of distorted J 1 - J 2 Heisenberg S  =  1/2 antiferromagnet in honeycomb lattice: a modified spin wave study

NASA Astrophysics Data System (ADS)

Ghorbani, Elaheh; Shahbazi, Farhad; Mosadeq, Hamid

2016-10-01

Using the modified spin wave method, we study the {{J}1}-{{J}2} Heisenberg model with first and second neighbor antiferromagnetic exchange interactions. For a symmetric S  =  1/2 model, with the same couplings for all the equivalent neighbors, we find three phases in terms of the frustration parameter \\barα={{J}2}/{{J}1} : (1) a commensurate collinear ordering with staggered magnetization (Néel.I state) for 0≤slant \\barα≲ 0.207 , (2) a magnetically gapped disordered state for 0.207≲ \\barα≲ 0.369 , preserving all the symmetries of the Hamiltonian and lattice, which by definition is a quantum spin liquid (QSL) state and (3) a commensurate collinear ordering in which two out of the three nearest neighbor magnetizations are antiparallel and the remaining pair are parallel (Néel.II state), for 0.396≲ \\barα≤slant 1 . We also explore the phase diagram of a distorted {{J}1}-{{J}2} model with S  =  1/2. Distortion is introduced as an inequality of one nearest neighbor coupling with the other two. This yields a richer phase diagram by the appearance of a new gapped QSL, a gapless QSL and also a valence bond crystal phase in addition to the previous three phases found for the undistorted model.

Finite-temperature behavior of a classical spin-orbit-coupled model for YbMgGaO4 with and without bond disorder

NASA Astrophysics Data System (ADS)

Parker, Edward; Balents, Leon

2018-05-01

We present the results of finite-temperature classical Monte Carlo simulations of a strongly spin-orbit-coupled nearest-neighbor triangular-lattice model for the candidate U (1 ) quantum spin liquid YbMgGaO4 at large system sizes. We find a single continuous finite-temperature stripe-ordering transition with slowly diverging heat capacity that completely breaks the sixfold ground-state degeneracy, despite the absence of a known conformal field theory describing such a transition. We also simulate the effect of random-bond disorder in the model, and find that even weak bond disorder destroys the transition by fragmenting the system into very large domains—possibly explaining the lack of observed ordering in the real material. The Imry-Ma argument only partially explains this fragility to disorder, and we extend the argument with a physical explanation for the preservation of our system's time-reversal symmetry even under a disorder model that preserves the same symmetry.

Dynamic Nuclear Polarization and other magnetic ideas at EPFL.

PubMed

Bornet, Aurélien; Milani, Jonas; Wang, Shutao; Mammoli, Daniele; Buratto, Roberto; Salvi, Nicola; Segaw, Takuya F; Vitzthum, Veronika; Miéville, Pascal; Chinthalapalli, Srinivas; Perez-Linde, Angel J; Carnevale, Diego; Jannin, Sami; Caporinia, Marc; Ulzega, Simone; Rey, Martial; Bodenhausen, Geoffrey

2012-01-01

Although nuclear magnetic resonance (NMR) can provide a wealth of information, it often suffers from a lack of sensitivity. Dynamic Nuclear Polarization (DNP) provides a way to increase the polarization and hence the signal intensities in NMR spectra by transferring the favourable electron spin polarization of paramagnetic centres to the surrounding nuclear spins through appropriate microwave irradiation. In our group at EPFL, two complementary DNP techniques are under investigation: the combination of DNP with magic angle spinning at temperatures near 100 K ('MAS-DNP'), and the combination of DNP at 1.2 K with rapid heating followed by the transfer of the sample to a high-resolution magnet ('dissolution DNP'). Recent applications of MAS-DNP to surfaces, as well as new developments of magnetization transfer of (1)H to (13)C at 1.2 K prior to dissolution will illustrate the work performed in our group. A second part of the paper will give an overview of some 'non-enhanced' activities of our laboratory in liquid- and solid-state NMR.

Quantum simulation of the Hubbard model with dopant atoms in silicon

PubMed Central

Salfi, J.; Mol, J. A.; Rahman, R.; Klimeck, G.; Simmons, M. Y.; Hollenberg, L. C. L.; Rogge, S.

2016-01-01

In quantum simulation, many-body phenomena are probed in controllable quantum systems. Recently, simulation of Bose–Hubbard Hamiltonians using cold atoms revealed previously hidden local correlations. However, fermionic many-body Hubbard phenomena such as unconventional superconductivity and spin liquids are more difficult to simulate using cold atoms. To date the required single-site measurements and cooling remain problematic, while only ensemble measurements have been achieved. Here we simulate a two-site Hubbard Hamiltonian at low effective temperatures with single-site resolution using subsurface dopants in silicon. We measure quasi-particle tunnelling maps of spin-resolved states with atomic resolution, finding interference processes from which the entanglement entropy and Hubbard interactions are quantified. Entanglement, determined by spin and orbital degrees of freedom, increases with increasing valence bond length. We find separation-tunable Hubbard interaction strengths that are suitable for simulating strongly correlated phenomena in larger arrays of dopants, establishing dopants as a platform for quantum simulation of the Hubbard model. PMID:27094205

Superconductivity on the brink of spin-charge order in doped honeycomb bilayer

NASA Astrophysics Data System (ADS)

Vafek, Oskar; Murray, James; Cvetkovic, Vladimir

2014-03-01

Using a controlled weak-coupling renormalization group approach, we establish the mechanism of unconventional superconductivity in the vicinity of spin or charge ordered excitonic states for the case of electrons on the Bernal stacked bilayer honeycomb lattice. With one electron per site this system exhibits nearly parabolically touching conduction and valence bands. Such a state is unstable towards a spontaneous symmetry breaking, and repulsive interactions favor excitonic order, such as a charge nematic and/or a layer antiferromagnet. We find that upon adding charge carriers to the system, the excitonic order is suppressed, and unconventional superconductivity appears in its place, before it is replaced by a Fermi liquid. We focus on firmly establishing this phenomenon using the RG formalism within an idealized model with parabolic touching. This work was supported by the NSF CAREER award under Grant No. DMR-0955561 (OV), NSF Cooperative Agreement No. DMR-0654118, and the State of Florida (OV,JM,CV), as well as by ICAM-I2CAM (NSF grant DMR-0844115) and by DoE Award DE-FG02-08ER46544 (JM).

Dimensional crossover and cold-atom realization of topological Mott insulators

PubMed Central

Scheurer, Mathias S.; Rachel, Stephan; Orth, Peter P.

2015-01-01

Interacting cold-atomic gases in optical lattices offer an experimental approach to outstanding problems of many body physics. One important example is the interplay of interaction and topology which promises to generate a variety of exotic phases such as the fractionalized Chern insulator or the topological Mott insulator. Both theoretically understanding these states of matter and finding suitable systems that host them have proven to be challenging problems. Here we propose a cold-atom setup where Hubbard on-site interactions give rise to spin liquid-like phases: weak and strong topological Mott insulators. They represent the celebrated paradigm of an interacting and topological quantum state with fractionalized spinon excitations that inherit the topology of the non-interacting system. Our proposal shall help to pave the way for a controlled experimental investigation of this exotic state of matter in optical lattices. Furthermore, it allows for the investigation of a dimensional crossover from a two-dimensional quantum spin Hall insulating phase to a three-dimensional strong topological insulator by tuning the hopping between the layers. PMID:25669431

Symmetry-protected topological phases of one-dimensional interacting fermions with spin-charge separation

NASA Astrophysics Data System (ADS)

Montorsi, Arianna; Dolcini, Fabrizio; Iotti, Rita C.; Rossi, Fausto

2017-06-01

The low energy behavior of a huge variety of one-dimensional interacting spinful fermionic systems exhibits spin-charge separation, described in the continuum limit by two sine-Gordon models decoupled in the charge and spin channels. Interaction is known to induce, besides the gapless Luttinger liquid phase, eight possible gapped phases, among which are the Mott, Haldane, charge-/spin-density, and bond-ordered wave insulators, and the Luther Emery liquid. Here we prove that some of these physically distinct phases have nontrivial topological properties, notably the presence of degenerate protected edge modes with fractionalized charge/spin. Moreover, we show that the eight gapped phases are in one-to-one correspondence with the symmetry-protected topological (SPT) phases classified by group cohomology theory in the presence of particle-hole symmetry P. The latter result is also exploited to characterize SPT phases by measurable nonlocal order parameters which follow the system evolution to the quantum phase transition. The implications on the appearance of exotic orders in the class of microscopic Hubbard Hamiltonians, possibly without P symmetry at higher energies, are discussed.

Quantum criticality among entangled spin chains

DOE PAGES

Blanc, N.; Trinh, J.; Dong, L.; ...

2017-12-11

Here, an important challenge in magnetism is the unambiguous identification of a quantum spin liquid, of potential importance for quantum computing. In such a material, the magnetic spins should be fluctuating in the quantum regime, instead of frozen in a classical long-range-ordered state. While this requirement dictates systems wherein classical order is suppressed by a frustrating lattice, an ideal system would allow tuning of quantum fluctuations by an external parameter. Conventional three-dimensional antiferromagnets can be tuned through a quantum critical point—a region of highly fluctuating spins—by an applied magnetic field. Such systems suffer from a weak specific-heat peak at themore » quantum critical point, with little entropy available for quantum fluctuations. Here we study a different type of antiferromagnet, comprised of weakly coupled antiferromagnetic spin-1/2 chains as realized in the molecular salt K 2PbCu(NO 2) 6. Across the temperature–magnetic field boundary between three-dimensional order and the paramagnetic phase, the specific heat exhibits a large peak whose magnitude approaches a value suggestive of the spinon Sommerfeld coefficient of isolated quantum spin chains. These results demonstrate an alternative approach for producing quantum matter via a magnetic-field-induced shift of entropy from one-dimensional short-range order to a three-dimensional quantum critical point.« less

Quantum criticality among entangled spin chains

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blanc, N.; Trinh, J.; Dong, L.

Here, an important challenge in magnetism is the unambiguous identification of a quantum spin liquid, of potential importance for quantum computing. In such a material, the magnetic spins should be fluctuating in the quantum regime, instead of frozen in a classical long-range-ordered state. While this requirement dictates systems wherein classical order is suppressed by a frustrating lattice, an ideal system would allow tuning of quantum fluctuations by an external parameter. Conventional three-dimensional antiferromagnets can be tuned through a quantum critical point—a region of highly fluctuating spins—by an applied magnetic field. Such systems suffer from a weak specific-heat peak at themore » quantum critical point, with little entropy available for quantum fluctuations. Here we study a different type of antiferromagnet, comprised of weakly coupled antiferromagnetic spin-1/2 chains as realized in the molecular salt K 2PbCu(NO 2) 6. Across the temperature–magnetic field boundary between three-dimensional order and the paramagnetic phase, the specific heat exhibits a large peak whose magnitude approaches a value suggestive of the spinon Sommerfeld coefficient of isolated quantum spin chains. These results demonstrate an alternative approach for producing quantum matter via a magnetic-field-induced shift of entropy from one-dimensional short-range order to a three-dimensional quantum critical point.« less

Quantum criticality among entangled spin chains

NASA Astrophysics Data System (ADS)

Blanc, N.; Trinh, J.; Dong, L.; Bai, X.; Aczel, A. A.; Mourigal, M.; Balents, L.; Siegrist, T.; Ramirez, A. P.

2018-03-01

An important challenge in magnetism is the unambiguous identification of a quantum spin liquid1,2, of potential importance for quantum computing. In such a material, the magnetic spins should be fluctuating in the quantum regime, instead of frozen in a classical long-range-ordered state. While this requirement dictates systems3,4 wherein classical order is suppressed by a frustrating lattice5, an ideal system would allow tuning of quantum fluctuations by an external parameter. Conventional three-dimensional antiferromagnets can be tuned through a quantum critical point—a region of highly fluctuating spins—by an applied magnetic field. Such systems suffer from a weak specific-heat peak at the quantum critical point, with little entropy available for quantum fluctuations6. Here we study a different type of antiferromagnet, comprised of weakly coupled antiferromagnetic spin-1/2 chains as realized in the molecular salt K2PbCu(NO2)6. Across the temperature-magnetic field boundary between three-dimensional order and the paramagnetic phase, the specific heat exhibits a large peak whose magnitude approaches a value suggestive of the spinon Sommerfeld coefficient of isolated quantum spin chains. These results demonstrate an alternative approach for producing quantum matter via a magnetic-field-induced shift of entropy from one-dimensional short-range order to a three-dimensional quantum critical point.

Transition from Spin Dewetting to continuous film in spin coating of Liquid Crystal 5CB.

PubMed

Dhara, Palash; Bhandaru, Nandini; Das, Anuja; Mukherjee, Rabibrata

2018-05-08

Spin dewetting refers to spontaneous rupture of the dispensed solution layer during spin coating, resulting in isolated but periodic, regular sized domains of the solute and is pre-dominant when the solute concentration (C n ) is very low. In this article we report how the morphology of liquid crystal (LC) 5CB thin films coated on flat and patterned PMMA substrate transform from spin dewetted droplets to continuous films with increase in C n . We further show that within the spin dewetted regime, with gradual increase in the solute concentration, periodicity of the isotropic droplets (λ D ) as well as their mean diameter (d D ), gradually decreases, till the film becomes continuous at a critical concentration (C n *). Interestingly, the trend that λ D reduces with increase in C n is exact opposite to what is observed in thermal/solvent vapor induced dewetting of a thin film. The spin dewetted droplets exhibit transient Radial texture, in contrast to Schlieren texture observed in elongated threads and continuous films of 5CB, which remains in the Nematic phase at room temperature. Finally we show that by casting the film on a grating patterned substrate it becomes possible to align the spin dewetted droplets along the contours substrate patterns.

Generation of spin currents from one-dimensional quantum spin liquid

NASA Astrophysics Data System (ADS)

Hirobe, Daichi; Kawamata, Takayuki; Oyanagi, Koichi; Koike, Yoji; Saitoh, Eiji

2018-03-01

Spin-Seebeck effects (SSEs) in a one-dimensional quantum spin liquid (QSL) system have been investigated in a Sr2CuO3/Pt hybrid structure. Sr2CuO3 contains one-dimensional spin- /1 2 chains in which typical spinons in QSL have been confirmed. Heat-induced voltage measured in a clean Pt/Sr2CuO3 exhibits anomalous sign reversal with decreasing temperature, the negative component of which can be attributed to the spinon-induced SSE. However, the SSE was found to be critically decreased upon the exposure of Sr2CuO3 to air, which can be associated with the chemical degradation of the interface of Sr2CuO3. Despite the drastic change in the SSE signals, properties of the one-dimensional QSL are little changed in the spin susceptibility as well as the thermal conductivity of Sr2CuO3. The SSE signal is also sensitive to the purity of Sr2CuO3; it is suppressed with a decrease in the purity of the primary compounds of the Sr2CuO3. The result indicates that the spinon-induced SSE in Sr2CuO3 is sensitive to the bulk condition due to the one-dimensional atomic channel for spin transport in Sr2CuO3. In a carefully prepared Sr2CuO3/Pt sample, we found that the spinon-induced SSE signal is tolerant to magnetic fields; it increases linearly with the field even up to 9 T. In contrast, SSEs are suppressed under such a high field in ferrimagnetic insulators Y3Fe5O12 or paramagnetic insulators Gd3Ga5O12, which is caused by the Zeeman gap in the spin-wave or paramagnetic spin excitations. The robustness of the spinon-induced SSE is consistent with the Tomonaga-Luttinger liquid theories.

ESR modes in a Strong-Leg Ladder in the Tomonaga-Luttinger Liquid Phase

NASA Astrophysics Data System (ADS)

Zvyagin, S.; Ozerov, M.; Maksymenko, M.; Wosnitza, J.; Honecker, A.; Landee, C. P.; Turnbull, M.; Furuya, S. C.; Giamarchi, T.

Magnetic excitations in the strong-leg quantum spin ladder compound (C7H10N)2CuBr4 (known as DIMPY) in the field-induced Tomonaga-Luttinger spin liquid phase are studied by means of high-field electron spin resonance (ESR) spectroscopy. The presence of a gapped ESR mode with unusual non-linear frequency-field dependence is revealed experimentally. Using a combination of analytic and exact diagonalization methods, we compute the dynamical structure factor and identify this mode with longitudinal excitations in the antisymmetric channel. We argue that these excitations constitute a fingerprint of the spin dynamics in a strong-leg spin-1/2 Heisenberg antiferromagnetic ladder and owe its ESR observability to the uniform Dzyaloshinskii-Moriya interaction. This work was partially supported by the DFG and Helmholtz Gemeinschaft (Germany), Swiss SNF under Division II, and ERC synergy UQUAM project. We acknowledge the support of the HLD at HZDR, member of the European Magnetic Field Laboratory (EMFL).

Innovative Plasma Disinfection Technique with the Reduced-pH Method and the Plasma-Treated Water (PTW) -Safety and Powerful Disinfection with Cryopreserved PTW-

NASA Astrophysics Data System (ADS)

Kitano, Katsuhisa; Ikawa, Satoshi; Nakashima, Yoichi; Tani, Atsushi; Yokoyama, Takashi; Ohshima, Tomoko

2015-09-01

Among the applications of the plasma disinfection to human body, plasma sterilization in liquid is crucial. We found that the plasma-treated water (PTW) has strong bactericidal activity under low pH condition and the half-lives of its activity depend on temperature. Lower temperature brings longer half-life and the bactericidal activity of PTW can be kept by cryopreservation. These physicochemical properties were in accordance with Arrhenius equation both in liquid and solid states. From the experimental results of ESR (Electron Spin Resonance) measurement of O2-in liquid against PTW with spin trapping method, half-lives of PTW were also in accordance with Arrhenius equation. It suggests that high concentration PTW as integrated value can be achieved by cooling of plasma apparatus. Pure PTW has disinfection power of 22 log reduction (B. subtilis). This corresponds to 65% H2O2, 14% hypochlorous acid and 0.33% peracetic acid, which are deadly poison for human. On the other hand, PTW is deactivated soon at body temperature. This indicates that toxicity to human body seems to be low. PTW, which is a sort of indirect plasma exposure, with pH and temperature controls could be applied for safety and powerful disinfection. MEXT (15H03583, 23340176, 25108505). NCCE (23-A-15).

Spin Superfluidity and Magnone BEC in He-3

NASA Astrophysics Data System (ADS)

Bunkov, Yury

2011-03-01

The spin superfluidity -- superfluidity in the magnetic subsystem of a condensed matter -- is manifested as the spontaneous phase-coherent precession of spins first discovered in 1984 in 3 He-B. This superfluid current of spins -- spin supercurrent -- is one more representative of superfluid currents known or discussed in other systems, such as the superfluid current of mass and atoms in superfluid 4 He; superfluid current of electric charge in superconductors; superfluid current of hypercharge in Standard Model of particle physics; superfluid baryonic current and current of chiral charge in quark matter; etc. Spin superfluidity can be described in terms of the Bose condensation of spin waves -- magnons. We discuss different states of magnon superfluidity with different types of spin-orbit coupling: in bulk 3 He-B; magnetically traped `` Q -balls'' at very low temperatures; in 3 He-A and 3 He-B immerged in deformed aerogel; etc. Some effects in normal 3 He can also be treated as a magnetic BEC of fermi liquid. A very similar phenomena can be observed also in a magnetic systems with dinamical frequensy shift, like MnC03 . We will discuss the main experimental signatures of magnons superfluidity: (i) spin supercurrent, which transports the magnetization on a macroscopic distance more than 1 cm long; (ii) spin current Josephson effect which shows interference between two condensates; (iii) spin current vortex -- a topological defect which is an analog of a quantized vortex in superfluids, of an Abrikosov vortex in superconductors, and cosmic strings in relativistic theories; (iv) Goldstone modes related to the broken U (1) symmetry -- phonons in the spin-superfluid magnon gas; etc. For recent review see Yu. M. Bunkov and G. E. Volovik J. Phys. Cond. Matter. 22, 164210 (2010) This work is partly supported by the Ministry of Education and Science of the Russian Federation (contract N 02.740.11.5217).

Experimental Investigation of Rotating Menisci

NASA Astrophysics Data System (ADS)

Reichel, Yvonne; Dreyer, Michael E.

2014-07-01

In upper stages of spacecrafts, Propellant Management Devices (PMD's) can be used to position liquid propellant over the outlet in the absence of gravity. Centrifugal forces due to spin of the upper stage can drive the liquid away from the desired location resulting in malfunction of the stage. In this study, a simplified model consisting of two parallel, segmented and unsegmented disks and a central tube assembled at the center of the upper disk is analyzed experimentally during rotation in microgravity. For each drop tower experiment, the angular speed caused by a centrifugal stage in the drop capsule is kept constant. Steady-states for the menisci between the disks are observed for moderate rotation. For larger angular speeds, a stable shape of the free surfaces fail to sustain and the liquid is driven away. Additionally, tests were performed without rotation to quantify two effects: the removal of a metallic cylinder around the model to establish the liquid column and the determination of the the settling time from terrestrial to microgravity conditions.

Direct evidence for dominant bond-directional interactions in a honeycomb lattice iridate Na 2IrO 3

DOE PAGES

Hwan Chun, Sae; Kim, Jong-Woo; Kim, Jungho; ...

2015-05-11

We show that heisenberg interactions are ubiquitous in magnetic materials and play a central role in modelling and designing quantum magnets. Bond-directional interactions offer a novel alternative to Heisenberg exchange and provide the building blocks of the Kitaev model, which has a quantum spin liquid as its exact ground state. Honeycomb iridates, A 2IrO 3 (A = Na, Li), offer potential realizations of the Kitaev magnetic exchange coupling, and their reported magnetic behaviour may be interpreted within the Kitaev framework. However, the extent of their relevance to the Kitaev model remains unclear, as evidence for bond-directional interactions has so farmore » been indirect. Here we present direct evidence for dominant bond-directional interactions in antiferromagnetic Na 2IrO 3 and show that they lead to strong magnetic frustration. Diffuse magnetic X-ray scattering reveals broken spin-rotational symmetry even above the Néel temperature, with the three spin components exhibiting short-range correlations along distinct crystallographic directions. Lastly, this spin- and real-space entanglement directly uncovers the bond-directional nature of these interactions, thus providing a direct connection between honeycomb iridates and Kitaev physics.« less

Ordered states in the Kitaev-Heisenberg model: From 1D chains to 2D honeycomb.

PubMed

Agrapidis, Cliò Efthimia; van den Brink, Jeroen; Nishimoto, Satoshi

2018-01-29

We study the ground state of the 1D Kitaev-Heisenberg (KH) model using the density-matrix renormalization group and Lanczos exact diagonalization methods. We obtain a rich ground-state phase diagram as a function of the ratio between Heisenberg (J = cosϕ) and Kitaev (K = sinϕ) interactions. Depending on the ratio, the system exhibits four long-range ordered states: ferromagnetic-z, ferromagnetic-xy, staggered-xy, Néel-z, and two liquid states: Tomonaga-Luttinger liquid and spiral-xy. The two Kitaev points [Formula: see text] and [Formula: see text] are singular. The ϕ-dependent phase diagram is similar to that for the 2D honeycomb-lattice KH model. Remarkably, all the ordered states of the honeycomb-lattice KH model can be interpreted in terms of the coupled KH chains. We also discuss the magnetic structure of the K-intercalated RuCl 3 , a potential Kitaev material, in the framework of the 1D KH model. Furthermore, we demonstrate that the low-lying excitations of the 1D KH Hamiltonian can be explained within the combination of the known six-vertex model and spin-wave theory.

Entangled spins and ghost-spins

NASA Astrophysics Data System (ADS)

Jatkar, Dileep P.; Narayan, K.

2017-09-01

We study patterns of quantum entanglement in systems of spins and ghost-spins regarding them as simple quantum mechanical toy models for theories containing negative norm states. We define a single ghost-spin as in [20] as a 2-state spin variable with an indefinite inner product in the state space. We find that whenever the spin sector is disentangled from the ghost-spin sector (both of which could be entangled within themselves), the reduced density matrix obtained by tracing over all the ghost-spins gives rise to positive entanglement entropy for positive norm states, while negative norm states have an entanglement entropy with a negative real part and a constant imaginary part. However when the spins are entangled with the ghost-spins, there are new entanglement patterns in general. For systems where the number of ghost-spins is even, it is possible to find subsectors of the Hilbert space where positive norm states always lead to positive entanglement entropy after tracing over the ghost-spins. With an odd number of ghost-spins however, we find that there always exist positive norm states with negative real part for entanglement entropy after tracing over the ghost-spins.

Invited review liquid crystal models of biological materials and silk spinning.

PubMed

Rey, Alejandro D; Herrera-Valencia, Edtson E

2012-06-01

A review of thermodynamic, materials science, and rheological liquid crystal models is presented and applied to a wide range of biological liquid crystals, including helicoidal plywoods, biopolymer solutions, and in vivo liquid crystals. The distinguishing characteristics of liquid crystals (self-assembly, packing, defects, functionalities, processability) are discussed in relation to biological materials and the strong correspondence between different synthetic and biological materials is established. Biological polymer processing based on liquid crystalline precursors includes viscoelastic flow to form and shape fibers. Viscoelastic models for nematic and chiral nematics are reviewed and discussed in terms of key parameters that facilitate understanding and quantitative information from optical textures and rheometers. It is shown that viscoelastic modeling the silk spinning process using liquid crystal theories sheds light on textural transitions in the duct of spiders and silk worms as well as on tactoidal drops and interfacial structures. The range and consistency of the predictions demonstrates that the use of mesoscopic liquid crystal models is another tool to develop the science and biomimetic applications of mesogenic biological soft matter. Copyright © 2011 Wiley Periodicals, Inc.

Kondo destruction in a quantum paramagnet with magnetic frustration

NASA Astrophysics Data System (ADS)

Zhang, Jiahao; Zhao, Hengcan; Lv, Meng; Hu, Sile; Isikawa, Yosikazu; Yang, Yi-feng; Si, Qimiao; Steglich, Frank; Sun, Peijie

2018-06-01

We report results of isothermal magnetotransport and susceptibility measurements at elevated magnetic fields B down to very low temperatures T on single crystals of the frustrated Kondo-lattice system CePdAl. They reveal a B*(T ) line within the paramagnetic part of the phase diagram. This line denotes a thermally broadened "small"-to-"large" Fermi-surface crossover which substantially narrows upon cooling. At B0 *=B*(T =0 ) =(4.6 ±0.1 ) T , this B*(T ) line merges with two other crossover lines, viz. Tp(B ) below and TFL(B ) above B0 *. Tp characterizes a frustration-dominated spin-liquid state, while TFL is the Fermi-liquid temperature associated with the lattice Kondo effect. Non-Fermi-liquid phenomena which are commonly observed near a "Kondo-destruction" quantum-critical point cannot be resolved in CePdAl. Our observations reveal a rare case where Kondo coupling, frustration, and quantum criticality are closely intertwined.

Distinct nature of orbital-selective Mott phases dominated by low-energy local spin fluctuations

NASA Astrophysics Data System (ADS)

Song, Ze-Yi; Jiang, Xiu-Cai; Lin, Hai-Qing; Zhang, Yu-Zhong

2017-12-01

Quantum orbital-selective Mott (OSM) transitions are investigated within dynamical mean-field theory based on a two-orbital Hubbard model with different bandwidth at half filling. We find two distinct OSM phases both showing coexistence of itinerant electrons and localized spins, dependent on whether the Hund's coupling is full or of Ising type. The critical values and the nature of the OSM transitions are efficiently determined by entanglement entropy. We reveal that vanishing of the Kondo energy scale evidenced by absence of local spin fluctuations at low frequency in local dynamical spin susceptibility is responsible for the appearance of non-Fermi-liquid OSM phase in Ising Hund's coupling case. We argue that this scenario can also be applied to account for emergent quantum non-Fermi liquid in the one-band Hubbard model when short-range antiferromagnetic order is considered.

A review of the quantum Hall effects in MgZnO/ZnO heterostructures

NASA Astrophysics Data System (ADS)

Falson, Joseph; Kawasaki, Masashi

2018-05-01

This review visits recent experimental efforts on high mobility two-dimensional electron systems (2DES) hosted at the Mg x Zn1-x O/ZnO heterointerface. We begin with the growth of these samples, and highlight the key characteristics of ozone-assisted molecular beam epitaxy required for their production. The transport characteristics of these structures are found to rival that of traditional semiconductor material systems, as signified by the high electron mobility (μ > 1000 000 cm2 Vs‑1) and rich quantum Hall features. Owing to a large effective mass and small dielectric constant, interaction effects are an order of magnitude stronger in comparison with the well studied GaAs-based 2DES. The strong correlation physics results in robust Fermi-liquid renormalization of the effective mass and spin susceptibility of carriers, which in turn dictates the parameter space for the quantum Hall effect. Finally, we explore the quantum Hall effect with a particular emphasis on the spin degree of freedom of carriers, and how their large spin splitting allows control of the ground states encountered at ultra-low temperatures within the fractional quantum Hall regime. We discuss in detail the physics of even-denominator fractional quantum Hall states, whose observation and underlying character remain elusive and exotic.

An apparatus for pulsed ESR and DNP experiments using optically excited triplet states down to liquid helium temperatures

NASA Astrophysics Data System (ADS)

Eichhorn, T. R.; Haag, M.; van den Brandt, B.; Hautle, P.; Wenckebach, W. Th.; Jannin, S.; van der Klink, J. J.; Comment, A.

2013-09-01

In standard Dynamic Nuclear Polarization (DNP) electron spins are polarized at low temperatures in a strong magnetic field and this polarization is transferred to the nuclear spins by means of a microwave field. To obtain high nuclear polarizations cryogenic equipment reaching temperatures of 1 K or below and superconducting magnets delivering several Tesla are required. This equipment strongly limits applications in nuclear and particle physics where beams of particles interact with the polarized nuclei, as well as in neutron scattering science. The problem can be solved using short-lived optically excited triplet states delivering the electron spin. The spin is polarized in the optical excitation process and both the cryogenic equipment and magnet can be simplified significantly. A versatile apparatus is described that allows to perform pulsed dynamic nuclear polarization experiments at X-band using short-lived optically excited triplet sates. The efficient 4He flow cryostat that cools the sample to temperatures between 4 K and 300 K has an optical access with a coupling stage for a fiber transporting the light from a dedicated laser system. It is further designed to be operated on a neutron beam. A combined pulse ESR/DNP spectrometer has been developed to observe and characterize the triplet states and to perform pulse DNP experiments. The ESR probe is based on a dielectric ring resonator of 7 mm inner diameter that can accommodate cubic samples of 5 mm length needed for neutron experiments. NMR measurements can be performed during DNP with a coil integrated in the cavity. With the presented apparatus a proton polarization of 0.5 has been achieved at 0.3 T.

Direct 1H NMR evidence of spin-rotation coupling as a source of para → ortho-H2 conversion in diamagnetic solvents.

PubMed

Terenzi, Camilla; Bouguet-Bonnet, Sabine; Canet, Daniel

2017-04-21

At ambient temperature, conversion from 100% enriched para-hydrogen (p-H 2 ; singlet state) to ortho-hydrogen (o-H 2 ; triplet state) leads necessarily to the thermodynamic equilibrium proportions: 75% of o-H 2 and 25% of p-H 2 . When p-H 2 is dissolved in a diamagnetic organic solvent, conversion is very slow and can be considered as arising from nuclear spin relaxation phenomena. A first relaxation mechanism, specific to the singlet state and involving a combination of auto-correlation and cross correlation spectral densities, can be retained: randomly fluctuating magnetic fields due to inter-molecular dipolar interactions. We demonstrate here that (i) this dipolar mechanism is not sufficient for accounting for the para→ortho conversion rate, (ii) spin-rotation interaction, an intra-molecular mechanism, behaves similarly to random-field interaction and, thus, may be involved in the singlet relaxation rate. Also, as the para→ortho conversion is monitored by proton nuclear magnetic resonance (NMR) of dissolved o-H 2 (p-H 2 is NMR-silent), one has to account for H 2 exchange between the liquid phase and the gas phase within the NMR tube, as well as for dissolution effects. Experimental evidence of the above statements is brought here in the case of two organic solvents: acetone-d 6 and carbon disulfide. The observed temperature dependence of the para→ortho conversion rate shows that spin-rotation can be the dominant contribution to the p-H 2 relaxation rate in the absence of tangible dipolar interactions. Our findings shed new light on the "mysterious" mechanism of the para→ortho conversion which has been searched for several decades.

Carbon nanotube fiber spun from wetted ribbon

DOEpatents

Zhu, Yuntian T; Arendt, Paul; Zhang, Xiefei; Li, Qingwen; Fu, Lei; Zheng, Lianxi

2014-04-29

A fiber of carbon nanotubes was prepared by a wet-spinning method involving drawing carbon nanotubes away from a substantially aligned, supported array of carbon nanotubes to form a ribbon, wetting the ribbon with a liquid, and spinning a fiber from the wetted ribbon. The liquid can be a polymer solution and after forming the fiber, the polymer can be cured. The resulting fiber has a higher tensile strength and higher conductivity compared to dry-spun fibers and to wet-spun fibers prepared by other methods.

Constraining spacetime nonmetricity with neutron spin rotation in liquid 4 He

DOE PAGES

Lehnert, Ralf; Snow, W. M.; Xiao, Zhi; ...

2017-09-10

General spacetime nonmetricity coupled to neutrons is studied. In this context, it is shown that certain nonmetricity components can generate a rotation of the neutron's spin. Available data on this effect obtained from slow-neutron propagation in liquid helium are then used to constrain isotropic nonmetricity components at the level of 10 -22GeV. These results represent the first limit on the nonmetricity ζ( 6) 2S 000 parameter as well as the first measurement of nonmetricity inside matter.

Divalent europium doped CaF 2 and BaF 2 nanocrystals from ionic liquids

DOE PAGES

Anghel, Sergiu; Golbert, Sebastian; Meijerink, Andries; ...

2016-10-11

A new, facile and quick synthesis method for Eu 2+ doped the alkaline earth fluorides was developed using ionic liquids as solvent, precursor and capping agent. Reductive atmosphere and very high temperatures were avoided, while still attaining the desired structure, small particle sizes and divalent oxidation state of the lanthanide. Here, this opens the door for the development of new Ln 2+ doped nanomaterials. Here, the successful Eu 2+ incorporation was proven by optical spectroscopic measurements which showed the spin and parity allowed f-d transitions of Eu 2+ in CaF 2:Eu 2+/BaF 2:Eu 2+. 4f 7-4f 7 transitions could bemore » observed at low temperatures (7 K).« less

Electron paramagnetic resonance studies of slowly tumbling vanadyl spin probes in nematic liquid crystals

NASA Technical Reports Server (NTRS)

Bruno, G. V.; Harrington, J. K.; Eastman, M. P.

1978-01-01

An analysis of EPR line shapes by the method of Polnaszek, Bruno, and Freed is made for slowly tumbling vanadyl spin probes in viscous nematic liquid crystals. The use of typical vanadyl complexes as spin probes for nematic liquid crystals is shown to simplify the theoretical analysis and the subsequent interpretation. Rotational correlation times tau and orientational ordering parameters S sub Z where slow tumbling effects are expected to be observed in vanadyl EPR spectra are indicated in a plot. Analysis of the inertial effects on the probe reorientation, which are induced by slowly fluctuating torque components of the local solvent structure, yield quantitative values for tau and S sub Z. The weakly ordered probe VOAA is in the slow tumbling region and displays these inertial effects throughout the nematic range of BEPC and Phase V. VOAA exhibits different reorientation behavior near the isotropic-nematic transition temperature than that displayed far below this transition temperature.

Physics of the spin gap in the S=1/2 Heisenberg antiferromagnet on kagome

NASA Astrophysics Data System (ADS)

Tchernyshyov, Oleg

2009-03-01

A combination of low spin and strong frustration makes the S=1/2 Heisenberg antiferromagnet on kagome a likely candidate for an unusual ground state and elementary excitations. Exact-diagonalization studies [1] on finite clusters point to a lack of magnetic order in the ground state and to an energy gap of order J/20 for S=1 excitations. The exact nature of the ground state and elementary excitations remains a subject of vigorous debate. Among the proposed ground states are chiral [2] and non-chiral [3] spin liquids and a valence-bond crystal (VBC) [4-5]; spin excitations range from deconfined spinons with a Bose [6] or Fermi statistics [2-3] to magnons [7]. We show that the system behaves as a collection of spinons, quasiparticles with S=1/2 and Fermi statistics, whose motion disturbs valence-bond order. Attraction between spinons, mediated by exchange, binds them into small, massive pairs of S=0 with a binding energy of 0.06 J [8]. The pair formation strongly suppresses the motion of individual spinons and makes the survival of the Singh-Huse VBC plausible. A spin excitation amounts to breaking up a pair into two (nearly) free spinons with S=1. The survival of the VBC is expected to lead to spinon confinement; however, small energy differences between various valence-bond configurations would make the confinement length large. [4pt] [1] Ch. Waldtmann et al., Eur. Phys. J. B 2, 510 (1998).[0pt] [2] J. B. Marston and C. Zeng, J. Appl. Phys. 69, 5962 (1991).[0pt] [3] M. B. Hastings, Phys. Rev. B 63, 014413 (2000).[0pt] [4] P. Nikolic and T. Senthil, Phys. Rev. B 68, 214415 (2003).[0pt] [5] R. R. P. Singh and D. A. Huse, Phys. Rev. B 76, 180407 (2007).[0pt] [6] S. Sachdev, Phys. Rev. B 45, 12377 (1992).[0pt] [7] R. R. P. Singh and D. A. Huse, arXiv:0801.2735. [0pt] [8] Z. Hao and O. Tchernyshyov, the subsequent talk.

Viscosity of a Suspension with Internal Rotation

NASA Astrophysics Data System (ADS)

Elisabeth, Lemaire; Laurent, Lobry; François, Peters

2008-07-01

When an insulating particle immersed into a low conducting liquid is submitted to a sufficiently high DC field, E, it can rotate spontaneously around itself along any axis perpendicular to the electric field. This symmetry break is known as Quincke rotation and could have important consequences on the rheology of such a suspension of particles (insulating particles dispersed in a slightly conducting liquid). Indeed, if the suspension is subject to a shear rate, and a DC electric field is applied in the velocity gradient direction, the spin rate of the particles is greater than in the absence of an E field, so that the macroscopic spin rate of the particles drives the suspending liquid and thus leads to a decrease of the apparent viscosity of the suspension. The purpose of this paper is to provide a relation between the apparent viscosity of the suspension, the spin rate of the particles and the E field intensity. The predictions of the model are compared to experimental data which have been obtained on a suspension of PMMA particles dispersed in a low polar dielectric liquid. The agreement between experiments and theory is rather good even if the model overestimates the viscosity decrease induced by the field.

Spinning disc atomisation process: Modelling and computations

NASA Astrophysics Data System (ADS)

Li, Yuan; Sisoev, Grigory; Shikhmurzaev, Yulii

2016-11-01

The atomisation of liquids using a spinning disc (SDA), where the centrifugal force is used to generate a continuous flow, with the liquid eventually disintegrating into drops which, on solidification, become particles, is a key element in many technologies. Examples of such technologies range from powder manufacturing in metallurgy to various biomedical applications. In order to be able to control the SDA process, it is necessary to understand it as a whole, from the feeding of the liquid and the wave pattern developing on the disc to the disintegration of the liquid film into filaments and these into drops. The SDA process has been the subject of a number of experimental studies and some elements of it, notably the film on a spinning disc and the dynamics of the jets streaming out from it, have been investigated theoretically. However, to date there have been no studies of the process as a whole, including, most importantly, the transition zone where the film that has already developed a certain wave pattern disintegrates into jets that spiral out. The present work reports some results of an ongoing project aimed at producing a definitive map of regimes occurring in the SDA process and their outcome.

Mechanism of a strange metal state near a heavy-fermion quantum critical point

NASA Astrophysics Data System (ADS)

Chang, Yung-Yeh; Paschen, Silke; Chung, Chung-Hou

2018-01-01

Unconventional metallic or strange metal (SM) behavior with non-Fermi liquid (NFL) properties, generic features of heavy-fermion systems near quantum phase transitions, are yet to be understood microscopically. A paradigmatic example is the magnetic field-tuned quantum critical heavy-fermion metal YbRh2Si2 , revealing a possible SM state over a finite range of fields at low temperatures when substituted with Ge. Above a critical field, the SM state gives way to a heavy Fermi liquid with Kondo correlation. The NFL behavior, most notably a linear-in-temperature electrical resistivity and a logarithmic-in-temperature followed by a power-law singularity in the specific heat coefficient at low temperatures, still lacks a definite understanding. We propose the following mechanism as origin of the experimentally observed behavior: a quasi-2 d fluctuating short-ranged resonating-valence-bond spin liquid competing with the Kondo correlation. Applying a field-theoretical renormalization group analysis on an effective field theory beyond a large-N approach to an antiferromagnetic Kondo-Heisenberg model, we identify the critical point and explain remarkably well the SM behavior. Our theory goes beyond the well-established framework of quantum phase transitions and serves as a basis to address open issues in quantum critical heavy-fermion systems.

Spin-polarized surface resonances accompanying topological surface state formation

PubMed Central

Jozwiak, Chris; Sobota, Jonathan A.; Gotlieb, Kenneth; Kemper, Alexander F.; Rotundu, Costel R.; Birgeneau, Robert J.; Hussain, Zahid; Lee, Dung-Hai; Shen, Zhi-Xun; Lanzara, Alessandra

2016-01-01

Topological insulators host spin-polarized surface states born out of the energetic inversion of bulk bands driven by the spin-orbit interaction. Here we discover previously unidentified consequences of band-inversion on the surface electronic structure of the topological insulator Bi2Se3. By performing simultaneous spin, time, and angle-resolved photoemission spectroscopy, we map the spin-polarized unoccupied electronic structure and identify a surface resonance which is distinct from the topological surface state, yet shares a similar spin-orbital texture with opposite orientation. Its momentum dependence and spin texture imply an intimate connection with the topological surface state. Calculations show these two distinct states can emerge from trivial Rashba-like states that change topology through the spin-orbit-induced band inversion. This work thus provides a compelling view of the coevolution of surface states through a topological phase transition, enabled by the unique capability of directly measuring the spin-polarized unoccupied band structure. PMID:27739428

Geometry of spin coherent states

NASA Astrophysics Data System (ADS)

Chryssomalakos, C.; Guzmán-González, E.; Serrano-Ensástiga, E.

2018-04-01

Spin states of maximal projection along some direction in space are called (spin) coherent, and are, in many respects, the ‘most classical’ available. For any spin s, the spin coherent states form a 2-sphere in the projective Hilbert space \

Spin-polarized confined states in Ag films on Fe(110)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moras, Paolo; Bihlmayer, G.; Vescovo, Elio

Spin- and angle-resolved photoemission spectroscopy of thin Ag(111) films on ferromagnetic Fe(110) shows a series of spin-polarized peaks. These features derive from Ag sp-bands, which form quantum well states and resonances due to confinement by a spin-dependent interface potential barrier. The spin-up states are broader and located at higher binding energy than the corresponding spin-down states at Gamma, although the differences attenuate near the Fermi level. The spin-down states display multiple gap openings, which interrupt their parabolic-like dispersion. As a result, first-principles calculations attribute these findings to the symmetry- and spin-selective hybridization of the Ag states with the exchange-split bandsmore » of the substrate.« less

Spin-polarized confined states in Ag films on Fe(110)

DOE PAGES

Moras, Paolo; Bihlmayer, G.; Vescovo, Elio; ...

2017-11-16

Spin- and angle-resolved photoemission spectroscopy of thin Ag(111) films on ferromagnetic Fe(110) shows a series of spin-polarized peaks. These features derive from Ag sp-bands, which form quantum well states and resonances due to confinement by a spin-dependent interface potential barrier. The spin-up states are broader and located at higher binding energy than the corresponding spin-down states at Gamma, although the differences attenuate near the Fermi level. The spin-down states display multiple gap openings, which interrupt their parabolic-like dispersion. As a result, first-principles calculations attribute these findings to the symmetry- and spin-selective hybridization of the Ag states with the exchange-split bandsmore » of the substrate.« less

Rigorous decoupling between edge states in frustrated spin chains and ladders

NASA Astrophysics Data System (ADS)

Chepiga, Natalia; Mila, Frédéric

2018-05-01

We investigate the occurrence of exact zero modes in one-dimensional quantum magnets of finite length that possess edge states. Building on conclusions first reached in the context of the spin-1/2 X Y chain in a field and then for the spin-1 J1-J2 Heisenberg model, we show that the development of incommensurate correlations in the bulk invariably leads to oscillations in the sign of the coupling between edge states, and hence to exact zero energy modes at the crossing points where the coupling between the edge states rigorously vanishes. This is true regardless of the origin of the frustration (e.g., next-nearest-neighbor coupling or biquadratic coupling for the spin-1 chain), of the value of the bulk spin (we report on spin-1/2, spin-1, and spin-2 examples), and of the value of the edge-state emergent spin (spin-1/2 or spin-1).

Spin-orbit evolution of Mercury revisited

NASA Astrophysics Data System (ADS)

Noyelles, Benoît; Frouard, Julien; Makarov, Valeri V.; Efroimsky, Michael

2014-10-01

Although it is accepted that the significant eccentricity of Mercury (0.206) favours entrapment into the 3:2 spin-orbit resonance, open are the questions of how and when the capture took place. A recent work by Makarov (Makarov, V.V. [2012]. Astrophys. J., 752, 73) has proven that trapping into this state is certain for eccentricities larger than 0.2, provided we use a realistic tidal model based on the Darwin-Kaula expansion of the tidal torque. While in Ibid. a Mercury-like planet had its eccentricity fixed, we take into account its evolution. To that end, a family of possible histories of the eccentricity is generated, based on synthetic time evolution consistent with the expected statistics of the distribution of eccentricity. We employ a model of tidal friction, which takes into account both the rheology and self-gravitation of the planet. As opposed to the commonly used constant time lag (CTL) and constant phase lag (CPL) models, the physics-based tidal model changes dramatically the statistics of the possible final spin states. First, we discover that after only one encounter with the spin-orbit 3:2 resonance this resonance becomes the most probable end-state. Second, if a capture into this (or any other) resonance takes place, the capture becomes final, several crossings of the same state being forbidden by our model. Third, within our model the trapping of Mercury happens much faster than previously believed: for most histories, 10-20 Myr are sufficient. Fourth, even a weak laminar friction between the solid mantle and a molten core would most likely result in a capture in the 2:1 or even higher resonance, which is confirmed both semi-analytically and by limited numerical simulations. So the principal novelty of our paper is that the 3:2 end-state is more ancient than the same end-state obtained when the constant time lag model is employed. The swift capture justifies our treatment of Mercury as a homogeneous, unstratified body whose liquid core had not yet formed by the time of trapping. We also provide a critical analysis of the hypothesis by Wieczorek et al. (Wieczorek, M.A., Correia, A.C.M., Le Feuvre, M., Laskar, J., Rambaux, N. [2012]. Nat. Geosci., 5, 18-21) that the early Mercury might had been retrograde, whereafter it synchronised its spin and then accelerated it to the 3:2 resonance. Accurate processing of the available data on cratering does not support that hypothesis, while the employment of a realistic rheology invalidates a key element of the hypothesis, an intermediate pseudosynchronous state needed to spin-up to the 3:2 resonance.

Resonant optical tunneling-induced enhancement of the photonic spin Hall effect

NASA Astrophysics Data System (ADS)

Jiang, Xing; Wang, Qingkai; Guo, Jun; Zhang, Jin; Chen, Shuqing; Dai, Xiaoyu; Xiang, Yuanjiang

2018-04-01

Due to the quantum analogy with optics, the resonant optical tunneling effect (ROTE) has been proposed to investigate both the fundamental physics and the practical applications of optical switches and liquid refractive index sensors. In this paper, the ROTE is used to enhance the spin Hall effect (SHE) of transmitted light. It is demonstrated that sandwiching a layer of a high-refractive-index medium (boron nitride crystal) between two low-refractive-index layers (silica) can effectively enhance the photonic SHE due to the increased refractive index gradient and an enhanced evanescent field near the interface between silica and boron nitride. A maximum transverse shift of the horizontal polarization state in the ROTE structure of about 22.25 µm has been obtained, which is at least three orders of magnitude greater than the transverse shift in the frustrated total internal reflection structure. Moreover, the SHE can be manipulated by controlling the component materials and the thickness of the ROTE structure. These findings open the possibility for future applications of photonic SHE in precision metrology and spin-based photonics.

Helical order and multiferroicity in the S =1/2 quasi-kagome system KCu3As2O7(OD)3

NASA Astrophysics Data System (ADS)

Nilsen, G. J.; Okamoto, Y.; Ishikawa, H.; Simonet, V.; Colin, C. V.; Cano, A.; Chapon, L. C.; Hansen, T.; Mutka, H.; Hiroi, Z.

2014-04-01

Several Cu2+ hydroxide minerals have been recently identified as candidate realizations of the S=1/2 kagome Heisenberg model. In this context, we have studied the distorted system KCu3As2O7(OD)3 using neutron scattering and bulk measurements. Although the distortion favors magnetic order over a spin liquid ground state, refinement of the magnetic diffraction pattern below TN1=7.05(5) K yields a complex helical structure with k =(0.77,0,0.11). This structure, as well as the spin excitation spectrum, are well described by a classical Heisenberg model with ferromagnetic nearest neighbor couplings. Multiferroicity is observed below TN1, with an unusual crossover between improper and pseudoproper behavior occurring at TN2=5.5 K. The polarization at T =2 K is P =1.5μCm-2. The properties of KCu3As2O7(OD)3 highlight the variety of physics which arise from the interplay of spin and orbital degrees of freedom in Cu2+ kagome systems.

Spin Glass Order by Antisite Disorder in the Highly Frustrated Spinel Oxide CoAl2O4

NASA Astrophysics Data System (ADS)

Hanashima, Kentaro; Kodama, Yuta; Akahoshi, Daisuke; Kanadani, Chikahide; Saito, Toshiaki

2013-02-01

We experimentally studied the effects of the intersite mixing disorder between the A-site and B-site on the magnetic properties of the highly frustrated spinel oxide CoAl2O4 by measuring DC and AC susceptibilities. We controlled the inversion parameter η systematically from 0.0467 to 0.153 for (Co1-η Alη)[Al2-ηCoη]O4 by changing the heat treatment condition of the sample preparation. For η≤ 0.0643, no magnetic transition is observed down to 2 K, indicating a spin liquid (SL) regime for η≤ 0.0643, whereas for η≥ 0.101, a spin glass (SG) transition emerges at about Tg = 4.5 K, which is almost independent of η. In addition, the coefficient of the H--Tg relation is fairly large compared with that of a conventional SG. Our results suggest that some degrees of additional exchange randomness and local distortion by the quenched antisite disorder lead to degeneracy breaking in the SL state and induce SG order.

Spin-photon interface and spin-controlled photon switching in a nanobeam waveguide

NASA Astrophysics Data System (ADS)

Javadi, Alisa; Ding, Dapeng; Appel, Martin Hayhurst; Mahmoodian, Sahand; Löbl, Matthias Christian; Söllner, Immo; Schott, Rüdiger; Papon, Camille; Pregnolato, Tommaso; Stobbe, Søren; Midolo, Leonardo; Schröder, Tim; Wieck, Andreas Dirk; Ludwig, Arne; Warburton, Richard John; Lodahl, Peter

2018-05-01

The spin of an electron is a promising memory state and qubit. Connecting spin states that are spatially far apart will enable quantum nodes and quantum networks based on the electron spin. Towards this goal, an integrated spin-photon interface would be a major leap forward as it combines the memory capability of a single spin with the efficient transfer of information by photons. Here, we demonstrate such an efficient and optically programmable interface between the spin of an electron in a quantum dot and photons in a nanophotonic waveguide. The spin can be deterministically prepared in the ground state with a fidelity of up to 96%. Subsequently, the system is used to implement a single-spin photonic switch, in which the spin state of the electron directs the flow of photons through the waveguide. The spin-photon interface may enable on-chip photon-photon gates, single-photon transistors and the efficient generation of a photonic cluster state.

Metal-insulator transitions

NASA Astrophysics Data System (ADS)

Imada, Masatoshi; Fujimori, Atsushi; Tokura, Yoshinori

1998-10-01

Metal-insulator transitions are accompanied by huge resistivity changes, even over tens of orders of magnitude, and are widely observed in condensed-matter systems. This article presents the observations and current understanding of the metal-insulator transition with a pedagogical introduction to the subject. Especially important are the transitions driven by correlation effects associated with the electron-electron interaction. The insulating phase caused by the correlation effects is categorized as the Mott Insulator. Near the transition point the metallic state shows fluctuations and orderings in the spin, charge, and orbital degrees of freedom. The properties of these metals are frequently quite different from those of ordinary metals, as measured by transport, optical, and magnetic probes. The review first describes theoretical approaches to the unusual metallic states and to the metal-insulator transition. The Fermi-liquid theory treats the correlations that can be adiabatically connected with the noninteracting picture. Strong-coupling models that do not require Fermi-liquid behavior have also been developed. Much work has also been done on the scaling theory of the transition. A central issue for this review is the evaluation of these approaches in simple theoretical systems such as the Hubbard model and t-J models. Another key issue is strong competition among various orderings as in the interplay of spin and orbital fluctuations. Experimentally, the unusual properties of the metallic state near the insulating transition have been most extensively studied in d-electron systems. In particular, there is revived interest in transition-metal oxides, motivated by the epoch-making findings of high-temperature superconductivity in cuprates and colossal magnetoresistance in manganites. The article reviews the rich phenomena of anomalous metallicity, taking as examples Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Ru compounds. The diverse phenomena include strong spin and orbital fluctuations, mass renormalization effects, incoherence of charge dynamics, and phase transitions under control of key parameters such as band filling, bandwidth, and dimensionality. These parameters are experimentally varied by doping, pressure, chemical composition, and magnetic fields. Much of the observed behavior can be described by the current theory. Open questions and future problems are also extracted from comparison between experimental results and theoretical achievements.

Experimental NMR spin-lattice relaxometry study in the liquid crystalline nematic phase of propylcyano-phenylcyclohexane.

PubMed

Acosta, R H; Pusiol, D J

2001-01-01

The NMR spin-lattice proton relaxation dispersion T1(nu(L)) of the liquid crystal propylcyano-phenylcyclohexane is studied over several decades of Larmor frequencies and at different temperatures in the nematic mesophase. The results show that the order fluctuation of the local nematic director contribution to T1(nu(L)) undergoes a transition between two power regimes: from T1(nu(L)) protional to nu(1/2)L to nu(alpha)L (alpha approximately 1/3) on going from low to high Larmor frequencies.

Role of quantum fluctuations on spin liquids and ordered phases in the Heisenberg model on the honeycomb lattice

NASA Astrophysics Data System (ADS)

Merino, Jaime; Ralko, Arnaud

2018-05-01

Motivated by the rich physics of honeycomb magnetic materials, we obtain the phase diagram and analyze magnetic properties of the spin-1 /2 and spin-1 J1-J2-J3 Heisenberg model on the honeycomb lattice. Based on the SU(2) and SU(3) symmetry representations of the Schwinger boson approach, which treats disordered spin liquids and magnetically ordered phases on an equal footing, we obtain the complete phase diagrams in the (J2,J3) plane. This is achieved using a fully unrestricted approach which does not assume any pre-defined Ansätze. For S =1 /2 , we find a quantum spin liquid (QSL) stabilized between the Néel, spiral, and collinear antiferromagnetic phases in agreement with previous theoretical work. However, by increasing S from 1 /2 to 1, the QSL is quickly destroyed due to the weakening of quantum fluctuations indicating that the model already behaves as a quasiclassical system. The dynamical structure factors and temperature dependence of the magnetic susceptibility are obtained in order to characterize all phases in the phase diagrams. Moreover, motivated by the relevance of the single-ion anisotropy, D , to various S =1 honeycomb compounds, we have analyzed the destruction of magnetic order based on an SU(3) representation of the Schwinger bosons. Our analysis provides a unified understanding of the magnetic properties of honeycomb materials realizing the J1-J2-J3 Heisenberg model from the strong quantum spin regime at S =1 /2 to the S =1 case. Neutron scattering and magnetic susceptibility experiments can be used to test the destruction of the QSL phase when replacing S =1 /2 by S =1 localized moments in certain honeycomb compounds.

Charge and spin in low-dimensional cuprates

NASA Astrophysics Data System (ADS)

Maekawa, Sadamichi; Tohyama, Takami

2001-03-01

One of the central issues in the study of high-temperature superconducting cuprates which are composed of two-dimensional (2D) CuO2 planes is whether the 2D systems with strong electron correlation behave as a Fermi liquid or a non-Fermi-liquid-like one-dimensional (1D) system with electron correlation. In this article, we start with the detailed examination of the electronic structure in cuprates and study theoretically the spin and charge dynamics in 1D and 2D cuprates. The theoretical background of spin-charge separation in the 1D model systems including the Hubbard and t-J models is presented. The first direct observation of collective modes of spin and charge excitations in a 1D cuprate, which are called spinons and holons respectively, in angle-resolved photoemission spectroscopy (ARPES) experiments is reviewed in the light of the theoretical results based on the numerically exact-diagonalization method. The charge and spin dynamics in 1D insulating cuprates is also discussed in connection with the spin-charge separation. The arguments are extended to the 2D cuprates, and the unique aspects of the electronic properties of high-temperature superconductors are discussed. Special emphasis is placed on the d-wave-like excitations in insulating 2D cuprates observed in ARPES experiments. We explain how the excitations are caused by the spin-charge separation. The charge stripes observed in the underdoped cuprates are examined in connection with spin-charge separation in real space.

NMR spin-rotation relaxation and diffusion of methane

NASA Astrophysics Data System (ADS)

Singer, P. M.; Asthagiri, D.; Chapman, W. G.; Hirasaki, G. J.

2018-05-01

The translational diffusion-coefficient and the spin-rotation contribution to the 1H NMR relaxation rate for methane (CH4) are investigated using MD (molecular dynamics) simulations, over a wide range of densities and temperatures, spanning the liquid, supercritical, and gas phases. The simulated diffusion-coefficients agree well with measurements, without any adjustable parameters in the interpretation of the simulations. A minimization technique is developed to compute the angular velocity for non-rigid spherical molecules, which is used to simulate the autocorrelation function for spin-rotation interactions. With increasing diffusivity, the autocorrelation function shows increasing deviations from the single-exponential decay predicted by the Langevin theory for rigid spheres, and the deviations are quantified using inverse Laplace transforms. The 1H spin-rotation relaxation rate derived from the autocorrelation function using the "kinetic model" agrees well with measurements in the supercritical/gas phase, while the relaxation rate derived using the "diffusion model" agrees well with measurements in the liquid phase. 1H spin-rotation relaxation is shown to dominate over the MD-simulated 1H-1H dipole-dipole relaxation at high diffusivity, while the opposite is found at low diffusivity. At high diffusivity, the simulated spin-rotation correlation time agrees with the kinetic collision time for gases, which is used to derive a new expression for 1H spin-rotation relaxation, without any adjustable parameters.

Undecidability of the spectral gap.

PubMed

Cubitt, Toby S; Perez-Garcia, David; Wolf, Michael M

2015-12-10

The spectral gap--the energy difference between the ground state and first excited state of a system--is central to quantum many-body physics. Many challenging open problems, such as the Haldane conjecture, the question of the existence of gapped topological spin liquid phases, and the Yang-Mills gap conjecture, concern spectral gaps. These and other problems are particular cases of the general spectral gap problem: given the Hamiltonian of a quantum many-body system, is it gapped or gapless? Here we prove that this is an undecidable problem. Specifically, we construct families of quantum spin systems on a two-dimensional lattice with translationally invariant, nearest-neighbour interactions, for which the spectral gap problem is undecidable. This result extends to undecidability of other low-energy properties, such as the existence of algebraically decaying ground-state correlations. The proof combines Hamiltonian complexity techniques with aperiodic tilings, to construct a Hamiltonian whose ground state encodes the evolution of a quantum phase-estimation algorithm followed by a universal Turing machine. The spectral gap depends on the outcome of the corresponding 'halting problem'. Our result implies that there exists no algorithm to determine whether an arbitrary model is gapped or gapless, and that there exist models for which the presence or absence of a spectral gap is independent of the axioms of mathematics.

Optical properties of spin-on deposited low temperature titanium oxide thin films

NASA Astrophysics Data System (ADS)

Rantala, J. T.; Kärkkäinen, A. H. O.

2003-06-01

This letter presents a method to fabricate high quality, high refractive index titanium oxide thin films by applying liquid phase spin-on deposition combined with low temperature annealing. The synthesis of the liquid form titanium oxide material is carried out using a sol-gel synthesis technique. The material can be annealed at low temperature (150 C°) to achieve relatively high refractive index of 1.94 at 632.8 nm wavelength, whereas annealing at 350 C° results in index of 2.03 at 632.8 nm. Film depositions are demonstrated on silicon substrates with 0.5% uniformity in thickness. Refractive indices and extinction coefficients are characterized over a broad wavelength range to demonstrate the optical performance of this novel aqueous phase spin-on deposited hybrid titanium oxide material.

ADRF experiments using near n.pi pulse strings. [Adiabatic Demagnetization due to Radio Frequency pulses

NASA Technical Reports Server (NTRS)

Rhim, W. K.; Burum, D. P.; Elleman, D. D.

1977-01-01

Adiabatic demagnetization (ADRF) can be achieved in a dipolar coupled nuclear spin system in solids by applying a string of short RF pulses and gradually modulating the pulse amplitudes or pulse angles. This letter reports an adiabatic inverse polarization effect in solids and a rotary spin echo phenomenon observed in liquids when the pulse angle is gradually changed across integral multiples of pi during a string of RF pulses. The RF pulse sequence used is illustrated along with the NMR signal from a CaF2 single crystal as observed between the RF pulses and the rotary spin echo signal observed in liquid C6F6 for n = 2. The observed effects are explained qualitatively on the basis of average Hamiltonian theory.

Second sound experiments in superfluid 3He-A1 phase in high magnetic fields

NASA Astrophysics Data System (ADS)

Bastea, Marina

The Asb1 phase of sp3He is the first observed magnetic superfluid, stable only in the presence of an external magnetic field. Due to the broken relative gauge and spin rotational symmetry, the two associated collective modes, the second sound and the longitudinal spin waves are expected to appear as a single mode which we call the spin-entropy wave. Our work is focused on consistently mapping the behavior of the spin-entropy wave in the superfluid Asb{1} phase of sp3He, under a wide range of experimental conditions. Our results address fundamental questions such as the identification of the order parameter symmetry in the superfluid states, the nature of the pairing state in the Asb1 phase and the superfluid density anisotropy. We extensively investigated the propagation of the spin-entropy wave as a function of temperature, magnetic field between 1 and 8 Tesla and liquid pressure up to 30 bar. Our results show that the superfluid density is directly proportional to the magnitude of the external field in the specified range, as predicted by theory. We discovered that in the vicinity of the transition to the Asb2 phase, over a fairly large temperature range, the spin-entropy wave suffers a divergent attenuation. The observed effects were suggested as evidence for the presence of a minority condensate population, "down spin" pairs, specific for the Asb2 phase, as predicted by Monien and Tewordt. We measured the superfluid density dependence on the pressure between 10 and 30 bar and directly related it to the fourth order coefficients of the Ginzburg-Landau free energy expansion. The pressure dependence of three of these coefficients and their strong coupling corrections was found to be consistent with the theoretical predictions of Sauls and Serene. Our results support the identification of the A phase as the Anderson-Brinkman-Morel axial state and provide an important consistency check for the phase diagram carried out by groups at USC and Cornell. We performed experiments in two different geometries (cylindrical and rectangular) for two relative orientations of the external field and the wave propagation direction, to measure the anisotropy of the superfluid density. We found that the spin-entropy wave propagation exhibits a non-linear character when the external field is perpendicular to the wave-vector. We modeled the textural configuration and the expected response of the system based on the free energy minimization criterion. The results of our theoretical model are in very good agreement with the experimental data.

Spin-polarized surface resonances accompanying topological surface state formation

DOE PAGES

Jozwiak, Chris; Sobota, Jonathan A.; Gotlieb, Kenneth; ...

2016-10-14

Topological insulators host spin-polarized surface states born out of the energetic inversion of bulk bands driven by the spin-orbit interaction. Here we discover previously unidentified consequences of band-inversion on the surface electronic structure of the topological insulator Bi 2Se 3. By performing simultaneous spin, time, and angle-resolved photoemission spectroscopy, we map the spin-polarized unoccupied electronic structure and identify a surface resonance which is distinct from the topological surface state, yet shares a similar spin-orbital texture with opposite orientation. Its momentum dependence and spin texture imply an intimate connection with the topological surface state. Calculations show these two distinct states canmore » emerge from trivial Rashba-like states that change topology through the spin-orbit-induced band inversion. As a result, this work thus provides a compelling view of the coevolution of surface states through a topological phase transition, enabled by the unique capability of directly measuring the spin-polarized unoccupied band structure.« less

Temperature dependence of the NMR spin-lattice relaxation rate for spin-1/2 chains

NASA Astrophysics Data System (ADS)

Coira, E.; Barmettler, P.; Giamarchi, T.; Kollath, C.

2016-10-01

We use recent developments in the framework of a time-dependent matrix product state method to compute the nuclear magnetic resonance relaxation rate 1 /T1 for spin-1/2 chains under magnetic field and for different Hamiltonians (XXX, XXZ, isotropically dimerized). We compute numerically the temperature dependence of the 1 /T1 . We consider both gapped and gapless phases, and also the proximity of quantum critical points. At temperatures much lower than the typical exchange energy scale, our results are in excellent agreement with analytical results, such as the ones derived from the Tomonaga-Luttinger liquid (TLL) theory and bosonization, which are valid in this regime. We also cover the regime for which the temperature T is comparable to the exchange coupling. In this case analytical theories are not appropriate, but this regime is relevant for various new compounds with exchange couplings in the range of tens of Kelvin. For the gapped phases, either the fully polarized phase for spin chains or the low-magnetic-field phase for the dimerized systems, we find an exponential decrease in Δ /(kBT ) of the relaxation time and can compute the gap Δ . Close to the quantum critical point our results are in good agreement with the scaling behavior based on the existence of free excitations.

Complete quantum control of a single quantum dot spin using ultrafast optical pulses.

PubMed

Press, David; Ladd, Thaddeus D; Zhang, Bingyang; Yamamoto, Yoshihisa

2008-11-13

A basic requirement for quantum information processing systems is the ability to completely control the state of a single qubit. For qubits based on electron spin, a universal single-qubit gate is realized by a rotation of the spin by any angle about an arbitrary axis. Driven, coherent Rabi oscillations between two spin states can be used to demonstrate control of the rotation angle. Ramsey interference, produced by two coherent spin rotations separated by a variable time delay, demonstrates control over the axis of rotation. Full quantum control of an electron spin in a quantum dot has previously been demonstrated using resonant radio-frequency pulses that require many spin precession periods. However, optical manipulation of the spin allows quantum control on a picosecond or femtosecond timescale, permitting an arbitrary rotation to be completed within one spin precession period. Recent work in optical single-spin control has demonstrated the initialization of a spin state in a quantum dot, as well as the ultrafast manipulation of coherence in a largely unpolarized single-spin state. Here we demonstrate complete coherent control over an initialized electron spin state in a quantum dot using picosecond optical pulses. First we vary the intensity of a single optical pulse to observe over six Rabi oscillations between the two spin states; then we apply two sequential pulses to observe high-contrast Ramsey interference. Such a two-pulse sequence realizes an arbitrary single-qubit gate completed on a picosecond timescale. Along with the spin initialization and final projective measurement of the spin state, these results demonstrate a complete set of all-optical single-qubit operations.

Comprehensive study of the dynamics of a classical Kitaev Spin Liquid

NASA Astrophysics Data System (ADS)

Samarakoon, Anjana; Banerjee, Arnab; Batista, Cristian; Kamiya, Yoshitomo; Tennant, Alan; Nagler, Stephen

Quantum spin liquids (QSLs) have achieved great interest in both theoretical and experimental condensed matter physics due to their remarkable topological properties. Among many different candidates, the Kitaev model on the honeycomb lattice is a 2D prototypical QSL which can be experimentally studied in materials based on iridium or ruthenium.Here we study the spin-1/2 Kitaev model using classical Monte-Carlo and semiclassical spin dynamics of classical spins on a honeycomb lattice. Both real and reciprocal space pictures highlighting the differences and similarities of the results to the linear spin wave theory will be discussed in terms dispersion relations of the pure-Kitaev limit and beyond. Interestingly, this technique could capture some of the salient features of the exact quantum solution of the Kitaev model, such as features resembling the Majorana-like mode comparable to the Kitaev energy, which is spectrally narrowed compared to the quantum result, can be explained by magnon excitations on fluctuating onedimensional manifolds (loops). Hence the difference from the classical limit to the quantum limit can be understood by the fractionalization of a magnon to Majorana fermions. The calculations will be directly compared with our neutron scattering data on α-RuCl3 which is a prime candidate for experimental realization of Kitaev physics.

The physics of quantum materials

NASA Astrophysics Data System (ADS)

Keimer, B.; Moore, J. E.

2017-11-01

The physical description of all materials is rooted in quantum mechanics, which describes how atoms bond and electrons interact at a fundamental level. Although these quantum effects can in many cases be approximated by a classical description at the macroscopic level, in recent years there has been growing interest in material systems where quantum effects remain manifest over a wider range of energy and length scales. Such quantum materials include superconductors, graphene, topological insulators, Weyl semimetals, quantum spin liquids, and spin ices. Many of them derive their properties from reduced dimensionality, in particular from confinement of electrons to two-dimensional sheets. Moreover, they tend to be materials in which electrons cannot be considered as independent particles but interact strongly and give rise to collective excitations known as quasiparticles. In all cases, however, quantum-mechanical effects fundamentally alter properties of the material. This Review surveys the electronic properties of quantum materials through the prism of the electron wavefunction, and examines how its entanglement and topology give rise to a rich variety of quantum states and phases; these are less classically describable than conventional ordered states also driven by quantum mechanics, such as ferromagnetism.

Two-dimensional H2 in Si: Raman scattering and modeling study

NASA Astrophysics Data System (ADS)

Melnikov, V. V.; Hiller, M.; Lavrov, E. V.

2018-03-01

Molecular hydrogen trapped within {111}-oriented platelets in silicon is studied by means of Raman scattering and first principles theory. The rotational transition S0(0 ) (J =0 →J =2 ) of para-H2 (nuclear spin I =0 ) at 353 cm-1 is used as a probe. We find that for temperatures below 100 K the S0(0 ) Raman line starts to broaden asymmetrically, which is interpreted as the onset of a phase transition from a state with a short-range order ("gaseous" or "liquid" phase) to a two-dimensional molecular crystal lying in the {111} plane of silicon. The shape of the S0(0 ) line at helium temperatures strongly depends on the relative content of ortho- (nuclear spin I =1 ) and para-H2 revealing the details of the intermolecular interaction. A comprehensive theoretical analysis based on ab initio calculations, molecular dynamics simulations, and rotational spectra modeling reveals that the phase transition to the crystalline state of the two-dimensional hydrogen does occur at temperatures substantially higher compared to those of bulk H2.

Dipolar order by disorder in the classical Heisenberg antiferromagnet on the kagome lattice

NASA Astrophysics Data System (ADS)

Chern, Gia-Wei

2014-03-01

The first experiments on the ``kagome bilayer'' SCGO triggered a wave of interest in kagome antiferromagnets in particular, and frustrated systems in general. A cluster of early seminal theoretical papers established kagome magnets as model systems for novel ordering phenomena, discussing in particular spin liquidity, partial order, disorder-free glassiness and order by disorder. Despite significant recent progress in understanding the ground state for the quantum S = 1 / 2 model, the nature of the low-temperature phase for the classical kagome Heisenberg antiferromagnet has remained a mystery: the non-linear nature of the fluctuations around the exponentially numerous harmonically degenerate ground states has not permitted a controlled theory, while its complex energy landscape has precluded numerical simulations at low temperature. Here we present an efficient Monte Carlo algorithm which removes the latter obstacle. Our simulations detect a low-temperature regime in which correlations saturate at a remarkably small value. Feeding these results into an effective model and analyzing the results in the framework of an appropriate field theory implies the presence of long-range dipolar spin order with a tripled unit cell.

Cobaltites: Emergence of magnetism and metallicity from a non-magnetic, insulating state

NASA Astrophysics Data System (ADS)

Phelan, Daniel Patrick

In cobalt oxides, the energy splitting between different spin-states of Co3+ ions can be quite small, which means that more than one spin-state can simultaneously co-exist in the same compound and that transitions between different spin-state can occur. This makes understanding the magnetic coupling between cobalt sites rather complex. Such is the case for pure and hole-doped LaCoO3. In its ground state, LaCoO3 is a non-magnetic insulator. The lack of a magnetic moment, is due to the fact that the ground spin-state of Co3+ ions is a low-spin, S=0, state. However, since a spin-state that has a net spin is on the order of 100 K higher in energy than the ground spin-state, a magnetic moment appears as the temperature is increased, and the system behaves as a paramagnet above 100 K. The higher-energy spin-state is either an intermediate-spin (S=1) state of a high-spin (S=2) state - an issue that has been debated for quite some time. When holes are chemically doped into the system, as in La1- xSrxCoO3 (LSCO), the non-magnetic, insulating ground state evolves into a ferromagnetic, metallic state. This evolution is complicated because it occurs due to the convoluted effects of Co4+ ions being doped into the system and the fact that the ground spin-state of Co3+ ions changes as a function of the hole concentration. In this dissertation, the magnetic transitions in pure and hole-doped LaCoO3 are investigated by neutron scattering techniques. In the pure compound, it is shown that thermally excited spins have both fluctuating ferromagnetic and antiferro-magnetic spin-correlations, which is suggested to result from a dynamic orbital ordering of the occupied e. g orbitals of the intermediate-spin state. It is also shown that the thermally excited spin-state is split in energy by 0.6 meV. In the hole-doped compound, LSCO, it is shown that the evolution into a metallic ferromagnet occurs by the percolation of isotropic ferromagnetic droplets. It is also shown that incommensurate spin-correlations co-exist and compete with ferromagnetic spin correlations in LSCO, and it is argued that this competition is manifested in the thermodynamic properties. The role of the lattice upon the magnetic transitions in the hole-doped compounds is addressed by simultaneous analysis of magnetic Bragg peaks, the local atomic structure, and the average crystal structure from powder neutron diffraction patterns of La1- xCaxCoO3 and La 1-xBaxCoO3. It is suggested that the fraction of ions with intermediate spin-states at a fixed hole concentration depends on the radius of the A-site dopant.

Focus: Two-dimensional electron-electron double resonance and molecular motions: The challenge of higher frequencies.

PubMed

Franck, John M; Chandrasekaran, Siddarth; Dzikovski, Boris; Dunnam, Curt R; Freed, Jack H

2015-06-07

The development, applications, and current challenges of the pulsed ESR technique of two-dimensional Electron-Electron Double Resonance (2D ELDOR) are described. This is a three-pulse technique akin to 2D Exchange Nuclear Magnetic Resonance, but involving electron spins, usually in the form of spin-probes or spin-labels. As a result, it required the extension to much higher frequencies, i.e., microwaves, and much faster time scales, with π/2 pulses in the 2-3 ns range. It has proven very useful for studying molecular dynamics in complex fluids, and spectral results can be explained by fitting theoretical models (also described) that provide a detailed analysis of the molecular dynamics and structure. We discuss concepts that also appear in other forms of 2D spectroscopy but emphasize the unique advantages and difficulties that are intrinsic to ESR. Advantages include the ability to tune the resonance frequency, in order to probe different motional ranges, while challenges include the high ratio of the detection dead time vs. the relaxation times. We review several important 2D ELDOR studies of molecular dynamics. (1) The results from a spin probe dissolved in a liquid crystal are followed throughout the isotropic → nematic → liquid-like smectic → solid-like smectic → crystalline phases as the temperature is reduced and are interpreted in terms of the slowly relaxing local structure model. Here, the labeled molecule is undergoing overall motion in the macroscopically aligned sample, as well as responding to local site fluctuations. (2) Several examples involving model phospholipid membranes are provided, including the dynamic structural characterization of the boundary lipid that coats a transmembrane peptide dimer. Additionally, subtle differences can be elicited for the phospholipid membrane phases: liquid disordered, liquid ordered, and gel, and the subtle effects upon the membrane, of antigen cross-linking of receptors on the surface of plasma membrane, vesicles can be observed. These 2D ELDOR experiments are performed as a function of mixing time, Tm, i.e., the time between the second and third π/2 pulses, which provides a third dimension. In fact, a fourth dimension may be added by varying the ESR frequency/magnetic field combination. Therefore, (3) it is shown how continuous-wave multifrequency ESR studies enable the decomposition of complex dynamics of, e.g., proteins by virtue of their respective time scales. These studies motivate our current efforts that are directed to extend 2D ELDOR to higher frequencies, 95 GHz in particular (from 9 and 17 GHz), in order to enable multi-frequency 2D ELDOR. This required the development of quasi-optical methods for performing the mm-wave experiments, which are summarized. We demonstrate state-of-the-art 95 GHz 2D ELDOR spectroscopy through its ability to resolve the two signals from a spin probe dissolved in both the lipid phase and the coexisting aqueous phase. As current 95 GHz experiments are restricted by limited spectral coverage of the π/2 pulse, as well as the very short T2 relaxation times of the electron spins, we discuss how these limitations are being addressed.

Focus: Two-dimensional electron-electron double resonance and molecular motions: The challenge of higher frequencies

NASA Astrophysics Data System (ADS)

Franck, John M.; Chandrasekaran, Siddarth; Dzikovski, Boris; Dunnam, Curt R.; Freed, Jack H.

2015-06-01

The development, applications, and current challenges of the pulsed ESR technique of two-dimensional Electron-Electron Double Resonance (2D ELDOR) are described. This is a three-pulse technique akin to 2D Exchange Nuclear Magnetic Resonance, but involving electron spins, usually in the form of spin-probes or spin-labels. As a result, it required the extension to much higher frequencies, i.e., microwaves, and much faster time scales, with π/2 pulses in the 2-3 ns range. It has proven very useful for studying molecular dynamics in complex fluids, and spectral results can be explained by fitting theoretical models (also described) that provide a detailed analysis of the molecular dynamics and structure. We discuss concepts that also appear in other forms of 2D spectroscopy but emphasize the unique advantages and difficulties that are intrinsic to ESR. Advantages include the ability to tune the resonance frequency, in order to probe different motional ranges, while challenges include the high ratio of the detection dead time vs. the relaxation times. We review several important 2D ELDOR studies of molecular dynamics. (1) The results from a spin probe dissolved in a liquid crystal are followed throughout the isotropic → nematic → liquid-like smectic → solid-like smectic → crystalline phases as the temperature is reduced and are interpreted in terms of the slowly relaxing local structure model. Here, the labeled molecule is undergoing overall motion in the macroscopically aligned sample, as well as responding to local site fluctuations. (2) Several examples involving model phospholipid membranes are provided, including the dynamic structural characterization of the boundary lipid that coats a transmembrane peptide dimer. Additionally, subtle differences can be elicited for the phospholipid membrane phases: liquid disordered, liquid ordered, and gel, and the subtle effects upon the membrane, of antigen cross-linking of receptors on the surface of plasma membrane, vesicles can be observed. These 2D ELDOR experiments are performed as a function of mixing time, Tm, i.e., the time between the second and third π/2 pulses, which provides a third dimension. In fact, a fourth dimension may be added by varying the ESR frequency/magnetic field combination. Therefore, (3) it is shown how continuous-wave multifrequency ESR studies enable the decomposition of complex dynamics of, e.g., proteins by virtue of their respective time scales. These studies motivate our current efforts that are directed to extend 2D ELDOR to higher frequencies, 95 GHz in particular (from 9 and 17 GHz), in order to enable multi-frequency 2D ELDOR. This required the development of quasi-optical methods for performing the mm-wave experiments, which are summarized. We demonstrate state-of-the-art 95 GHz 2D ELDOR spectroscopy through its ability to resolve the two signals from a spin probe dissolved in both the lipid phase and the coexisting aqueous phase. As current 95 GHz experiments are restricted by limited spectral coverage of the π/2 pulse, as well as the very short T2 relaxation times of the electron spins, we discuss how these limitations are being addressed.

Ground-state energies of the nonlinear sigma model and the Heisenberg spin chains

NASA Technical Reports Server (NTRS)

Zhang, Shoucheng; Schulz, H. J.; Ziman, Timothy

1989-01-01

A theorem on the O(3) nonlinear sigma model with the topological theta term is proved, which states that the ground-state energy at theta = pi is always higher than the ground-state energy at theta = 0, for the same value of the coupling constant g. Provided that the nonlinear sigma model gives the correct description for the Heisenberg spin chains in the large-s limit, this theorem makes a definite prediction relating the ground-state energies of the half-integer and the integer spin chains. The ground-state energies obtained from the exact Bethe ansatz solution for the spin-1/2 chain and the numerical diagonalization on the spin-1, spin-3/2, and spin-2 chains support this prediction.

The effects of high concentrations of ionic liquid on GB1 protein structure and dynamics probed by high-resolution magic-angle-spinning NMR spectroscopy.

PubMed

Warner, Lisa; Gjersing, Erica; Follett, Shelby E; Elliott, K Wade; Dzyuba, Sergei V; Varga, Krisztina

2016-12-01

Ionic liquids have great potential in biological applications and biocatalysis, as some ionic liquids can stabilize proteins and enhance enzyme activity, while others have the opposite effect. However, on the molecular level, probing ionic liquid interactions with proteins, especially in solutions containing high concentration of ionic liquids, has been challenging. In the present work the 13 C, 15 N-enriched GB1 model protein was used to demonstrate applicability of high-resolution magic-angle-spinning (HR-MAS) NMR spectroscopy to investigate ionic liquid - protein interactions. Effect of an ionic liquid (1-butyl-3-methylimidazolium bromide, [C 4 -mim]Br) on GB1was studied over a wide range of the ionic liquid concentrations (0.6 to 3.5 M, which corresponds to 10%-60% v/v). Interactions between GB1 and [C 4 -mim]Br were observed from changes in the chemical shifts of the protein backbone as well as the changes in 15 N ps-ns dynamics and rotational correlation times. Site-specific interactions between the protein and [C 4 -mim]Br were assigned using 3D methods under HR-MAS conditions. Thus, HR-MAS NMR is a viable tool that could aid in elucidation of the molecular mechanism of ionic liquid - protein interactions.

Trajectory Prediction of Spin-Stabilized Projectiles With a Steady Liquid Payload

DTIC Science & Technology

2011-11-01

analysis assumes the effect of a liquid payload is similar to the Magnus effect . Spectral analysis used to numerically compute liquid-fill induced...the internal motion of a liquid payload can induce destabilizing moments on the projectile. This report creates a method to include the effect of... effect , liquid payload moments are added to the applied loads on the projectile. These loads are computed by solving the linearized Navier-Stokes

Viscosity Difference Measurements for Normal and Para Liquid Hydrogen Mixtures

NASA Technical Reports Server (NTRS)

Webeler, R.; Bedard, F.

1961-01-01

The absence of experimental data in the literature concerning a viscosity difference for normal and equilibrium liquid hydrogen may be attributed to the limited reproducibility of "oscillating disk" measurements in a liquid-hydrogen environment. Indeed, there is disagreement over the viscosity values for equilibrium liquid hydrogen even without proton spin considerations. Measurements presented here represent the first application of the piezoelectric alpha quartz torsional oscillator technique to liquid-hydrogen viscosity measurements.

Spreading dynamics of superposed liquid drops on a spinning disk

NASA Astrophysics Data System (ADS)

Sahoo, Subhadarshinee; Orpe, Ashish V.; Doshi, Pankaj

2018-01-01

We have experimentally studied simultaneous spreading of superposed drops of two Newtonian liquids on top of a horizontal spinning disk using the flow visualization technique. An inner drop of high surface tension liquid is placed centrally on the disk followed by a drop of outer liquid (lower surface tension) placed exactly above that. The disk is then rotated at a desired speed for a range of volume ratios of two liquids. Such an arrangement of two superposed liquid drops does not affect the spreading behavior of the outer liquid but influences that of the inner liquid significantly. The drop spreads to a larger extent and breaks into more fingers (Nf) as compared to the case where the same liquid is spreading in the absence of outer liquid. The experimentally observed number of fingers is compared with the prediction using available theory for single liquid. It is found that the theory over-predicts the value of Nf for the inner liquid while it is covered by an outer liquid. We provide a theoretical justification for this observation using linear stability analysis. Our analysis demonstrates that for small but finite surface tension ratio of the two liquids, the presence of the outer interface reduces the value of the most unstable wave number which is equivalent to the decrease in the number of fingers observed experimentally. Finally, sustained rotation of the disk leads to the formation of droplets at the tip of the fingers traveling outwards.

Local density of states in two-dimensional topological superconductors under a magnetic field: Signature of an exterior Majorana bound state

NASA Astrophysics Data System (ADS)

Suzuki, Shu-Ichiro; Kawaguchi, Yuki; Tanaka, Yukio

2018-04-01

We study quasiparticle states on a surface of a topological insulator (TI) with proximity-induced superconductivity under an external magnetic field. An applied magnetic field creates two Majorana bound states: a vortex Majorana state localized inside a vortex core and an exterior Majorana state localized along a circle centered at the vortex core. We calculate the spin-resolved local density of states (LDOS) and demonstrate that the shrinking of the radius of the exterior Majorana state, predicted in R. S. Akzyanov et al., Phys. Rev. B 94, 125428 (2016), 10.1103/PhysRevB.94.125428, under a strong magnetic field can be seen in LDOS without smeared out by nonzero-energy states. The spin-resolved LDOS further reveals that the spin of the exterior Majorana state is strongly spin-polarized. Accordingly, the induced odd-frequency spin-triplet pairs are found to be spin-polarized as well. In order to detect the exterior Majorana states, however, the Fermi energy should be closed to the Dirac point to avoid contributions from continuum levels. We also study a different two-dimensional topological-superconducting system where a two-dimensional electron gas with the spin-orbit coupling is sandwiched between an s -wave superconductor and a ferromagnetic insulator. We show that the radius of an exterior Majorana state can be tuned by an applied magnetic field. However, on the contrary to the results at a TI surface, neither the exterior Majorana state nor the induced odd-frequency spin-triplet pairs are spin-polarized. We conclude that the spin polarization of the Majorana state is attributed to the spin-polarized Landau level, which is characteristic for systems with the Dirac-like dispersion.

Entanglement sum rules.

PubMed

Swingle, Brian

2013-09-06

We compute the entanglement entropy of a wide class of models that may be characterized as describing matter coupled to gauge fields. Our principle result is an entanglement sum rule that states that the entropy of the full system is the sum of the entropies of the two components. In the context of the models we consider, this result applies to the full entropy, but more generally it is a statement about the additivity of universal terms in the entropy. Our proof simultaneously extends and simplifies previous arguments, with extensions including new models at zero temperature as well as the ability to treat finite temperature crossovers. We emphasize that while the additivity is an exact statement, each term in the sum may still be difficult to compute. Our results apply to a wide variety of phases including Fermi liquids, spin liquids, and some non-Fermi liquid metals. For example, we prove that our model of an interacting Fermi liquid has exactly the log violation of the area law for entanglement entropy predicted by the Widom formula in agreement with earlier arguments.

π Spin Berry Phase in a Quantum-Spin-Hall-Insulator-Based Interferometer: Evidence for the Helical Spin Texture of the Edge States

NASA Astrophysics Data System (ADS)

Chen, Wei; Deng, Wei-Yin; Hou, Jing-Min; Shi, D. N.; Sheng, L.; Xing, D. Y.

2016-08-01

The quantum spin Hall insulator is characterized by helical edge states, with the spin polarization of the electron being locked to its direction of motion. Although the edge-state conduction has been observed, unambiguous evidence of the helical spin texture is still lacking. Here, we investigate the coherent edge-state transport in an interference loop pinched by two point contacts. Because of the helical character, the forward interedge scattering enforces a π spin rotation. Two successive processes can only produce a nontrivial 2 π or trivial 0 spin rotation, which can be controlled by the Rashba spin-orbit coupling. The nontrivial spin rotation results in a geometric π Berry phase, which can be detected by a π phase shift of the conductance oscillation relative to the trivial case. Our results provide smoking gun evidence for the helical spin texture of the edge states. Moreover, it also provides the opportunity to all electrically explore the trajectory-dependent spin Berry phase in condensed matter.

EPR and optical studies of Cu2+ ions doped in magnesium potassium phosphate hexahydrate single crystals

NASA Astrophysics Data System (ADS)

Kripal, Ram; Shukla, Santwana

2011-03-01

An electron paramagnetic resonance (EPR) study of Cu2+-doped magnesium potassium phosphate is performed at liquid nitrogen temperature (LNT; 77 K). Two magnetically non-equivalent sites for Cu2+ are observed. The spin Hamiltonian parameters are determined with the fitting of spectra to a rhombic symmetry crystalline field. The ground state wavefunction is also determined. The g-anisotropy is evaluated and compared with the experimental value. With the help of an optical study, the nature of the bonding in the complex is discussed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Semenov, A. N.

We propose a new spin-glass model with no positional quenched disorder which is regarded as a coarse-grained model of a structural glass-former. The model is analyzed in the 1D case when the number N of states of a primary cell is large. For N → ∞, the model exhibits a sharp freezing transition of the thermodynamic origin. It is shown both analytically and numerically that the glass transition is accompanied by a significant growth of a static length scale ξ pointing to the structural (equilibrium) nature of dynamical slowdown effects in supercooled liquids.

Antiferroquadrupolar correlations in the quantum spin ice candidate Pr2Zr2O7

NASA Astrophysics Data System (ADS)

Petit, S.; Lhotel, E.; Guitteny, S.; Florea, O.; Robert, J.; Bonville, P.; Mirebeau, I.; Ollivier, J.; Mutka, H.; Ressouche, E.; Decorse, C.; Ciomaga Hatnean, M.; Balakrishnan, G.

2016-10-01

We present an experimental study of the quantum spin ice candidate pyrochlore compound Pr2Zr2O7 by means of magnetization measurements, specific heat, and neutron scattering up to 12 T and down to 60 mK. When the field is applied along the [111 ] and [1 1 ¯0 ] directions, k =0 field-induced structures settle in. We find that the ordered moment rises slowly, even at very low temperature, in agreement with macroscopic magnetization. Interestingly, for H ∥[1 1 ¯0 ] , the ordered moment appears on the so-called α chains only. The spin excitation spectrum is essentially inelastic and consists in a broad flat mode centered at about 0.4 meV with a magnetic structure factor which resembles the spin ice pattern. For H ∥[1 1 ¯0 ] (at least up to 2.5 T), we find that a well-defined mode forms from this broad response, whose energy increases with H , in the same way as the temperature of the specific-heat anomaly. We finally discuss these results in the light of mean field calculations and propose an interpretation where quadrupolar interactions play a major role, overcoming the magnetic exchange. In this picture, the spin ice pattern appears shifted up to finite energy because of those interactions. We then propose a range of acceptable parameters for Pr2Zr2O7 that allow to reproduce several experimental features observed under field. With these parameters, the actual ground state of this material would be an antiferroquadrupolar liquid with spin-ice-like excitations.

The topological basis realization and the corresponding XXX spin chain

NASA Astrophysics Data System (ADS)

Sun, C. F.; Xue, K.; Wang, G. C.; Zhou, C. C.; Du, G. J.

2011-06-01

In this paper, it is shown that the XXX model can be constructed from the Temperley-Lieb algebra (TLA) generator. We find that the topological basis states are the two eigenstaes of a closed four-qubit Heisenberg XXX spin chain. Specifically, the spin single states and the energy single state of the system all fall on the topological basis states. It is worth mentioning that for the closed 2N-qubit (N=2, 3, 4, ...) Heisenberg XXX spin chain, all the topological basis states for 2N particles are the spin single states of the system. And the number of the topological basis states is equal to the number of the spin single states of the system, which is \\frac{(2N)!}{N!(N+1)!} .

Physics and application of persistent spin helix state in semiconductor heterostructures

NASA Astrophysics Data System (ADS)

Kohda, Makoto; Salis, Gian

2017-07-01

In order to utilize the spin degree of freedom in semiconductors, control of spin states and transfer of the spin information are fundamental requirements for future spintronic devices and quantum computing. Spin orbit (SO) interaction generates an effective magnetic field for moving electrons and enables spin generation, spin manipulation and spin detection without using external magnetic field and magnetic materials. However, spin relaxation also takes place due to a momentum dependent SO-induced effective magnetic field. As a result, SO interaction is considered to be a double-edged sword facilitating spin control but preventing spin transport over long distances. The persistent spin helix (PSH) state solves this problem since uniaxial alignment of the SO field with SU(2) symmetry enables the suppression of spin relaxation while spin precession can still be controlled. Consequently, understanding the PSH becomes an important step towards future spintronic technologies for classical and quantum applications. Here, we review recent progress of PSH in semiconductor heterostructures and its device application. Fundamental physics of SO interaction and the conditions of a PSH state in semiconductor heterostructures are discussed. We introduce experimental techniques to observe a PSH and explain both optical and electrical measurements for detecting a long spin relaxation time and the formation of a helical spin texture. After emphasizing the bulk Dresselhaus SO coefficient γ, the application of PSH states for spin transistors and logic circuits are discussed.

SPIN EFFECT ON THE POSITION OF REGGE POLES (in Russian)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Azimov, Ya.I.

1962-12-01

An accumulation of poles in the l-plane STAl = -(3n - 5)/2!, found by V. N. Gribov et al. (Phys. Rev. Lett., 9: 239(1962)), imposes a certain limitation on the asymptotic behavior of scattering amplitudes. The effects of particle spin on the position of the accumulations were analyzed using the simple case of two neutral spinless particles ( rature of the d mesons) in which spin particles (nucleon pairs) appear at an intermediate stage. The amplitude near the particle production threshold is proportional to pl, where p is particle production momentum, l is the orbital moment. The l magnitude dependsmore » on the orbital rature of the d -meson moment J and the total particle spin. The minimum value of l is J -- 2 122 to 158 deg , where 122 to 158 deg is the spin of each particle. The analysis indicates accumulation of poles at J = --1/2 + 20. Thus, the accumulation appears in spinless particle scattering amplitudes and all amplitudes related to it by a unitarity condition. Similarly, the n- particle production threshold for identical spins 122 to 158 deg leads to pole accumulations at J == --(3n -- 5)/2 + n 122 to 158 deg . The case of intermediate N-- N pairs was analyzed as a case of pole accumulation at arbitrary energy. In the first postulation relativistic theory considering high particle spin posed certain difficulties, however, elementary particles do not possess spins larger than a 1. Higher spins can be found in nuclei, however, data on nuclear amplitude anomalies are not yet sufficient. The second postulation is more detailed, and it is possible that the liquidation of accumulations could be achieved without special conditions. It was also observed that due to the gradient invariability the two-photon intermediate state does not result in accumulations either in the 1 or in 0. (R.V.J.)« less

Topologically non-trivial electronic and magnetic states in doped copper Kagome lattices

NASA Astrophysics Data System (ADS)

Guterding, Daniel; Jeschke, Harald O.; Valenti, Roser

We present a theoretical investigation of doped copper kagome materials based on natural minerals Herbertsmithite [ZnCu3(OH)6Cl2] and Barlowite[Cu4(OH)6FBr]. Using ab-initio density functional theory calculations we estimate the stability of the hypothetical compounds against structural distortions and analyze their electronic and magnetic properties. We find that materials based on Herbertsmithite present an ideal playground for investigating the interplay of non-trivial band-topology and strong electronic correlation effects. In particular, we propose candidates for the Quantum Spin Hall effect at filling 4/3 and the Quantum Anomalous Hall effect at filling 2/3. For the Barlowite system we point out a route to realize a Quantum Spin Liquid. This work was supported by Deutsche Forschungsgemeinschaft under Grant No. SFB/TR 49 and the National Science Foundation under Grant No. PHY11-25915.

Spatial correlations in driven-dissipative photonic lattices

NASA Astrophysics Data System (ADS)

Biondi, Matteo; Lienhard, Saskia; Blatter, Gianni; Türeci, Hakan E.; Schmidt, Sebastian

2017-12-01

We study the nonequilibrium steady-state of interacting photons in cavity arrays as described by the driven-dissipative Bose–Hubbard and spin-1/2 XY model. For this purpose, we develop a self-consistent expansion in the inverse coordination number of the array (∼ 1/z) to solve the Lindblad master equation of these systems beyond the mean-field approximation. Our formalism is compared and benchmarked with exact numerical methods for small systems based on an exact diagonalization of the Liouvillian and a recently developed corner-space renormalization technique. We then apply this method to obtain insights beyond mean-field in two particular settings: (i) we show that the gas–liquid transition in the driven-dissipative Bose–Hubbard model is characterized by large density fluctuations and bunched photon statistics. (ii) We study the antibunching–bunching transition of the nearest-neighbor correlator in the driven-dissipative spin-1/2 XY model and provide a simple explanation of this phenomenon.

Non-Fermi-Liquid Behavior in Transport Through Co-Doped Au Chains

NASA Astrophysics Data System (ADS)

Di Napoli, S.; Weichselbaum, A.; Roura-Bas, P.; Aligia, A. A.; Mokrousov, Y.; Blügel, S.

2013-05-01

We calculate the conductance as a function of temperature G(T) through Au monatomic chains containing one Co atom as a magnetic impurity, and connected to two conducting leads with a fourfold symmetry axis. Using the information derived from ab initio calculations, we construct an effective model H^eff that hybridizes a 3d7 quadruplet at the Co site with two 3d8 triplets through the hopping of 5dxz and 5dyz electrons of Au. The quadruplet is split by spin anisotropy due to spin-orbit coupling. Solving H^eff with the numerical renormalization group we find that at low temperatures G(T)=a-bT and the ground state impurity entropy is ln⁡(2)/2, a behavior similar to the two-channel Kondo model. Stretching the chain leads to a non-Kondo phase, with the physics of the underscreened Kondo model at the quantum critical point.

Enhancement of room temperature ferromagnetism in tin oxide nanocrystal using organic solvents

NASA Astrophysics Data System (ADS)

Sakthiraj, K.; Hema, M.; Balachandra Kumar, K.

2017-10-01

The effect of organic solvents (ethanol & ethylene glycol) on the room temperature ferromagnetism in nanocrystalline tin oxide has been studied. The samples were synthesized using sol-gel method with the mixture of water & organic liquid as solvent. It is found that pristine SnO2 nanocrystal contain two different types of paramagnetic centres over their surface:(i) surface chemisorbed oxygen species and (ii) Sn interstitial & oxygen vacancy defect pair. The magnetic moment induced in the as-prepared samples is mainly contributed by the alignment of local spin moments resulting from these defects. These surface defect states are highly activated by the usage of ethylene glycol solvent rather than ethylene in tin oxide nanostructure synthesis. Powder X-ray diffraction, transmission electron microscope imaging, energy dispersive spectrometry, Fourier transformed infrared spectroscopy, UV-vis absorption spectroscopy, photoluminescence spectroscopy, vibrating sample magnetometer measurement and electron spin resonance spectroscopy were employed to characterize the nanostructured tin oxide materials.

Magnetic-field-temperature phase diagram of alternating ferrimagnetic chains: Spin-wave theory from a fully polarized vacuum

NASA Astrophysics Data System (ADS)

da Silva, W. M.; Montenegro-Filho, R. R.

2017-12-01

Quantum critical (QC) phenomena can be accessed by studying quantum magnets under an applied magnetic field (B ). The QC points are located at the end points of magnetization plateaus and separate gapped and gapless phases. In one dimension, the low-energy excitations of the gapless phase form a Luttinger liquid (LL), and crossover lines bound insulating (plateau) and LL regimes, as well as the QC regime. Alternating ferrimagnetic chains have a spontaneous magnetization at T =0 and gapped excitations at zero field. Besides the plateau at the fully polarized (FP) magnetization, due to the gap there is another magnetization plateau at the ferrimagnetic (FRI) magnetization. We develop spin-wave theories to study the thermal properties of these chains under an applied magnetic field: one from the FRI classical state and another from the FP state, comparing their results with quantum Monte Carlo data. We deepen the theory from the FP state, obtaining the crossover lines in the T vs B low-T phase diagram. In particular, from local extreme points in the susceptibility and magnetization curves, we identify the crossover between an LL regime formed by excitations from the FRI state to another built from excitations of the FP state. These two LL regimes are bounded by an asymmetric domelike crossover line, as observed in the phase diagram of other quantum magnets under an applied magnetic field.

Protocol for generating multiphoton entangled states from quantum dots in the presence of nuclear spin fluctuations

NASA Astrophysics Data System (ADS)

Denning, Emil V.; Iles-Smith, Jake; McCutcheon, Dara P. S.; Mork, Jesper

2017-12-01

Multiphoton entangled states are a crucial resource for many applications in quantum information science. Semiconductor quantum dots offer a promising route to generate such states by mediating photon-photon correlations via a confined electron spin, but dephasing caused by the host nuclear spin environment typically limits coherence (and hence entanglement) between photons to the spin T2* time of a few nanoseconds. We propose a protocol for the deterministic generation of multiphoton entangled states that is inherently robust against the dominating slow nuclear spin environment fluctuations, meaning that coherence and entanglement is instead limited only by the much longer spin T2 time of microseconds. Unlike previous protocols, the present scheme allows for the generation of very low error probability polarization encoded three-photon GHZ states and larger entangled states, without the need for spin echo or nuclear spin calming techniques.

Role of entropy and structural parameters in the spin-state transition of LaCoO3

NASA Astrophysics Data System (ADS)

Chakrabarti, Bismayan; Birol, Turan; Haule, Kristjan

2017-11-01

The spin-state transition in LaCoO3 has eluded description for decades despite concerted theoretical and experimental effort. In this study, we approach this problem using fully charge self-consistent density functional theory + embedded dynamical mean field theory (DFT+DMFT). We show from first principles that LaCoO3 cannot be described by a single, pure spin state at any temperature. Instead, we observe a gradual change in the population of higher-spin multiplets with increasing temperature, with the high-spin multiplets being excited at the onset of the spin-state transition followed by the intermediate-spin multiplets being excited at the metal-insulator-transition temperature. We explicitly elucidate the critical role of lattice expansion and oxygen octahedral rotations in the spin-state transition. We also reproduce, from first principles, that the spin-state transition and the metal-insulator transition in LaCoO3 occur at different temperature scales. In addition, our results shed light on the importance of electronic entropy in driving the spin-state transition, which has so far been ignored in all first-principles studies of this material.

Spin-Controlled Conductivity in a Thiophene-Functionalized Iron-Bis(dicarbollide)

NASA Astrophysics Data System (ADS)

Beach, Benjamin; Sauriol, Dustin; Derosa, Pedro

2016-04-01

The relationship between spin state and conductivity is studied for a thiophene-functionalized iron(III)-bis(dicarbollide) with one or two thiophenes at each end of the cage. Iron has a high ground state spin that can be adjusted by external electromagnetic fields to produce different magnetic states. The hypothesis explored here is that changes in the spin state of these Fe-containing molecules can lead to significant changes in molecular conductivity. Two examples of the possible application of such spin-dependent conductivity are its use as a molecular switch, the basic building block in digital logic, or as a memory bit. The molecules were first optimized using the Becke-3 Lee-Yang-Parr functional (B3LYP) with the 6-31G(d) basis set. A relaxed molecular geometry at each spin state was then placed between gold electrodes to conduct spin-polarized electron transport calculations with the density functional theory/non-equilibrium Green's functions formalism. The revised Perdew-Burke-Ernzerhf solids exchange-correlation functional (PBES) with double zeta polarized basis set was used. The result of these calculations show that the conductivity increases with the spin state. The cage structure is shown to exhibit fully delocalized molecular orbitals (MOs) appropriate for high conductivity and thus, in this system, the conductivity depends on the position of the MOs relative to the Fermi level. Minority spins are responsible for the conductivity of the doublet spin state while majority spins dominate for the quartet and sextet spin states as they are found closer to the Fermi level when they are occupied. Energy calculations predict a difference in energy between the more and the less conductive spin states (sextet and doublet respectively) that is 15-20 times greater than the thermal energy, which would imply stability at room temperature; however, the energy difference is sufficiently small that transitions between spin states can be induced.

Spin-injection optical pumping of molten cesium salt and its NMR diagnosis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ishikawa, Kiyoshi

2015-07-15

Nuclear spin polarization of cesium ions in the salt was enhanced during optical pumping of cesium vapor at high magnetic field. Significant motional narrowing and frequency shift of NMR signals were observed by intense laser heating of the salt. When the hyperpolarized salt was cooled by blocking the heating laser, the signal width and frequency changed during cooling and presented the phase transition from liquid to solid. Hence, we find that the signal enhancement is mostly due to the molten salt and nuclear spin polarization is injected into the salt efficiently in the liquid phase. We also show that opticalmore » pumping similarly induces line narrowing in the solid phase. The use of powdered salt provided an increase in effective surface area and signal amplitude without glass wool in the glass cells.« less

Observation of non-Fermi liquid behavior in hole-doped Eu2Ir2O7

NASA Astrophysics Data System (ADS)

Banerjee, A.; Sannigrahi, J.; Giri, S.; Majumdar, S.

2017-12-01

The Weyl semimetallic compound Eu2Ir2O7 and its hole-doped derivatives (which are achieved by substituting trivalent Eu by divalent Sr) are investigated through transport, magnetic, and calorimetric studies. The metal-insulator transition (MIT) temperature is found to get substantially reduced with hole doping, and for 10% Sr doping the composition is metallic down to temperature as low as 5 K. These doped compositions are found to violate the Mott-Ioffe-Regel condition for minimum electrical conductivity and show a distinct signature of non-Fermi liquid behavior at low temperature. The MIT in the doped compounds does not correlate with the magnetic transition point, and Anderson-Mott-type disorder-induced localization may be attributed to the ground-state insulating phase. The observed non-Fermi liquid behavior can be understood on the basis of disorder-induced distribution of the spin-orbit-coupling parameter, which is markedly different in the case of Ir4 + and Ir5 + ions.

Thermal transport in topological-insulator-based superconducting hybrid structures with mixed singlet and triplet pairing states.

PubMed

Li, Hai; Zhao, Yuan Yuan

2017-11-22

In the framework of the Bogoliubov-de Gennes equation, we investigate the thermal transport properties in topological-insulator-based superconducting hybrid structures with mixed spin-singlet and spin-triplet pairing states, and emphasize the different manifestations of the spin-singlet and spin-triplet pairing states in the thermal transport signatures. It is revealed that the temperature-dependent differential thermal conductance strongly depends on the components of the pairing state, and the negative differential thermal conductance only occurs in the spin-singlet pairing state dominated regime. It is also found that the thermal conductance is profoundly sensitive to the components of the pairing state. In the spin-singlet pairing state controlled regime, the thermal conductance obviously oscillates with the phase difference and junction length. With increasing the proportion of the spin-triplet pairing state, the oscillating characteristic of the thermal conductance fades out distinctly. These results suggest an alternative route for distinguishing the components of pairing states in topological-insulator-based superconducting hybrid structures.

Non-Fermi-liquid to Fermi-liquid transports in iron-pnictide Ba(Fe1-x Co x )2As2 and the electronic correlation strength in superconductors newly probed by the normal-state Hall angle

NASA Astrophysics Data System (ADS)

Wang, L. M.; Wang, Chih-Yi; Zen, Sha-Min; Chang, Jin-Yuan; Kuo, C. N.; Lue, C. S.; Chang, L. J.; Su, Y.; Wolf, Th; Adelmann, P.

2017-03-01

Electrical transports in iron-pnictide Ba(Fe1-x Co x )2As2 (BFCA) single crystals are heavily debated in terms of the hidden Fermi-liquid (HFL) and holographic theories. Both HFL and holographic theories provide consistent physic pictures and propose a universal expression of resistivity to describe the crossover of transports from the non-Fermi-liquid (FL) to FL behavior in these so-called ‘strange metal’ systems. The deduced spin exchange energy J and model-dependent energy scale W in BFCA are almost the same, or are of the same order of several hundred Kelvin for over-doped BFCA, which is in agreement with the HFL theory. Moreover, a drawn line of W/3.5 for BFCA in the higher-doping region up to the right demonstrates the crossover from non-FL-like behavior to FL-like behavior at high doping, and shows a new phase diagram of BFCA. The electronic correlation strength in superconductors has been newly probed by the normal-state Hall angle, which found that, for the first time, correlation strength can be characterized by the ratios of T c to the Fermi temperature T F, J/T F, and the transverse mass to longitudinal mass.

Magnetic Field Dependence of Excitations Near Spin-Orbital Quantum Criticality

NASA Astrophysics Data System (ADS)

Biffin, A.; Rüegg, Ch.; Embs, J.; Guidi, T.; Cheptiakov, D.; Loidl, A.; Tsurkan, V.; Coldea, R.

2017-02-01

The spinel FeSc2 S4 has been proposed to realize a near-critical spin-orbital singlet (SOS) state, where entangled spin and orbital moments fluctuate in a global singlet state on the verge of spin and orbital order. Here we report powder inelastic neutron scattering measurements that observe the full bandwidth of magnetic excitations and we find that spin-orbital triplon excitations of an SOS state can capture well key aspects of the spectrum in both zero and applied magnetic fields up to 8.5 T. The observed shift of low-energy spectral weight to higher energies upon increasing applied field is naturally explained by the entangled spin-orbital character of the magnetic states, a behavior that is in strong contrast to spin-only singlet ground state systems, where the spin gap decreases upon increasing applied field.

Thermoelectronic transport through spin-crossover single molecule Fe[(H2Bpz2)2bipy

NASA Astrophysics Data System (ADS)

Liu, N.; Zhu, L.; Yao, K. L.

2018-04-01

By means of density functional theory combined with the method of Keldysh nonequilibrium Green’s function, the thermal transport properties of high- and low-spin states of mononuclear FeII molecules with spin-crossover characteristics are studied. It is found that the high-spin molecular junction has a larger current than the low-spin one, producing thermally-induced switching effect. Furthermore, for high spin state molecule, the spin-up thermo-current is strongly blocked, thus achieving a pure thermo spin current. The enhanced Seebeck coefficient and the figure of merit value of high-spin state indicate that it is an ideal candidate for thermoelectric applications.

Large Spun Formed Friction-Stir Welded Tank Domes for Liquid Propellant Tanks Made from AA2195: A Technology Demonstration for the Next Generation of Heavy Lift Launchers

NASA Technical Reports Server (NTRS)

Stachulla, M.; Pernpeinter, R.; Brewster J.; Curreri, P.; Hoffman, E.

2010-01-01

Improving structural efficiency while reducing manufacturing costs are key objectives when making future heavy-lift launchers more performing and cost efficient. The main enabling technologies are the application of advanced high performance materials as well as cost effective manufacture processes. This paper presents the status and main results of a joint industrial research & development effort to demonstrate TRL 6 of a novel manufacturing process for large liquid propellant tanks for launcher applications. Using high strength aluminium-lithium alloy combined with the spin forming manufacturing technique, this development aims at thinner wall thickness and weight savings up to 25% as well as a significant reduction in manufacturing effort. In this program, the concave spin forming process is used to manufacture tank domes from a single flat plate. Applied to aluminium alloy, this process allows reaching the highest possible material strength status T8, eliminating numerous welding steps which are typically necessary to assemble tank domes from 3D-curved panels. To minimize raw material costs for large diameter tank domes for launchers, the dome blank has been composed from standard plates welded together prior to spin forming by friction stir welding. After welding, the dome blank is contoured in order to meet the required wall thickness distribution. For achieving a material state of T8, also in the welding seams, the applied spin forming process allows the required cold stretching of the 3D-curved dome, with a subsequent ageing in a furnace. This combined manufacturing process has been demonstrated up to TRL 6 for tank domes with a 5.4 m diameter. In this paper, the manufacturing process as well as test results are presented. Plans are shown how this process could be applied to future heavy-lift launch vehicles developments, also for larger dome diameters.

Unconventional high-Tc superconductivity in fullerides.

PubMed

Takabayashi, Yasuhiro; Prassides, Kosmas

2016-09-13

A3C60 molecular superconductors share a common electronic phase diagram with unconventional high-temperature superconductors such as the cuprates: superconductivity emerges from an antiferromagnetic strongly correlated Mott-insulating state upon tuning a parameter such as pressure (bandwidth control) accompanied by a dome-shaped dependence of the critical temperature, Tc However, unlike atom-based superconductors, the parent state from which superconductivity emerges solely by changing an electronic parameter-the overlap between the outer wave functions of the constituent molecules-is controlled by the C60 (3-) molecular electronic structure via the on-molecule Jahn-Teller effect influence of molecular geometry and spin state. Destruction of the parent Mott-Jahn-Teller state through chemical or physical pressurization yields an unconventional Jahn-Teller metal, where quasi-localized and itinerant electron behaviours coexist. Localized features gradually disappear with lattice contraction and conventional Fermi liquid behaviour is recovered. The nature of the underlying (correlated versus weak-coupling Bardeen-Cooper-Schrieffer theory) s-wave superconducting states mirrors the unconventional/conventional metal dichotomy: the highest superconducting critical temperature occurs at the crossover between Jahn-Teller and Fermi liquid metal when the Jahn-Teller distortion melts.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'. © 2016 The Author(s).

Unconventional high-Tc superconductivity in fullerides

PubMed Central

Takabayashi, Yasuhiro; Prassides, Kosmas

2016-01-01

A3C60 molecular superconductors share a common electronic phase diagram with unconventional high-temperature superconductors such as the cuprates: superconductivity emerges from an antiferromagnetic strongly correlated Mott-insulating state upon tuning a parameter such as pressure (bandwidth control) accompanied by a dome-shaped dependence of the critical temperature, Tc. However, unlike atom-based superconductors, the parent state from which superconductivity emerges solely by changing an electronic parameter—the overlap between the outer wave functions of the constituent molecules—is controlled by the C603− molecular electronic structure via the on-molecule Jahn–Teller effect influence of molecular geometry and spin state. Destruction of the parent Mott–Jahn–Teller state through chemical or physical pressurization yields an unconventional Jahn–Teller metal, where quasi-localized and itinerant electron behaviours coexist. Localized features gradually disappear with lattice contraction and conventional Fermi liquid behaviour is recovered. The nature of the underlying (correlated versus weak-coupling Bardeen–Cooper–Schrieffer theory) s-wave superconducting states mirrors the unconventional/conventional metal dichotomy: the highest superconducting critical temperature occurs at the crossover between Jahn–Teller and Fermi liquid metal when the Jahn–Teller distortion melts. This article is part of the themed issue ‘Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene’. PMID:27501971

Direct comparison of current-induced spin polarization in topological insulator Bi2Se3 and InAs Rashba states

DOE PAGES

Li, C. H.; van ‘t Erve, O. M. J.; Rajput, S.; ...

2016-11-17

Three-dimensional topological insulators (TIs) exhibit time-reversal symmetry protected, linearly dispersing Dirac surface states with spin–momentum locking. Band bending at the TI surface may also lead to coexisting trivial two-dimensional electron gas (2DEG) states with parabolic energy dispersion. A bias current is expected to generate spin polarization in both systems, although with different magnitude and sign. Here we compare spin potentiometric measurements of bias current-generated spin polarization in Bi2Se3(111) where Dirac surface states coexist with trivial 2DEG states, and in InAs(001) where only trivial 2DEG states are present. We observe spin polarization arising from spin–momentum locking in both cases, with oppositemore » signs of the measured spin voltage. We present a model based on spin dependent electrochemical potentials to directly derive the sign expected for the Dirac surface states, and show that the dominant contribution to the current-generated spin polarization in the TI is from the Dirac surface states.« less

Evidence for a Nematic Phase in La 1.75 Sr 0.25 NiO 4

DOE PAGES

Zhong, Ruidan; Winn, Barry L.; Gu, Genda; ...

2017-04-28

Determining the nature of electronic states in doped Mott insulators remains a challenging task. In the case of tetragonal La 2 - xSr xNiO 4, the occurrence of diagonal charge and spin stripe order in the ground state is now well established. In contrast, the nature of the high-temperature “disordered” state from which the stripe order develops has long been a subject of controversy, with considerable speculation regarding a polaronic liquid. Following the recent detection of dynamic charge stripes, in this paper we use neutron scattering measurements on an x = 0.25 crystal to demonstrate that the dispersion of themore » charge-stripe excitations is anisotropic. Finally, this observation provides compelling evidence for the presence of electronic nematic order.« less

Evidence for a Nematic Phase in La 1.75 Sr 0.25 NiO 4

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhong, Ruidan; Winn, Barry L.; Gu, Genda

Determining the nature of electronic states in doped Mott insulators remains a challenging task. In the case of tetragonal La 2 - xSr xNiO 4, the occurrence of diagonal charge and spin stripe order in the ground state is now well established. In contrast, the nature of the high-temperature “disordered” state from which the stripe order develops has long been a subject of controversy, with considerable speculation regarding a polaronic liquid. Following the recent detection of dynamic charge stripes, in this paper we use neutron scattering measurements on an x = 0.25 crystal to demonstrate that the dispersion of themore » charge-stripe excitations is anisotropic. Finally, this observation provides compelling evidence for the presence of electronic nematic order.« less

Magnetic susceptibility of Inconel alloys 718, 625, and 600 at cryogenic temperatures

NASA Technical Reports Server (NTRS)

Goldberg, Ira B.; Mitchell, Michael R.; Murphy, Allan R.; Goldfarb, Ronald B.; Loughran, Robert J.

1990-01-01

After a hydrogen fuel bleed valve problem on the Discovery Space Shuttle was traced to the strong magnetization of Inconel 718 in the armature of the linear variable differential transformer near liquid hydrogen temperatures, the ac magnetic susceptibility of three samples of Inconel 718 of slightly different compositions, one sample of Inconel 625, and on sample of Inconel 600 were measured as a function of temperature. Inconel 718 alloys are found to exhibit a spin glass state below 16 K. Inconel 600 exhibits three different magnetic phases, the lowest-temperature state (below 6 K) being somewhat similar to that of Inconel 718. The magnetic states of the Inconel alloys and their magnetic susceptibilities appear to be strongly dependent on the exact composition of the alloy.

Correlations and Werner states in finite spin linear arrays

NASA Astrophysics Data System (ADS)

Wells, P. R.; Chaves, C. M.; d'Albuquerque e Castro, J.; Koiller, Belita

2013-10-01

Pairwise quantum correlations in the ground state of an N-spins antiferromagnetic Heisenberg chain are investigated. By varying the exchange coupling between two neighboring sites, it is possible to reversibly drive spins from entangled to disentangled states. For even N, the two-spin density matrix is written in the form of a Werner state, allowing identification of its single parameter with the usual spin-spin correlation function. The N = 4 chain is identified as a promising system for practical demonstrations of non-classical correlations and the realization of Werner states in familiar condensed matter systems. Fabrication and measurement ingredients are within current capabilities.

Spin State of Co3+ Ions in Layered GdBaCo2O5.5 Cobaltite in the Paramagnetic Phase

NASA Astrophysics Data System (ADS)

Solin, N. I.; Naumov, S. V.; Telegin, S. V.

2018-04-01

A new scheme interpreting the changes in the spin state of Co3+ ions in GdBaCo2O5.5 in the course of the metal-insulator transition is proposed. The transition occurs gradually within a wide ( 100 K) temperature range. The changes in the spin state of Co3+ ions are revealed using the data on the linear thermal expansion. In the metallic state, less than one-half of Co3+ ions are in the high-spin (HS, S = 2) state in octahedra, whereas the remaining ions are in the low-spin (LS, S = 0) state. The transition to the nonmetallic state occurs owing to the transformation of the HS state to the LS state in octahedra and to the transformation of some part of LS Co3+ in pyramids to the intermediate-spin (IS, S = 1) state.

Methyl fluoride-13C in nematic liquid crystals: Anisotropy of the indirect 13C-19F spin-spin coupling and of the 1H, 13C, and 19F chemical shieldings

NASA Astrophysics Data System (ADS)

Jokisaari, J.; Hiltunen, Y.; Lounila, J.

1986-09-01

The anisotropy of the indirect 13C-19F spin-spin coupling tensor of methyl fluoride-13C in the liquid crystals ZLI 1167, EBBA, their mixtures, phase IV, and phase 1221 was studied by applying 1H and 19F NMR spectroscopy. The relative anisotropy ΔJCF/JCF gets values between -4.3 (in ZLI 1167) and +30.7 (in EBBA) when determined in the conventional way from the experimental dipolar coupling constants taking into account only harmonic vibrational corrections. The inclusion of the deformational corrections in both the direct and indirect C-F coupling tensors leads to a constant, solvent independent relative anisotropy of -2.5±0.2. This result is also obtained when a mixture of the liquid crystals ZLI 1167 and EBBA is used which mixture gives an undistorted geometry for methyl fluoride. The chemical shielding anisotropies ΔσH, ΔσC, and ΔσF for methyl fluoride were determined by applying the method of mixing two thermotropic nematogens (ZLI 1167 and EBBA) with opposite anisotropies of diamagnetic susceptibility. The results ΔσH =+5.2±0.2 ppm, ΔσC =+87±4 ppm, and ΔσF =-90±4 ppm are in fair agreement with theoretical calculations.

Magnetic ground state of the layered honeycomb compound Na2Co2TeO6

NASA Astrophysics Data System (ADS)

Bera, A. K.; Yusuf, S. M.

2018-04-01

The magnetic correlations in the 2D layered honeycomb compound Na2Co2TeO6 has been investigated. The temperature dependent susceptibility curve reveals a transition to the magnetically ordered state at TN ˜ 25 K. The temperature dependent neutron diffraction study confirms an antiferromagnetic ordering below TN. The magnetic ground state is determined to be a zigzag antiferromagnet that appears due to competing exchange interactions beyond nearest neighbors. The moments align along the crystallographic b axis with reduced ordered magnetic moment values of 2.72(2) μB/Co2+ and 2.52(3) μB/Co2+ for two Co sites, respectively. In comparison to the theoretical phase diagram the determined zigzag antiferromagnetic ground state suggests that the compound Na2Co2TeO6 is situated in the proximity to the quantum spin liquid state in the phase diagram.

Observation of quantum entanglement between a photon and a single electron spin confined to an InAs quantum dot

NASA Astrophysics Data System (ADS)

Schaibley, John; Burgers, Alex; McCracken, Greg; Duan, Luming; Berman, Paul; Steel, Duncan; Bracker, Allan; Gammon, Daniel; Sham, Lu

2013-03-01

A single electron spin confined to a single InAs quantum dot (QD) can serve as a qubit for quantum information processing. By utilizing the QD's optically excited trion states in the presence of an externally applied magnetic field, the QD spin can be rapidly initialized, manipulated and read out. A key resource for quantum information is the ability to entangle distinct QD spins. One approach relies on intermediate spin-photon entanglement to mediate the entanglement between distant QD spin qubits. We report a demonstration of quantum entanglement between a photon's polarization state and the spin state of a single electron confined to a single QD. Here, the photon is spontaneously emitted from one of the QD's trion states. The emitted photon's polarization along the detection axis is entangled with the resulting spin state of the QD. By performing projective measurements on the photon's polarization state and correlating these measurements with the state of the QD spin in two different bases, we obtain a lower bound on the entanglement fidelity of 0.59 (after background correction). The fidelity bound is limited almost entirely by the timing resolution of our single photon detector. The spin-photon entanglement generation rate is 3 ×103 s-1. Supported by: NSF, MURI, AFOSR, DARPA, ARO.

Electrical control of flying spin precession in chiral 1D edge states

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nakajima, Takashi; Komiyama, Susumu; Lin, Kuan-Ting

2013-12-04

Electrical control and detection of spin precession are experimentally demonstrated by using spin-resolved edge states in the integer quantum Hall regime. Spin precession is triggered at a corner of a biased metal gate, where electron orbital motion makes a sharp turn leading to a nonadiabatic change in the effective magnetic field via spin-orbit interaction. The phase of precession is controlled by the group velocity of edge-state electrons tuned by gate bias voltage: Spin-FET-like coherent control of spin precession is thus realized by all-electrical means.

Full-gap superconductivity in spin-polarised surface states of topological semimetal β-PdBi2.

PubMed

Iwaya, K; Kohsaka, Y; Okawa, K; Machida, T; Bahramy, M S; Hanaguri, T; Sasagawa, T

2017-10-17

A bulk superconductor possessing a topological surface state at the Fermi level is a promising system to realise long-sought topological superconductivity. Although several candidate materials have been proposed, experimental demonstrations concurrently exploring spin textures and superconductivity at the surface have remained elusive. Here we perform spectroscopic-imaging scanning tunnelling microscopy on the centrosymmetric superconductor β-PdBi 2 that hosts a topological surface state. By combining first-principles electronic-structure calculations and quasiparticle interference experiments, we determine the spin textures at the surface, and show not only the topological surface state but also all other surface bands exhibit spin polarisations parallel to the surface. We find that the superconducting gap fully opens in all the spin-polarised surface states. This behaviour is consistent with a possible spin-triplet order parameter expected for such in-plane spin textures, but the observed superconducting gap amplitude is comparable to that of the bulk, suggesting that the spin-singlet component is predominant in β-PdBi 2 .Although several materials have been proposed as topological superconductors, spin textures and superconductivity at the surface remain elusive. Here, Iwaya et al. determine the spin textures at the surface of a superconductor β-PdBi 2 and find the superconducting gap opening in all spin-polarised surface states.

Magnetically aligned phospholipid bilayers in weak magnetic fields: optimization, mechanism, and advantages for X-band EPR studies.

PubMed

Cardon, Thomas B; Tiburu, Elvis K; Lorigan, Gary A

2003-03-01

Our lab is developing a spin-labeled EPR spectroscopic technique complementary to solid-state NMR studies to study the structure, orientation, and dynamics of uniaxially aligned integral membrane proteins inserted into magnetically aligned discotic phospholipid bilayers, or bicelles. The focus of this study is to optimize and understand the mechanisms involved in the magnetic alignment process of bicelle disks in weak magnetic fields. Developing experimental conditions for optimized magnetic alignment of bicelles in low magnetic fields may prove useful to study the dynamics of membrane proteins and its interactions with lipids, drugs, steroids, signaling events, other proteins, etc. In weak magnetic fields, the magnetic alignment of Tm(3+)-doped bicelle disks was thermodynamically and kinetically very sensitive to experimental conditions. Tm(3+)-doped bicelles were magnetically aligned using the following optimized procedure: the temperature was slowly raised at a rate of 1.9K/min from an initial temperature being between 298 and 307K to a final temperature of 318K in the presence of a static magnetic field of 6300G. The spin probe 3beta-doxyl-5alpha-cholestane (cholestane) was inserted into the bicelle disks and utilized to monitor bicelle alignment by analyzing the anisotropic hyperfine splitting for the corresponding EPR spectra. The phases of the bicelles were determined using solid-state 2H NMR spectroscopy and compared with the corresponding EPR spectra. Macroscopic alignment commenced in the liquid crystalline nematic phase (307K), continued to increase upon slowly raising the temperature, and was well-aligned in the liquid crystalline lamellar smectic phase (318K).

Mobile bound states of Rydberg excitations in a lattice

NASA Astrophysics Data System (ADS)

Letscher, Fabian; Petrosyan, David

2018-04-01

Spin-lattice models play a central role in the studies of quantum magnetism and nonequilibrium dynamics of spin excitations—-magnons. We show that a spin lattice with strong nearest-neighbor interactions and tunable long-range hopping of excitations can be realized by a regular array of laser-driven atoms, with an excited Rydberg state representing the spin-up state and a Rydberg-dressed ground state corresponding to the spin-down state. We find exotic interaction-bound states of magnons that propagate in the lattice via the combination of resonant two-site hopping and nonresonant second-order hopping processes. Arrays of trapped Rydberg-dressed atoms can thus serve as a flexible platform to simulate and study fundamental few-body dynamics in spin lattices.

Short-range magentic correlations and dynamic orbital ordering in the thermally activated spin state of LaCoO3

NASA Astrophysics Data System (ADS)

Rosenkranz, S.; Phelan, D.; Louca, D.; Lee, S. H.; Chupas, P. J.; Osborn, R.; Zheng, H.; Mitchell, J. F.

2006-03-01

The cobalt perovskites La1-xSrxCoO3 show intriguing spin, lattice, and orbital properties similar to the ones observed in colossal magnetoresistive manganites. The x=0 parent compound is a non-magnetic insulator at low temperatures, but shows evidence of a spin-state transition of the cobalt ions above 50K from a low-spin to an intermediate or high-spin configuration. Using high resolution, inelastic neutron scattering, we observe a distinct low energy excitation at 0.6meV coincident with the thermally induced spin state transition observed in susceptibility measurements. The thermal activation of this excited spin state also leads to short-range, dynamic ferro- and antiferromagnetic correlations. These observations are consistent with the activation of a zero-field split intermediate spin state as well as the presence of dynamic orbital ordering of these excited states. Work supported by US DOE BES-DMS W-31-109-ENG-38 and NSF DMR-0454672

Spin injection and inverse Edelstein effect in the surface states of topological Kondo insulator SmB6

PubMed Central

Song, Qi; Mi, Jian; Zhao, Dan; Su, Tang; Yuan, Wei; Xing, Wenyu; Chen, Yangyang; Wang, Tianyu; Wu, Tao; Chen, Xian Hui; Xie, X. C.; Zhang, Chi; Shi, Jing; Han, Wei

2016-01-01

There has been considerable interest in exploiting the spin degrees of freedom of electrons for potential information storage and computing technologies. Topological insulators (TIs), a class of quantum materials, have special gapless edge/surface states, where the spin polarization of the Dirac fermions is locked to the momentum direction. This spin–momentum locking property gives rise to very interesting spin-dependent physical phenomena such as the Edelstein and inverse Edelstein effects. However, the spin injection in pure surface states of TI is very challenging because of the coexistence of the highly conducting bulk states. Here, we experimentally demonstrate the spin injection and observe the inverse Edelstein effect in the surface states of a topological Kondo insulator, SmB6. At low temperatures when only surface carriers are present, a clear spin signal is observed. Furthermore, the magnetic field angle dependence of the spin signal is consistent with spin–momentum locking property of surface states of SmB6. PMID:27834378

Spin injection and inverse Edelstein effect in the surface states of topological Kondo insulator SmB 6

DOE PAGES

Song, Qi; Mi, Jian; Zhao, Dan; ...

2016-11-11

There has been considerable interest in exploiting the spin degrees of freedom of electrons for potential information storage and computing technologies. Topological insulators (TIs), a class of quantum materials, have special gapless edge/surface states, where the spin polarization of the Dirac fermions is locked to the momentum direction. This spin–momentum locking property gives rise to very interesting spin-dependent physical phenomena such as the Edelstein and inverse Edelstein effects. However, the spin injection in pure surface states of TI is very challenging because of the coexistence of the highly conducting bulk states. Here, we experimentally demonstrate the spin injection and observemore » the inverse Edelstein effect in the surface states of a topological Kondo insulator, SmB 6. At low temperatures when only surface carriers are present, a clear spin signal is observed. Moreover, the magnetic field angle dependence of the spin signal is consistent with spin–momentum locking property of surface states of SmB6.« less

Catalystlike effect of orbital angular momentum on the conversion of transverse to three-dimensional spin states within tightly focused radially polarized beams

NASA Astrophysics Data System (ADS)

Han, Lei; Liu, Sheng; Li, Peng; Zhang, Yi; Cheng, Huachao; Zhao, Jianlin

2018-05-01

We report on the catalystlike effect of orbital angular momentum (OAM) on local spin-state conversion within the tightly focused radially polarized beams associated with optical spin-orbit interaction. It is theoretically demonstrated that the incident OAM can lead to a conversion of purely transverse spin state to a three-dimensional spin state on the focal plane. This conversion can be conveniently manipulated by altering the sign and value of the OAM. By comparing the total OAM and spin angular momentum (SAM) on the incident plane to those on the focal plane, it is indicated that the incident OAM have no participation in the angular momentum intertransfer, and just play a role as a catalyst of local SAM conversion. Such an effect of OAM sheds new light on the optical spin-orbit interaction in tight-focusing processes. The resultant three-dimensional spin states may provide more degrees of freedom in optical manipulation and spin-dependent directive coupling.

Protecting a Diamond Quantum Memory by Charge State Control.

PubMed

Pfender, Matthias; Aslam, Nabeel; Simon, Patrick; Antonov, Denis; Thiering, Gergő; Burk, Sina; Fávaro de Oliveira, Felipe; Denisenko, Andrej; Fedder, Helmut; Meijer, Jan; Garrido, Jose A; Gali, Adam; Teraji, Tokuyuki; Isoya, Junichi; Doherty, Marcus William; Alkauskas, Audrius; Gallo, Alejandro; Grüneis, Andreas; Neumann, Philipp; Wrachtrup, Jörg

2017-10-11

In recent years, solid-state spin systems have emerged as promising candidates for quantum information processing. Prominent examples are the nitrogen-vacancy (NV) center in diamond, phosphorus dopants in silicon (Si:P), rare-earth ions in solids, and V Si -centers in silicon-carbide. The Si:P system has demonstrated that its nuclear spins can yield exceedingly long spin coherence times by eliminating the electron spin of the dopant. For NV centers, however, a proper charge state for storage of nuclear spin qubit coherence has not been identified yet. Here, we identify and characterize the positively charged NV center as an electron-spin-less and optically inactive state by utilizing the nuclear spin qubit as a probe. We control the electronic charge and spin utilizing nanometer scale gate electrodes. We achieve a lengthening of the nuclear spin coherence times by a factor of 4. Surprisingly, the new charge state allows switching of the optical response of single nodes facilitating full individual addressability.

Majorana spin in magnetic atomic chain systems

NASA Astrophysics Data System (ADS)

Li, Jian; Jeon, Sangjun; Xie, Yonglong; Yazdani, Ali; Bernevig, B. Andrei

2018-03-01

In this paper, we establish that Majorana zero modes emerging from a topological band structure of a chain of magnetic atoms embedded in a superconductor can be distinguished from trivial localized zero energy states that may accidentally form in this system using spin-resolved measurements. To demonstrate this key Majorana diagnostics, we study the spin composition of magnetic impurity induced in-gap Shiba states in a superconductor using a hybrid model. By examining the spin and spectral densities in the context of the Bogoliubov-de Gennes (BdG) particle-hole symmetry, we derive a sum rule that relates the spin densities of localized Shiba states with those in the normal state without superconductivity. Extending our investigations to a ferromagnetic chain of magnetic impurities, we identify key features of the spin properties of the extended Shiba state bands, as well as those associated with a localized Majorana end mode when the effect of spin-orbit interaction is included. We then formulate a phenomenological theory for the measurement of the local spin densities with spin-polarized scanning tunneling microscopy (STM) techniques. By combining the calculated spin densities and the measurement theory, we show that spin-polarized STM measurements can reveal a sharp contrast in spin polarization between an accidental-zero-energy trivial Shiba state and a Majorana zero mode in a topological superconducting phase in atomic chains. We further confirm our results with numerical simulations that address generic parameter settings.

Epitaxial strain-mediated spin-state transitions: can we switch off magnetism?

NASA Astrophysics Data System (ADS)

Rondinelli, James; Spaldin, Nicola

2008-03-01

We use first-principles density functional theory calculations to explore spin-state transitions in epitaxially strained LaCoO3. While high-spin to low-spin state transitions in minerals are common in geophysics, where pressures can reach over 200 GPa, we explore whether heteroepitaxial strain can achieve similar transitions with moderate strain in thin films. LaCoO3 is known to undergo a low-spin (S=0, t2g^6eg^0) to intermediate-spin (S=1, t2g^5eg^1) or high-spin (S=2, t2g^4eg^2) state transition with increasing temperature, and thus makes it a promising candidate material for strain-mediated spin transitions. Here we discuss the physics of the low-spin transition and changes in the electronic structure of LaCoO3, most notably, the metal-insulator transition that accompanies the spin-state transitions with epitaxial strain. As thin film growth techniques continue to reach atomic-level precision, we suggest this is another approach for controlling magnetism in complex oxide heterostructures.

Yrare low-spin positive-parity states in N = 88 66 154 Dy

NASA Astrophysics Data System (ADS)

Zimba, G. L.; Bvumbi, S. P.; Masiteng, L. P.; Jones, P.; Sharpey-Schafer, J. F.; Majola, S. N. T.; Dinoko, T. S.; Shirinda, O.; Lawrie, J. J.; Easton, J. E.; Khumalo, N. A.; Msebi, L.; Mashita, P. I.; Papka, P.; Roux, D. G.; Negi, D.

2018-04-01

Low-spin positive-parity yrare states of 66 154 Dy88 were established using the 155Gd(3He,4n) reaction at a beam energy of E_{lab} = 37.5 MeV. The AFRODITE spectrometer array at iThemba LABS was used to record γγ coincidences and measure DCO ratios and polarisation asymmetries. The K^{π}=2+ γ band has been observed up to spin 13+ in the odd spins and to 12+ in the even spins. The staggering parameter S( I) of the γ band is compared to that found in other N = 88 isotones. Different behaviour of S( I) with increasing spin is observed for each of the isotones. We conjecture that the variation in S( I) is mainly due to mixing of the even-spin states with the same spin and parity states in neighbouring rotational bands. A second K^{π}=2+ band has been established up to a spin of 12+ in the even spins. We suggest that this is a γ band based on the J^{π} = 0+ state at Ex = 660.6 keV.

Magnetic excitations in Kondo liquid: superconductivity and hidden magnetic quantum critical fluctuations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Yifeng; Urbano, Ricardo; Nicholas, Curro

2009-01-01

We report Knight shift experiments on the superconducting heavy electron material CeCoIn{sub 5} that allow one to track with some precision the behavior of the heavy electron Kondo liquid in the superconducting state with results in agreement with BCS theory. An analysis of the {sup 115}In nuclear quadrupole resonance (NQR) spin-lattice relaxation rate T{sub 1}{sup -1} measurements under pressure reveals the presence of 2d magnetic quantum critical fluctuations in the heavy electron component that are a promising candidate for the pairing mechanism in this material. Our results are consistent with an antiferromagnetic quantum critical point (QCP) located at slightly negativemore » pressure in CeCoIn{sub 5} and provide additional evidence for significant similarities between the heavy electron materials and the high T{sub c} cuprates.« less

Direct 1H NMR evidence of spin-rotation coupling as a source of para → ortho-H2 conversion in diamagnetic solvents

NASA Astrophysics Data System (ADS)

Terenzi, Camilla; Bouguet-Bonnet, Sabine; Canet, Daniel

2017-04-01

At ambient temperature, conversion from 100% enriched para-hydrogen (p-H2; singlet state) to ortho-hydrogen (o-H2; triplet state) leads necessarily to the thermodynamic equilibrium proportions: 75% of o-H2 and 25% of p-H2. When p-H2 is dissolved in a diamagnetic organic solvent, conversion is very slow and can be considered as arising from nuclear spin relaxation phenomena. A first relaxation mechanism, specific to the singlet state and involving a combination of auto-correlation and cross correlation spectral densities, can be retained: randomly fluctuating magnetic fields due to inter-molecular dipolar interactions. We demonstrate here that (i) this dipolar mechanism is not sufficient for accounting for the p a r a →o r t h o conversion rate, (ii) spin-rotation interaction, an intra-molecular mechanism, behaves similarly to random-field interaction and, thus, may be involved in the singlet relaxation rate. Also, as the p a r a →o r t h o conversion is monitored by proton nuclear magnetic resonance (NMR) of dissolved o-H2 (p-H2 is NMR-silent), one has to account for H2 exchange between the liquid phase and the gas phase within the NMR tube, as well as for dissolution effects. Experimental evidence of the above statements is brought here in the case of two organic solvents: acetone-d6 and carbon disulfide. The observed temperature dependence of the p a r a →o r t h o conversion rate shows that spin-rotation can be the dominant contribution to the p-H2 relaxation rate in the absence of tangible dipolar interactions. Our findings shed new light on the "mysterious" mechanism of the p a r a →o r t h o conversion which has been searched for several decades.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andreev, Pavel A., E-mail: andreevpa@physics.msu.ru; Kuz’menkov, L.S., E-mail: lsk@phys.msu.ru

We consider quantum plasmas of electrons and motionless ions. We describe separate evolution of spin-up and spin-down electrons. We present corresponding set of quantum hydrodynamic equations. We assume that plasmas are placed in an uniform external magnetic field. We account different occupation of spin-up and spin-down quantum states in equilibrium degenerate plasmas. This effect is included via equations of state for pressure of each species of electrons. We study oblique propagation of longitudinal waves. We show that instead of two well-known waves (the Langmuir wave and the Trivelpiece–Gould wave), plasmas reveal four wave solutions. New solutions exist due to bothmore » the separate consideration of spin-up and spin-down electrons and different occupation of spin-up and spin-down quantum states in equilibrium state of degenerate plasmas.« less

Solution of the Lindblad equation for spin helix states.

PubMed

Popkov, V; Schütz, G M

2017-04-01

Using Lindblad dynamics we study quantum spin systems with dissipative boundary dynamics that generate a stationary nonequilibrium state with a nonvanishing spin current that is locally conserved except at the boundaries. We demonstrate that with suitably chosen boundary target states one can solve the many-body Lindblad equation exactly in any dimension. As solution we obtain pure states at any finite value of the dissipation strength and any system size. They are characterized by a helical stationary magnetization profile and a ballistic spin current which is independent of system size, even when the quantum spin system is not integrable. These results are derived in explicit form for the one-dimensional spin-1/2 Heisenberg chain and its higher-spin generalizations, which include the integrable spin-1 Zamolodchikov-Fateev model and the biquadratic Heisenberg chain.

Spinning Disc Technology – Residence Time Distribution and Efficiency in Textile Wastewater Treatment Application

NASA Astrophysics Data System (ADS)

Iacob Tudose, E. T.; Zaharia, C.

2018-06-01

The spinning disc (SD) technology has received increased attention in the last years due to its enhanced fluid flow features resulting in improved property transfers. The actual study focuses on characterization of the flow within a spinning disc system based on experimental data used to establish the residence time distribution (RTD) and its dependence on the feeding liquid flowrate and the disc rotational speed. To obtain these data, an inert tracer (sodium chloride) was injected as a pulse input in the liquid stream entering the disc and the salt concentration of the liquid leaving the disc was continuously recorded. The obtained data indicate that an increase in the liquid flowrate from 10 L/h to 30 L/h determines a narrower RTD function. Also, at rotational speed of 200 rpm, the residence time distribution is broader than that for 500 rpm and 800 rpm. The RTD data suggest that depending on the needed flow characteristics, one can choose a certain flowrate and rotational speed domain for its application. Also, the SD technology was used to process textile wastewater treated with bentonite (as both coagulation and discoloration agent) in order to investigate whether the quality indicators such as the total suspended solid content, turbidity and discoloration, can be improved. The experimental results are promising since the discoloration and the removals of suspended solids attained values of over 40%, and respectively, 50 %, depending on the effluent flowrate (10 l/h and 30 L/h), and the disc rotational speed (200 rpm, 550 rpm and 850 rpm) without any other addition of chemicals, or initiation of other simultaneous treatment processes (e.g., advanced oxidative, or reductive, or biochemical processes). This recommends spinning disc technology as a suitable and promising tool to improve different wastewater characteristics.

Confinement effects on dipolar relaxation by translational dynamics of liquids in porous silica glasses

NASA Astrophysics Data System (ADS)

Korb, J.-P.; Xu, Shu; Jonas, J.

1993-02-01

A theory of dipolar relaxation by translational diffusion of a nonwetting liquid confined in model porous media is presented. We obtain expressions of the rates of spin-lattice relaxation 1/T1, spin-spin relaxation 1/T2, and spin-lattice relaxation in the rotating frame 1/T1ρ, which depend on the average pore size d. The frequency variations of these rates are intermediate between the two-dimensional and three-dimensional results. At small frequency they vary logarithmically for small d and tend progressively to a constant with increasing d. For small pore sizes we obtain quadratic confinement dependences of these rates (∝1/d2), at variance with the linear (∝1/d) relation coming from the biphasic fast exchange model usually applied for a wetting liquid in porous media. We apply such a theory to the 1H NMR relaxation of methylcyclohexane liquid in sol-gel porous silica glasses with a narrow pore-size distribution. The experiments confirm the theoretical predictions for very weak interacting solvent in porous silica glasses of pore sizes varying in the range of 18.4-87.2 Å and in the bulk. At the limit of small pores, the logarithmic frequency dependencies of 1/T1ρ and 1/T1 observed over several decades of frequency are interpreted with a model of unbounded two-dimensional diffusion in a layered geometry. The leveling off of the 1/T1ρ low-frequency dependence is interpreted in terms of the bounded two-dimensional diffusion due to the finite length L of the pores. An estimate of a finite size of L=100 Å is in excellent agreement with the experimental results of the transmission electron microscopy study of platinium-carbon replicated xerogels.

The effects of high concentrations of ionic liquid on GB1 protein structure and dynamics probed by high-resolution magic-angle-spinning NMR spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Warner, Lisa; Gjersing, Erica; Follett, Shelby E.

Ionic liquids have great potential in biological applications and biocatalysis, as some ionic liquids can stabilize proteins and enhance enzyme activity, while others have the opposite effect. However, on the molecular level, probing ionic liquid interactions with proteins, especially in solutions containing high concentrations of ionic liquids, has been challenging. In the present work the 13C, 15N-enriched GB1 model protein was used to demonstrate applicability of high-resolution magic-angle-spinning (HR-MAS) NMR spectroscopy to investigate ionic liquid-protein interactions. Effect of an ionic liquid (1-butyl-3-methylimidazolium bromide, [C 4-mim]Br) on GB1was studied over a wide range of the ionic liquid concentrations (0.6-3.5 M, whichmore » corresponds to 10-60% v/v). Interactions between GB1 and [C 4-mim]Br were observed from changes in the chemical shifts of the protein backbone as well as the changes in 15N ps-ns dynamics and rotational correlation times. Site-specific interactions between the protein and [C 4-mim]Br were assigned using 3D methods under HR-MAS conditions. Furthermore, HR-MAS NMR is a viable tool that could aid in elucidation of molecular mechanisms of ionic liquid-protein interactions.« less

The effects of high concentrations of ionic liquid on GB1 protein structure and dynamics probed by high-resolution magic-angle-spinning NMR spectroscopy

DOE PAGES

Warner, Lisa; Gjersing, Erica; Follett, Shelby E.; ...

2016-08-11

Ionic liquids have great potential in biological applications and biocatalysis, as some ionic liquids can stabilize proteins and enhance enzyme activity, while others have the opposite effect. However, on the molecular level, probing ionic liquid interactions with proteins, especially in solutions containing high concentrations of ionic liquids, has been challenging. In the present work the 13C, 15N-enriched GB1 model protein was used to demonstrate applicability of high-resolution magic-angle-spinning (HR-MAS) NMR spectroscopy to investigate ionic liquid-protein interactions. Effect of an ionic liquid (1-butyl-3-methylimidazolium bromide, [C 4-mim]Br) on GB1was studied over a wide range of the ionic liquid concentrations (0.6-3.5 M, whichmore » corresponds to 10-60% v/v). Interactions between GB1 and [C 4-mim]Br were observed from changes in the chemical shifts of the protein backbone as well as the changes in 15N ps-ns dynamics and rotational correlation times. Site-specific interactions between the protein and [C 4-mim]Br were assigned using 3D methods under HR-MAS conditions. Furthermore, HR-MAS NMR is a viable tool that could aid in elucidation of molecular mechanisms of ionic liquid-protein interactions.« less

Femtosecond optical reflectivity measurements of lattice-mediated spin repulsions in photoexcited LaCoO3 thin films

NASA Astrophysics Data System (ADS)

Bielecki, J.; Rata, A. D.; Börjesson, L.

2014-01-01

We present results on the temperature dependence of ultrafast electron and lattice dynamics, measured with pump-probe transient reflectivity experiments, of an epitaxially grown LaCoO3 thin film under tensile strain. Probing spin-polarized transitions into the antibonding eg band provides a measure of the low-spin fraction, both as a function of temperature and time after photoexcitation. It is observed that femtosecond laser pulses destabilize the constant low-spin fraction (˜63%-64%) in equilibrium into a thermally activated state, driven by a subpicosecond change in spin gap Δ. From the time evolution of the low-spin fraction, it is possible to disentangle the thermal and lattice contributions to the spin state. A lattice mediated spin repulsion, identified as the governing factor determining the equilibrium spin state in thin-film LaCoO3, is observed. These results suggests that time-resolved spectroscopy is a sensitive probe of the spin state in LaCoO3 thin films, with the potential to bring forward quantitative insight into the complicated interplay between structure and spin state in LaCoO3.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoshizumi, K.; Sasaki, A.; Kohda, M.

We demonstrate gate-controlled switching between persistent spin helix (PSH) state and inverse PSH state, which are detected by quantum interference effect on magneto-conductance. These special symmetric spin states showing weak localization effect give rise to a long spin coherence when the strength of Rashba spin-orbit interaction (SOI) is close to that of Dresselhaus SOI. Furthermore, in the middle of two persistent spin helix states, where the Rashba SOI can be negligible, the bulk Dresselhaus SOI parameter in a modulation doped InGaAs/InAlAs quantum well is determined.

KENNEDY SPACE CENTER, FLA. - The overhead crane settles the Mars Exploration Rover 2 (MER-2) entry vehicle onto a spin table for a dry-spin test. The MER Mission consists of two identical rovers designed to cover roughly 110 yards each Martian day over various terrain. Each rover will carry five scientific instruments that will allow it to search for evidence of liquid water that may have been present in the planet's past. Identical to each other, the rovers will land at different regions of Mars. Launch for MER-2 (MER-A) is scheduled for June 5.

NASA Image and Video Library

2003-04-30

KENNEDY SPACE CENTER, FLA. - The overhead crane settles the Mars Exploration Rover 2 (MER-2) entry vehicle onto a spin table for a dry-spin test. The MER Mission consists of two identical rovers designed to cover roughly 110 yards each Martian day over various terrain. Each rover will carry five scientific instruments that will allow it to search for evidence of liquid water that may have been present in the planet's past. Identical to each other, the rovers will land at different regions of Mars. Launch for MER-2 (MER-A) is scheduled for June 5.

Spin-dependent recombination probed through the dielectric polarizability

PubMed Central

Bayliss, Sam L.; Greenham, Neil C.; Friend, Richard H.; Bouchiat, Hélène; Chepelianskii, Alexei D

2015-01-01

Despite residing in an energetically and structurally disordered landscape, the spin degree of freedom remains a robust quantity in organic semiconductor materials due to the weak coupling of spin and orbital states. This enforces spin-selectivity in recombination processes which plays a crucial role in optoelectronic devices, for example, in the spin-dependent recombination of weakly bound electron-hole pairs, or charge-transfer states, which form in a photovoltaic blend. Here, we implement a detection scheme to probe the spin-selective recombination of these states through changes in their dielectric polarizability under magnetic resonance. Using this technique, we access a regime in which the usual mixing of spin-singlet and spin-triplet states due to hyperfine fields is suppressed by microwave driving. We present a quantitative model for this behaviour which allows us to estimate the spin-dependent recombination rate, and draw parallels with the Majorana–Brossel resonances observed in atomic physics experiments. PMID:26439933

Prediction of EPR Spectra of Lyotropic Liquid Crystals using a Combination of Molecular Dynamics Simulations and the Model-Free Approach.

PubMed

Prior, Christopher; Oganesyan, Vasily S

2017-09-21

We report the first application of fully atomistic molecular dynamics (MD) simulations to the prediction of the motional electron paramagnetic resonance (EPR) spectra of lyotropic liquid crystals in different aggregation states doped with a paramagnetic spin probe. The purpose of this study is twofold. First, given that EPR spectra are highly sensitive to the motions and order of the spin probes doped within lyotropic aggregates, simulation of EPR line shapes from the results of MD modelling provides an ultimate test bed for the force fields currently employed to model such systems. Second, the EPR line shapes are simulated using the motional parameters extracted from MD trajectories using the Model-Free (MF) approach. Thus a combined MD-EPR methodology allowed us to test directly the validity of the application of the MF approach to systems with multi-component molecular motions. All-atom MD simulations using the General AMBER Force Field (GAFF) have been performed on sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium chloride (DTAC) liquid crystals. The resulting MD trajectories were used to predict and interpret the EPR spectra of pre-micellar, micellar, rod and lamellar aggregates. The predicted EPR spectra demonstrate good agreement with most of experimental line shapes thus confirming the validity of both the force fields employed and the MF approach for the studied systems. At the same time simulation results confirm that GAFF tends to overestimate the packing and the order of the carbonyl chains of the surfactant molecules. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Spin transition in a four-coordinate iron oxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kawakami, T.; Sutou, S.; Hirama, H.

2009-01-01

The spin transition, or spin crossover, is a manifestation of electronic instability induced by external constraints such as pressure1. Among known examples that exhibit spin transition, 3d ions with d6 electron configurations represent the vast majority, but the spin transition observed thus far has been almost exclusively limited to that between high-spin (S = 2) and low-spin (S = 0) states2-9. Here we report a novel high-spin to intermediate-spin (S = 1) state transition at 33 GPa induced by pressurization of an antiferromagnetic insulator SrFeO2 with a square planar coordination10. The change in spin multiplicity brings to ferromagnetism as wellmore » as metallicity, yet keeping the ordering temperature far above ambient. First-principles calculations attribute the origin of the transition to the strong inlayer hybridization between Fe dx 2 -y 2 O p , leading to a pressure-induced electronic instability toward the depopulation of Fe dx 2 -y 2 O p antibonding states. Furthermore, the ferromagnetic S = 1 state is half-metallic due to the inception of half-occupied spin-down (dxz, dyz) degenerate states upon spin transition. These results highlight the square-planar coordinated iron oxides as a new class of magnetic and electric materials and provide new avenues toward realizing multi-functional sensors and data-storage devices.« less

Modelling magnetic anisotropy of single-chain magnets in |d/J| ≥ 1 regime

NASA Astrophysics Data System (ADS)

Haldar, Sumit; Raghunathan, Rajamani; Sutter, Jean-Pascal; Ramasesha, S.

2017-11-01

Single-molecule magnets (SMMs) with single-ion anisotropies comparable to exchange interactions J between spins have recently been synthesised. Here, we provide theoretical insights into the magnetism of such systems. We study spin chains with site-spins, s = 1, 3/2 and 2 and strength of on-site anisotropy comparable to the exchange constants between the spins. We find that large on-site anisotropies lead to crossing of the states with different MS values in the same spin manifold to which they belong in the absence of anisotropy. When on-site anisotropy is increased further, we also find that the MS states of the higher energy spin states descend below the MS states of the ground spin manifold. Giant spin in this limit is no longer conserved and describing the axial and rhombic anisotropies of the molecule, DM and EM, respectively, is not possible. However, the giant spin of the low-lying large MS states is very nearly an integer and, using this spin value, it is possible to construct an effective spin-Hamiltonian and compute the molecular magnetic anisotropy constants DM and EM. We report effect of finite sizes, rotations of site anisotropies and chain dimerisation on the effective anisotropy of the spin chains.

Detecting π-phase superfluids with p-wave symmetry in a quasi-1D optical lattice

NASA Astrophysics Data System (ADS)

Liu, Bo; Li, Xiaopeng; Hulet, Randall G.; Liu, W. Vincent

2016-05-01

We propose an experimental protocol to create a p-wave superfluid in a spin-polarized cold Fermi gas tuned by an s-wave Feshbach resonance. A crucial ingredient is to add an anisotropic 3D optical lattice and tune the fillings of two spins to the s and p band, respectively. The pairing order parameter is confirmed to inherit p-wave symmetry in its center-of-mass motion. We find that it can further develop into a state of unexpected π-phase modulation in a broad parameter regime. Experimental signatures are predicted in the momentum distributions, density of states and spatial densities for a realistic experimental setup. The π-phase p-wave superfluid is reminiscent of the π-state in superconductor-ferromagnet heterostructures but differs in symmetry and physical origin. The spatially-varying phases of the superfluid gap provide a novel approach to synthetic magnetic fields for neutral atoms. It would represent another example of p-wave pairing, first discovered in He-3 liquids. Work supported in part by U.S. ARO, AFOSR, NSF, ONR, Charles E. Kaufman Foundation, and The Pittsburgh Foundation, LPS-MPO-CMTC, JQI-NSF-PFC, ARO-Atomtronics-MURI, the Welch Foundation, ARO-MURI and NSF of China.

The breakout of the Hot CNO cycle via ^18Ne resonant states

NASA Astrophysics Data System (ADS)

Almaraz-Calderon, S.; Tan, W.; Aprahamian, A.; Bucher, B.; Gorres, J.; Roberts, A.; Villano, A.; Wiescher, M.; Brune, C.; Heinen, Z.; Massey, T.; Ozkan, N.; Guray, R. T.; Mach, H.

2010-11-01

The energy generation rate in the HCNO cycle is limited by the β decay of the waiting point nuclei ^14O and ^15O. However, when the temperatures and densities are high enough (e.g. Novae and X-ray Bursts) it is possible to bypass them by p/α captures resulting in a thermonuclear runaway towards the rp-process. One of the two paths for breakouts from the HCNO cycle is the reaction chain ^14O(α,p)^17F(p,γ)^18Ne(α,p), which proceeds through resonant states on ^18Ne, making their reactions rates very sensitive on the partial and total widths, excitation energies and spins of such resonances. We studied the resonant states in ^18Ne via ^16O(^3He,n) reaction. The neutrons were measured with an array of liquid scintillators using Time-of-Flight and pulse-shape discrimination techniques. The charged particles were detected in coincidence with neutrons by an array of silicon detectors, allowing us to measure α, p, p' and 2p decay branching ratios. Tentative spin assignments were made in comparison with zero range DWBA calculations. This new information will be included in reaction network calculations to evaluate its impact on the nuclear energy generation that occurs in these stellar explosive environments.

Liquid crystalline spinning of spider silk

NASA Astrophysics Data System (ADS)

Vollrath, Fritz; Knight, David P.

2001-03-01

Spider silk has outstanding mechanical properties despite being spun at close to ambient temperatures and pressures using water as the solvent. The spider achieves this feat of benign fibre processing by judiciously controlling the folding and crystallization of the main protein constituents, and by adding auxiliary compounds, to create a composite material of defined hierarchical structure. Because the `spinning dope' (the material from which silk is spun) is liquid crystalline, spiders can draw it during extrusion into a hardened fibre using minimal forces. This process involves an unusual internal drawdown within the spider's spinneret that is not seen in industrial fibre processing, followed by a conventional external drawdown after the dope has left the spinneret. Successful copying of the spider's internal processing and precise control over protein folding, combined with knowledge of the gene sequences of its spinning dopes, could permit industrial production of silk-based fibres with unique properties under benign conditions.