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Sample records for driven superconducting phase

  1. Enhancement of superconductivity by pressure-driven phase competition in electronic order

    SciTech Connect

    Chen, Xiao-Jia; Struzhkin, Viktor V.; Yu, Yong; Goncharov, Alexander F.; Lin, Cheng-Tian; Mao, Ho-kwang; Hemley, Russell J.

    2010-08-19

    Finding ways to achieve higher values of the transition temperature, Tc, in superconductors remains a great challenge. The superconducting phase is often one of several competing types of electronic order, including antiferromagnetism and charge density waves. An emerging trend documented in heavy-fermion and organic conductors is that the maximum Tc for superconductivity occurs under external conditions that cause the critical temperature for a competing order to go to zero. Recently, such competition has been found in multilayer copper oxide high-temperature superconductors (HTSCs) that possess two crystallographically inequivalent CuO2 planes in the unit cell. However, whether the competing electronic state can be suppressed to enhance Tc in HTSCs remains an open question. Here we show that pressure-driven phase competition leads to an unusual two-step enhancement of c in optimally doped trilayer Bi2Sr2Ca2Cu3O10+δ (Bi2223). We find that Tc first increases with pressure and then decreases after passing through a maximum. Unexpectedly, Tc increases again when the pressure is further raised above a critical value of around 24 GPa, surpassing the first maximum. The presence of this critical pressure is a manifestation of the crossover from the competing order to superconductivity in the inner of the three CuO2 planes. We suggest that the increase at higher pressures occurs as a result of competition between pairing and phase ordering in different CuO2 planes.

  2. Driven superconducting quantum circuits

    NASA Astrophysics Data System (ADS)

    Nakamura, Yasunobu

    2014-03-01

    Driven nonlinear quantum systems show rich phenomena in various fields of physics. Among them, superconducting quantum circuits have very attractive features such as well-controlled quantum states with design flexibility, strong nonlinearity of Josephson junctions, strong coupling to electromagnetic driving fields, little internal dissipation, and tailored coupling to the electromagnetic environment. We have investigated properties and functionalities of driven superconducting quantum circuits. A transmon qubit coupled to a transmission line shows nearly perfect spatial mode matching between the incident and scattered microwave field in the 1D mode. Dressed states under a driving field are studied there and also in a semi-infinite 1D mode terminated by a resonator containing a flux qubit. An effective Λ-type three-level system is realized under an appropriate driving condition. It allows ``impedance-matched'' perfect absorption of incident probe photons and down conversion into another frequency mode. Finally, the weak signal from the qubit is read out using a Josephson parametric amplifier/oscillator which is another nonlinear circuit driven by a strong pump field. This work was partly supported by the Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST), Project for Developing Innovation Systems of MEXT, MEXT KAKENHI ``Quantum Cybernetics,'' and the NICT Commissioned Research.

  3. Long-range spin current driven by superconducting phase difference in a josephson junction with double layer ferromagnets.

    PubMed

    Hikino, S; Yunoki, S

    2013-06-01

    We theoretically study spin current through ferromagnet (F) in a Josephson junction composed of s-wave superconductors and two layers of ferromagnets. Using quasiclassical theory, we show that the long-range spin current can be driven by the superconducting phase difference without a voltage drop. The origin of this spin current is due to spin-triplet Cooper pairs (STCs) formed by electrons of equal spin, which are induced by the proximity effect inside the F. We find that the spin current carried by the STCs exhibits long-range propagation in the F even where the Josephson charge current is practically zero. We also show that this spin current persists over a remarkably longer distance than the ordinary spin current carried by spin polarized conduction electrons in the F. Our results thus indicate the promising potential of Josephson junctions based on multilayer ferromagnets for spintronics applications with long-range propagating spin current. PMID:25167525

  4. Thermodynamic signature of a magnetic-field-driven phase transition within the superconducting state of an underdoped cuprate

    NASA Astrophysics Data System (ADS)

    Kemper, J. B.; Vafek, O.; Betts, J. B.; Balakirev, F. F.; Hardy, W. N.; Liang, Ruixing; Bonn, D. A.; Boebinger, G. S.

    2016-01-01

    More than a quarter century after the discovery of the high-temperature superconductor (HTS) YBa2Cu3O6+δ (YBCO; ref. ), studies continue to uncover complexity in its phase diagram. In addition to HTS and the pseudogap, there is growing evidence for multiple phases with boundaries which are functions of temperature (T), doping (p) and magnetic field. Here we report the low-temperature electronic specific heat (Celec) of YBa2Cu3O6.43 and YBa2Cu3O6.47 (p = 0.076 and 0.084) up to a magnetic field (H) of 34.5 T, a poorly understood region of the underdoped H-T-p phase space. We observe two regimes in the low-temperature limit: below a characteristic magnetic field H' ~ 12-15 T, Celec/T obeys an expected H1/2 behaviour; however, near H' there is a sharp inflection followed by a linear-in-H behaviour. H' rests deep within the superconducting phase and, thus, the linear-in-H behaviour is observed in the zero-resistance regime. In the limit of zero temperature, Celec/T is proportional to the zero-energy electronic density of states. At one of our dopings, the inflection is sharp only at lowest temperatures, and we thus conclude that this inflection is evidence of a magnetic-field-driven quantum phase transition.

  5. Zeeman-driven phase transition within the superconducting state of {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2}.

    SciTech Connect

    Wright, J. A.; Green, E.; kuhns, P.; Reyes, A.; Brooks, J.; Schlueter, J.; Kato, R.; Yamamoto, H.; Kobayashi, M.; Brown , S. E.

    2011-08-16

    {sup 13}C nuclear magnetic resonance measurements were performed on {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2}, with the external field placed parallel to the quasi-2D conducting layers. The absorption spectrum is used to determine the electronic spin polarization M{sub s} as a function of external field H at a temperature T = 0.35 K. A discontinuity in the derivative dM{sub s}/dH at an applied field of H{sub s} = 213 {+-} 3 kOe is taken as evidence for a Zeeman-driven transition within the superconducting state and stabilization of inhomogeneous superconductivity.

  6. Superconducting Coplanar Switch and Phase Shifter for CMB Applications

    NASA Astrophysics Data System (ADS)

    Bordier, G.; Cammilleri, V. D.; Belier, B.; Bleurvacq, N.; Gadot, F.; Ghribi, A.; Piat, M.; Tartari, A.; Zanonni, M.

    2016-08-01

    The next generations of cosmic microwave background (CMB) instruments will be dedicated to the detection and characterization of CMB B-modes. To measure this tiny signal, instruments need to control and minimize systematics. Signal modulation is one way to achieve such a control. A new generation of focal planes will include the entire detection chain. In this context, we present a superconducting coplanar switch driven by DC current. It consists of a superconducting microbridge which commutes between its on (superconducting) and off (normal metal) states, depending on the amplitude of the injected current compared to the critical current. If the current injected inside the bridge is lower than the critical current, the phase of the signal passing through the bridge is tunable. A first prototype of this component working as a switch and as a phase shifter at 10 GHz has been made. The principle, the setup, and the first measurements made at 4 K will be shown.

  7. High-Tc superconducting monolithic phase shifter

    NASA Astrophysics Data System (ADS)

    Takemoto-Kobayashi, June H.; Jackson, Charles M.; Pettiette-Hall, Claire L.; Burch, John F.

    1992-03-01

    A high temperature superconducting (HTS) X-band phase shifter using a distributed Josephson inductance (DJI) approach was designed and fabricated. Phase swings of over 60 deg were measured at 65 K and below, with measurable phase shifts at temperatures above 77 K. High quality HTS films and superconducting quantum interference devices (SQUIDs) were deposited by laser ablation. A total of 40 HTS step edge SQUIDs were successfully integrated into a monolithic HTS circuit to produce a phase shifter in a resonant configuration. The magnitude of the Josephson inductance is calculated and a lumped element model is compared to measurements.

  8. Theoretical prediction of a time-reversal broken chiral superconducting phase driven by electronic correlations in a single TiSe₂ layer.

    PubMed

    Ganesh, R; Baskaran, G; van den Brink, Jeroen; Efremov, Dmitry V

    2014-10-24

    Bulk TiSe2 is an intrinsically layered transition metal dichalcogenide hosting both superconducting and charge-density-wave ordering. Motivated by the recent progress in preparing two-dimensional transition metal dichalcogenides, we study these frustrated orderings in a single trilayer of TiSe2. Using a renormalization group approach, we find that electronic correlations can give rise to charge-density-wave order and two kinds of superconductivity. One possible superconducting state corresponds to unconventional s(+-) pairing. The other is particularly exciting as it is chiral, breaking time-reversal symmetry. Its stability depends on the precise strength and screening of the electron-electron interactions in two-dimensional TiSe2. PMID:25379930

  9. Detection of geometric phases in superconducting nanocircuits

    NASA Astrophysics Data System (ADS)

    Falci, Giuseppe; Fazio, Rosario; Palma, G. Massimo; Siewert, Jens; Vedral, Vlatko

    2000-09-01

    When a quantum-mechanical system undergoes an adiabatic cyclic evolution, it acquires a geometrical phase factor in addition to the dynamical one; this effect has been demonstrated in a variety of microscopic systems. Advances in nanotechnology should enable the laws of quantum dynamics to be tested at the macroscopic level, by providing controllable artificial two-level systems (for example, in quantum dots and superconducting devices). Here we propose an experimental method to detect geometric phases in a superconducting device. The setup is a Josephson junction nanocircuit consisting of a superconducting electron box. We discuss how interferometry based on geometrical phases may be realized, and show how the effect may be applied to the design of gates for quantum computation.

  10. Phase competition in trisected superconducting dome

    PubMed Central

    Vishik, I. M.; Hashimoto, M.; He, Rui-Hua; Lee, Wei-Sheng; Schmitt, Felix; Lu, Donghui; Moore, R. G.; Zhang, C.; Meevasana, W.; Sasagawa, T.; Uchida, S.; Fujita, Kazuhiro; Ishida, S.; Ishikado, M.; Yoshida, Yoshiyuki; Eisaki, Hiroshi; Hussain, Zahid; Devereaux, Thomas P.; Shen, Zhi-Xun

    2012-01-01

    A detailed phenomenology of low energy excitations is a crucial starting point for microscopic understanding of complex materials, such as the cuprate high-temperature superconductors. Because of its unique momentum-space discrimination, angle-resolved photoemission spectroscopy (ARPES) is ideally suited for this task in the cuprates, where emergent phases, particularly superconductivity and the pseudogap, have anisotropic gap structure in momentum space. We present a comprehensive doping- and temperature-dependence ARPES study of spectral gaps in Bi2Sr2CaCu2O8+δ, covering much of the superconducting portion of the phase diagram. In the ground state, abrupt changes in near-nodal gap phenomenology give spectroscopic evidence for two potential quantum critical points, p = 0.19 for the pseudogap phase and p = 0.076 for another competing phase. Temperature dependence reveals that the pseudogap is not static below Tc and exists p > 0.19 at higher temperatures. Our data imply a revised phase diagram that reconciles conflicting reports about the endpoint of the pseudogap in the literature, incorporates phase competition between the superconducting gap and pseudogap, and highlights distinct physics at the edge of the superconducting dome. PMID:23093670

  11. Reversibility Of Superconducting Nb Weak Links Driven By The Proximity Effect In A Quantum Interference Device

    NASA Astrophysics Data System (ADS)

    Kumar, Nikhil; Fournier, T.; Courtois, H.; Winkelmann, C. B.; Gupta, Anjan K.

    2015-04-01

    We demonstrate the role of the proximity effect in the thermal hysteresis of superconducting constrictions. From the analysis of successive thermal instabilities in the transport characteristics of micron-size superconducting quantum interference devices with a well-controlled geometry, we obtain a complete picture of the different thermal regimes. These determine whether or not the junctions are hysteretic. Below the superconductor critical temperature, the critical current switches from a classical weak-link behavior to one driven by the proximity effect. The associated small amplitude of the critical current makes it robust with respect to the heat generation by phase slips, leading to a nonhysteretic behavior.

  12. Odd-frequency Superconductivity in Driven Systems

    NASA Astrophysics Data System (ADS)

    Triola, Christopher; Balatsky, Alexander

    We show that Berezinskii's classification of the symmetries of Cooper pair amplitudes in terms of parity under transformations that invert spin, space, time, and orbital degrees of freedom holds for driven systems even in the absence of translation invariance. We then discuss the conditions under which pair amplitudes which are odd in frequency can emerge in driven systems. Considering a model Hamiltonian for a superconductor coupled to an external driving potential, we investigate the influence of the drive on the anomalous Green's function, density of states, and spectral function. We find that the anomalous Green's function develops odd in frequency component in the presence of an external drive. Furthermore we investigate how these odd-frequency terms are related to satellite features in the density of states and spectral function. Supported by US DOE BES E 304.

  13. Electric-field-driven hole carriers and superconductivity in diamond

    NASA Astrophysics Data System (ADS)

    Nakamura, K.; Rhim, S. H.; Sugiyama, A.; Sano, K.; Akiyama, T.; Ito, T.; Weinert, M.; Freeman, A. J.

    2013-06-01

    First-principles calculations of electric-field-driven superconductivity at the hydrogenated diamond (110) surface are presented. While the hydrogens on the surface effectively maintain the intrinsic sp3 covalent nature of diamond, the hole carriers induced by an external negative electric field (E-field) lead to a metallic surface region. Importantly, the concentration of hole carriers, confined within a few carbon layers of thickness ˜5-10 Å below the surface, exceeds 1021 cm-3, which is larger than the critical hole density responsible for superconductivity in the boron-doped diamond, while the calculated electron-phonon coupling constants are comparable in magnitude, suggesting the possibility of superconductivity with enhanced critical field.

  14. Phase competition in trisected superconducting dome

    NASA Astrophysics Data System (ADS)

    Vishik, Inna

    2012-02-01

    The momentum-resolved nature of angle-resolved photoemission spectroscopy (ARPES) has made it a key probe of emergent phases in the cuprates, such as superconductivity and the pseudogap, which have anisotropic momentum-space structure. ARPES can be used to infer the origin of spectral gaps from their distinct phenomenology---temperature, doping, and momentum dependence, and this principle has been used to argue that the pseudogap is a distinct phase from superconductivity, rather than a precursor [1]. We have studied Bi2Sr2CaCu2O8+δ (Bi-2212) using laser-ARPES, and our data give evidence for three distinct quantum phases comprising the superconducting ground state, accompanied by abrupt changes at p˜0.076 and p˜0.19 in the doping-and-temperature dependence of the gaps near the bond-diagonal (nodal) direction [2]. The latter doping likely marks the quantum critical point of the pseudogap, while the former represents a distinct competing phase at the edge of the superconducting dome. Additionally, we find that the pseudogap advances closer towards the node when superconductivity is weak, just below Tc or at low doping, and retreats towards the antinode well below Tc and at higher doping. This phase competition picture together with the two critical doping are synthesized into our proposed phase diagram, which also reconciles conflicting phase diagrams commonly used in the field. Our results underscore the importance of quantum critical phenomena to cuprate superconductivity, provide a microscopic picture of phase competition in momentum space, and predict the existence of phase boundaries inside the superconducting dome which are different from simple extrapolations from outside the dome. [4pt] [1] I. M. Vishik, W. S. Lee, R.-H. He, M. Hashimoto, Z. Hussain, T. P. Devereaux, and Z.-X. Shen. New J. Phys. 12, 105008 (2010). [0pt] [2] I. M. Vishik, M. Hashimoto, R.-H. He, W. S. Lee, F. Schmitt, D. H. Lu, R.G. Moore, C. Zhang, W. Meevasana, T. Sasagawa, S. Uchida, K

  15. Chaotic Dynamics of Driven Flux Drops: A Superconducting ``Dripping Faucet''

    NASA Astrophysics Data System (ADS)

    Field, Stuart B.; Stan, Gheorghe

    2008-02-01

    When a current is applied to a type-I superconducting strip containing a narrow channel across its width, magnetic flux spots nucleate at the edge and are then driven along the channel by the current. These flux “drops” are reminiscent of water drops dripping from a faucet, a model system for studying low-dimensional chaos. We use a novel high-bandwidth Hall probe to detect in real time the motion of individual flux spots moving along the channel. Analyzing the time series consisting of the intervals between successive flux drops, we find distinct regions of chaotic behavior characterized by positive Lyapunov exponents, indicating that there is a close analogy between the dynamics of the superconducting and water drop systems.

  16. Phase transformations in superconducting and non-superconducting perovskites

    SciTech Connect

    Mitchell, T.E.

    1992-01-01

    Most of the high {Tc} superconductors and other perovskite-related cuprates exhibit some kind of structural instability. For example, tetragonal-to-orthorhombic phase transformations occur in the Y-Ba-Cu-O and La-Sr-Cu-O systems while crystal structures in the Bi-Ca-Sr-Cu-O and Tl-Ba-Ca-Cu-O systems have incommensurate periodicities associated with displacements of the heavy cations. In YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}, the transformation is due to the ordering of oxygen vacancies while in La{sub 2-x}Sr{sub x}CuO{sub 4} the transformation is accompanied by tilting of the (CuO{sub 6}) octahedra. Such tilting and distortion of the co-ordination octahedra commonly occur in perovskite-related compounds and transformations between the structures are frequently martensitic. Phase transformations in the superconducting cuprates have been investigated by transmission electron microscopy but none of them appear to be martensitic. The phase transformations are accompanied by twinning and the resulting configurations are used to calculate twin boundary energies.

  17. Phase transformations in superconducting and non-superconducting perovskites

    SciTech Connect

    Mitchell, T.E.

    1992-07-01

    Most of the high {Tc} superconductors and other perovskite-related cuprates exhibit some kind of structural instability. For example, tetragonal-to-orthorhombic phase transformations occur in the Y-Ba-Cu-O and La-Sr-Cu-O systems while crystal structures in the Bi-Ca-Sr-Cu-O and Tl-Ba-Ca-Cu-O systems have incommensurate periodicities associated with displacements of the heavy cations. In YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}, the transformation is due to the ordering of oxygen vacancies while in La{sub 2-x}Sr{sub x}CuO{sub 4} the transformation is accompanied by tilting of the [CuO{sub 6}] octahedra. Such tilting and distortion of the co-ordination octahedra commonly occur in perovskite-related compounds and transformations between the structures are frequently martensitic. Phase transformations in the superconducting cuprates have been investigated by transmission electron microscopy but none of them appear to be martensitic. The phase transformations are accompanied by twinning and the resulting configurations are used to calculate twin boundary energies.

  18. Light-driven phase shifter

    DOEpatents

    Early, James W.

    1990-01-01

    A light-driven phase shifter is provided for modulating a transmission light beam. A gaseous medium such as argon is provided with electron energy states excited to populate a metastable state. A tunable dye laser is selected with a wavelength effective to deplete the metastable electron state and may be intensity modulated. The dye laser is directed through the gaseous medium to define a first optical path having an index of refraction determined by the gaseous medium having a depleted metastable electron state. A transmission laser beam is also directed through the gaseous medium to define a second optical path at least partially coincident with the first optical path. The intensity of the dye laser beam may then be varied to phase modulate the transmission laser beam.

  19. Reentrant Phase Coherence in Superconducting Nanowire Composites.

    PubMed

    Ansermet, Diane; Petrović, Alexander P; He, Shikun; Chernyshov, Dmitri; Hoesch, Moritz; Salloum, Diala; Gougeon, Patrick; Potel, Michel; Boeri, Lilia; Andersen, Ole Krogh; Panagopoulos, Christos

    2016-01-26

    The short coherence lengths characteristic of low-dimensional superconductors are associated with usefully high critical fields or temperatures. Unfortunately, such materials are often sensitive to disorder and suffer from phase fluctuations in the superconducting order parameter which diverge with temperature T, magnetic field H, or current I. We propose an approach to overcome synthesis and fluctuation problems: building superconductors from inhomogeneous composites of nanofilaments. Macroscopic crystals of quasi-one-dimensional Na2-δMo6Se6 featuring Na vacancy disorder (δ ≈ 0.2) are shown to behave as percolative networks of superconducting nanowires. Long-range order is established via transverse coupling between individual one-dimensional filaments, yet phase coherence remains unstable to fluctuations and localization in the zero (T,H,I) limit. However, a region of reentrant phase coherence develops upon raising (T,H,I). We attribute this phenomenon to an enhancement of the transverse coupling due to electron delocalization. Our observations of reentrant phase coherence coincide with a peak in the Josephson energy EJ at nonzero (T,H,I), which we estimate using a simple analytical model for a disordered anisotropic superconductor. Na2-δMo6Se6 is therefore a blueprint for a future generation of nanofilamentary superconductors with inbuilt resilience to phase fluctuations at elevated (T,H,I). PMID:26727335

  20. Two distinct superconducting phases in LiFeAs.

    PubMed

    Nag, P K; Schlegel, R; Baumann, D; Grafe, H-J; Beck, R; Wurmehl, S; Büchner, B; Hess, C

    2016-01-01

    A non-trivial temperature evolution of superconductivity including a temperature-induced phase transition between two superconducting phases or even a time-reversal symmetry breaking order parameter is in principle expected in multiband superconductors such as iron-pnictides. Here we present scanning tunnelling spectroscopy data of LiFeAs which reveal two distinct superconducting phases: at = 18 K a partial superconducting gap opens, evidenced by subtle, yet clear features in the tunnelling spectra, i.e. particle-hole symmetric coherence peak and dip-hump structures. At Tc = 16 K, these features substantiate dramatically and become characteristic of full superconductivity. Remarkably, the distance between the dip-hump structures and the coherence peaks remains practically constant in the whole temperature regimeT ≤ . This rules out the connection of the dip-hump structures to an antiferromagnetic spin resonance. PMID:27297474

  1. Two distinct superconducting phases in LiFeAs

    PubMed Central

    Nag, P. K.; Schlegel, R.; Baumann, D.; Grafe, H.-J.; Beck, R.; Wurmehl, S.; Büchner, B.; Hess, C.

    2016-01-01

    A non-trivial temperature evolution of superconductivity including a temperature-induced phase transition between two superconducting phases or even a time-reversal symmetry breaking order parameter is in principle expected in multiband superconductors such as iron-pnictides. Here we present scanning tunnelling spectroscopy data of LiFeAs which reveal two distinct superconducting phases: at = 18 K a partial superconducting gap opens, evidenced by subtle, yet clear features in the tunnelling spectra, i.e. particle-hole symmetric coherence peak and dip-hump structures. At Tc = 16 K, these features substantiate dramatically and become characteristic of full superconductivity. Remarkably, the distance between the dip-hump structures and the coherence peaks remains practically constant in the whole temperature regimeT ≤ . This rules out the connection of the dip-hump structures to an antiferromagnetic spin resonance. PMID:27297474

  2. Two distinct superconducting phases in LiFeAs

    NASA Astrophysics Data System (ADS)

    Nag, P. K.; Schlegel, R.; Baumann, D.; Grafe, H.-J.; Beck, R.; Wurmehl, S.; Büchner, B.; Hess, C.

    2016-06-01

    A non-trivial temperature evolution of superconductivity including a temperature-induced phase transition between two superconducting phases or even a time-reversal symmetry breaking order parameter is in principle expected in multiband superconductors such as iron-pnictides. Here we present scanning tunnelling spectroscopy data of LiFeAs which reveal two distinct superconducting phases: at = 18 K a partial superconducting gap opens, evidenced by subtle, yet clear features in the tunnelling spectra, i.e. particle-hole symmetric coherence peak and dip-hump structures. At Tc = 16 K, these features substantiate dramatically and become characteristic of full superconductivity. Remarkably, the distance between the dip-hump structures and the coherence peaks remains practically constant in the whole temperature regimeT ≤ . This rules out the connection of the dip-hump structures to an antiferromagnetic spin resonance.

  3. Precision vector control of a superconducting RF cavity driven by an injection locked magnetron

    DOE PAGESBeta

    Chase, Brian; Pasquinelli, Ralph; Cullerton, Ed; Varghese, Philip

    2015-03-01

    The technique presented in this paper enables the regulation of both radio frequency amplitude and phase in narrow band devices such as a Superconducting RF (SRF) cavity driven by constant power output devices i.e. magnetrons [1]. The ability to use low cost high efficiency magnetrons for accelerator RF power systems, with tight vector regulation, presents a substantial cost savings in both construction and operating costs - compared to current RF power system technology. An operating CW system at 2.45 GHz has been experimentally developed. Vector control of an injection locked magnetron has been extensively tested and characterized with a SRFmore » cavity as the load. Amplitude dynamic range of 30 dB, amplitude stability of 0.3% r.m.s, and phase stability of 0.26 degrees r.m.s. has been demonstrated.« less

  4. Precision vector control of a superconducting RF cavity driven by an injection locked magnetron

    SciTech Connect

    Chase, Brian; Pasquinelli, Ralph; Cullerton, Ed; Varghese, Philip

    2015-03-01

    The technique presented in this paper enables the regulation of both radio frequency amplitude and phase in narrow band devices such as a Superconducting RF (SRF) cavity driven by constant power output devices i.e. magnetrons [1]. The ability to use low cost high efficiency magnetrons for accelerator RF power systems, with tight vector regulation, presents a substantial cost savings in both construction and operating costs - compared to current RF power system technology. An operating CW system at 2.45 GHz has been experimentally developed. Vector control of an injection locked magnetron has been extensively tested and characterized with a SRF cavity as the load. Amplitude dynamic range of 30 dB, amplitude stability of 0.3% r.m.s, and phase stability of 0.26 degrees r.m.s. has been demonstrated.

  5. Superconducting/non-superconducting phase boundary in the low temperature tetragonal phase of (La,RE)-Sr-Cu-O

    SciTech Connect

    Buechner, B.; Breuer, M.; Cramm, M.; Freimuth, A.; Micklitz, H.; Schlabitz, W.; Kampf, A.P.

    1994-04-01

    From measurements of the structural, superconducting and normal state transport properties of rare earth doped La{sub 2{minus}x}Sr{sub x}CuO{sub 4} the authors find a phase boundary between a superconducting and a non-superconducting state of the low temperature tetragonal phase. This phase boundary is determined by the magnitude of the buckling of the Cu-O-Cu bonds in the CuO{sub 2} layers, suggesting the importance of spin-orbit coupling for the electronic properties of these compounds.

  6. Fluctuation driven electroweak phase transition

    NASA Technical Reports Server (NTRS)

    Gleiser, Marcelo; Kolb, Edward W.

    1991-01-01

    We examine the dynamics of the electroweak phase transition in the early Universe. For Higgs masses in the range 46 less than or = M sub H less than or = 150 GeV and top quark masses less than 200 GeV, regions of symmetric and asymmetric vacuum coexist to below the critical temperature, with thermal equilibrium between the two phases maintained by fluctuations of both phases. We propose that the transition to the asymmetric vacuum is completed by percolation of these subcritical fluctuations. Our results are relevant to scenarios of baryogenesis that invoke a weakly first-order phase transition at the electroweak scale.

  7. Superconducting phase diagram of itinerant antiferromagnets

    NASA Astrophysics Data System (ADS)

    Rømer, A. T.; Eremin, I.; Hirschfeld, P. J.; Andersen, B. M.

    2016-05-01

    We study the phase diagram of the Hubbard model in the weak-coupling limit for coexisting spin-density-wave order and spin-fluctuation-mediated superconductivity. Both longitudinal and transverse spin fluctuations contribute significantly to the effective interaction potential, which creates Cooper pairs of the quasiparticles of the antiferromagnetic metallic state. We find a dominant dx2-y2-wave solution in both electron- and hole-doped cases. In the quasi-spin-triplet channel, the longitudinal fluctuations give rise to an effective attraction supporting a p -wave gap, but are overcome by repulsive contributions from the transverse fluctuations which disfavor p -wave pairing compared to dx2-y2. The subleading pair instability is found to be in the g -wave channel, but complex admixtures of d and g are not energetically favored since their nodal structures coincide. Inclusion of interband pairing, in which each fermion in the Cooper pair belongs to a different spin-density-wave band, is considered for a range of electron dopings in the regime of well-developed magnetic order. We demonstrate that these interband pairing gaps, which are nonzero in the magnetic state, must have the same parity under inversion as the normal intraband gaps. The self-consistent solution to the full system of five coupled gap equations gives intraband and interband pairing gaps of dx2-y2 structure and similar gap magnitude. In conclusion, the dx2-y2 gap dominates for both hole and electron doping inside the spin-density-wave phase.

  8. Optimization of the superconducting phase of hydrogen sulfide

    SciTech Connect

    Degtyarenko, N. N.; Masur, E. A.

    2015-12-15

    The electron and phonon spectra, as well as the densities of electron and phonon states of the SH{sub 3} phase and the stable orthorhombic structure of hydrogen sulfide SH{sub 2}, are calculated for the pressure interval 100–225 GPa. It is found that the I4/mmm phase can be responsible for the superconducting properties of metallic hydrogen sulfide along with the SH{sub 3} phase. Sequential stages for obtaining and conservation of the SH{sub 2} phase are proposed. The properties of two (SH{sub 2} and SH{sub 3}) superconducting phases of hydrogen sulfide are compared.

  9. Signature of Cooper pairs in the non-superconducting phases of amorphous superconducting tantalum films

    NASA Astrophysics Data System (ADS)

    Li, Yize Stephanie

    2015-02-01

    We have studied the magnetic field or disorder induced insulating and metallic phases in amorphous Ta superconducting thin films. The evolution of the nonlinear transport in the insulating phase exhibits a non-monotonic behavior as the magnetic field is increased. We suggest that this observation could be evidence of the presence of localized Cooper pairs in the insulating phase. As the metallic phase intervenes the superconducting and insulating states in Ta films, this result further reveals that Cooper pairs also exist in the metallic ground state.

  10. Pressure-driven formation and stabilization of superconductive chromium hydrides

    PubMed Central

    Yu, Shuyin; Jia, Xiaojing; Frapper, Gilles; Li, Duan; Oganov, Artem R.; Zeng, Qingfeng; Zhang, Litong

    2015-01-01

    Chromium hydride is a prototype stoichiometric transition metal hydride. The phase diagram of Cr-H system at high pressures remains largely unexplored due to the challenges in dealing with the high activation barriers and complications in handing hydrogen under pressure. We have performed an extensive structural study on Cr-H system at pressure range 0 ∼ 300 GPa using an unbiased structure prediction method based on evolutionary algorithm. Upon compression, a number of hydrides are predicted to become stable in the excess hydrogen environment and these have compositions of Cr2Hn (n = 2–4, 6, 8, 16). Cr2H3, CrH2 and Cr2H5 structures are versions of the perfect anti-NiAs-type CrH with ordered tetrahedral interstitial sites filled by H atoms. CrH3 and CrH4 exhibit host-guest structural characteristics. In CrH8, H2 units are also identified. Our study unravels that CrH is a superconductor at atmospheric pressure with an estimated transition temperature (T c) of 10.6 K, and superconductivity in CrH3 is enhanced by the metallic hydrogen sublattice with T c of 37.1 K at 81 GPa, very similar to the extensively studied MgB2. PMID:26626579

  11. Pressure-driven formation and stabilization of superconductive chromium hydrides.

    PubMed

    Yu, Shuyin; Jia, Xiaojing; Frapper, Gilles; Li, Duan; Oganov, Artem R; Zeng, Qingfeng; Zhang, Litong

    2015-01-01

    Chromium hydride is a prototype stoichiometric transition metal hydride. The phase diagram of Cr-H system at high pressures remains largely unexplored due to the challenges in dealing with the high activation barriers and complications in handing hydrogen under pressure. We have performed an extensive structural study on Cr-H system at pressure range 0 ∼ 300 GPa using an unbiased structure prediction method based on evolutionary algorithm. Upon compression, a number of hydrides are predicted to become stable in the excess hydrogen environment and these have compositions of Cr2Hn (n = 2-4, 6, 8, 16). Cr2H3, CrH2 and Cr2H5 structures are versions of the perfect anti-NiAs-type CrH with ordered tetrahedral interstitial sites filled by H atoms. CrH3 and CrH4 exhibit host-guest structural characteristics. In CrH8, H2 units are also identified. Our study unravels that CrH is a superconductor at atmospheric pressure with an estimated transition temperature (T c) of 10.6 K, and superconductivity in CrH3 is enhanced by the metallic hydrogen sublattice with T c of 37.1 K at 81 GPa, very similar to the extensively studied MgB2. PMID:26626579

  12. Quantum phase slip phenomenon in ultra-narrow superconducting nanorings

    PubMed Central

    Arutyunov, Konstantin Yu.; Hongisto, Terhi T.; Lehtinen, Janne S.; Leino, Leena I.; Vasiliev, Alexander L.

    2012-01-01

    The smaller the system, typically - the higher is the impact of fluctuations. In narrow superconducting wires sufficiently close to the critical temperature Tc thermal fluctuations are responsible for the experimentally observable finite resistance. Quite recently it became possible to fabricate sub-10 nm superconducting structures, where the finite resistivity was reported within the whole range of experimentally obtainable temperatures. The observation has been associated with quantum fluctuations capable to quench zero resistivity in superconducting nanowires even at temperatures T→0. Here we demonstrate that in tiny superconducting nanorings the same phenomenon is responsible for suppression of another basic attribute of superconductivity - persistent currents - dramatically affecting their magnitude, the period and the shape of the current-phase relation. The effect is of fundamental importance demonstrating the impact of quantum fluctuations on the ground state of a macroscopically coherent system, and should be taken into consideration in various nanoelectronic applications. PMID:22389762

  13. An Electron Bunch Compression Scheme for a Superconducting Radio Frequency Linear Accelerator Driven Light Source

    SciTech Connect

    C. Tennant, S.V. Benson, D. Douglas, P. Evtushenko, R.A. Legg

    2011-09-01

    We describe an electron bunch compression scheme suitable for use in a light source driven by a superconducting radio frequency (SRF) linac. The key feature is the use of a recirculating linac to perform the initial bunch compression. Phasing of the second pass beam through the linac is chosen to de-chirp the electron bunch prior to acceleration to the final energy in an SRF linac ('afterburner'). The final bunch compression is then done at maximum energy. This scheme has the potential to circumvent some of the most technically challenging aspects of current longitudinal matches; namely transporting a fully compressed, high peak current electron bunch through an extended SRF environment, the need for a RF harmonic linearizer and the need for a laser heater. Additional benefits include a substantial savings in capital and operational costs by efficiently using the available SRF gradient.

  14. Flux Pinning in the Superconducting Phases of UPt_3

    NASA Astrophysics Data System (ADS)

    Shung, Emmin; Rosenbaum, Thomas F.

    1997-03-01

    We examine the effectiveness of bulk and surface pinning in the superconducting phases of UPt_3. Using high resolution Hall probe arrays, we measure locally the magnetization hysteresis and relaxation in a single crystal torus. The toroidal topology allows us to distinguish surface and bulk pinning effects by measuring the local magnetization over the hole, the bulk, and the interface. By comparing field cooled and zero field cooled measurements, we attempt to correlate the changes in flux pinning with the transition between the two superconducting phases. (R. J. Zieve et. al., Phys. Rev. B51), 12041 (1995)

  15. Process for preparing superconducting film having substantially uniform phase development

    DOEpatents

    Bharacharya, Raghuthan; Parilla, Philip A.; Blaugher, Richard D.

    1995-01-01

    A process for preparing a superconducting film, such as a thallium-barium-calcium-copper oxide superconducting film, having substantially uniform phase development. The process comprises providing an electrodeposition bath having one or more soluble salts of one or more respective potentially superconducting metals in respective amounts adequate to yield a superconducting film upon subsequent appropriate treatment. Should all of the metals required for producing a superconducting film not be made available in the bath, such metals can be a part of the ambient during a subsequent annealing process. A soluble silver salt in an amount between about 0.1% and about 4.0% by weight of the provided other salts is also provided to the bath, and the bath is electrically energized to thereby form a plated film. The film is annealed in ambient conditions suitable to cause formation of a superconductor film. Doping with silver reduces the temperature at which the liquid phase appears during the annealing step, initiates a liquid phase throughout the entire volume of deposited material, and influences the nucleation and growth of the deposited material.

  16. Process for preparing superconducting film having substantially uniform phase development

    DOEpatents

    Bharacharya, R.; Parilla, P.A.; Blaugher, R.D.

    1995-12-19

    A process is disclosed for preparing a superconducting film, such as a thallium-barium-calcium-copper oxide superconducting film, having substantially uniform phase development. The process comprises providing an electrodeposition bath having one or more soluble salts of one or more respective potentially superconducting metals in respective amounts adequate to yield a superconducting film upon subsequent appropriate treatment. Should all of the metals required for producing a superconducting film not be made available in the bath, such metals can be a part of the ambient during a subsequent annealing process. A soluble silver salt in an amount between about 0.1% and about 4.0% by weight of the provided other salts is also provided to the bath, and the bath is electrically energized to thereby form a plated film. The film is annealed in ambient conditions suitable to cause formation of a superconductor film. Doping with silver reduces the temperature at which the liquid phase appears during the annealing step, initiates a liquid phase throughout the entire volume of deposited material, and influences the nucleation and growth of the deposited material. 3 figs.

  17. Structural phase transitions and superconductivity in lanthanum copper oxides

    SciTech Connect

    Crawford, M.K.; Harlow, R.L.; McCarron, E.M.

    1996-12-31

    Despite the enormous effort expended over the past ten years to determine the mechanism underlying high temperature superconductivity in cuprates there is still no consensus on the physical origin of this fascinating phenomenon. This is a consequence of a number of factors, among which are the intrinsic difficulties in understanding the strong electron correlations in the copper oxides, determining the roles played by antiferromagnetic interactions and low dimensionality, analyzing the complex phonon dispersion relationships, and characterizing the phase diagrams which are functions of the physical parameters of temperature and pressure, as well as the chemical parameters of stoichiometry and hole concentration. In addition to all of these intrinsic difficulties, extrinsic materials issues such as sample quality and homogeneity present additional complications. Within the field of high temperature superconductivity there exists a subfield centered around the material originally reported to exhibit high temperature superconductivity by Bednorz and Mueller, Ba doped La{sub 2}CuO{sub 4}. This is structurally the simplest cuprate superconductor. The authors report on studies of phase differences observed between such base superconductors doped with Ba or Sr. What these studies have revealed is a fascinating interplay of structural, magnetic and superconducting properties which is unique in the field of high temperature superconductivity and is summarized in this paper.

  18. Pressure-driven dome-shaped superconductivity and electronic structural evolution in tungsten ditelluride

    NASA Astrophysics Data System (ADS)

    Pan, Xing-Chen; Chen, Xuliang; Liu, Huimei; Feng, Yanqing; Wei, Zhongxia; Zhou, Yonghui; Chi, Zhenhua; Pi, Li; Yen, Fei; Song, Fengqi; Wan, Xiangang; Yang, Zhaorong; Wang, Baigeng; Wang, Guanghou; Zhang, Yuheng

    2015-07-01

    Tungsten ditelluride has attracted intense research interest due to the recent discovery of its large unsaturated magnetoresistance up to 60 T. Motivated by the presence of a small, sensitive Fermi surface of 5d electronic orbitals, we boost the electronic properties by applying a high pressure, and introduce superconductivity successfully. Superconductivity sharply appears at a pressure of 2.5 GPa, rapidly reaching a maximum critical temperature (Tc) of 7 K at around 16.8 GPa, followed by a monotonic decrease in Tc with increasing pressure, thereby exhibiting the typical dome-shaped superconducting phase. From theoretical calculations, we interpret the low-pressure region of the superconducting dome to an enrichment of the density of states at the Fermi level and attribute the high-pressure decrease in Tc to possible structural instability. Thus, tungsten ditelluride may provide a new platform for our understanding of superconductivity phenomena in transition metal dichalcogenides.

  19. Pressure-driven dome-shaped superconductivity and electronic structural evolution in tungsten ditelluride

    PubMed Central

    Pan, Xing-Chen; Chen, Xuliang; Liu, Huimei; Feng, Yanqing; Wei, Zhongxia; Zhou, Yonghui; Chi, Zhenhua; Pi, Li; Yen, Fei; Song, Fengqi; Wan, Xiangang; Yang, Zhaorong; Wang, Baigeng; Wang, Guanghou; Zhang, Yuheng

    2015-01-01

    Tungsten ditelluride has attracted intense research interest due to the recent discovery of its large unsaturated magnetoresistance up to 60 T. Motivated by the presence of a small, sensitive Fermi surface of 5d electronic orbitals, we boost the electronic properties by applying a high pressure, and introduce superconductivity successfully. Superconductivity sharply appears at a pressure of 2.5 GPa, rapidly reaching a maximum critical temperature (Tc) of 7 K at around 16.8 GPa, followed by a monotonic decrease in Tc with increasing pressure, thereby exhibiting the typical dome-shaped superconducting phase. From theoretical calculations, we interpret the low-pressure region of the superconducting dome to an enrichment of the density of states at the Fermi level and attribute the high-pressure decrease in Tc to possible structural instability. Thus, tungsten ditelluride may provide a new platform for our understanding of superconductivity phenomena in transition metal dichalcogenides. PMID:26203922

  20. Superconducting high-pressure phases of disilane.

    PubMed

    Jin, Xilian; Meng, Xing; He, Zhi; Ma, Yanming; Liu, Bingbing; Cui, Tian; Zou, Guangtian; Mao, Ho-Kwang

    2010-06-01

    High-pressure structures of disilane (Si(2)H(6)) are investigated extensively by means of first-principles density functional theory and a random structure-searching method. Three metallic structures with P-1, Pm-3m, and C2/c symmetries are found, which are more stable than those of XY(3)-type candidates under high pressure. Enthalpy calculations suggest a remarkably wide decomposition (Si and H(2)) pressure range below 135 GPa, above which three metallic structures are stable. Perturbative linear-response calculations for Pm-3m disilane at 275 GPa show a large electron-phonon coupling parameter lambda of 1.397 and the resulting superconducting critical temperature beyond the order of 10(2) K. PMID:20479272

  1. Superconducting high-pressure phases of disilane

    PubMed Central

    Jin, Xilian; Meng, Xing; He, Zhi; Ma, Yanming; Liu, Bingbing; Cui, Tian; Zou, Guangtian; Mao, Ho-kwang

    2010-01-01

    High-pressure structures of disilane (Si2H6) are investigated extensively by means of first-principles density functional theory and a random structure-searching method. Three metallic structures with P-1, Pm-3m, and C2/c symmetries are found, which are more stable than those of XY3-type candidates under high pressure. Enthalpy calculations suggest a remarkably wide decomposition (Si and H2) pressure range below 135 GPa, above which three metallic structures are stable. Perturbative linear-response calculations for Pm-3m disilane at 275 GPa show a large electron-phonon coupling parameter λ of 1.397 and the resulting superconducting critical temperature beyond the order of 102 K. PMID:20479272

  2. Superconducting resonator used as a beam phase detector.

    SciTech Connect

    Sharamentov, S. I.; Pardo, R. C.; Ostroumov, P. N.; Clifft, B. E.; Zinkann, G. P.; Physics

    2003-05-01

    Beam-bunch arrival time has been measured for the first time by operating superconducting cavities, normally part of the linac accelerator array, in a bunch-detecting mode. The very high Q of the superconducting cavities provides high sensitivity and allows for phase-detecting low-current beams. In detecting mode, the resonator is operated at a very low field level comparable to the field induced by the bunched beam. Because of this, the rf field in the cavity is a superposition of a 'pure' (or reference) rf and the beam-induced signal. A new method of circular phase rotation (CPR), allowing extraction of the beam phase information from the composite rf field was developed. Arrival time phase determination with CPR is better than 1{sup o} (at 48 MHz) for a beam current of 100 nA. The electronics design is described and experimental data are presented.

  3. The phase diagram and Bose metal in superconducting nanowires

    NASA Astrophysics Data System (ADS)

    Morgan-Wall, Tyler; Hughes, Hannah; Hartman, Nikolaus; Markovic, Nina

    We experimentally investigated the transport properties of thin, narrow superconducting aluminum nanowires as a function of magnetic field and temperature. We characterized the full superconducting phase diagram with respect to magnetic field and temperature, and show the onset of a flux-flow phase for certain values of temperature and magnetic field. The flux-flow resistance follows the Bardeen-Stephen model and it is shown that the resistance increases linearly with respect to magnetic field in this region of the phase diagram. In addition, we show the saturation to a non-zero finite resistance state below the normal state resistance for certain magnetic fields as the temperature decreases to zero. This work is supported by NSF DMR-1507782.

  4. Investigation of an electronically tuned 100 GHz superconducting phase shifter

    SciTech Connect

    Tvack, E.K.; Shen, Z.Y.; Dang, H.; Radparvar, M.; Faris, S.M. )

    1991-03-01

    This paper presents the results of an investigation aimed at realizing a tunable superconducting mm-wave phase shifter. The tuning mechanism is based on inductance modulation of NbN microstrips by excess quasiparticle injection. When measured by a dc method, using the interference patterns and resonances of specially designed dc SQUIDs, the inductance of NbN microstrips can be varied by up to 300%. Based on these results, we have designed and fabricated superconducting microstrip interferometers to operate as low power 100 GHz phase shifters. The 100 GHZ signal is coupled into and out of the interferometers by finline antennas. Amplitude modulation of the output is used as the criterion for phase shift in one of the interferometer branches.

  5. Cerenkov Radiator Driven by a Superconducting RF Electron Gun

    SciTech Connect

    Poole, B R; Harris, J R

    2011-03-07

    The Naval Postgraduate School (NPS), Niowave, Inc., and Boeing have recently demonstrated operation of the first superconducting RF electron gun based on a quarter wave resonator structure. In preliminary tests, this gun has produced 10 ps long bunches with charge in excess of 78 pC, and with beam energy up to 396 keV. Initial testing occurred at Niowave's Lansing, MI facility, but the gun and diagnostic beam line are planned for installation in California in the near future. The design of the diagnostic beam line is conducive to the addition of a Cerenkov radiator without interfering with other beam line operations. Design and simulations of a Cerenkov radiator, consisting of a dielectric lined waveguide will be presented. The dispersion relation for the structure is determined and the beam interaction is studied using numerical simulations. The characteristics of the microwave radiation produced in both the short and long bunch regimes will be presented.

  6. Reentrant topological phase transitions in a disordered spinless superconducting wire

    NASA Astrophysics Data System (ADS)

    Rieder, Maria-Theresa; Brouwer, Piet W.; Adagideli, İnanç

    2013-08-01

    In a one-dimensional spinless p-wave superconductor with coherence length ξ, disorder induces a phase transition between a topologically nontrivial phase and a trivial insulating phase at the critical mean-free path l=ξ/2. Here, we show that a multichannel spinless p-wave superconductor goes through an alternation of topologically trivial and nontrivial phases upon increasing the disorder strength, the number of phase transitions being equal to the channel number N. The last phase transition, from a nontrivial phase into the trivial phase, takes place at a mean-free path l=ξ/(N+1), parametrically smaller than the critical mean-free path in one dimension. Our result is valid in the limit that the wire width W is much smaller than the superconducting coherence length ξ.

  7. Superconducting magnets for muon capture and phase rotation

    SciTech Connect

    Green, M.A.; Weggel, R.J.

    1999-07-26

    There are two key systems that must operate efficiently, in order for a muon collider to be a viable option for high energy physics. These systems are the muon production and collection system and the muon cooling system. Both systems require the use of high field superconducting solenoid magnets. This paper describes the supcrconducting solenoid system used for the capture and phase rotation of the pions that are produced on a target in a high intensity proton beam.

  8. Chern-Simons-Higgs transitions out of topological superconducting phases

    NASA Astrophysics Data System (ADS)

    Clarke, David J.; Nayak, Chetan

    2015-10-01

    In this study, we examine effective field theories of superconducting phases with topological order, making a connection to proposed realizations of exotic topological phases (including those hosting Ising and Fibonacci anyons) in superconductor-quantum Hall heterostructures. Our effective field theories for the non-Abelian superconducting states are non-Abelian Chern-Simons theories in which the condensation of vortices carrying non-Abelian gauge flux leads to the associated Abelian quantum Hall states. This Chern-Simons-Higgs condensation process is dual to the emergence of superconducting non-Abelian topological phases in coupled chain constructions. In such transitions, the chiral central charge of the system generally changes, so they fall outside the description of bosonic condensation transitions put forth by Bais and Slingerland [F. A. Bais and J. K. Slingerland, Phys. Rev. B 79, 045316 (2009), 10.1103/PhysRevB.79.045316] (though the two approaches agree when the described transitions coincide). Our condensation process may be generalized to Chern-Simons theories based on arbitrary Lie groups, always describing a transition from a Lie algebra to its Cartan subalgebra. We include several instructive examples of such transitions.

  9. Photonic phase transition in circuit quantum electrodynamics lattices coupled to superconducting phase qubits

    NASA Astrophysics Data System (ADS)

    Liu, YiMin; Jin, WuYin; You, JiaBin

    2014-11-01

    A hybrid quantum architecture was proposed to engineer a localization-delocalization phase transition of light in a two-dimension square lattices of superconducting coplanar waveguide resonators, which are interconnected by current-biased Josephson junction phase qubits. We find that the competition between the on-site repulsion and the nonlocal photonic hopping leads to the Mott insulator-superfluid transition. By using the mean-field approach and the quantum master equation, the phase boundary between these two different phases could be obtained when the dissipative effects of superconducting resonators and phase qubit are considered. The good tunability of the effective on-site repulsion and photon-hopping strengths enable quantum simulation on condensed matter physics and many-body models using such a superconducting resonator lattice system. The experimental feasibility is discussed using the currently available technology in the circuit QED.

  10. Phase Separation of Superconducting Phases in the Penson-Kolb-Hubbard Model

    NASA Astrophysics Data System (ADS)

    Jerzy Kapcia, Konrad; Czart, Wojciech Robert; Ptok, Andrzej

    2016-04-01

    In this paper, we determine the phase diagrams (for T = 0 as well as T > 0) of the Penson-Kolb-Hubbard model for two dimensional square lattice within Hartree-Fock mean-field theory focusing on an investigation of superconducting phases and on a possibility of the occurrence of the phase separation. We obtain that the phase separation, which is a state of coexistence of two different superconducting phases (with s- and η-wave symmetries), occurs in definite ranges of the electron concentration. In addition, increasing temperature can change the symmetry of the superconducting order parameter (from η-wave into s-wave). The system considered exhibits also an interesting multicritical behaviour including bicritical points. The relevance of the results to experiments for real materials is also discussed.

  11. Observation of Berry's Phase in a Superconducting Qubit

    NASA Astrophysics Data System (ADS)

    Leek, P. J.; Fink, J. M.; Blais, A.; Schoelkopf, R. J.; Wallraff, A.

    2008-03-01

    In quantum information science, the phase of a wavefunction plays an important role in encoding information. While most experiments in this field rely on dynamic effects to manipulate this information, an alternative approach is to use geometric phase, which has been argued to have potential fault tolerance [1]. Here we demonstrate the controlled accumulation of a geometric phase, Berry's phase, in a superconducting qubit, manipulating the qubit geometrically using microwave radiation, and observing the accumulated phase in an interference experiment [2]. This is achieved utilising the excellent phase coherence and qubit control possible in Circuit QED [3]. We find excellent agreement with Berry's predictions, and also observe a geometry dependent contribution to dephasing. [1] J.A. Jones et al, Nature 403, 869 (2000) [2] P.J. Leek et al, Science, 22 November 2007 (10.1126/science.1149858) [3] A. Wallraff et al, Nature 431, 162 (2004)

  12. On excess conductivity of wide superconducting films with phase slippage

    SciTech Connect

    Kulikovsky, A.; Erganokov, Kh.; Bielska-Lewandowska, H.

    1997-02-01

    Properties of wide superconducting tin films in the resistive current state with phase slippage have been studied experimentally. The authors have observed a region of excess conductivity on the current-voltage characteristics of the samples. Experimental results were discussed in view of the theory establishing the relationship between an interference term of the total current and excess current in weak superconductors. They derived the equation to evaluate the inelastic scattering time of superconductor {tau}{sub E} using the excess current of wide films with phase slippage. Their {tau}{sub E} values are in a good agreement with those obtained by other methods.

  13. On the high-pressure superconducting phase in platinum hydride

    NASA Astrophysics Data System (ADS)

    Szczȩśniak, D.; Zemła, T. P.

    2015-08-01

    Motivated by the ambiguous experimental data for the superconducting phase in silane (SiH4), which may originate from platinum hydride (PtH), we provide a theoretical study of the superconducting state in the latter alloy. The quantitative estimates of the thermodynamics of PtH at 100 GPa are given for a wide range of Coulomb pseudopotential values ({μ }*) within the Eliashberg formalism. The obtained critical temperature value ({T}{{C}}\\in < 12.94,20.01> for {μ }*\\in < 0.05,0.15> ) agrees well with the experimental TC for SiH4, which may be ascribed to PtH. Moreover, the calculated characteristic thermodynamic ratios exceed the predictions of the Bardeen-Cooper-Schrieffer theory, implying the occurrence of strong-coupling and retardation effects in PtH. We note that our results may be of high relevance for future theoretical and experimental studies on hydrides.

  14. Enhanced Cooper pairing versus suppressed phase coherence shaping the superconducting dome in coupled aluminum nanograins

    NASA Astrophysics Data System (ADS)

    Pracht, Uwe S.; Bachar, Nimrod; Benfatto, Lara; Deutscher, Guy; Farber, Eli; Dressel, Martin; Scheffler, Marc

    2016-03-01

    The development of the fundamental superconducting (SC) energy scales—the SC energy gap Δ and the superfluid stiffness J —of granular aluminum, i.e., thin films composed of coupled nanograins, is studied by means of optical THz spectroscopy. Starting from well-coupled grains, Δ grows as the grains are progressively decoupled, causing the unconventional increase of Tc with sample resistivity. When the grain coupling is suppressed further, Δ saturates while the critical temperature Tc decreases, concomitantly with a sharp decline of J , delimiting a SC dome in the phase diagram. This crossover to a phase-driven SC transition is accompanied by an optical gap surviving into the normal state above Tc. We demonstrate that granular aluminum is an ideal testbed to understand the interplay between quantum confinement and global SC phase coherence due to nanoinhomogeneity.

  15. Josephson phase diffusion in the superconducting quantum interference device ratchet

    SciTech Connect

    Spiechowicz, Jakub; Łuczka, Jerzy

    2015-05-15

    We study diffusion of the Josephson phase in the asymmetric superconducting quantum interference device (SQUID) subjected to a time-periodic current and pierced by an external magnetic flux. We analyze a relation between phase diffusion and quality of transport characterized by the dc voltage across the SQUID and efficiency of the device. In doing so, we concentrate on the previously reported regime [J. Spiechowicz and J. Łuczka, New J. Phys. 17, 023054 (2015)] for which efficiency of the SQUID attains a global maximum. For long times, the mean-square displacement of the phase is a linear function of time, meaning that diffusion is normal. Its coefficient is small indicating rather regular phase evolution. However, it can be magnified several times by tailoring experimentally accessible parameters like amplitudes of the ac current or external magnetic flux. Finally, we prove that in the deterministic limit this regime is essentially non-chaotic and possesses an unexpected simplicity of attractors.

  16. Josephson phase diffusion in the superconducting quantum interference device ratchet.

    PubMed

    Spiechowicz, Jakub; Łuczka, Jerzy

    2015-05-01

    We study diffusion of the Josephson phase in the asymmetric superconducting quantum interference device (SQUID) subjected to a time-periodic current and pierced by an external magnetic flux. We analyze a relation between phase diffusion and quality of transport characterized by the dc voltage across the SQUID and efficiency of the device. In doing so, we concentrate on the previously reported regime [J. Spiechowicz and J. Łuczka, New J. Phys. 17, 023054 (2015)] for which efficiency of the SQUID attains a global maximum. For long times, the mean-square displacement of the phase is a linear function of time, meaning that diffusion is normal. Its coefficient is small indicating rather regular phase evolution. However, it can be magnified several times by tailoring experimentally accessible parameters like amplitudes of the ac current or external magnetic flux. Finally, we prove that in the deterministic limit this regime is essentially non-chaotic and possesses an unexpected simplicity of attractors. PMID:26026322

  17. Magnetism and superconductivity driven by identical 4f states in a heavy-fermion metal

    SciTech Connect

    Thompson, Joe E; Nair, S; Stockert, O; Witte, U; Nicklas, M; Schedler, R; Bianchi, A; Fisk, Z; Wirth, S; Steglich, K

    2009-01-01

    The apparently inimical relationship between magnetism and superconductivity has come under increasing scrutiny in a wide range of material classes, where the free energy landscape conspires to bring them in close proximity to each other. Particularly enigmatic is the case when these phases microscopically interpenetrate, though the manner in which this can be accomplished remains to be fully comprehended. Here, we present combined measurements of elastic neutron scattering, magnetotransport, and heat capacity on a prototypical heavy fermion system, in which antiferromagnetism and superconductivity are observed. Monitoring the response of these states to the presence of the other, as well as to external thermal and magnetic perturbations, points to the possibility that they emerge from different parts of the Fermi surface. Therefore, a single 4f state could be both localized and itinerant, thus accounting for the coexistence of magnetism and superconductivity.

  18. Monolithic mm-wave phase shifter using optically activated superconducting switches

    NASA Technical Reports Server (NTRS)

    Romanofsky, Robert R. (Inventor); Bhasin, Kul B. (Inventor)

    1992-01-01

    A phase shifter is disclosed having a reference path and a delay path, light sources, and superconductive switches. Each of the superconductive switches is terminated in a virtual short circuit, which may be a radial stub. Switching between the reference path and delayed path is accomplished by illuminating the superconductive switches connected to the desired path, while not illuminating the superconductive switches connected to the other path.

  19. Phase structure of cold magnetized color superconducting quark matter

    NASA Astrophysics Data System (ADS)

    Allen, PG; Grunfeld, AG; Scoccola, NN

    2016-04-01

    The influence of intense magnetic fields on the behavior of color superconducting cold quark matter is investigated using an SU(2) f NJL-type model for which a novel regulation scheme is introduced. In such a scheme the contributions which are explicitly dependent on the magnetic field turn out to be finite and, thus, do not require to be regularized. As a result of this, non-physical oscillations that arise from regularizing magnetic field dependent terms are naturally removed, and oscillations that are actually physical can be better appreciated. The phase diagrams in the ẽB – μ plane are presented for different values of the diquark coupling.

  20. Interlayer tunneling spectroscopy of mixed-phase BSCCO superconducting whiskers

    NASA Astrophysics Data System (ADS)

    Kizilaslan, O.; Truccato, M.; Simsek, Y.; Aksan, M. A.; Koval, Y.; Müller, P.

    2016-06-01

    In this work, we present a study on the interlayer tunneling spectroscopy (ITS) of mixed-phase BiSrCaCuO (BSCCO) superconducting whiskers. The tunneling experiments were carried out on the artificial cross-whisker (twist angle of 90°) junctions. A multiple superconducting energy gap in the cross-whisker junctions was observed, which is attributed to the presence of different doping levels of two Bi2Sr2CaCu2O8+δ phases (Bi-2212), rather than two different phases, in the BSCCO whiskers, namely Bi2Sr2CaCu2O8+δ and Bi2Sr2Ca2Cu3O8+δ (Bi-2212 and Bi-2223). The temperature dependence of the energy gaps was discussed in the framework of the BCS T-dependence. On the other hand, the carrier concentration of the cross-whisker junction was changed by the carrier injection process. The effects of the carrier injection on the critical current, I c, and the ITS of intrinsic Josephson junctions were investigated in details.

  1. Superconductivity

    SciTech Connect

    Langone, J.

    1989-01-01

    This book explains the theoretical background of superconductivity. Includes discussion of electricity, material fabrication, maglev trains, the superconducting supercollider, and Japanese-US competition. The authors reports the latest discoveries.

  2. Novel Superoxygenated Phases in Superconducting Cuprate Thin Films

    NASA Astrophysics Data System (ADS)

    Zhang, C.; Zhang, H.; Gauquelin, N.; Botton, G. A.; McMahon, C.; Hawthorn, D. G.; Wei, J. Y. T.

    The superconducting critical temperature (Tc) of hole-doped cuprates tends to increase with their lattice complexity, which is generally correlated with higher states of oxidation. For YBa2Cu3O7 - δ (YBCO-123), it is known that solid-state reaction in high-pressure oxygen can induce the formation of more complex and oxidized phases such as Y2Ba4Cu7O15 - δ (YBCO-247) and Y2Ba4Cu8O16 (YBCO-248). In this work, we apply this superoxygenation concept of material synthesis to nanoscale thin films which, owing to their large surface-to-volume ratio, are more thermodynamically reactive than bulk samples. Epitaxial thin films of YBCO-123 were grown by pulsed laser deposition on (La , Sr) (Al , Ta) O3 substrates, and post-annealed in up to 500 atm of oxygen at 800C. Our post-annealed films show robust superconducting transitions with Tc ranging from 80 to 93K. Transmission electron microscopy and X-ray absorption spectroscopy were used to probe the lattice structure and oxygen stoichiometry. Our measurements show clear evidence of conversion to YBCO-247 and YBCO-248 in the superoxygenated films, as well as YBCO-125, a novel YBCO phase that has three CuO chains per unit cell and potentially higher Tc. Work supported by NSERC, CFI/OIT, and CIFAR.

  3. Simulation of fast-ion-driven Alfvén eigenmodes on the Experimental Advanced Superconducting Tokamak

    NASA Astrophysics Data System (ADS)

    Hu, Youjun; Todo, Y.; Pei, Youbin; Li, Guoqiang; Qian, Jinping; Xiang, Nong; Zhou, Deng; Ren, Qilong; Huang, Juan; Xu, Liqing

    2016-02-01

    Kinetic-MHD hybrid simulations are carried out to investigate possible fast-ion-driven modes on the Experimental Advanced Superconducting Tokamak. Three typical kinds of fast-ion-driven modes, namely, toroidicity-induced Alfvén eigenmodes, reversed shear Alfvén eigenmodes, and energetic-particle continuum modes, are observed simultaneously in the simulations. The simulation results are compared with the results of an ideal MHD eigenvalue code, which shows agreement with respect to the mode frequency, dominant poloidal mode numbers, and radial location. However, the modes in the hybrid simulations take a twisted structure on the poloidal plane, which is different from the results of the ideal MHD eigenvalue code. The twist is due to the radial phase variation of the eigenfunction, which may be attributed to the non-perturbative kinetic effects of the fast ions. By varying the stored energy of fast ions to change the fast ion drive in the simulations, it is demonstrated that the twist (i.e., the radial phase variation) is positively correlated with the fast ion drive.

  4. Superconducting phases of monolayer transition-metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Sosenko, Evan; Aji, Vivek

    Layered group-VI dichalcogenides, e.g., MoS2, are two dimensional materials that engender novel coupled spin and valley physics. Characterized by strong spin-orbit coupling and inversion symmetry breaking, they give rise to novel phenomena such as the spin Hall and valley Hall effect. In this talk, I focus on the intrinsic and substrate induced superconducting phases expected in this new class of materials. We will discuss the nature of the quasiparticles resulting from valley discriminating, pair breaking processes, and the effect of the BCS phase on the nature of opto-electronic coupling and nontrivial Berry curvature associated with the bands near each valley. We would like to acknowledge support from ARO W911NF1510079.

  5. Phase-controlled superconducting heat-flux quantum modulator

    NASA Astrophysics Data System (ADS)

    Giazotto, F.; Martínez-Pérez, M. J.

    2012-09-01

    We theoretically put forward the concept of a phase-controlled superconducting heat-flux quantum modulator. Its operation relies on phase-dependent heat current predicted to occur in temperature-biased Josephson tunnel junctions. The device behavior is investigated as a function of temperature bias across the junctions, bath temperature, and junctions asymmetry as well. In a realistic Al-based setup the structure could provide temperature modulation amplitudes up to ˜50 mK with flux-to-temperature transfer coefficients exceeding ˜125 mK/Φ0 below 1 K, and temperature modulation frequency of the order of a few MHz. The proposed structure appears as a promising building-block for the implementation of caloritronic devices operating at cryogenic temperatures.

  6. Coherent Population Trapping in a Superconducting Phase Qubit

    NASA Astrophysics Data System (ADS)

    Kelly, William R.; Dutton, Zachary; Ohki, Thomas A.; Schlafer, John; Mookerji, Bhaskar; Kline, Jeffery S.; Pappas, David P.

    2010-03-01

    The phenomenon of Coherent Population Trapping (CPT) of an atom (or solid state ``artificial atom''), and the associated effect of Electromagnetically Induced Transparency (EIT), are clear demonstrations of quantum interference due to coherence in multi-level quantum systems. We report observation of CPT in a superconducting phase qubit by simultaneously driving two coherent transitions in a λ-type configuration, utilizing the three lowest lying levels of a local minimum of the phase qubit. We observe ˜60% suppression of excited state population under conditions of two-photon resonance, where EIT and CPT are expected to occur. We present data and matching theoretical simulations showing the development of CPT in time. We also used the observed time dependence of the excited state population to characterize quantum dephasing times of the system, as predicted in [1]. [1] K.V. Murali, Z. Dutton, W.D. Oliver, D.S. Crankshaw, and T.P.Orlando, Phys. Rev. Lett. 93, 087003 (2004).

  7. Phase-controlled coherent population trapping in superconducting quantum circuits

    NASA Astrophysics Data System (ADS)

    Cheng, Guang-Ling; Wang, Yi-Ping; Chen, Ai-Xi

    2015-04-01

    We investigate the influences of the-applied-field phases and amplitudes on the coherent population trapping behavior in superconducting quantum circuits. Based on the interactions of the microwave fields with a single Δ-type three-level fluxonium qubit, the coherent population trapping could be obtainable and it is very sensitive to the relative phase and amplitudes of the applied fields. When the relative phase is tuned to 0 or π, the maximal atomic coherence is present and coherent population trapping occurs. While for the choice of π/2, the atomic coherence becomes weak. Meanwhile, for the fixed relative phase π/2, the value of coherence would decrease with the increase of Rabi frequency of the external field coupled with two lower levels. The responsible physical mechanism is quantum interference induced by the control fields, which is indicated in the dressed-state representation. The microwave coherent phenomenon is present in our scheme, which will have potential applications in optical communication and nonlinear optics in solid-state devices. Project supported by the National Natural Science Foundation of China (Grant Nos. 11165008 and 11365009), the Foundation of Young Scientist of Jiangxi Province, China (Grant No. 20142BCB23011), and the Scientific Research Foundation of Jiangxi Provincial Department of Education (Grant No. GJJ13348).

  8. Quantum phase flip gate between distant nitrogen-vacancy-center ensembles coupled to superconducting flux qubits

    NASA Astrophysics Data System (ADS)

    Liu, A.-Peng; Cheng, Liu-Yong; Chen, Li; Su, Shi-Lei; Wang, Hong-Fu; Zhang, Shou

    2014-11-01

    We propose a scheme for realizing a quantum controlled phase flip (CPF) gate between two distant nitrogen-vacancy-center spin ensembles (NVEs). The two NVEs couple magnetically with two inductively coupled superconducting flux qubits (FQs). By using an additional energy level of the nitrogen-vacancy (NV) center, the CPF gate can be implemented within the null- and single-excitation subspaces and the external classical driven field is needless in our scheme. Because of the adoption of NVE instead of single NV center, the CPF operation can be greatly speeded up. Besides, we show that this gate provides us a source of cluster states generation on NVEs. Analyses on the influences of dissipation show that this gate is robust.

  9. Superconducting squid amplifiers for IR detectors and other applications: Phase 2. Final report. [IR (Infrared)

    SciTech Connect

    Osterman, D.

    1993-05-01

    The subject of this report is a completed Phase II SBIR project to develop a superconducting analog multiplexer circuit. The intended application of the multiplexer is as a component of processing circuitry for a superconducting infrared focal plane array (IR FPA). Development of the IR FPA is in progress under a separate contract. Among the accomplishments that are described below is the fabrication and testing of a functioning, superconducting, 20-input multiplexer, appropriate for use with an IR FPA. The motivation for developing a superconducting multiplexer circuit derives primarily from the significant potential advantages of an all-superconducting IR FPA system, i.e. a system in which the detectors, as well as the associated processing circuitry, are superconducting. Section III of this report reviews the subject of superconducting IR FPAs. Chief among the advantages of such systems is the potential for larger arrays with greater numbers of detectors than is now possible.

  10. Ultrasonic signatures at the superconducting and the pseudogap phase boundaries in YBCO cuprates.

    SciTech Connect

    Shehter, Arkady; Migliori, Albert; Betts, Jonathan B.; Balakirev, Fedor F.; McDonald, Ross David; Riggs, Scott C.; Ramshaw, Brad; Liang, Ruixing; Hardy, Walter N.; Bonn, Doug A.

    2012-08-28

    A major issue in the understanding of cuprate superconductors is the nature of the metallic state from which high temperature superconductivity emerges. Central to this issue is the pseudogap region of the doping-temperature phase diagram that extends from room temperature to the superconducting transition. Although polarized neutron scattering studies hint at magnetic order associated with the pseudogap, there is no clear thermodynamic evidence for a phase boundary. Such evidence has a straightforward physical interpretation, however, it is difficult to obtain over a temperature range wide enough to encompass both the pseudogap and superconducting phases. We address this by measuring the elastic response of detwinned single crystals, an underdoped YBCO{sub 6.60} with superconducting transition at T{sub c} = 61.6K and a slightly overdoped YBCO{sub 6.98} with T{sub c} = 88.0K. We observe a discontinuity in the elastic moduli across the superconducting transition. Its magnitude requires that pair formation is coincident with superconducting coherence (the onset of the Meissner effect). For both crystals the elastic response reveals a phase transition at the pseudogap boundary. In slightly overdoped YBCO that transition is 20K below T{sub c}, extending the pseudogap phase boundary inside the superconducting dome. This supports a description of the metallic state in cuprates where a pseudogap phase boundary evolves into a quantum critical point masked by the superconducting dome.

  11. High-pressure superconducting phase diagram of 6Li: Isotope effects in dense lithium

    PubMed Central

    Schaeffer, Anne Marie; Temple, Scott R.; Bishop, Jasmine K.; Deemyad, Shanti

    2015-01-01

    We measured the superconducting transition temperature of 6Li between 16 and 26 GPa, and report the lightest system to exhibit superconductivity to date. The superconducting phase diagram of 6Li is compared with that of 7Li through simultaneous measurement in a diamond anvil cell (DAC). Below 21 GPa, Li exhibits a direct (the superconducting coefficient, α, Tc∝M−α, is positive), but unusually large isotope effect, whereas between 21 and 26 GPa, lithium shows an inverse superconducting isotope effect. The unusual dependence of the superconducting phase diagram of lithium on its atomic mass opens up the question of whether the lattice quantum dynamic effects dominate the low-temperature properties of dense lithium. PMID:25538300

  12. Superconductivity and Phase Separation in Oxygenated LANTHANUM(2-X) Strontium(x) Copper OXYGEN(4+DELTA)

    NASA Astrophysics Data System (ADS)

    Feng, Hung-Hsu

    1995-01-01

    In spite of the intensive, world-wide study of high temperature superconductors since their discovery ten years ago, the understanding of the microscopic mechanism of high temperature superconductivity is still limited. Phenomenologically, the hole concentration (P) is the most important parameter for manipulating the superconducting properties. Various physical properties have been established in terms of P to search for universal behaviors among the high-T_{c} cuprates. Recently, the phenomenon of clustering of holes in real space has been investigated for the high-T_ {c} cuprates, experimentally and theoretically. The realization of clustering of holes in the high- T_{c} cuprates will provide a new concept of the underlying electronic structure in them. In this work, we have studied the physical properties and behavior of phase separation for oxygenated rm La_{2-x}Sr_{x}CuO _{4+delta} (x = 0, 0.05; 0 < delta < 0.12), and compared the results to that of cation doped La_ {2-x}M_{x}CuO_4. We have, for the first time, synthesized two series of La_2CuO_{4+delta } (0 < delta < 0.12) and La_{1.95}Sr_{0.05 }CuO_{4+delta} (0 < delta <= 0.05) exhibiting consistent and reproducible physical properties. The results of this study show the following: (1) An anomalous electronic state with T_{c} ~ 15 K corresponding to P ~ 0.125 is found in both oxygenated La_2CuO _{4+delta} and La_{1.95}Sr_{0.05}CuO _{4+delta} systems. This indicates that all the T_{c } anomalies observed in cation doped La_{2-x}M_{x}CuO _4 and anion doped La_2CuO _{4+delta} are electronically driven and are of a common origin. (2) A two-superconducting phase region, T_{c} ~ 15 K and ~ 32 K, is found both in oxygenated La_2CuO _{4+delta} and La_{1.95}Sr_{0.05}CuO _{4+delta} in the same hole concentration range (P > 0.1) but in different oxygen concentration ranges. This indicates that the phase separation is electronically driven. (3) A universal physical picture in terms of phase separation and hole

  13. Free-electron laser multiplex driven by a superconducting linear accelerator.

    PubMed

    Plath, Tim; Amstutz, Philipp; Bödewadt, Jörn; Brenner, Günter; Ekanayake, Nagitha; Faatz, Bart; Hacker, Kirsten; Honkavaara, Katja; Lazzarino, Leslie Lamberto; Lechner, Christoph; Maltezopoulos, Theophilos; Scholz, Matthias; Schreiber, Siegfried; Vogt, Mathias; Zemella, Johann; Laarmann, Tim

    2016-09-01

    Free-electron lasers (FELs) generate femtosecond XUV and X-ray pulses at peak powers in the gigawatt range. The FEL user facility FLASH at DESY (Hamburg, Germany) is driven by a superconducting linear accelerator with up to 8000 pulses per second. Since 2014, two parallel undulator beamlines, FLASH1 and FLASH2, have been in operation. In addition to the main undulator, the FLASH1 beamline is equipped with an undulator section, sFLASH, dedicated to research and development of fully coherent extreme ultraviolet photon pulses using external seed lasers. In this contribution, the first simultaneous lasing of the three FELs at 13.4 nm, 20 nm and 38.8 nm is presented. PMID:27577757

  14. Superconductivity

    NASA Astrophysics Data System (ADS)

    Yeo, Yung K.

    Many potential high-temperature superconductivity (HTS) military applications have been demonstrated by low-temperature superconductivity systems; they encompass high efficiency electric drives for naval vessels, airborne electric generators, energy storage systems for directed-energy weapons, electromechanical launchers, magnetic and electromagnetic shields, and cavity resonators for microwave and mm-wave generation. Further HST applications in militarily relevant fields include EM sensors, IR focal plane arrays, SQUIDs, magnetic gradiometers, high-power sonar sources, and superconducting antennas and inertial navigation systems. The development of SQUID sensors will furnish novel magnetic anomaly detection methods for ASW.

  15. Pressure-induced superconducting phase in the charge-density-wave compound terbium tritelluride.

    PubMed

    Hamlin, J J; Zocco, D A; Sayles, T A; Maple, M B; Chu, J-H; Fisher, I R

    2009-05-01

    A series of high-pressure electrical resistivity measurements on single crystals of TbTe3 reveal a complex phase diagram involving the interplay of superconducting, antiferromagnetic and charge-density-wave order. The onset of superconductivity reaches a maximum of almost 4 K (onset) near approximately 12.4 GPa. PMID:19518815

  16. Pressure-induced electronic phase separation of magnetism and superconductivity in CrAs

    SciTech Connect

    Khasanov, Rustem; Guguchia, Zurab; Eremin, Ilya; Luetkens, Hubertus; Amato, Alex; Biswas, Pabitra K.; Ruegg, Christian; Susner, Michael A.; Sefat, Athena S.; Zhigadlo, Nikolai D.; Morenzoni, Elvezio

    2015-09-08

    We report that the recent discovery of pressure (p) induced superconductivity in the binary helimagnet CrAs has raised questions on how superconductivity emerges from the magnetic state and on the mechanism of the superconducting pairing. In the present work the suppression of magnetism and the occurrence of superconductivity in CrAs were studied by means of muon spin rotation. The magnetism remains bulk up to p ≃ 3.5 kbar while its volume fraction gradually decreases with increasing pressure until it vanishes at p ≃ 7 kbar. At 3.5 kbar superconductivity abruptly appears with its maximum Tc ≃ 1.2 K which decreases upon increasing the pressure. In the intermediate pressure region (3.5≲ p ≲ 7 kbar) the superconducting and the magnetic volume fractions are spatially phase separated and compete for phase volume. Our results indicate that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature (Tc) and of the superfluid density (ρs). A scaling of ρs with Tc3.2 as well as the phase separation between magnetism and superconductivity point to a conventional mechanism of the Cooper-pairing in CrAs.

  17. Pressure-induced electronic phase separation of magnetism and superconductivity in CrAs.

    PubMed

    Khasanov, Rustem; Guguchia, Zurab; Eremin, Ilya; Luetkens, Hubertus; Amato, Alex; Biswas, Pabitra K; Rüegg, Christian; Susner, Michael A; Sefat, Athena S; Zhigadlo, Nikolai D; Morenzoni, Elvezio

    2015-01-01

    The recent discovery of pressure (p) induced superconductivity in the binary helimagnet CrAs has raised questions on how superconductivity emerges from the magnetic state and on the mechanism of the superconducting pairing. In the present work the suppression of magnetism and the occurrence of superconductivity in CrAs were studied by means of muon spin rotation. The magnetism remains bulk up to p ≃ 3.5 kbar while its volume fraction gradually decreases with increasing pressure until it vanishes at p ≃ 7 kbar. At 3.5 kbar superconductivity abruptly appears with its maximum Tc ≃ 1.2 K which decreases upon increasing the pressure. In the intermediate pressure region (3.5 < or ~  p < or ~ 7 kbar) the superconducting and the magnetic volume fractions are spatially phase separated and compete for phase volume. Our results indicate that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature (Tc) and of the superfluid density (ρs). A scaling of ρs with Tc(3.2) as well as the phase separation between magnetism and superconductivity point to a conventional mechanism of the Cooper-pairing in CrAs. PMID:26346548

  18. Pressure-induced electronic phase separation of magnetism and superconductivity in CrAs

    DOE PAGESBeta

    Khasanov, Rustem; Guguchia, Zurab; Eremin, Ilya; Luetkens, Hubertus; Amato, Alex; Biswas, Pabitra K.; Ruegg, Christian; Susner, Michael A.; Sefat, Athena S.; Zhigadlo, Nikolai D.; et al

    2015-09-08

    We report that the recent discovery of pressure (p) induced superconductivity in the binary helimagnet CrAs has raised questions on how superconductivity emerges from the magnetic state and on the mechanism of the superconducting pairing. In the present work the suppression of magnetism and the occurrence of superconductivity in CrAs were studied by means of muon spin rotation. The magnetism remains bulk up to p ≃ 3.5 kbar while its volume fraction gradually decreases with increasing pressure until it vanishes at p ≃ 7 kbar. At 3.5 kbar superconductivity abruptly appears with its maximum Tc ≃ 1.2 K which decreasesmore » upon increasing the pressure. In the intermediate pressure region (3.5≲ p ≲ 7 kbar) the superconducting and the magnetic volume fractions are spatially phase separated and compete for phase volume. Our results indicate that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature (Tc) and of the superfluid density (ρs). A scaling of ρs with Tc3.2 as well as the phase separation between magnetism and superconductivity point to a conventional mechanism of the Cooper-pairing in CrAs.« less

  19. Pressure-induced electronic phase separation of magnetism and superconductivity in CrAs

    PubMed Central

    Khasanov, Rustem; Guguchia, Zurab; Eremin, Ilya; Luetkens, Hubertus; Amato, Alex; Biswas, Pabitra K.; Rüegg, Christian; Susner, Michael A.; Sefat, Athena S.; Zhigadlo, Nikolai D.; Morenzoni, Elvezio

    2015-01-01

    The recent discovery of pressure (p) induced superconductivity in the binary helimagnet CrAs has raised questions on how superconductivity emerges from the magnetic state and on the mechanism of the superconducting pairing. In the present work the suppression of magnetism and the occurrence of superconductivity in CrAs were studied by means of muon spin rotation. The magnetism remains bulk up to p  3.5 kbar while its volume fraction gradually decreases with increasing pressure until it vanishes at p  7 kbar. At 3.5 kbar superconductivity abruptly appears with its maximum Tc  1.2 K which decreases upon increasing the pressure. In the intermediate pressure region (3.5  p  7 kbar) the superconducting and the magnetic volume fractions are spatially phase separated and compete for phase volume. Our results indicate that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature (Tc) and of the superfluid density (ρs). A scaling of ρs with as well as the phase separation between magnetism and superconductivity point to a conventional mechanism of the Cooper-pairing in CrAs. PMID:26346548

  20. Exploring quantum phases by driven dissipation

    NASA Astrophysics Data System (ADS)

    Lang, Nicolai; Büchler, Hans Peter

    2015-07-01

    Dephasing and decay are the intrinsic dissipative processes prevalent in any open quantum system and the dominant mechanisms for the loss of coherence and entanglement. This inadvertent effect not only can be overcome but can even be capitalized on in a dissipative quantum simulation by means of tailored couplings between the quantum system and the environment. In this context it has been demonstrated that universal quantum computation can be performed using purely dissipative elements, and furthermore, the efficient preparation of highly entangled states is possible. In this article, we are interested in nonequilibrium phase transitions appearing in purely dissipative systems and the exploration of quantum phases in terms of a dissipative quantum simulation. To elucidate these concepts, we scrutinize exemplarily two paradigmatic models: the transverse-field Ising model and the considerably more complex Z2 lattice gauge theory. We show that the nonequilibrium phase diagrams parallel the quantum phase diagrams of the Hamiltonian "blueprint" theories.

  1. Controlling An Inverter-Driven Three-Phase Motor

    NASA Technical Reports Server (NTRS)

    Dolland, C.

    1984-01-01

    Control system for three-phase permanent-magnet motor driven by linecommutated inverter uses signals generated by integrating back emf of each phase of motor. High-pass filter network eliminates low-frequency components from control loop while maintaining desired power factor.

  2. Driven diffusion in the two-dimensional lattice Coulomb gas: A model for flux flow in superconducting networks

    SciTech Connect

    Lee, J. ); Teitel, S. )

    1994-08-01

    We carry out driven-diffusion Monte Carlo simulations of the two-dimensional classical lattice Coulomb gas in an applied uniform electric field, as a model for vortex motion due to an applied dc current in a periodic superconducting network. A finite-size version of dynamic scaling is used to extract the dynamic critical exponent [ital z], and infer the nonlinear response at the transition temperature. We consider the Coulomb gases [ital f]=0 and [ital f]=1/2, corresponding to a superconducting network with an applied transverse magnetic field of zero, and one-half flux quantum per unit cell, respectively.

  3. Dynamic compaction of high-temperature superconducting YBa2Cu3O(x) powders by laser-driven shocks

    NASA Astrophysics Data System (ADS)

    Darquey, P.; Kieffer, J. C.; Gauthier, J.; Pepin, H.; Chaker, M.; Champagne, B.; Villeneuve, D.; Baldis, H.

    1991-10-01

    Laser-driven shocks are successfully used to density high-temperature superconducting YBa2Cu3O7 ceramic powders. Pressures of 10 GPa on a nanosecond time scale were generated by producing a confined plasma with a high-intensity laser pulse. Significant consolidation is generated up to 300 microns below the irradiated surface. Magnetic susceptibility measurements indicate that the pinning of the intergranular vortices is strongly affected by the shock propagation. Recovery of superconductivity in compacted material is obtained with a postshock oxygen annealing.

  4. Chirp-driven giant phase space vortices

    NASA Astrophysics Data System (ADS)

    Trivedi, Pallavi; Ganesh, Rajaraman

    2016-06-01

    In a collisionless, unbounded, one-dimensional plasma, modelled using periodic boundary conditions, formation of steady state phase space coherent structures or phase space vortices (PSV) is investigated. Using a high resolution one-dimensional Vlasov-Poisson solver based on piecewise-parabolic advection scheme, the formation of giant PSV is addressed numerically. For an infinitesimal external drive amplitude and wavenumber k, we demonstrate the existence of a window of chirped external drive frequency that leads to the formation of giant PSV. The linear, small amplitude, external drive, when chirped, is shown to couple effectively to the plasma and increase both streaming of "untrapped" and "trapped" particle fraction. The steady state attained after the external drive is turned off and is shown to lead to a giant PSV with multiple extrema and phase velocities, with excess density fraction, defined as the deviation from the Maxwellian background, Δ n / n 0 ≃ 20 % - 25 % . It is shown that the process depends on the chirp time duration Δt. The excess density fraction Δn/n0, which contains both trapped and untrapped particle contribution, is also seen to scale with Δt, only inhibited by the gradient of the distribution in velocity space. Both single step drive and multistep chirp processes are shown to lead to steady state giant PSV, with multiple extrema due to embedded holes and clumps, long after the external drive is turned off.

  5. Signature of Cooper pairs in the Metallic and Insulating Phases of Homogeneously Disordered Superconducting Ta Films

    NASA Astrophysics Data System (ADS)

    Li, Yize Stephanie

    With the increase of magnetic field or the decrease of sample thickness, homogeneously disordered superconducting Ta films undergo a superconductor-metal-insulator phase transition. Each phase displays remarkably different nonlinear current-voltage (I-V) characteristics. The evolution of the nonlinear transport in the insulating phase exhibits a non-monotonic behavior as the magnetic field is increased, which could be evidence of the presence of localized Cooper pairs in the insulating phase. As the metallic phase intervenes the superconducting and insulating states in Ta films, we further suggest that Cooper pairs also exist in the metallic ground state. Data acquisition for this work was completed at the University of Virginia.

  6. Dynamic phases, pinning, and pattern formation for driven dislocation assemblies

    SciTech Connect

    Zhou, Caizhi; Reichhardt, Charles; Olson Reichhardt, Cynthia J.; Beyerlein, Irene J.

    2015-01-23

    We examine driven dislocation assemblies and show that they can exhibit a set of dynamical phases remarkably similar to those of driven systems with quenched disorder such as vortices in superconductors, magnetic domain walls, and charge density wave materials. These phases include pinned-jammed, fluctuating, and dynamically ordered states, and each produces distinct dislocation patterns as well as specific features in the noise fluctuations and transport properties. Lastly, our work suggests that many of the results established for systems with quenched disorder undergoing plastic depinning transitions can be applied to dislocation systems, providing a new approach for understanding pattern formation and dynamics in these systems.

  7. Dynamic phases, pinning, and pattern formation for driven dislocation assemblies

    DOE PAGESBeta

    Zhou, Caizhi; Reichhardt, Charles; Olson Reichhardt, Cynthia J.; Beyerlein, Irene J.

    2015-01-23

    We examine driven dislocation assemblies and show that they can exhibit a set of dynamical phases remarkably similar to those of driven systems with quenched disorder such as vortices in superconductors, magnetic domain walls, and charge density wave materials. These phases include pinned-jammed, fluctuating, and dynamically ordered states, and each produces distinct dislocation patterns as well as specific features in the noise fluctuations and transport properties. Lastly, our work suggests that many of the results established for systems with quenched disorder undergoing plastic depinning transitions can be applied to dislocation systems, providing a new approach for understanding pattern formation andmore » dynamics in these systems.« less

  8. Dynamic Phases, Pinning, and Pattern Formation for Driven Dislocation Assemblies

    PubMed Central

    Zhou, Caizhi; Reichhardt, Charles; Olson Reichhardt, Cynthia J.; Beyerlein, Irene J.

    2015-01-01

    We examine driven dislocation assemblies and show that they can exhibit a set of dynamical phases remarkably similar to those of driven systems with quenched disorder such as vortices in superconductors, magnetic domain walls, and charge density wave materials. These phases include pinned-jammed, fluctuating, and dynamically ordered states, and each produces distinct dislocation patterns as well as specific features in the noise fluctuations and transport properties. Our work suggests that many of the results established for systems with quenched disorder undergoing plastic depinning transitions can be applied to dislocation systems, providing a new approach for understanding pattern formation and dynamics in these systems. PMID:25613839

  9. Dynamic Phases, Pinning, and Pattern Formation for Driven Dislocation Assemblies

    NASA Astrophysics Data System (ADS)

    Zhou, Caizhi; Reichhardt, Charles; Olson Reichhardt, Cynthia J.; Beyerlein, Irene J.

    2015-01-01

    We examine driven dislocation assemblies and show that they can exhibit a set of dynamical phases remarkably similar to those of driven systems with quenched disorder such as vortices in superconductors, magnetic domain walls, and charge density wave materials. These phases include pinned-jammed, fluctuating, and dynamically ordered states, and each produces distinct dislocation patterns as well as specific features in the noise fluctuations and transport properties. Our work suggests that many of the results established for systems with quenched disorder undergoing plastic depinning transitions can be applied to dislocation systems, providing a new approach for understanding pattern formation and dynamics in these systems.

  10. Phase diagram of the Kohn-Luttinger superconducting state for bilayer graphene

    NASA Astrophysics Data System (ADS)

    Kagan, Maxim Yu.; Mitskan, Vitaly A.; Korovushkin, Maxim M.

    2015-06-01

    The effect of Coulomb interaction between Dirac fermions on the formation of the Kohn-Luttinger superconducting state in bilayer doped graphene is studied disregarding of the effect of the van der Waals potential of the substrate and impurities. The phase diagram determining the boundaries of superconductive domains with different types of symmetry of the order parameter is built using the extended Hubbard model in the Born weak-coupling approximation with allowance for the intratomic, interatomic, and interlayer Coulomb interactions between electrons. It is shown that the Kohn-Luttinger polarization contributions up to the second order of perturbation theory in the Coulomb interaction inclusively and an account for the long-range intraplane Coulomb interactions significantly affect the competition between the superconducting phases with the f-, p + ip-, and d + id-wave symmetries of the order parameter. It is demonstrated that the account for the interlayer Coulomb interaction enhances the critical temperature of the transition to the superconducting phase.

  11. Controlling the magnetic state of a carbon nanotube Josephson junction with the superconducting phase

    NASA Astrophysics Data System (ADS)

    Delagrange, Raphaelle; Weil, R.; Kasumov, A.; Bouchiat, H.; Deblock, R.; Luitz, D. J.; Meden, V.

    The Kondo effect is a many-body phenomenon that screens the magnetic moment of an impurity in a metal. The associated singlet state can be probed in a single impurity by electronic transport in a quantum dot (QD), here made of a carbon nanotube (CNT), which provides a localized electron between the two contacts. Using superconducting leads, one can investigate the competition between the Kondo effect and the superconductivity induced in the CNT. The superconductivity can destroy the Kondo singlet in favor of a magnetic doublet, leading to a sign reversal of the supercurrent in the S-CNT-S junction. This singlet-doublet transition depends on the Kondo temperature and the superconducting gap, as well as the position of the impurity level. We demonstrate experimentally that the superconducting phase difference across the QD can also control this magnetic transition. We use the measurement of the relation between the supercurrent and this superconducting phase as a tool to probe the transition. We show that it has a distinctly anharmonic behavior, that reveals the phase-mediated singlet to doublet transition, in good agreement with finite temperature quantum Monte Carlo calculations. We extract as well a phase diagram of the phase-controlled quantum transition at zero temperature.

  12. Superconductivity:

    NASA Astrophysics Data System (ADS)

    Sacchetti, N.

    In this paper a short historical account of the discovery of superconductivity and of its gradual development is given. The physical interpretation of its various aspects took about forty years (from 1911 to 1957) to reach a successful description of this phenomenon in terms of a microscopic theory At the very end it seemed that more or less everything could be reasonably interpreted even if modifications and refinements of the original theory were necessary. In 1986 the situation changed abruptly when a cautious but revolutionary paper appeared showing that superconductivity was found in certain ceramic oxides at temperatures above those up to then known. A rush of frantic experimental activity started world-wide and in less than one year it was shown that superconductivity is a much more widespread phenomenon than deemed before and can be found at temperatures well above the liquid air boiling point. The complexity and the number of the substances (mainly ceramic oxides) involved call for a sort of modern alchemy if compounds with the best superconducting properties are to be manufactured. We don't use the word alchemy in a deprecatory sense but just to emphasise that till now nobody can say why these compounds are what they are: superconductors.

  13. High temperature superconductivity in sulfur hydride under ultrahigh pressure: A complex superconducting phase beyond conventional BCS

    NASA Astrophysics Data System (ADS)

    Bussmann-Holder, Annette; Köhler, Jürgen; Whangbo, M.-H.; Bianconi, Antonio; Simon, Arndt

    2016-05-01

    The recent report of superconductivity under high pressure at the record transition temperature of Tc =203 K in pressurized H2S has been identified as conventional in view of the observation of an isotope effect upon deuteration. Here it is demonstrated that conventional theories of superconductivity in the sense of BCS or Eliashberg formalisms cannot account for the pressure dependence of the isotope coefficient. The only way out of the dilemma is a multi-band approach of superconductivity where already small interband coupling suffices to achieve the high values of Tc together with the anomalous pressure dependent isotope coefficient. In addition, it is shown that anharmonicity of the hydrogen bonds vanishes under pressure whereas anharmonic phonon modes related to sulfur are still active.

  14. A PROCEDURE TO SET PHASE AND AMPLITUDE OF THE RF IN THE SNS LINAC'S SUPERCONDUCTING CAVITIES

    SciTech Connect

    L.M. YOUNG

    2001-06-01

    This paper describes a procedure to set the phase and amplitude of the RF fields in the Spallation Neutron Source (SNS) linac's superconducting cavities. The linac uses superconducting cavities to accelerate the H{sup -} ion beam from the normal conducting linac at 185 MeV to a final energy of {approx}1 GeV. There are two types of cavities in the linac, 33 cavities with a geometric beta of 0.61 and 48 cavities with a geometric beta of 0.81. The correct phase setting of any single superconducting cavity depends on the RF phase and amplitude of all the preceding superconducting cavities. For the beam to be properly accelerated it must arrive at each cavity with a relative phase ({phi}{sub s}), called the synchronous phase, of about -20 degrees. That is, it must arrive early with respect to the phase at which it would gain the maximum energy by 20 degrees. This timing provides the longitudinal focusing. Beam particles arriving slightly later gain more energy and move faster relative to the synchronous beam particle. The problem is to set the phase and amplitude of each cavity in the linac so that the synchronous particle arrives at each cavity with the correct phase. The amplitude of each superconducting cavity will be adjusted as high as possible constrained only by the available RF power and the breakdown field of the cavity.

  15. Phase congruency map driven brain tumour segmentation

    NASA Astrophysics Data System (ADS)

    Szilágyi, Tünde; Brady, Michael; Berényi, Ervin

    2015-03-01

    Computer Aided Diagnostic (CAD) systems are already of proven value in healthcare, especially for surgical planning, nevertheless much remains to be done. Gliomas are the most common brain tumours (70%) in adults, with a survival time of just 2-3 months if detected at WHO grades III or higher. Such tumours are extremely variable, necessitating multi-modal Magnetic Resonance Images (MRI). The use of Gadolinium-based contrast agents is only relevant at later stages of the disease where it highlights the enhancing rim of the tumour. Currently, there is no single accepted method that can be used as a reference. There are three main challenges with such images: to decide whether there is tumour present and is so localize it; to construct a mask that separates healthy and diseased tissue; and to differentiate between the tumour core and the surrounding oedema. This paper presents two contributions. First, we develop tumour seed selection based on multiscale multi-modal texture feature vectors. Second, we develop a method based on a local phase congruency based feature map to drive level-set segmentation. The segmentations achieved with our method are more accurate than previously presented methods, particularly for challenging low grade tumours.

  16. Diagnosis of Interaction-driven Topological Phase via Exact Diagonalization.

    PubMed

    Wu, Han-Qing; He, Yuan-Yao; Fang, Chen; Meng, Zi Yang; Lu, Zhong-Yi

    2016-08-01

    We propose a general scheme for diagnosing interaction-driven topological phases in the weak interaction regime using exact diagonalization (ED). The scheme comprises the analysis of eigenvalues of the point-group operators for the many-body eigenstates and the correlation functions for physical observables to extract the symmetries of the order parameters and the topological numbers of the underlying ground states at the thermodynamic limit from a relatively small size system afforded by ED. As a concrete example, we investigate the interaction effects on the half-filled spinless fermions on the checkerboard lattice with a quadratic band crossing point. Numerical results support the existence of a spontaneous quantum anomalous Hall phase purely driven by a nearest-neighbor weak repulsive interaction, separated from a nematic Mott insulator phase at strong repulsive interaction by a first-order phase transition. PMID:27541471

  17. Diagnosis of Interaction-driven Topological Phase via Exact Diagonalization

    NASA Astrophysics Data System (ADS)

    Wu, Han-Qing; He, Yuan-Yao; Fang, Chen; Meng, Zi Yang; Lu, Zhong-Yi

    2016-08-01

    We propose a general scheme for diagnosing interaction-driven topological phases in the weak interaction regime using exact diagonalization (ED). The scheme comprises the analysis of eigenvalues of the point-group operators for the many-body eigenstates and the correlation functions for physical observables to extract the symmetries of the order parameters and the topological numbers of the underlying ground states at the thermodynamic limit from a relatively small size system afforded by ED. As a concrete example, we investigate the interaction effects on the half-filled spinless fermions on the checkerboard lattice with a quadratic band crossing point. Numerical results support the existence of a spontaneous quantum anomalous Hall phase purely driven by a nearest-neighbor weak repulsive interaction, separated from a nematic Mott insulator phase at strong repulsive interaction by a first-order phase transition.

  18. Solid–Liquid Phase Change Driven by Internal Heat Generation

    SciTech Connect

    John Crepeau; Ali s. Siahpush

    2012-07-01

    This article presents results of solid-liquid phase change, the Stefan Problem, where melting is driven internal heat generation, in a cylindrical geometry. The comparison between a quasi-static analytical solution for Stefan numbers less than one and numerical solutions shows good agreement. The computational results of phase change with internal heat generation show how convection cells form in the liquid region. A scale analysis of the same problem shows four distinct regions of the melting process.

  19. Separating pairing from quantum phase coherence dynamics above the superconducting transition by femtosecond spectroscopy

    PubMed Central

    Madan, I.; Kurosawa, T.; Toda, Y.; Oda, M.; Mertelj, T.; Kusar, P.; Mihailovic, D.

    2014-01-01

    In classical superconductors an energy gap and phase coherence appear simultaneously with pairing at the transition to the superconducting state. In high-temperature superconductors, the possibility that pairing and phase coherence are distinct and independent processes has led to intense experimental search of their separate manifestations. Using femtosecond spectroscopy methods we now show that it is possible to clearly separate fluctuation dynamics of the superconducting pairing amplitude from the phase relaxation above the critical transition temperature. Empirically establishing a close correspondence between the superfluid density measured by THz spectroscopy and superconducting optical pump-probe response over a wide region of temperature, we find that in differently doped Bi2Sr2CaCu2O8+δ crystals the pairing gap amplitude monotonically extends well beyond Tc, while the phase coherence shows a pronounced power-law divergence as T → Tc, thus showing that phase coherence and gap formation are distinct processes which occur on different timescales. PMID:25014162

  20. Classification of topological phases in periodically driven interacting systems

    NASA Astrophysics Data System (ADS)

    Else, Dominic V.; Nayak, Chetan

    2016-05-01

    We consider topological phases in periodically driven (Floquet) systems exhibiting many-body localization, protected by a symmetry G . We argue for a general correspondence between such phases and topological phases of undriven systems protected by symmetry Z ⋊G where the additional Z accounts for the discrete time-translation symmetry. Thus, for example, the bosonic phases in d spatial dimensions without intrinsic topological order [symmetry-protected topological (SPT) phases] are classified by the cohomology group Hd +1[Z ⋊G ,U (1 ) ] . For unitary symmetries, we interpret the additional resulting Floquet phases in terms of the lower-dimensional SPT phases that are pumped to the boundary during one time step. These results also imply the existence of novel symmetry-enriched topological (SET) orders protected solely by the periodicity of the drive.

  1. Theory of phase dynamics in intrinsic Josephson junctions with multigap superconducting layers

    NASA Astrophysics Data System (ADS)

    Ota, Y.; Machida, M.; Koyama, T.

    2011-11-01

    We construct a theory of dynamical behavior in intrinsic Josephson junction stacks with multigap superconducting layers. The theory predicts the existence of two kinds of phase modes, one of which is the Josephson-plasma mode and other of which is the Leggett’s mode. We discuss a cooperative phenomena induced by inter-band Josephson coupling in addition to capacitive and inductive couplings between the superconducting layers.

  2. Pressure-induced phase transition and superconductivity in YBa2Cu4O8

    NASA Astrophysics Data System (ADS)

    Souliou, S. M.; Subedi, A.; Song, Y. T.; Lin, C. T.; Syassen, K.; Keimer, B.; Le Tacon, M.

    2014-10-01

    We investigate the pressure and temperature dependence of the lattice dynamics of the underdoped, stoichiometric, high-temperature superconductor YBa2Cu4O8 by means of Raman spectroscopy and ab initio calculations. This system undergoes a reversible pressure-induced structural phase transition around 10 GPa to a collapsed orthorhombic structure that is well reproduced by the calculation. The coupling of the B1g-like buckling phonon mode to the electronic continuum is used to probe superconductivity. In the low pressure phase, self-energy effects through the superconducting transition renormalize this phonon, and the amplitude of this renormalization strongly increases with pressure. Whereas our calculation indicates that this mode's coupling to the electronic system is only marginally affected by the structural phase transition, the aforementioned renormalization is completely suppressed in the high pressure phase, demonstrating that under hydrostatic pressures higher than 10 GPa, superconductivity in YBa2Cu4O8 is greatly weakened or obliterated.

  3. Superconducting resonator used as a phase and energy detector for linac setup

    NASA Astrophysics Data System (ADS)

    Lobanov, Nikolai R.

    2016-07-01

    Booster linacs for tandem accelerators and positive ion superconducting injectors have matured into standard features of many accelerator laboratories. Both types of linac are formed as an array of independently-phased resonators operating at room temperature or in a superconducting state. Each accelerating resonator needs to be individually set in phase and amplitude for optimum acceleration efficiency. The modularity of the linac allows the velocity profile along the structure to be tailored to accommodate a wide range charge to mass ratio. The linac setup procedure, described in this paper, utilizes a superconducting resonator operating in a beam bunch phase detection mode. The main objective was to derive the full set of phase distributions for quick and efficient tuning of the entire accelerator. The phase detector was operated in overcoupling mode in order to minimize de-tuning effects of microphonic background. A mathematical expression was derived to set a limit on resonator maximum accelerating field during the crossover search to enable extracting unambiguous beam phase data. A set of equations was obtained to calculate the values of beam phase advance and energy gain produced by accelerating resonators. An extensive range of linac setting up configurations was conducted to validate experimental procedures and analytical models. The main application of a superconducting phase detector is for fast tuning for beams of ultralow intensities, in particular in the straight section of linac facilities.

  4. Self-optimized superconductivity attainable by interlayer phase separation at cuprate interfaces.

    PubMed

    Misawa, Takahiro; Nomura, Yusuke; Biermann, Silke; Imada, Masatoshi

    2016-07-01

    Stabilizing superconductivity at high temperatures and elucidating its mechanism have long been major challenges of materials research in condensed matter physics. Meanwhile, recent progress in nanostructuring offers unprecedented possibilities for designing novel functionalities. Above all, thin films of cuprate and iron-based high-temperature superconductors exhibit remarkably better superconducting characteristics (for example, higher critical temperatures) than in the bulk, but the underlying mechanism is still not understood. Solving microscopic models suitable for cuprates, we demonstrate that, at an interface between a Mott insulator and an overdoped nonsuperconducting metal, the superconducting amplitude is always pinned at the optimum achieved in the bulk, independently of the carrier concentration in the metal. This is in contrast to the dome-like dependence in bulk superconductors but consistent with the astonishing independence of the critical temperature from the carrier density x observed at the interfaces of La2CuO4 and La2-x Sr x CuO4. Furthermore, we identify a self-organization mechanism as responsible for the pinning at the optimum amplitude: An emergent electronic structure induced by interlayer phase separation eludes bulk phase separation and inhomogeneities that would kill superconductivity in the bulk. Thus, interfaces provide an ideal tool to enhance and stabilize superconductivity. This interfacial example opens up further ways of shaping superconductivity by suppressing competing instabilities, with direct perspectives for designing devices. PMID:27482542

  5. Self-optimized superconductivity attainable by interlayer phase separation at cuprate interfaces

    PubMed Central

    Misawa, Takahiro; Nomura, Yusuke; Biermann, Silke; Imada, Masatoshi

    2016-01-01

    Stabilizing superconductivity at high temperatures and elucidating its mechanism have long been major challenges of materials research in condensed matter physics. Meanwhile, recent progress in nanostructuring offers unprecedented possibilities for designing novel functionalities. Above all, thin films of cuprate and iron-based high-temperature superconductors exhibit remarkably better superconducting characteristics (for example, higher critical temperatures) than in the bulk, but the underlying mechanism is still not understood. Solving microscopic models suitable for cuprates, we demonstrate that, at an interface between a Mott insulator and an overdoped nonsuperconducting metal, the superconducting amplitude is always pinned at the optimum achieved in the bulk, independently of the carrier concentration in the metal. This is in contrast to the dome-like dependence in bulk superconductors but consistent with the astonishing independence of the critical temperature from the carrier density x observed at the interfaces of La2CuO4 and La2−xSrxCuO4. Furthermore, we identify a self-organization mechanism as responsible for the pinning at the optimum amplitude: An emergent electronic structure induced by interlayer phase separation eludes bulk phase separation and inhomogeneities that would kill superconductivity in the bulk. Thus, interfaces provide an ideal tool to enhance and stabilize superconductivity. This interfacial example opens up further ways of shaping superconductivity by suppressing competing instabilities, with direct perspectives for designing devices. PMID:27482542

  6. Evidence for broken time-reversal symmetry in the superconducting phase of URu2Si2

    NASA Astrophysics Data System (ADS)

    Schemm, E. R.; Baumbach, R. E.; Tobash, P. H.; Ronning, F.; Bauer, E. D.; Kapitulnik, A.

    2015-04-01

    Recent experimental and theoretical interest in the superconducting phase of the heavy-fermion material URu2Si2 has led to a number of proposals in which the superconducting order parameter breaks time-reversal symmetry (TRS). In this study we measure the polar Kerr effect (PKE) as a function of temperature for several high-quality single crystals of URu2Si2 . We find an onset of PKE below the superconducting transition that is consistent with a TRS-breaking order parameter. This effect appears to be independent of an additional, possibly extrinsic, PKE generated above the hidden order transition at THO=17.5 K, and contains a structure below Tc suggestive of additional physics within the superconducting state.

  7. Phase separation and coarsening in electrostatically driven granular media.

    SciTech Connect

    Aranson, I. S.; Meerson, B.; Sasorov, P. V.; Vinokur, V. M.; Materials Science Division; Hebrew Univ. of Jerusalem; Inst. of Theoretical and Experimental Physics

    2002-05-20

    A continuum model for the phase separation and coarsening in electrostatically driven granular media is formulated in terms of a Ginzburg-Landau equation subject to conservation of the total number of grains. In the regime of well-developed clusters, the continuum model is used to derive 'sharp-interface' equations that govern the dynamics of the interphase boundary. The model captures the essential physics of this system.

  8. Superconductivity in the high-Tc Bi-Ca-Sr-Cu-O system - Phase identification

    NASA Technical Reports Server (NTRS)

    Hazen, R. M.; Prewitt, C. T.; Angel, R. J.; Ross, N. L.; Finger, L. W.

    1988-01-01

    Four phases are observed in superconducting Bi-Ca-Sr-Cu-O samples. The superconducting phase, with onset temperature near 120 K, is a 15.4-A-layered compound with composition near Bi2Ca1Sr2Cu2O9 and an A-centered orthorhombic unit subcell 5.41 x 5.44 x 30.78 A. X-ray diffraction and electron microscopy data are consistent with a structure of alternating perovskite and Bi2O2 layers. High-resolution transmission electron microscopy images reveal a b-axis superstructure of 27.2 A, numerous (001) stacking faults, and other defects.

  9. Nonlinear Phase Dynamics in a Driven Bosonic Josephson Junction

    SciTech Connect

    Boukobza, Erez; Moore, Michael G.; Cohen, Doron; Vardi, Amichay

    2010-06-18

    We study the collective dynamics of a driven two-mode Bose-Hubbard model in the Josephson interaction regime. The classical phase space is mixed, with chaotic and regular components, which determine the dynamical nature of the fringe visibility. For a weak off-resonant drive, where the chaotic component is small, the many-body dynamics corresponds to that of a Kapitza pendulum, with the relative phase {phi} between the condensates playing the role of the pendulum angle. Using a master equation approach we show that the modulation of the intersite potential barrier stabilizes the {phi}={pi} 'inverted pendulum' coherent state, and protects the fringe visibility.

  10. Giant phonon anomaly associated with superconducting fluctuations in the pseudogap phase of cuprates

    PubMed Central

    Liu, Ye-Hua; Konik, Robert M.; Rice, T. M.; Zhang, Fu-Chun

    2016-01-01

    The pseudogap in underdoped cuprates leads to significant changes in the electronic structure, and was later found to be accompanied by anomalous fluctuations of superconductivity and certain lattice phonons. Here we propose that the Fermi surface breakup due to the pseudogap, leads to a breakup of the pairing order into two weakly coupled sub-band amplitudes, and a concomitant low energy Leggett mode due to phase fluctuations between them. This increases the temperature range of superconducting fluctuations containing an overdamped Leggett mode. In this range inter-sub-band phonons show strong damping due to resonant scattering into an intermediate state with a pair of overdamped Leggett modes. In the ordered state, the Leggett mode develops a finite energy, changing the anomalous phonon damping into an anomaly in the dispersion. This proposal explains the intrinsic connection between the anomalous pseudogap phase, enhanced superconducting fluctuations and giant anomalies in the phonon spectra. PMID:26785835

  11. Giant phonon anomaly associated with superconducting fluctuations in the pseudogap phase of cuprates

    DOE PAGESBeta

    Liu, Ye-Hua; Konik, Robert M.; Rice, T. M.; Zhang, Fu-Chun

    2016-01-20

    The pseudogap in underdoped cuprates leads to significant changes in the electronic structure, and was later found to be accompanied by anomalous fluctuations of superconductivity and certain lattice phonons. Here we propose that the Fermi surface breakup due to the pseudogap, leads to a breakup of the pairing order into two weakly coupled sub-band amplitudes, and a concomitant low energy Leggett mode due to phase fluctuations between them. This increases the temperature range of superconducting fluctuations containing an overdamped Leggett mode. In this range inter-sub-band phonons show strong damping due to resonant scattering into an intermediate state with a pairmore » of overdamped Leggett modes. In the ordered state, the Leggett mode develops a finite energy, changing the anomalous phonon damping into an anomaly in the dispersion. Finally, this proposal explains the intrinsic connection between the anomalous pseudogap phase, enhanced superconducting fluctuations and giant anomalies in the phonon spectra.« less

  12. Superconductivity in the new ternary phase of the Ta-Hf-B system

    NASA Astrophysics Data System (ADS)

    Correa, Lucas Eduardo; Santos, Frederico Benedetto; Nunes, Carlos Angelo; Coelho, Gilberto Carvalho; Renosto, Sergio Tuan; Fisk, Zachary; Da Silva Machado, Antonio Jefferson

    2014-03-01

    In the Ta-B binary system the TaB phase crystallizes in the orthorhombic symmetry with CrB prototype structure which displays superconducting critical temperature close to 4.0 K. To our knowledge this binary phase (CrB prototype structure) is a just stable phase in all temperature range. In this work we will show that the substitution of Ta for Hf it is able to produce a allotropic transformation from CrB to FeB prototype structure. These results represent a new pseudo-ternary phase in the Ta - Hf -B system which is stable in high temperature. The phase found in this work present superconducting critical temperature close to 6.9 K which is sustained by specific heat, magnetization and resistivity measurements.

  13. Elucidating the magnetic and superconducting phases in the alkali metal intercalated iron chalcogenides

    NASA Astrophysics Data System (ADS)

    Wang, Meng; Yi, Ming; Tian, Wei; Bourret-Courchesne, Edith; Birgeneau, Robert J.

    2016-02-01

    The complex interdigitated phases have greatly frustrated attempts to document the basic features of the superconductivity in the alkali metal intercalated iron chalcogenides. Here, using elastic neutron scattering, energy-dispersive x-ray spectroscopy, and resistivity measurements, we elucidate the relations of these phases in RbxFeySe2 -zSz . We find (i) the iron content is crucial in stabilizing the stripe antiferromagnetic (AF) phase with rhombic iron vacancy order (y ≈1.5 ) , the block AF phase with √{5 }×√{5 } iron vacancy order (y ≈1.6 ) , and the iron vacancy-free phase (y ≈2 ) ; and (ii) the iron vacancy-free superconducting phase (z =0 ) evolves into an iron vacancy-free metallic phase with sulfur substitution (z >1.5 ) due to the progressive decrease of the electronic correlation strength. Both the stripe AF phase and the block AF phase are Mott insulators. The iron-rich compounds (y >1.6 ) undergo a first order transition from an iron vacancy disordered phase at high temperatures into the √{5 }×√{5 } iron vacancy ordered phase and the iron vacancy-free phase below Ts. Our data demonstrate that there are miscibility gaps between these three phases. The existence of the miscibility gaps in the iron content is a key to understanding the relationship between these complicated phases.

  14. Electron-driven chemistry of halogenated compounds in condensed phases

    NASA Astrophysics Data System (ADS)

    Perry, C. C.; Faradzhev, N. S.; Fairbrother, D. H.; Madey, T. E.

    The focus of this review is the effect of H2O on the electron-driven chemistry of condensed halogenated compounds. We present data with emphasis on results from the authors' laboratories for halomethanes (CF2Cl2, CCl4, CH3I, CDCl3, CD2Cl2) and SF6. The halogenated species are suspended in or adsorbed on the surface of ultrathin films of amorphous solid water (ice) condensed on metal surfaces. Bombardment of the film by X-rays or energetic electrons leads to the release of low-energy secondary electrons; these are responsible for much of the rich electron-driven chemistry, which includes molecular decomposition, desorption of charged and neutral fragments, radical formation, anion solvation, and condensed-phase reactions. Potential implications of this work range from environmental remediation of toxic compounds to atmospheric ozone depletion.

  15. Shrinking of the Cooper Pair Insulator Phase in Thin Films with Ultrasmall Superconducting Islands

    NASA Astrophysics Data System (ADS)

    Joy, J. C.; Zhang, X.; Zhao, C.; Valles, J. M., Jr.; Fernandes, G.; Xu, J. M.

    The ubiquity of the bosonic Cooper Pair Insulator (CPI) phase near the two-dimensional superconductor to insulator transition (SIT) is a long standing question. While a number of two dimensional materials exhibit bosonic insulating phases similar to the Mott Insulator in arrays of ultrasmall, Josephson coupled superconducting islands, others show behaviors consistent with a fermionic insulating phase. Utilizing specially prepared anodized aluminum oxide substrates, we are able to fabricate films reminiscent of arrays of superconducting islands whose properties are tunable by varying the substrate morphology. Our recent work has focused on arrays of islands which possess an energy level spacing comparable to the mean field superconducting gap, where one expects pair breaking followed by fermionic Anderson Localization as the dominant mechanism by which superconductivity is destroyed. Early results show that the paradigmatic bosonic insulator exists only very near the disorder tuned SIT, while films only marginally deeper in the insulating phase exhibit transport distinct from the CPI's reentrant, activated transport. We are grateful for the support of NSF Grant No. DMR-1307290, the AFOSR, and the AOARD. Currently at Northwestern Polytechnical University, Xian, China.

  16. Neutron scattering study on the magnetic and superconducting phases of MnP

    NASA Astrophysics Data System (ADS)

    Yano, Shinichiro; Lancon, Diane; Ronnow, Henrik; Hansen, Thomas; Gardner, Jason

    We have performed series of neutron scattering experiments on MnP. MnP has been investigated for decades because of its rich magnetic phase diagram. The magnetic structure of MnP is ferromagnetic (FM) below TC = 291 K. It transforms into a helimagnetic structure at TS = 47 K with a propagation vector q = 0 . 117a* . Superconductivity was found in MnP under pressures of 8 GPa with a TSC around 1 K by J.-G. Cheng. Since Mn-based superconductors are rare, and the superconducting phase occurs in the vicinity of FM, new magnetic and helimagnetic phases, there is a need to understand how the magnetism evolves as one approach the superconducting state. MnP is believed to be a double helix magnetic structure at TS = 47 K. We observed new 2 δ and 3 δ satellite peaks whose intensity are 200 ~ 1000 times smaller than these of 1 δ satellite peaks on the cold triple axis spectrometer SIKA under zero magnetic fields. We also found the periods of helimagnetic structure changes as a function of temperature. If time permits, we will discuss recent experiments under pressure. However, we have complete picture of magnetic structure of this system with and without applied pressure, revealing the interplay between the magnetic and superconducting phases.

  17. Doping driven small-to-large Fermi surface transition and d-wave superconductivity in a two-dimensional Kondo lattice

    NASA Astrophysics Data System (ADS)

    Eder, R.; Wróbel, P.

    2011-07-01

    We study the two-dimensional Kondo lattice model with an additional Heisenberg exchange between localized spins. In a first step, we use mean-field theory with two order parameters. The first order parameter is a complex pairing amplitude between conduction electrons and localized spins that describes condensation of Kondo (or Zhang-Rice) singlets. A nonvanishing value implies that the localized spins contribute to the Fermi surface volume. The second-order parameter describes singlet pairing between the localized spins and competes with the Kondo-pairing order parameter. Reduction of the carrier density in the conduction band reduces the energy gain due to the formation of the large Fermi surface and induces a phase transition to a state with strong singlet correlations between the localized spins and a Fermi surface that comprises only the conduction electrons. The model thus shows a doping driven change of its Fermi surface volume. At intermediate doping and low temperature, there is a phase where both order parameters coexist, which has a gapped large Fermi surface and dx2-y2 superconductivity. The theory thus qualitatively reproduces the phase diagram of cuprate superconductors. In the second part of this paper, we show how the two phases with different Fermi surface volume emerge in a strong-coupling theory applicable in the limit of large Kondo exchange. The large Fermi surface phase corresponds to a “vacuum” of localized Kondo singlets with uniform phase, and the quasiparticles are spin-1/2 charge fluctuations around this fully paired state. In the small Fermi surface phase, the quasiparticles correspond to propagating Kondo singlets or triplets whereby the phase of a given Kondo singlet corresponds to its momentum. In this picture, a phase transition occurs for low filling of the conduction band as well.

  18. COOLING OF COMPACT STARS WITH COLOR SUPERCONDUCTING PHASE IN QUARK-HADRON MIXED PHASE

    SciTech Connect

    Noda, Tsuneo; Hashimoto, Masa-aki; Yasutake, Nobutoshi; Maruyama, Toshiki; Tatsumi, Toshitaka; Fujimoto, Masayuki E-mail: hashimoto@phys.kyushu-u.ac.jp

    2013-03-01

    We present a new scenario for the cooling of compact stars considering the central source of Cassiopeia A (Cas A). The Cas A observation shows that the central source is a compact star that has high effective temperature, and it is consistent with the cooling without exotic phases. The observation also gives the mass range of M {>=} 1.5 M {sub Sun }, which may conflict with the current plausible cooling scenario of compact stars. There are some cooled compact stars such as Vela or 3C58, which can barely be explained by the minimal cooling scenario, which includes the neutrino emission by nucleon superfluidity (PBF). Therefore, we invoke the exotic cooling processes, where a heavier star cools faster than lighter one. However, the scenario seems to be inconsistent with the observation of Cas A. Therefore, we present a new cooling scenario to explain the observation of Cas A by constructing models that include a quark color superconducting (CSC) phase with a large energy gap; this phase appears at ultrahigh density regions and reduces neutrino emissivity. In our model, a compact star has a CSC quark core with a low neutrino emissivity surrounded by high emissivity region made by normal quarks. We present cooling curves obtained from the evolutionary calculations of compact stars: while heavier stars cool slowly, and lighter ones indicate the opposite tendency without considering nucleon superfluidity. Furthermore, we show that our scenario is consistent with the recent observations of the effective temperature of Cas A during the last 10 years, including nucleon superfluidity.

  19. Topological Phase Transition between s+- and s++ Superconducting Phases from Competing Electron--Electron and Electron--Phonon Interactions

    NASA Astrophysics Data System (ADS)

    Kim, Ki-Seok; Gammag, Rayda

    2013-06-01

    We discover a topological phase transition between conventional s+- and s++ superconducting phases by tuning the ratio of electron--electron and electron--phonon coupling constants in an FeAs-type two-band structure. Proving the existence of this unexpected quantum criticality within the mean-field theory, we propose that the quantum critical point be identified with a critical spin liquid state of an ``extended'' Dirac spectrum, where critical superconducting fluctuations cause screening of charge degrees of freedom for electronic excitations, which allows spinon excitations to carry only the spin quantum number 1/2. The emergence of the critical spin liquid state at the s+--s++ superconducting quantum critical point leads us to predict a metal--insulator--metal crossover behavior in electrical resistivity above the superconducting transition temperatures as the ratio of the electron--electron and electron--phonon coupling constants is increased. In addition, we uncover that the competition between electron--electron repulsion and electron--phonon attraction gives rise to a huge enhancement of the superconducting transition temperature near the quantum critical point which is several hundreds percent larger than that of the case when only one of the two is taken into account. Our renormalization group analysis claims that this mechanism for the enhancement of the critical temperature is not limited to superconductivity but can be applied to various Fermi surface instabilities, proposing an underlying universal structure, which turns out to be essentially identical to that of a recent study [Phys. Rev. Lett. 108 (2012) 046601] on the enhancement of the Kondo temperature in the presence of Rashba spin--orbit interaction. We speculate that the existence of this possible ``deconfined'' quantum criticality can be verified not only theoretically but also experimentally, particularly, in Li2(Pd1-xPtx)3B superconductors, varying x from 0 to 1.

  20. Elastic moduli across the superconducting and pseudogap phase boundaries in four cuprate compounds

    NASA Astrophysics Data System (ADS)

    Ramshaw, Brad; Shekhter, Arkady; Betts, Jon; Migliori, Albert

    2013-03-01

    A detailed understanding of the physics of the cuprate superconductors relies on an experimental determination of the thermodynamic phase diagram. Resonant ultrasound spectroscopy (RUS) is a unique thermodynamic probe, capable of measuring part per million changes in elastic moduli, and has access to symmetry information. Here we present a symmetry analysis of changes in the elastic moduli across the superconducting and psedogap phase boundaries in several classes of cuprates: YBCO, LSCO, Hg-1201, and Tl-2201.

  1. Evolution of microstructure during formation of Nb3Sn superconducting phase

    NASA Astrophysics Data System (ADS)

    Singh, A. K.; Kumar, Shivendra; Pasi, Satya Prakash; Laik, A.; Hussain, M. M.; Abdulla, K. K.; Dey, G. K.

    2013-02-01

    Nb3Sn based multi-filamentary superconducting wires with critical temperature (Tc) of 17.5 K was indigenously developed. A critical temperature (Tc) of 17.5 K was obtained. Characterization of the microstructure of the wires revealed almost complete conversion of the Nb filaments to Nb3Sn phase. The phase formed was nano-crystalline in nature and was slight hypo-stoichiometric with respect to Sn.

  2. Phase Diagram and High-Temperature Superconductivity of Compressed Selenium Hydrides.

    PubMed

    Zhang, Shoutao; Wang, Yanchao; Zhang, Jurong; Liu, Hanyu; Zhong, Xin; Song, Hai-Feng; Yang, Guochun; Zhang, Lijun; Ma, Yanming

    2015-01-01

    Recent discovery of high-temperature superconductivity (Tc = 190 K) in sulfur hydrides at megabar pressures breaks the traditional belief on the Tc limit of 40 K for conventional superconductors, and opens up the doors in searching new high-temperature superconductors in compounds made up of light elements. Selenium is a sister and isoelectronic element of sulfur, with a larger atomic core and a weaker electronegativity. Whether selenium hydrides share similar high-temperature superconductivity remains elusive, but it is a subject of considerable interest. First-principles swarm structure predictions are performed in an effort to seek for energetically stable and metallic selenium hydrides at high pressures. We find the phase diagram of selenium hydrides is rather different from its sulfur analogy, which is indicated by the emergence of new phases and the change of relative stabilities. Three stable and metallic species with stoichiometries of HSe2, HSe and H3Se are identified above ~120 GPa and they all exhibit superconductive behaviors, of which the hydrogen-rich HSe and H3Se phases show high Tc in the range of 40-110 K. Our simulations established the high-temperature superconductive nature of selenium hydrides and provided useful route for experimental verification. PMID:26490223

  3. Phase Diagram and High-Temperature Superconductivity of Compressed Selenium Hydrides

    NASA Astrophysics Data System (ADS)

    Zhang, Shoutao; Wang, Yanchao; Zhang, Jurong; Liu, Hanyu; Zhong, Xin; Song, Hai-Feng; Yang, Guochun; Zhang, Lijun; Ma, Yanming

    2015-10-01

    Recent discovery of high-temperature superconductivity (Tc = 190 K) in sulfur hydrides at megabar pressures breaks the traditional belief on the Tc limit of 40 K for conventional superconductors, and opens up the doors in searching new high-temperature superconductors in compounds made up of light elements. Selenium is a sister and isoelectronic element of sulfur, with a larger atomic core and a weaker electronegativity. Whether selenium hydrides share similar high-temperature superconductivity remains elusive, but it is a subject of considerable interest. First-principles swarm structure predictions are performed in an effort to seek for energetically stable and metallic selenium hydrides at high pressures. We find the phase diagram of selenium hydrides is rather different from its sulfur analogy, which is indicated by the emergence of new phases and the change of relative stabilities. Three stable and metallic species with stoichiometries of HSe2, HSe and H3Se are identified above ~120 GPa and they all exhibit superconductive behaviors, of which the hydrogen-rich HSe and H3Se phases show high Tc in the range of 40-110 K. Our simulations established the high-temperature superconductive nature of selenium hydrides and provided useful route for experimental verification.

  4. Phase Diagram and High-Temperature Superconductivity of Compressed Selenium Hydrides

    PubMed Central

    Zhang, Shoutao; Wang, Yanchao; Zhang, Jurong; Liu, Hanyu; Zhong, Xin; Song, Hai-Feng; Yang, Guochun; Zhang, Lijun; Ma, Yanming

    2015-01-01

    Recent discovery of high-temperature superconductivity (Tc = 190 K) in sulfur hydrides at megabar pressures breaks the traditional belief on the Tc limit of 40 K for conventional superconductors, and opens up the doors in searching new high-temperature superconductors in compounds made up of light elements. Selenium is a sister and isoelectronic element of sulfur, with a larger atomic core and a weaker electronegativity. Whether selenium hydrides share similar high-temperature superconductivity remains elusive, but it is a subject of considerable interest. First-principles swarm structure predictions are performed in an effort to seek for energetically stable and metallic selenium hydrides at high pressures. We find the phase diagram of selenium hydrides is rather different from its sulfur analogy, which is indicated by the emergence of new phases and the change of relative stabilities. Three stable and metallic species with stoichiometries of HSe2, HSe and H3Se are identified above ~120 GPa and they all exhibit superconductive behaviors, of which the hydrogen-rich HSe and H3Se phases show high Tc in the range of 40–110 K. Our simulations established the high-temperature superconductive nature of selenium hydrides and provided useful route for experimental verification. PMID:26490223

  5. Superconducting H5S2 phase in sulfur-hydrogen system under high-pressure.

    PubMed

    Ishikawa, Takahiro; Nakanishi, Akitaka; Shimizu, Katsuya; Katayama-Yoshida, Hiroshi; Oda, Tatsuki; Suzuki, Naoshi

    2016-01-01

    Recently, hydrogen sulfide was experimentally found to show the high superconducting critical temperature (Tc) under high-pressure. The superconducting Tc shows 30-70 K in pressure range of 100-170 GPa (low-Tc phase) and increases to 203 K, which sets a record for the highest Tc in all materials, for the samples annealed by heating it to room temperature at pressures above 150 GPa (high-Tc phase). Here we present a solid H5S2 phase predicted as the low-Tc phase by the application of the genetic algorithm technique for crystal structure searching and first-principles calculations to sulfur-hydrogen system under high-pressure. The H5S2 phase is thermodynamically stabilized at 110 GPa, in which asymmetric hydrogen bonds are formed between H2S and H3S molecules. Calculated Tc values show 50-70 K in pressure range of 100-150 GPa within the harmonic approximation, which can reproduce the experimentally observed low-Tc phase. These findings give a new aspect of the excellent superconductivity in compressed sulfur-hydrogen system. PMID:26983593

  6. Superconducting H5S2 phase in sulfur-hydrogen system under high-pressure

    NASA Astrophysics Data System (ADS)

    Ishikawa, Takahiro; Nakanishi, Akitaka; Shimizu, Katsuya; Katayama-Yoshida, Hiroshi; Oda, Tatsuki; Suzuki, Naoshi

    2016-03-01

    Recently, hydrogen sulfide was experimentally found to show the high superconducting critical temperature (Tc) under high-pressure. The superconducting Tc shows 30–70 K in pressure range of 100–170 GPa (low-Tc phase) and increases to 203 K, which sets a record for the highest Tc in all materials, for the samples annealed by heating it to room temperature at pressures above 150 GPa (high-Tc phase). Here we present a solid H5S2 phase predicted as the low-Tc phase by the application of the genetic algorithm technique for crystal structure searching and first-principles calculations to sulfur-hydrogen system under high-pressure. The H5S2 phase is thermodynamically stabilized at 110 GPa, in which asymmetric hydrogen bonds are formed between H2S and H3S molecules. Calculated Tc values show 50–70 K in pressure range of 100–150 GPa within the harmonic approximation, which can reproduce the experimentally observed low-Tc phase. These findings give a new aspect of the excellent superconductivity in compressed sulfur-hydrogen system.

  7. Superconducting H5S2 phase in sulfur-hydrogen system under high-pressure

    PubMed Central

    Ishikawa, Takahiro; Nakanishi, Akitaka; Shimizu, Katsuya; Katayama-Yoshida, Hiroshi; Oda, Tatsuki; Suzuki, Naoshi

    2016-01-01

    Recently, hydrogen sulfide was experimentally found to show the high superconducting critical temperature (Tc) under high-pressure. The superconducting Tc shows 30–70 K in pressure range of 100–170 GPa (low-Tc phase) and increases to 203 K, which sets a record for the highest Tc in all materials, for the samples annealed by heating it to room temperature at pressures above 150 GPa (high-Tc phase). Here we present a solid H5S2 phase predicted as the low-Tc phase by the application of the genetic algorithm technique for crystal structure searching and first-principles calculations to sulfur-hydrogen system under high-pressure. The H5S2 phase is thermodynamically stabilized at 110 GPa, in which asymmetric hydrogen bonds are formed between H2S and H3S molecules. Calculated Tc values show 50–70 K in pressure range of 100–150 GPa within the harmonic approximation, which can reproduce the experimentally observed low-Tc phase. These findings give a new aspect of the excellent superconductivity in compressed sulfur-hydrogen system. PMID:26983593

  8. Spontaneous formation of superconducting NiBi3 phase in Ni-Bi bilayer films

    NASA Astrophysics Data System (ADS)

    Siva, Vantari; Senapati, Kartik; Satpati, Biswarup; Prusty, Sudakshina; Avasthi, D. K.; Kanjilal, D.; Sahoo, Pratap K.

    2015-02-01

    We report the spontaneous formation of superconducting NiBi3 phase in thermally evaporated Ni-Bi bilayer films. High reaction-diffusion coefficient of Bi is believed to drive the formation of NiBi3 during the deposition of Bi on the Ni film. Cross sectional transmission electron microscopy and glancing incidence X-ray depth profiling confirmed the presence of NiBi3 throughout the top Bi layer. Superconducting transition at ˜3.9 K, close to the bulk value, was confirmed by transport and magnetization measurements. The bilayers were irradiated with varying fluence of 100 MeV Au ions to study the robustness of superconducting order in presence of large concentration of defects. Superconducting parameters of NiBi3, such as transition temperature and upper critical field, remained unchanged upto an ion dose of 1 × 1014 ions/cm2. The diffusive formation of NiBi3 in Ni opens the possibility of studying superconducting proximity effect at a truly clean superconductor-ferromagnet interface.

  9. Spontaneous formation of superconducting NiBi{sub 3} phase in Ni-Bi bilayer films

    SciTech Connect

    Siva, Vantari; Senapati, Kartik Prusty, Sudakshina; Sahoo, Pratap K.; Satpati, Biswarup

    2015-02-28

    We report the spontaneous formation of superconducting NiBi{sub 3} phase in thermally evaporated Ni-Bi bilayer films. High reaction-diffusion coefficient of Bi is believed to drive the formation of NiBi{sub 3} during the deposition of Bi on the Ni film. Cross sectional transmission electron microscopy and glancing incidence X-ray depth profiling confirmed the presence of NiBi{sub 3} throughout the top Bi layer. Superconducting transition at ∼3.9 K, close to the bulk value, was confirmed by transport and magnetization measurements. The bilayers were irradiated with varying fluence of 100 MeV Au ions to study the robustness of superconducting order in presence of large concentration of defects. Superconducting parameters of NiBi{sub 3}, such as transition temperature and upper critical field, remained unchanged upto an ion dose of 1 × 10{sup 14} ions/cm{sup 2}. The diffusive formation of NiBi{sub 3} in Ni opens the possibility of studying superconducting proximity effect at a truly clean superconductor-ferromagnet interface.

  10. Superconducting matrix fault current limiter with current-driven trigger mechanism

    DOEpatents

    Yuan; Xing

    2008-04-15

    A modular and scalable Matrix-type Fault Current Limiter (MFCL) that functions as a "variable impedance" device in an electric power network, using components made of superconducting and non-superconducting electrically conductive materials. An inductor is connected in series with the trigger superconductor in the trigger matrix and physically surrounds the superconductor. The current surge during a fault will generate a trigger magnetic field in the series inductor to cause fast and uniform quenching of the trigger superconductor to significantly reduce burnout risk due to superconductor material non-uniformity.

  11. Phase diagram of van der Waals-like phase separation in a driven granular gas.

    PubMed

    Khain, Evgeniy; Meerson, Baruch; Sasorov, Pavel V

    2004-11-01

    Equations of granular hydrostatics are used to compute the phase diagram of the recently discovered van der Waals-like phase separation in a driven granular gas. The model two-dimensional system consists of smooth hard disks in a rectangular box, colliding inelastically with each other and driven by a "thermal" wall at zero gravity. The spinodal line and the critical point of the phase separation are determined. Close to the critical point, the spinodal and binodal (coexistence) lines are determined analytically. Effects of the finite size of the confining box in the direction parallel to the thermal wall are investigated. These include suppression of the phase separation by heat conduction in the lateral direction and a change from supercritical to subcritical bifurcation. PMID:15600606

  12. The non-magnetic collapsed tetragonal phase of CaFe2As2 and superconductivity in the iron pnictides

    NASA Astrophysics Data System (ADS)

    Soh, J. H.; Tucker, G. S.; Pratt, D. K.; Abernathy, D. L.; Stone, M. B.; Ran, S.; Bud'Ko, S. L.; Canfield, P. C.; Kreyssig, A.; McQueeney, R. J.; Goldman, A. I.

    2014-03-01

    The relationship between antiferromagnetic spin fluctuations and superconductivity has become a central topic of research in studies of superconductivity in the iron pnictides. We present unambiguous evidence of the absence of magnetic fluctuations in the non-superconducting collapsed tetragonal phase of CaFe2As2 via inelastic neutron scattering time-of-flight data, which is consistent with the view that spin fluctuations are a necessary ingredient for unconventional superconductivity in the iron pnictides. We demonstrate that the collapsed tetragonal phase of CaFe2As2 is non-magnetic, and discuss this result in light of recent reports of high-temperature superconductivity in the collapsed tetragonal phase of closely related compounds. Work at the Ames Laboratory was supported by the Department of Energy, Basic Energy Sciences. Work at ORNL's Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences.

  13. Suppression of superconductivity and structural phase transitions under pressure in tetragonal FeS

    PubMed Central

    Lai, Xiaofang; Liu, Ying; Lü, Xujie; Zhang, Sijia; Bu, Kejun; Jin, Changqing; Zhang, Hui; Lin, Jianhua; Huang, Fuqiang

    2016-01-01

    Pressure is a powerful tool to study iron-based superconductors. Here, we report systematic high-pressure transport and structural characterizations of the newly discovered superconductor FeS. It is found that superconductor FeS (tetragonal) partly transforms to a hexagonal structure at 0.4 GPa, and then completely transforms to an orthorhombic phase at 7.4 GPa and finally to a monoclinic phase above 9.0 GPa. The superconducting transition temperature of tetragonal FeS was gradually depressed by pressure, different from the case in tetragonal FeSe. With pressure increasing, the S-Fe-S angles only slightly change but the anion height deviates farther from 1.38 Å. This change of anion height, together with the structural instability under pressure, should be closely related to the suppression of superconductivity. We also observed an anomalous metal-semiconductor transition at 6.0 GPa and an unusual increased resistance with further compression above 9.6 GPa. The former can be ascribed to the tetragonal-orthorhombic structural phase transition, and the latter to the electronic structure changes of the high-pressure monoclinic phase. Finally, a phase diagram of tetragonal FeS as functions of pressure and temperature was mapped out for the first time, which will shed new light on understanding of the structure and physics of the superconducting FeS. PMID:27498699

  14. Suppression of superconductivity and structural phase transitions under pressure in tetragonal FeS.

    PubMed

    Lai, Xiaofang; Liu, Ying; Lü, Xujie; Zhang, Sijia; Bu, Kejun; Jin, Changqing; Zhang, Hui; Lin, Jianhua; Huang, Fuqiang

    2016-01-01

    Pressure is a powerful tool to study iron-based superconductors. Here, we report systematic high-pressure transport and structural characterizations of the newly discovered superconductor FeS. It is found that superconductor FeS (tetragonal) partly transforms to a hexagonal structure at 0.4 GPa, and then completely transforms to an orthorhombic phase at 7.4 GPa and finally to a monoclinic phase above 9.0 GPa. The superconducting transition temperature of tetragonal FeS was gradually depressed by pressure, different from the case in tetragonal FeSe. With pressure increasing, the S-Fe-S angles only slightly change but the anion height deviates farther from 1.38 Å. This change of anion height, together with the structural instability under pressure, should be closely related to the suppression of superconductivity. We also observed an anomalous metal-semiconductor transition at 6.0 GPa and an unusual increased resistance with further compression above 9.6 GPa. The former can be ascribed to the tetragonal-orthorhombic structural phase transition, and the latter to the electronic structure changes of the high-pressure monoclinic phase. Finally, a phase diagram of tetragonal FeS as functions of pressure and temperature was mapped out for the first time, which will shed new light on understanding of the structure and physics of the superconducting FeS. PMID:27498699

  15. Suppression of superconductivity and structural phase transitions under pressure in tetragonal FeS

    NASA Astrophysics Data System (ADS)

    Lai, Xiaofang; Liu, Ying; Lü, Xujie; Zhang, Sijia; Bu, Kejun; Jin, Changqing; Zhang, Hui; Lin, Jianhua; Huang, Fuqiang

    2016-08-01

    Pressure is a powerful tool to study iron-based superconductors. Here, we report systematic high-pressure transport and structural characterizations of the newly discovered superconductor FeS. It is found that superconductor FeS (tetragonal) partly transforms to a hexagonal structure at 0.4 GPa, and then completely transforms to an orthorhombic phase at 7.4 GPa and finally to a monoclinic phase above 9.0 GPa. The superconducting transition temperature of tetragonal FeS was gradually depressed by pressure, different from the case in tetragonal FeSe. With pressure increasing, the S-Fe-S angles only slightly change but the anion height deviates farther from 1.38 Å. This change of anion height, together with the structural instability under pressure, should be closely related to the suppression of superconductivity. We also observed an anomalous metal-semiconductor transition at 6.0 GPa and an unusual increased resistance with further compression above 9.6 GPa. The former can be ascribed to the tetragonal-orthorhombic structural phase transition, and the latter to the electronic structure changes of the high-pressure monoclinic phase. Finally, a phase diagram of tetragonal FeS as functions of pressure and temperature was mapped out for the first time, which will shed new light on understanding of the structure and physics of the superconducting FeS.

  16. Characterization & Transport Signatures of Periodically Driven Topological Phases

    NASA Astrophysics Data System (ADS)

    Fruchart, Michel; Delplace, Pierre; Gawedzki, Krzysztof; Carpentier, David

    The discovery of the Quantum Hall Effect in the 80's opened the field of topological phases of matter, which has been renewed by the discovery of a new kind of topological insulator in 2005, this time in a time-reversal invariant system. In order to obtain a material with tunable topological properties, research were carried out on out-of-equilibrium systems subject to a periodic drive. Such periodically driven topological phases turn out to be richer that their equilibrium counterparts. We consider a 2D crystal subject to a drive periodic in time, constrained so that is is time-reversal invariant and show that such a system is characterized by Z2 indices attached to a gap (and not to a band), which we explicitly construct. To probe these out-of-equilibrium phases in a phase coherent regime, we use standard transport measurements. With the help of numerical simulations, we show that the running time-averaged differential conductances are quantized in a topological gap, and that multi-terminal setups enable to probe the chirality of the out-of-equilibrium topological states.

  17. Noble metals (Ag, Au) nanoparticles addition effects on superconducting properties of CuTl-1223 phase

    NASA Astrophysics Data System (ADS)

    Jabbar, Abdul; Mumtaz, Muhammad; Nadeem, Kashif

    2015-03-01

    Low anisotropic (Cu0.5Tl0.5) Ba2Ca2Cu3O10 - δ (CuTl-1223) high temperature superconducting phase was synthesized by solid-state reaction, silver (Ag) nanoparticles were prepared by sol-gel method and gold (Au) nanoparticles were extracted from colloidal solution. We added Ag and Au nanoparticles in CuTl-1223 matrix separately with same concentration during the final sintering process to get (M)x/CuTl-1223; M = Ag nanoparticles or Au nanoparticles (x = 0 and 1.0 wt.%) nano-superconductor composites. We investigated and compared the effects of these noble metals nanoparticles addition on structural, morphological and superconducting transport properties of CuTl-1223 phase. The crystal structure of the host CuTl-1223 superconducting phase was not affected significantly after the addition of these nanoparticles. The enhancement of superconducting properties was observed after the addition of both Ag and Au nanoparticles, which is most probably due to improved inter-grains weak-links and reduction of defects such as oxygen deficiencies, etc. The reduction of normal state room temperature resistivity is the finger prints of the reduction of barriers and facilitation to the carriers transport across the inter-crystallite sites due to improved inter-grains weak-links. The greater improvement of superconducting properties in Ag nanoparticles added samples is attributed to the higher conductivity of silver as compared to gold, which also suits for practical applications due to lower cost and easy synthesis of Ag nanoparticles as compared to Au nanoparticles.

  18. Novel superconducting phases of Tl-based compounds

    NASA Technical Reports Server (NTRS)

    Kostadinov, I. Z.; Mateev, M.; Michov, M.; Skumriev, V.; Tsakin, E.

    1991-01-01

    Researchers report the measurements of the I(sub c)(T) of the 102 K phase. They also discuss briefly the composition of the lattice parameters and the ac susceptibility relation to the grain size and microstructure.

  19. Metallic Nonsuperconducting Phase and D -Wave Superconductivity in Zn-Substituted La{sub 1.85}Sr{sub 0.15}CuO{sub 4}

    SciTech Connect

    Karpinska, K.; Cieplak, Marta Z.; Guha, S.; Malinowski, A.; Skoskiewicz, T.; Plesiewicz, W.; Berkowski, M.; Boyce, B.; Lemberger, Thomas R.; Lindenfeld, P.

    2000-01-03

    Measurements of the resistivity, magnetoresistance, and penetration depth were made on films of La{sub 1.85} Sr{sub 0.15} CuO{sub 4} , with up to 12 at. % of Zn substituted for the Cu. The results show that the quadratic temperature dependence of the inverse square of the penetration depth, indicative of d -wave superconductivity, is not affected by doping. The suppression of superconductivity leads to a metallic nonsuperconducting phase, as expected for a pairing mechanism related to spin fluctuations. The metal-insulator transition occurs in the vicinity of k{sub F}l{approx_equal}1 , and appears to be disorder driven, with the carrier concentration unaffected by doping. (c) 1999 The American Physical Society.

  20. Phenomenological theory of the superconducting state inside the hidden-order phase of URu2Si2

    NASA Astrophysics Data System (ADS)

    Kang, Jian; Fernandes, Rafael M.

    2015-08-01

    Recent experiments have unveiled important properties of the ground state of the elusive heavy fermion URu2Si2 . While tetragonal symmetry-breaking was reported below the hidden-order (HO) transition at THO≈17.5 K , time-reversal symmetry breaking was observed below the superconducting transition temperature Tcsuperconducting state, such an order parameter is incompatible with broken tetragonal symmetry. Here, we employ a phenomenological model to investigate the properties of a chiral superconducting state that develops inside the hidden-order phase. In this case, there are actually two superconducting transition temperatures: while Tc marks a normal-state to superconducting transition, Tc*superconducting-to-superconducting transition in which time-reversal symmetry is broken. In the phase Tc*superconducting transition, this mode becomes soft near a superconducting-to-superconducting transition, which in principle allows for its detection by Raman spectroscopy. Finally, we investigate the impact of twin domains on the anisotropic properties of the superconducting state, and propose experiments in mechanically strained samples to explore the interplay between hidden order and superconductivity in URu2Si2 .

  1. Superconducting magnets for induction linac phase rotation in a neutrino factory

    NASA Astrophysics Data System (ADS)

    Green, M. A.; Yu, S.

    2002-05-01

    The neutrino factory [1-3] consists of a target section where pions are produced and captured in a solenoidal magnetic field. Pions in a range of energies from 100 Mev to 400 MeV decay into muons in an 18-meter long channel of 1.25 T superconducting solenoids. The warm bore diameter of these solenoids is about 600 mm. The phase rotation section slows down the high-energy muon and speeds up the low energy muons to an average momentum of 200 MeV/c. The phase-rotation channel consists of three induction linac channels with a short cooling section and a magnetic flux reversal section between the first and second induction linacs and a drift space between the second and third induction linacs. The length of the phase rotation channel will be about 320 meters. The superconducting coils in the channel are 0.36 m long with a gap of 0.14 m between the coils. The magnetic induction within the channel will be 1.25 T. For 260 meters of the 320-meter long channel, the solenoids are inside the induction linac. This paper discusses the design parameters for the superconducting solenoids in the neutrino factory phase-rotation channel.

  2. Superconductivity in the T2 phase of the Ta-Ge-B system

    NASA Astrophysics Data System (ADS)

    Correa, Lucas Eduardo; Nunes, Carlos; Coelho, Gilberto; Silva, Antonio Augusto; Fisk, Zack; Jefferson Machado, Antonio

    2012-02-01

    In the Ta-Ge system the αTa5Ge3 phase is not superconductor. Considering the high solubility of this phase for boron, in this work it has been evaluated the effect of boron doping in αTa5Ge3 on the electrical, heat capacity and magnetic properties of the produced materials. It has been shown that boron doping promoted superconductivity for some specific composition. The Ta5GeB2, also named T2 phase, crystallizes in the tetragonal symmetry with Cr5B3 prototype structure. In this composition the sample presented the maximum superconducting critical temperature (3.4 K). Others systems that exhibit the existence of the T2 phase present superconductivity such as Mo5SiB2 (Tc ˜5.5 K), Nb5Si3-xBx (Tcmax ˜7.8 K) and W5SiB2 (Tc ˜5.5 K). Thus, Ta5GeB2 is more one example.

  3. Ligand-Driven Phase Separation in Binary Particle Brush Materials

    NASA Astrophysics Data System (ADS)

    Bockstaller, Michael; Schmitt, Michael; Zhang, Jianan; Yan, Jiajun; Matyjaszewski, Krzysztof

    The tethering of polymer chains to the surface of nanoparticles (to form so-called `particle brush materials') has emerged as an effective means to enable the bottom-up assembly of one-component hybrid materials with controlled microstructure and improved mechanical stability as well as novel optical or acoustic properties. The polymer-like interactions and response of these particle-brush materials suggest intriguing new opportunities to control structure formation in multicomponent particle mixtures. This contribution will demonstrate that polymer-ligand interactions can drive phase separation processes in mixed particle systems that share analogies to those of regular binary polymer blends. The role of particle size, density and degree of polymerization of tethered chains as well as the interaction parameter between the distinct tethered chains on the mechanism and kinetics of phase separation processes in mixed particle brush systems will be discussed. Ligand-driven phase separation will be shown to enable the efficient fabrication of monochromatic domain structured in mixed quantum dot systems that might find application in next generation quantum dot-enabled LEDs. Support by the National Science Foundation (via Grant DMR-1410845) is gratefully acknowledged.

  4. Strong vacuum squeezing from bichromatically driven Kerrlike cavities: from optomechanics to superconducting circuits

    PubMed Central

    Garcés, Rafael; de Valcárcel, Germán J.

    2016-01-01

    Squeezed light, displaying less fluctuation than vacuum in some observable, is key in the flourishing field of quantum technologies. Optical or microwave cavities containing a Kerr nonlinearity are known to potentially yield large levels of squeezing, which have been recently observed in optomechanics and nonlinear superconducting circuit platforms. Such Kerr-cavity squeezing however suffers from two fundamental drawbacks. First, optimal squeezing requires working close to turning points of a bistable cycle, which are highly unstable against noise thus rendering optimal squeezing inaccessible. Second, the light field has a macroscopic coherent component corresponding to the pump, making it less versatile than the so-called squeezed vacuum, characterised by a null mean field. Here we prove analytically and numerically that the bichromatic pumping of optomechanical and superconducting circuit cavities removes both limitations. This finding should boost the development of a new generation of robust vacuum squeezers in the microwave and optical domains with current technology. PMID:26916946

  5. Current-phase relationship, thermal and quantum phase slips in superconducting nanowires made on a scaffold created using adhesive tape.

    PubMed

    Bae, Myung-Ho; Dinsmore, Robert C; Aref, Thomas; Brenner, Matthew; Bezryadin, Alexey

    2009-05-01

    Quantum phase slippage (QPS) in a superconducting nanowire is a new candidate for developing a quantum bit [Mooij et al. New J. Phys. 2005, 7, 219; Mooij et al. Nat. Phys. 2006, 2, 169; Khlebnikov http://arxiv.org/abs/quant-ph/0210019 2007]. It has also been theoretically predicted that the occurrence of QPS significantly changes the current-phase relationship (CPR) of the wire due to the tunneling between topologically different metastable states [Khlebnikov Phys. Rev. B 2008, 78, 014512]. We present studies on the microwave response of the superconducting nanowires to reveal their CPRs. First, we demonstrate a simple nanowire fabrication technique, based on commercially available adhesive tapes, which allows making thin superconducting wire from different metals. We compare the resistance vs temperature curves of Mo(76)Ge(24) and Al nanowires to the classical and quantum models of phase slips. In order to describe the experimentally observed microwave responses of these nanowires, we use the McCumber-Stewart model [McCumber J. Appl. Phys. 1968, 39, 3113; Stewart Appl. Phys. Lett. 1968, 12, 277], which is generalized to include either classical or quantum CPR. PMID:19344118

  6. Ostwald-Driven Phase Separation in Bimetallic Nanoparticle Assemblies.

    PubMed

    Prévot, Geoffroy; Nguyen, Nhat Tai; Alloyeau, Damien; Ricolleau, Christian; Nelayah, Jaysen

    2016-04-26

    The compositional stability of bimetallic nanoparticles (NPs) is crucial for many applications. We have studied the coarsening of amorphous carbon-supported Au-Pd NPs during annealing at 873 K. Using scanning transmission electron microscopy and energy-dispersive spectroscopy measurements, we show that, despite a complete miscibility of the two metals, the particle assembly undergoes a phase separation during annealing, which leads to two distinct populations: Au-rich NPs with a mean radius of 3.5 nm and large Pd-rich NPs with a mean radius of 25 nm. Thermodynamic calculations and kinetic Monte Carlo simulations explain this behavior that is driven by the competition between surface and mixing energy and by the different mobilities of the two atomic species. PMID:26989906

  7. Topological superconducting phases from inversion symmetry breaking order in spin-orbit-coupled systems

    NASA Astrophysics Data System (ADS)

    Wang, Yuxuan; Cho, Gil Young; Hughes, Taylor L.; Fradkin, Eduardo

    2016-04-01

    We analyze the superconducting instabilities in the vicinity of the quantum-critical point of an inversion symmetry breaking order. We first show that the fluctuations of the inversion symmetry breaking order lead to two degenerate superconducting (SC) instabilities, one in the s -wave channel, and the other in a time-reversal invariant odd-parity pairing channel (the simplest case being the same as the of 3He-B phase). Remarkably, we find that unlike many well-known examples, the selection of the pairing symmetry of the condensate is independent of the momentum-space structure of the collective mode that mediates the pairing interaction. We found that this degeneracy is a result of the existence of a conserved fermionic helicity χ , and the two degenerate channels correspond to even and odd combinations of SC order parameters with χ =±1 . As a result, the system has an enlarged symmetry U (1 ) ×U (1 ) , with each U (1 ) corresponding to one value of the helicity χ . Because of the enlarged symmetry, this system admits exotic topological defects such as a fractional quantum vortex, which we show has a Majorana zero mode bound at its core. We discuss how the enlarged symmetry can be lifted by small perturbations, such as the Coulomb interaction or Fermi surface splitting in the presence of broken inversion symmetry, and we show that the resulting superconducting state can be topological or trivial depending on parameters. The U (1 ) ×U (1 ) symmetry is restored at the phase boundary between the topological and trivial SC states, and allows for a transition between topologically distinct SC phases without the vanishing of the order parameter. We present a global phase diagram of the superconducting states and discuss possible experimental implications.

  8. Planned High-gradient Flat-beam-driven Dielectric Wakefield Experiments at the Fermilab’s Advanced Superconducting Test Accelerator

    SciTech Connect

    Lemery, Francois; Mihalcea, Daniel; Piot, Philippe; Zhu, Jun

    2014-07-01

    In beam driven dielectric wakefield acceleration (DWA), high-gradient short-wavelength accelerating fields are generally achieved by employing dielectric-lined waveguides (DLWs)  with small aperture which constraints the beam sizes. In this paper we investigate the possibility of using a low-energy (50-MeV) flat beams to induce high-gradient wakes in a slab-symmetric DLW. We demonstrate via numerical simulations the possibility to produce axial electric field with peak amplitude close to 0.5 GV/m. Our studies are carried out using the Fermilab's Advanced Superconducting Test Accelerator (ASTA) photoinjector beamline. We finally discuss a possible experiment that could be performed in the ASTA photoinjector and eventually at higher energies.  

  9. Stripe-like nanoscale structural phase separation in superconducting BaPb1-xBixO3

    DOE PAGESBeta

    Giraldo-Gallo, P.; Zhang, Y.; Parra, C.; Manoharan, H. C.; Beasley, M. R.; Geballe, T. H.; Kramer, M. J.; Fisher, I. R.

    2015-09-16

    The phase diagram of BaPb1-xBixO3 exhibits a superconducting “dome” in the proximity of a charge density wave phase. For the superconducting compositions, the material coexists as two structural polymorphs. Here we show, via high resolution transmission electron microscopy, that the structural dimorphism is accommodated in the form of partially disordered nanoscale stripes. Identification of the morphology of the nanoscale structural phase separation enables determination of the associated length scales, which we compare to the Ginzburg-Landau coherence length. Thus, we find that the maximum Tc occurs when the superconducting coherence length matches the width of the partially disordered stripes, implying amore » connection between the structural phase separation and the shape of the superconducting dome.« less

  10. Stripe-like nanoscale structural phase separation in superconducting BaPb1−xBixO3

    PubMed Central

    Giraldo-Gallo, P.; Zhang, Y.; Parra, C.; Manoharan, H.C.; Beasley, M.R.; Geballe, T.H.; Kramer, M.J.; Fisher, I.R.

    2015-01-01

    The phase diagram of BaPb1−xBixO3 exhibits a superconducting dome in the proximity of a charge density wave phase. For the superconducting compositions, the material coexists as two structural polymorphs. Here we show, via high-resolution transmission electron microscopy, that the structural dimorphism is accommodated in the form of partially disordered nanoscale stripes. Identification of the morphology of the nanoscale structural phase separation enables determination of the associated length scales, which we compare with the Ginzburg–Landau coherence length. We find that the maximum Tc occurs when the superconducting coherence length matches the width of the partially disordered stripes, implying a connection between the structural phase separation and the shape of the superconducting dome. PMID:26373890

  11. The research of parallel-coupled linear-phase superconducting filter

    NASA Astrophysics Data System (ADS)

    Zhang, Tianliang; Zhou, Liguo; Yang, Kai; Luo, Chao; Jiang, Mingyan; Dang, Wei; Ren, Xiangyang

    2015-12-01

    This paper presents a research on the mechanism of a linear phase filter constructed with parallel-connected sub-networks, considering that linear phase characteristic of a filter can be achieved when the group delays of sub-networks compensate each other. This paper also gives several coupling and routing diagrams of linear phase filters with different parallel-connected networks, and then the coupling matrixes of three 8-order filters and one 10-order filter are synthesized. One of the coupling matrixes is utilized to design a 8-order parallel-connected network high temperature superconducting (HTS) linear phase filter with two pairs of transmission zeros, so as to verify the correctness of theory data and the feasibility of the circuit design for the proposed 8-order and higher order parallel-connected network linear phase filter. The HTS linear phase filter is designed on YBCO/LaAlO3/YBCO superconducting substrate, at 77 K, the measured center frequency is 2000 MHz with a bandwidth of 30 MHz, the insertion loss is less than 0.3 dB and the reflection is better than -12.5 dB in passband. The group delay is less than ±5 ns over the 60% passband, which shows that the filter has a good linear phase characteristic.

  12. Multiple quantum phase transitions and superconductivity in Ce-based heavy fermions.

    PubMed

    Weng, Z F; Smidman, M; Jiao, L; Lu, Xin; Yuan, H Q

    2016-09-01

    Heavy fermions have served as prototype examples of strongly-correlated electron systems. The occurrence of unconventional superconductivity in close proximity to the electronic instabilities associated with various degrees of freedom points to an intricate relationship between superconductivity and other electronic states, which is unique but also shares some common features with high temperature superconductivity. The magnetic order in heavy fermion compounds can be continuously suppressed by tuning external parameters to a quantum critical point, and the role of quantum criticality in determining the properties of heavy fermion systems is an important unresolved issue. Here we review the recent progress of studies on Ce based heavy fermion superconductors, with an emphasis on the superconductivity emerging on the edge of magnetic and charge instabilities as well as the quantum phase transitions which occur by tuning different parameters, such as pressure, magnetic field and doping. We discuss systems where multiple quantum critical points occur and whether they can be classified in a unified manner, in particular in terms of the evolution of the Fermi surface topology. PMID:27533524

  13. Multiple quantum phase transitions and superconductivity in Ce-based heavy fermions

    NASA Astrophysics Data System (ADS)

    Weng, Z. F.; Smidman, M.; Jiao, L.; Lu, Xin; Yuan, H. Q.

    2016-09-01

    Heavy fermions have served as prototype examples of strongly-correlated electron systems. The occurrence of unconventional superconductivity in close proximity to the electronic instabilities associated with various degrees of freedom points to an intricate relationship between superconductivity and other electronic states, which is unique but also shares some common features with high temperature superconductivity. The magnetic order in heavy fermion compounds can be continuously suppressed by tuning external parameters to a quantum critical point, and the role of quantum criticality in determining the properties of heavy fermion systems is an important unresolved issue. Here we review the recent progress of studies on Ce based heavy fermion superconductors, with an emphasis on the superconductivity emerging on the edge of magnetic and charge instabilities as well as the quantum phase transitions which occur by tuning different parameters, such as pressure, magnetic field and doping. We discuss systems where multiple quantum critical points occur and whether they can be classified in a unified manner, in particular in terms of the evolution of the Fermi surface topology.

  14. Microstructural magnetic phases in superconducting FeTe0.65Se0.35

    NASA Astrophysics Data System (ADS)

    Wittlin, A.; Aleshkevych, P.; Przybylińska, H.; Gawryluk, D. J.; Dłużewski, P.; Berkowski, M.; Puźniak, R.; Gutowska, M. U.; Wiśniewski, A.

    2012-06-01

    In this paper, we address a number of outstanding issues concerning the nature and the role of magnetic inhomogeneities in the iron chalcogenide system FeTe1-xSex and their correlation with superconductivity in this system. We report morphology of superconducting single crystals of FeTe0.65Se0.35 studied with transmission electron microscopy, high-angle annular dark-field scanning transmission electron microscopy and their magnetic and superconducting properties characterized with magnetization, specific heat and magnetic resonance spectroscopy. Our data demonstrate the presence of nanoscale hexagonal regions coexisting with a tetragonal host lattice, a chemical disorder demonstrating a nonhomogeneous distribution of host atoms in the crystal lattice, as well as iron-deficient bands hundreds of nanometres in length. From the magnetic data and ferromagnetic resonance temperature dependence, we attribute magnetic phases in Fe-Te-Se to Fe3O4 inclusions and to hexagonal symmetry nanoscale regions with a structure of the Fe7Se8 type. Our results suggest that a nonhomogeneous distribution of host atoms might be an intrinsic feature of superconducting Fe-Te-Se chalcogenides and we find a surprising correlation indicating that a faster grown crystal of inferior crystallographic properties is a better superconductor.

  15. Geometric phases and quantum correlations of superconducting two-qubit system with dissipative effect

    NASA Astrophysics Data System (ADS)

    Xue, Liyuan; Yu, Yanxia; Cai, Xiaoya; Pan, Hui; Wang, Zisheng

    2016-01-01

    We investigate time-dependent Pancharatnam phases and the relations between such geometric phases and quantum correlations, i.e., quantum discord and concurrence, of superconducting two-qubit coupling system in dissipative environment with the mixture effects of four different eigenstates of density matrix. We find that the time-dependent Pancharatnam phases not only keep the motion memory of such a two-qubit system, but also include the information of quantum correlations. We show that the sudden died and alive phenomena of quantum entanglement are intrinsic in the transition of Pancharatnam phase in the X-state and the complex oscillations of Pancharatnam phase in the Y-state. The faster the Pancharatnam phases change, the slower the quantum correlations decay. In particular, we find that a subspace of quantum entanglement can exist in the Y-state by choosing suitable coupling parameters between two-qubit system and its environment, or initial conditions.

  16. Electrostatically Driven Granular Media: Phase Transitions, Patterns and Vortices

    NASA Astrophysics Data System (ADS)

    Aranson, Igor

    2003-03-01

    Large ensembles of small particles display fascinating collective behavior when they acquire an electric charge and respond to competing long-range electromagnetic and short-range contact forces. Many industrial technologies face the challenge of assembling and separating such single- or multi-component micro and nano- size ensembles. The dynamics of conducting microparticles in strong electric field in the air or in deep vacuum was studied in Refs. [1,2]. Phase transitions and clustering instability of the electrostatically driven granular gas were found. A continuum model for the phase separation and coarsening in was formulated in terms of a Ginzburg-Landau equation subject to conservation of the total number of grains. In the regime of well-developed clusters, the continuum model is used to derive "sharp-interface" equations that govern the dynamics of the interphase boundary. The situation is remarkably different when the cell is filled with poorly conducting liquid (toluene-ethanol mixute). We have found that metallic particles form a rich variety of phases not observed in the air-filled cell. These phases include static precipitates: honeycombs lattices and Wigner crystals; and novel dynamic condensates: toroidal vortices and pulsating rings. The observed phenomena are attributed to interaction between particles and electro-hydrodynamic flows produced by the action of the electric field on ionic charges in the bulk of liquid. 1. I.S. Aranson, D. Blair, V.A. Kalatsky, G.W. Crabtree, W.-K. Kwok, V.M. Vinokur, and U.Welp, Phys. Rev. Lett. 84, 3306 (2000) 2. I.S. Aranson, B. Meerson, P.V. Sasorov, and V.M. Vinokur, Phys. Rev. Lett. 88, 204301 (2002)

  17. First-Order 0-π Quantum Phase Transition in the Kondo Regime of a Superconducting Carbon-Nanotube Quantum Dot

    NASA Astrophysics Data System (ADS)

    Maurand, Romain; Meng, Tobias; Bonet, Edgar; Florens, Serge; Marty, Laëtitia; Wernsdorfer, Wolfgang

    2012-01-01

    We study a carbon-nanotube quantum dot embedded in a superconducting-quantum-interference-device loop in order to investigate the competition of strong electron correlations with a proximity effect. Depending on whether local pairing or local magnetism prevails, a superconducting quantum dot will exhibit a positive or a negative supercurrent, referred to as a 0 or π Josephson junction, respectively. In the regime of a strong Coulomb blockade, the 0-to-π transition is typically controlled by a change in the discrete charge state of the dot, from even to odd. In contrast, at a larger tunneling amplitude, the Kondo effect develops for an odd-charge (magnetic) dot in the normal state, and quenches magnetism. In this situation, we find that a first-order 0-to-π quantum phase transition can be triggered at a fixed valence when superconductivity is brought in, due to the competition of the superconducting gap and the Kondo temperature. The superconducting-quantum-interference-device geometry together with the tunability of our device allows the exploration of the associated phase diagram predicted by recent theories. We also report on the observation of anharmonic behavior of the current-phase relation in the transition regime, which we associate with the two accessible superconducting states. Our results finally demonstrate that the spin-singlet nature of the Kondo state helps to enhance the stability of the 0 phase far from the mixed-valence regime in odd-charge superconducting quantum dots.

  18. Superconducting extended objects and applications to the phase structure of quantum chromodynamics

    NASA Astrophysics Data System (ADS)

    Skagerstam, B.-S.; Stern, A.

    1982-03-01

    In a previous work the dynamics of relativistic extended objects (i.e., strings, shells, etc.) coupled to Abelian or non-Abelian gauge fields was developed. The extended objects possessed an electriclike current which was defined in the associated Lie algebra of the gauge group under consideration. In the present paper, the interaction between the extended objects and gauge fields is slightly modified so that the objects behave like superconductors. By this we mean (a) the electrical conductivity is infinite and (b) for objects other than strings, a magnetic shielding or Meissner effect (with zero penetration depth) is present. Both (a) and (b) are features which occur in the classical description of the system. We also develop the dynamics for a system which is dual to the one described above. That is, instead of possessing an electric current, the objects here carry a magnetic current (Abelian or non-Abelian). Furthermore, the magnetic conductivity is infinite, and for objects other than strings an electric shielding or "dual" Meissner effect is present. The systems developed here contain Dirac's extended electron model and the MIT bag model as special cases. The former coincides with the description of an electrically charged shell. In the latter, we verify that the dynamics of a cavity within a (magnetic) superconducting vacuum is identical to that of a glueball in the MIT bag. This agrees with the view that the true quantum-chromodynamic (QCD) vacuum may be in a magnetic superconducting phase, and that the "dual" Meissner effect may be relevant for the confinement question. We also examine the possibility of the QCD vacuum being in an electric (or conventional) superconducting phase and a mixed superconducting phase, and comment on the confinement question for these two cases.

  19. Topological excitations and the phase diagram of the superconducting cuprates

    NASA Astrophysics Data System (ADS)

    Marino, Eduardo C.; Silva Neto, Marcello B.

    2002-03-01

    We study the destruction of long-range antiferromagnetic order in the high-Tc superconductors La2-xSrxCuO4 and YBa2Cu3O6+x, within the framework of the CP1-nonlinear sigma model coupled to Dirac fermions that describe the doped holes. Skyrmion topological defects are shown to be introduced by doping and their energy is used as an order parameter for the antiferromagnetic state. We obtain analytic expressions for the skyrmion energy as a function of doping which allow us to plot the curves TN(xc)×xc and M(x)×x, for the two compounds, in good quantitative agreement with the experimental data. We also discuss stripes formation and analyse its effects on the curves of the phase diagram.

  20. Experimental magnetization evidence for two superconducting phases in Bi bicrystals with large crystallite disorientation angles

    SciTech Connect

    Muntyanu, F. M.; Gilewski, A.; Nenkov, K.; Warchulska, J.; Zaleski, A. J.

    2006-04-01

    Magnetization measurements prove that the magnetic properties of large-angle ({theta}>30 deg. ) bismuth bicrystals with a crystallite interface (CI) of twisting types essentially differ from well-known results on single-crystalline specimens. Two superconducting phases with T{sub c}{approx}8.4 K and {approx}4.3 K were observed at the CI of bicrystals while ordinary rhombohedral Bi is not a superconductor. We conclude that these phases have to do with the central part and the adjacent layers of the CI of bicrystals.

  1. Geometric Phases, Noise and Non-adiabatic Effects in Multi-level Superconducting Systems

    NASA Astrophysics Data System (ADS)

    Berger, S.; Pechal, M.; Abdumalikov, A. A.; Steffen, L.; Fedorov, A.; Wallraff, A.; Filipp, S.

    2012-02-01

    Geometric phases depend neither on time nor on energy, but only on the trajectory of the quantum system in state space. In previous studies [1], we have observed them in a Cooper pair box qubit, a system with large anharmonicity. We now make use of a superconducting transmon-type qubit with low anharmonicity to study geometric phases in a multi-level system. We measure the contribution of the second excited state to the geometric phase and find very good agreement with theory treating higher levels perturbatively. Furthermore, we quantify non-adiabatic corrections by decreasing the manipulation time in order to optimize our geometric gate. Geometric phases have also been shown to be resilient against adiabatic field fluctuations [2]. Here, we analyze the effect of artificially added noise on the geometric phase for different system trajectories. [1] P. J. Leek et al., Science 318, 1889 (2007) [2] S. Filipp et al., Phys. Rev. Lett. 102, 030404 (2009)

  2. Decoupling of the superconducting and magnetic/structural phase transitions in electron-doped BaFe2As2

    SciTech Connect

    Canfield, P.C.; Bud'ko, S.L.; Ni, Ni; Yan, J.Q.; Kracher, A.

    2009-08-03

    Study and comparison of over 30 examples of electron-doped BaFe{sub 2}As{sub 2} for transition metal (TM) = Co, Ni, Cu, and (Co/Cu mixtures) have led to an understanding that the suppression of the structural/antiferromagnetic phase transition to low-enough temperature in these compounds is a necessary condition for superconductivity but not a sufficient one. Whereas the structural/antiferromagnetic transitions are suppressed by the number of TM dopant ions (or changes in the c axis) the superconducting dome exists over a limited range of values of the number of valence electrons added by doping (or values of the a/c ratio). By choosing which combination of dopants is used we can change the relative positions of the upper phase lines and the superconducting dome, even to the extreme limit of suppressing the upper structural and magnetic phase transitions without the stabilization of a lower-temperature superconducting dome.

  3. Enhancement of superconductivity under pressure and the magnetic phase diagram of tantalum disulfide single crystals

    PubMed Central

    Abdel-Hafiez, M.; Zhao, X.-M.; Kordyuk, A. A.; Fang, Y.-W.; Pan, B.; He, Z.; Duan, C.-G.; Zhao, J.; Chen, X.-J.

    2016-01-01

    In low-dimensional electron systems, charge density waves (CDW) and superconductivity are two of the most fundamental collective quantum phenomena. For all known quasi-two-dimensional superconductors, the origin and exact boundary of the electronic orderings and superconductivity are still attractive problems. Through transport and thermodynamic measurements, we report on the field-temperature phase diagram in 2H-TaS2 single crystals. We show that the superconducting transition temperature (Tc) increases by one order of magnitude from temperatures at 0.98 K up to 9.15 K at 8.7 GPa when the Tc becomes very sharp. Additionally, the effects of 8.7 GPa illustrate a suppression of the CDW ground state, with critically small Fermi surfaces. Below the Tc the lattice of magnetic flux lines melts from a solid-like state to a broad vortex liquid phase region. Our measurements indicate an unconventional s-wave-like picture with two energy gaps evidencing its multi-band nature. PMID:27534898

  4. Enhancement of superconductivity under pressure and the magnetic phase diagram of tantalum disulfide single crystals.

    PubMed

    Abdel-Hafiez, M; Zhao, X-M; Kordyuk, A A; Fang, Y-W; Pan, B; He, Z; Duan, C-G; Zhao, J; Chen, X-J

    2016-01-01

    In low-dimensional electron systems, charge density waves (CDW) and superconductivity are two of the most fundamental collective quantum phenomena. For all known quasi-two-dimensional superconductors, the origin and exact boundary of the electronic orderings and superconductivity are still attractive problems. Through transport and thermodynamic measurements, we report on the field-temperature phase diagram in 2H-TaS2 single crystals. We show that the superconducting transition temperature (Tc) increases by one order of magnitude from temperatures at 0.98 K up to 9.15 K at 8.7 GPa when the Tc becomes very sharp. Additionally, the effects of 8.7 GPa illustrate a suppression of the CDW ground state, with critically small Fermi surfaces. Below the Tc the lattice of magnetic flux lines melts from a solid-like state to a broad vortex liquid phase region. Our measurements indicate an unconventional s-wave-like picture with two energy gaps evidencing its multi-band nature. PMID:27534898

  5. Superconducting Meissner effect bearings for cryogenic turbomachines, phase 2

    NASA Astrophysics Data System (ADS)

    Valenzuela, Javier A.; Martin, Jerry L.

    1994-02-01

    This is the final report of a Phase 2 SBIR project to develop Meissner effect bearings for miniature cryogenic turbomachines. The bearing system was designed for use in miniature cryogenic turboexpanders in reverse-Brayton-cycle cryocoolers. The cryocoolers are designed to cool sensors on satellites. Existing gas bearings for this application run in a relatively warm state. The heat loss from the bearings into the shaft and into the cold process gas imposes a penalty on the cycle efficiency. By using cold Meissner effect bearings, this heat loss could be minimized, and the input power per unit of cooling for these cryocoolers could be reduced. Two bearing concepts were explored in this project. The first used an all-magnetic passive radial suspension to position the shaft over a range of temperatures from room temperature to 77 K. This bearing concept was proven to be feasible, but impractical for the miniature high-speed turbine application since it lacked the required shaft positioning accuracy. A second bearing concept was then developed. In this concept, the Meissner effect bearings are combined with self-acting gas bearings. The Meissner effect bearing provides the additional stiffness and damping required to stabilize the shaft at low temperature, while the gas bearing provides the necessary accuracy to allow very small turbine tip clearances (5mm) and high speeds (greater than 500,000 rpm).

  6. Optimal Control of Quantum Measurement for Superconducting Phase Qubits

    NASA Astrophysics Data System (ADS)

    Wilhelm, Frank; Egger, Daniel

    2015-03-01

    Pulses to steer the time evolution of quantum systems can be designed with optimal control theory. In most cases it is the coherent processes that can be controlled and one optimizes the time evolution towards a target unitary process, sometimes also in the presence of non-controllable incoherent processes. Here we show how to extend the GRAPE algorithm in the case where the incoherent processes are controllable and the target time evolution is a non-unitary quantum channel. We perform a gradient search on a fidelity measure based on Choi matrices. We illustrate our algorithm by optimizing a phase qubit measurement pulse. We show how this technique can lead to large measurement contrast close to 99%. We also show, within the validity of our model, that this algorithm can produce short 1.4 ns pulses with 98.2% contrast. Work posted at arXiv:1408.6086, in press at Physical Review A Supported by the EU through SCALEQIT.

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  8. Interplay between quantum confinement and Fulde-Ferrell-Larkin-Ovchinnikov phase in superconducting nanofilms

    NASA Astrophysics Data System (ADS)

    Wójcik, P.; Zegrodnik, M.

    2016-09-01

    In superconducting nanofilms the energy quantization induced by the confinement in the direction perpendicular to the film splits the band of single-electron states into series of subbands. The quantum size effect leads to the experimentally observed oscillations of the critical magnetic field with increasing nanofilm thickness. Here, we study the influence of the quantum confinement on the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase in superconducting nanofilms. We show that the range of the magnetic fields for which the FFLO phase is stable oscillates as a function of the film thickness with the phase shift equal to one half of the period corresponding to the critical magnetic field oscillations. Due to the multiband character of the system a division of the FFLO phase stability region appears leading to a phase diagram which is qualitatively different than the one corresponding to a single-band situation. The number of subregions created in such manner depends on the number of bands participating in the formation of the paired state.

  9. Nonlinear instabilities driven by coherent phase-space structures

    NASA Astrophysics Data System (ADS)

    Lesur, Maxime

    2012-10-01

    Coherent phase-space (PS) structures are an important feature of plasma turbulence. They can drive nonlinear instabilities [1], intermittency in drift-wave turbulence [2], and transport [3]. We aim at a comprehensive understanding of turbulence, not just as an ensemble of waves, as quasilinear theory implies, but as a mixture of coupled waves and localized structures. This work, which focuses on isolated PS structures, is a fundamental advance in this direction. We analyze the effects of self-binding negative fluctuations (PS holes) on stability, intermittency and anomalous resistivity, both analytically and numerically. We present a new theory which describes the growth of a hole or clump [4]. We find that PS holes grow nonlinearly, independently of linear stability. Numerical simulations clarify the physics of nonlinear instabilities in both subcritical and supercritical conditions. When many resonances are unstable, several holes can coalesce into one main macro-scale structure, which survives much longer than a quasilinear diffusion time, suggesting that it may be crucial to resolve phase-space turbulence in analytical and numerical studies of transport. These findings are applied to two fundamental paradigms of plasma physics: bump-on-tail instabilities in 1D electronic plasma and current-driven ion-acoustic instabilities electron-ion plasma. Our results expose important limits of routinely-used linear and quasilinear theories.[4pt] [1] T.H. Dupree, Phys. Fluids 15, 334 (1972); R.H. Berman et al., Phys. Rev. Lett. 48, 1249 (1982).[0pt] [2] P.W. Terry, P.H. Diamond, and T.S. Hahm, Phys. Fluids B 2, 2048 (1990).[0pt] [3] H. Biglari et al., Phys. Fluids 31, 2644 (1988); Y. Kosuga et al., Phys. Plasmas 18, 122305 (2011).[0pt] [4] M. Lesur, P.H. Diamond, submitted to Phys. Rev. Lett.

  10. Phase Relations and Defect Chemistry of Bismuth Strontium Calcium Copper Oxide Superconducting Oxides at Elevated Temperature

    NASA Astrophysics Data System (ADS)

    Hong, Byungsun

    1992-01-01

    Subsolidus phase relations in the system (Bi-Sr -Ca-Cu)-O at 800^circC were investigated via powder X-ray diffraction and electron probe microanalysis of solid-state reaction products. The only truly quaternary compound detected is the superconducting phase of n = 2 in Bi_2(Sr _{rm x}Ca_ {rm 1-x})_{ rm n+1}Cu_{rm n}O_{rm y} . The n = 2 phase is compatible with eight different binary or ternary phases. Tie lines, tie triangles, and compatibility tetrahedra involving superconducting phases were determined. The cation solubility limits of the n = 2 and n = 3 superconducting phases were established along tie lines with compatible phases via EPMA on bi- (or poly -) phasic samples prepared at 860^circ C. In each case football-shaped volumes in composition space were established as the solubility limits which bordered on the nominal compositions 2212 or 2223 with the long axis parallel to the Sr-Ca side of the quaternary but also extending toward Bi and Cu. T_{rm c} variations could be correlated with variations in Sr or (Bi+Sr) content and the length of the c-axis parameter. Via in-situ high temperature (550-650 ^circC) electrical conductivity and Seebeck coefficient measurements in Bi_ {2.1}Sr_{1.9} (Ca_{rm 1-x}Y _{rm x})Cu _2O_{rm y} , a point defect model/diagram is presented which explains the variation of thermopower with composition in the system. The reference, insulating composition should be between Bi_{2.1}Sr _{1.9}Ca_ {0.2}Y_{0.8} Cu_2O_{8.45 } and Bi_{2.1}Sr _{1.9}Ca_ {0.3}Y_{0.7} Cu_2O_{8.4 }. Y-contents higher than x = 0.8 result in a second phase. A structural phase transition from pseudo -tetragonal to orthorhombic takes place at x = 0.5, and plays a major role in determining the physical properties. Oxygen transfer from the Bi-O block to the Cu-O based perovskite block is suggested at the phase boundary of x = 0.5. Jonker analysis and oxygen pressure dependence of carrier concentration confirm p-type behavior despite the change in sign of the thermopower

  11. Renormalization-group investigation of a superconducting U(r)-phase transition using five loops calculations

    NASA Astrophysics Data System (ADS)

    Kalagov, G. A.; Kompaniets, M. V.; Nalimov, M. Yu.

    2016-04-01

    We have studied a Fermi system with attractive U (r)-symmetric interaction at the finite temperatures by the quantum field renormalization group (RG) method. The RG functions have been calculated in the framework of dimensional regularization and minimal subtraction scheme up to five loops. It has been found that for r ≥ 4 the RG flux leaves the system's stability region - the system undergoes a first order phase transition. To estimate the temperature of the transition to superconducting or superfluid phase the RG analysis for composite operators has been performed using three-loops approximation. The result of this analysis shows that for 3D systems estimated phase transition temperature is higher then well known theoretical estimations based on continuous phase transition formalism.

  12. Low temperature phase formation of Tl-based superconducting thin films in reduced oxygen atmosphere

    NASA Technical Reports Server (NTRS)

    Wu, C. Y.; Foong, F.; Liou, S. H.; Ho, J. C.

    1993-01-01

    Tl-Ba-Cu-Cu-O superconducting thin films were prepared by magnetron sputtering with postannealing in a reduced oxygen atmosphere. Single-phase Tl2Ba2Ca2Cu3O(x) can form on the MgO substrate at 800 C under P(O2) about 0.1 atm. However the phase formation temperature can be affected by the starting composition of the film. Tl1Ba2Ca2Cu3O(x) phase can be formed by simply lowering the Tl2O pressure. The thermal stability of Tl1Ba2Ca2Cu3O(x) phase was studied by resistivity measurements at high temperatures.

  13. The Kohn-Luttinger mechanism and phase diagram of the superconducting state in the Shubin-Vonsovsky model

    SciTech Connect

    Kagan, M. Yu.; Val'kov, V. V.; Mitskan, V. A.; Korovuskin, M. M.

    2013-10-15

    Using the Shubin-Vonsovsky model in the weak-coupling regime W > U > V (W is the bandwidth, U is the Hubbard onsite repulsion, and V is the Coulomb interaction at neighboring sites) based on the Kohn-Luttinger mechanism, we determined the regions of the existence of the superconducting phases with the d{sub xy}, p, s, and d{sub x{sup 2}-y{sup 2}} symmetry types of the order parameter. It is shown that the effective interaction in the Cooper channel considerably depends not only on single-site but also on intersite Coulomb correlations. This is demonstrated by the example of the qualitative change and complication of the phase diagram of the superconducting state. The superconducting (SC) phase induction mechanism is determined taking into account polarization contributions in the second-order perturbation theory in the Coulomb interaction. The results obtained for the angular dependence of the superconducting gap in different channels are compared with angule-resolved photoemission spectroscopy (ARPES) results. The influence of long-range hops in the phase diagram and critical superconducting transition temperature in different channels is analyzed. The conditions for the appearance of the Kohn-Luttinger superconductivity with the d{sub x{sup 2}-y{sup 2}} symmetry and high critical temperatures T{sub c} {approx} 100 K near the half-filling are determined.

  14. Phase transitions, metallization, superconductivity and magnetic ordering in dense carbon disulfide and chemical analogs

    NASA Astrophysics Data System (ADS)

    Dias, Liyanagamage Ranganath Prabashwara

    Under high pressure, simple molecular solids transform into non-molecular (extended) solids as compression energies approach those of strong covalent bonds in constituent chemical species, often with advanced mechanical, optical, electronic, and magnetic properties. The primary goal of this research is to investigate the pressure-induced molecular to nonmolecular solids, via discoveries of new states, structures, fundamental properties, and novel phenomena in carbon disulfide and its chemical analogs under extreme conditions of pressure and temperature. Spectral, structural, resistance, and theoretical evidences show simple molecular CS2 undergoes transformations to an insulating black polymer with three-fold carbon atoms at ~9 GPa, to a semiconducting polymer above 30 GPa, and finally to a metallic solid above 50 GPa. The metallic phase is a highly disordered 3D network structure with four-fold carbon atoms. Based on first-principles calculations, we consider two plausible structures for the metallic phase: α-chalcopyrite and tridymite, both exhibiting metallic ground states. Remarkably, low-temperature, dense CS2 not only becomes metallic, but also shows the coexistence of superconductivity and spin-fluctuations. This is the first such observation of superconductivity in simple diamagnetic molecular solids like CS2 at high pressure. The superconductivity in CS2 arises from a highly disordered state at a relatively high transition temperature of ~6.2 K and is, interestingly, preceded by a magnetic ordering transition at ~45.2 K. Based on the x-ray scattering data, we suggest that the local structure changes from tetrahedral to octahedral and the associated spin-fluctuations are responsible for the observed magnetic ordering and superconductivity. A number of related molecular analogs and main group IV disulfides were also studied at high pressure and revealed systematic trends. The above-mentioned findings are important for understanding novel properties of 3D

  15. Transient analysis of superconducting generator under the three phases of sudden grounding fault condition

    NASA Astrophysics Data System (ADS)

    Chun, Yon-Do; Kim, Youn-Hyun; Kim, Sol; Lee, Ju

    2002-08-01

    This paper presents 2-D transient analysis of 30 kV A superconducting AC generator (SCG) using the finite element method (FEM). The compensated 2-D model obtained by lengthening the airgap of the original 2-D model is proposed for the efficient transient analysis. The performance of SCG is analyzed by taking into account the rotation, external circuit equations, and eddy current effect of the damper. The eddy current losses occurring in the dampers are analyzed during the transient state under the three phases of sudden grounding fault condition in the armature. Moving line technique is introduced to carry out the dynamic FEM analysis efficiently without remesh of the total elements.

  16. Development of a fast scintillator based beam phase measurement system for compact superconducting cyclotrons

    SciTech Connect

    Bhattacharjee, Tanushyam; Kanti Dey, Malay; Dhara, Partha; Roy, Suvodeep; Debnath, Jayanta; Balakrishna Bhole, Rajendra; Dutta, Atanu; Pradhan, Jedidiah; Pal, Sarbajit; Pal, Gautam; Roy, Amitava; Chakrabarti, Alok

    2013-05-15

    In an isochronous cyclotron, measurements of central phase of the ion beam with respect to rf and the phase width provide a way to tune the cyclotron for maximum energy gain per turn and efficient extraction. We report here the development of a phase measurement system and the measurements carried out at the Variable Energy Cyclotron Centre's (VECC's) K= 500 superconducting cyclotron. The technique comprises detecting prompt {gamma}-rays resulting from the interaction of cyclotron ion beam with an aluminium target mounted on a radial probe in coincidence with cyclotron rf. An assembly comprising a fast scintillator and a liquid light-guide inserted inside the cyclotron was used to detect the {gamma}-rays and to transfer the light signal outside the cyclotron where a matching photo-multiplier tube was used for light to electrical signal conversion. The typical beam intensity for this measurement was a few times 10{sup 11} pps.

  17. Performance of the Phase 1 superconducting x-ray lithography source (SXLS) at BNL

    SciTech Connect

    Murphy, J.B.; Biscardi, R.; Halama, H.; Heese, R.; Kramer, S.; Nawrocky, R.; Krishnaswamy, J.

    1992-06-01

    The Phase I SXLS electron storage ring has a circumference of 8.5 meters, it uses conventional dipole magnets, B {le} 1.1 T and p = 60 cm, and it is capable of operating in the range of 50--250 MeV. It is the forerunner of the Phase II SXLS ring which will operate at 700 MeV and will make use of superconducting dipoles, B{sub o} = 3.87 Tesla, as a source of {lambda}{sub c} = 10 angstrom x-rays for proximity printing lithography. The Phase I storage ring has been successfully commissioned; stored currents in excess of one ampere have been achieved. A report on the performance of the machine is presented.

  18. Performance of the Phase 1 superconducting x-ray lithography source (SXLS) at BNL

    SciTech Connect

    Murphy, J.B.; Biscardi, R.; Halama, H.; Heese, R.; Kramer, S.; Nawrocky, R. ); Krishnaswamy, J. )

    1992-01-01

    The Phase I SXLS electron storage ring has a circumference of 8.5 meters, it uses conventional dipole magnets, B {le} 1.1 T and p = 60 cm, and it is capable of operating in the range of 50--250 MeV. It is the forerunner of the Phase II SXLS ring which will operate at 700 MeV and will make use of superconducting dipoles, B{sub o} = 3.87 Tesla, as a source of {lambda}{sub c} = 10 angstrom x-rays for proximity printing lithography. The Phase I storage ring has been successfully commissioned; stored currents in excess of one ampere have been achieved. A report on the performance of the machine is presented.

  19. Effect of strain on the martensitic phase transition in superconducting Nb/sub 3/Sn

    SciTech Connect

    Hoard, R.W.; Scanlan, R.M.; Smith, G.S.; Farrell, C.L.

    1980-09-22

    The connection between the cubic-to-tetragonal martensitic phase transformation and the phenomenon of superconductivity in A15 compounds is being investigated. The degradation of the critical parameters, such as T/sub c/, H/sub c2/, and J/sub c/, with mechanical straining is of particular interest. Low-temperature x-ray diffraction experiments are performed on Nb/sub 3/Sn ribbons (with the bronze layers etched off) mounted on copper and indium sample stages. The cryostat used is unique in that it has a vacuum mechanical insert which allows the superconductor to be placed under both compressive and tensile strains while at low temperatures. Preliminary results indicate that the martensitic phase transition temperature, T/sub m/, increases with compressive strains. Other effects of strain on tetragonal phase production are also discussed.

  20. Self-driven cooling loop for a large superconducting magnet in space

    NASA Technical Reports Server (NTRS)

    Mord, A. J.; Snyder, H. A.

    1992-01-01

    Pressurized cooling loops in which superfluid helium circulation is driven by the heat being removed have been previously demonstrated in laboratory tests. A simpler and lighter version which eliminates a heat exchanger by mixing the returning fluid directly with the superfluid helium bath was analyzed. A carefully designed flow restriction must be used to prevent boiling in this low-pressure system. A candidate design for Astromag is shown that can keep the magnet below 2.0 K during magnet charging. This gives a greater margin against accidental quench than approaches that allow the coolant to warm above the lambda point. A detailed analysis of one candidate design is presented.

  1. Passive Superconducting Flux Conservers for Rotating-Magnetic-Field-Driven Field-Reversed Configurations

    SciTech Connect

    Oz, E.; Myers, C. E.; Edwards, M. R.; Berlinger, B.; Brooks, A.; Cohen, S. A.

    2011-01-05

    The Princeton Field-Reversed Configuration (PFRC) experiment employs an odd-parity rotating magnetic field (RMFo) current drive and plasma heating system to form and sustain high-Β plasmas. For radial confinement, an array of coaxial, internal, passive, flux-conserving (FC) rings applies magnetic pressure to the plasma while still allowing radio-frequency RMFo from external coils to reach the plasma. The 3 ms pulse duration of the present experiment is limited by the skin time (τfc) of its room-temperature copper FC rings. To explore plasma phenomena with longer characteristic times, the pulse duration of the next-generation PFRC-2 device will exceed 100 ms, necessitating FC rings with (τfc > 300 ms. In this paper we review the physics of internal, discrete, passive FCs and describe the evolution of the PFRC's FC array. We then detail new experiments that have produced higher performance FC rings that contain embedded high-temperature superconducting (HTS) tapes. Several HTS tape winding configurations have been studied and a wide range of extended skin times, from 0.4 s to over 103 s, has been achieved. The new FC rings must carry up to 3 kA of current to balance the expected PFRC-2 plasma pressure, so the dependence of the HTS-FC critical current on the winding configuration and temperature was also studied. From these experiments, the key HTS-FC design considerations have been identified and HTS-FC rings with the desired performance characteristics have been produced.

  2. Geometric phase of a qubit driven by a phase noise laser under non-Markovian dynamics

    SciTech Connect

    Berrada, K.

    2014-01-15

    Robustness of the geometric phase (GP) with respect to the environmental effects is a basic condition for an effective quantum computation. Here, we study quantitatively the GP of a two-level atom system driven by a phase noise laser under non-Markovian dynamics in terms of different parameters involved in the whole system. We find that with the change of the damping coupling, the GP is very sensitive to its properties exhibiting long collapse and revival phenomena, which play a significant role in enhancing the stabilization and control of the system dynamics. Moreover, we show that the GP can be considered as a tool for testing and characterizing the nature of the qubit–environment coupling. Due to the significance of how a system is quantum correlated with its environment in the construction of a scalable quantum computer, the entanglement dynamics between the qubit with its environment under external classical noise is evaluated and investigated during the time evolution. -- Highlights: •Geometric phase under noise phase laser. •Dynamics of the geometric phase under non-Markovian dynamics in the presence of classical noise. •Solution of master equation of the system in terms atomic inversion. •Nonlocal correlation between the system and its environment under non-Markovianity.

  3. Crystal structure instability of FeSe grains: Formation of non-superconducting phase at the grain surface

    NASA Astrophysics Data System (ADS)

    Izawa, Hiroki; Tanaka, Yuji; Mizuguchi, Yoshikazu; Miura, Osuke

    2016-05-01

    We investigated the magnetization and crystal structure of FeSe polycrystalline samples with various grain sizes. For the samples with large grains, a large magnetic critical current density J c was observed. For the samples with small grains, superconductivity signals were not observed; instead, magnetization hysteresis, which is not a result of superconductivity, was observed. In the X-ray diffraction pattern for the samples with small grains, broad additional peaks were observed, corresponding to the formation of the non-superconducting (monoclinic) Fe–Se phase at the FeSe grain surface. The crystal structure instability at the grain surface would be the reason for the low superconducting properties of the Fe-chalcogenide polycrystalline wires investigated thus far.

  4. Epitaxial growth of hexagonal tungsten bronze Cs x WO3 films in superconducting phase region exceeding bulk limit

    NASA Astrophysics Data System (ADS)

    Soma, Takuto; Yoshimatsu, Kohei; Ohtomo, Akira

    2016-07-01

    We report epitaxial synthesis of superconducting Cs x WO3 (x = 0.11, 0.20, and 0.31) films on Y-stabilized ZrO2 (111) substrates. The hexagonal crystal structure was verified not only for the composition within the stable region of the bulk (x = 0.20 and 0.31), but also for the out-of-range composition (x = 0.11). The onset of the superconducting transition was recorded at 5.8 K for x = 0.11. We found a strong correlation between the superconducting transition temperature (T C) and the c-axis length, irrespective of the Cs content. These results indicated that the hidden superconducting phase region of hexagonal tungsten bronze is accessible using epitaxial synthesis of lightly doped films.

  5. Magnetic and superconducting phase diagram of the half-Heusler topological semimetal HoPdBi.

    PubMed

    Nikitin, A M; Pan, Y; Mao, X; Jehee, R; Araizi, G K; Huang, Y K; Paulsen, C; Wu, S C; Yan, B H; de Visser, A

    2015-07-15

    We report a study of the magnetic and electronic properties of the non-centrosymmetric half-Heusler antiferromagnet HoPdBi (TN = 2.0 K). Magnetotransport measurements show HoPdBi has a semimetallic behavior with a carrier concentration n = 3.7 × 10(18) cm(-3) extracted from the Shubnikov-de Haas effect. The magnetic phase diagram in the field-temperature plane has been determined by transport, magnetization, and thermal expansion measurements: magnetic order is suppressed at BM ~ 3.6 T for T --> 0. Superconductivity with Tc ~ 1.9 K is found in the antiferromagnetic phase. Ac-susceptibility measurements provide solid evidence for bulk superconductivity below Tc = 0.75 K with a screening signal close to a volume fraction of 100%. The upper critical field shows an unusual linear temperature variation with Bc2(T --> 0) = 1.1 T. We also report electronic structure calculations that classify HoPdBi as a new topological semimetal, with a non-trivial band inversion of 0.25 eV. PMID:26086396

  6. Superconducting scanning tunneling microscopy tips in a magnetic field: Geometry-controlled order of the phase transition

    SciTech Connect

    Eltschka, Matthias Jäck, Berthold; Assig, Maximilian; Etzkorn, Markus; Ast, Christian R.; Kondrashov, Oleg V.; Skvortsov, Mikhail A.; Kern, Klaus

    2015-09-21

    The properties of geometrically confined superconductors significantly differ from their bulk counterparts. Here, we demonstrate the geometrical impact for superconducting scanning tunneling microscopy (STM) tips, where the confinement ranges from the atomic to the mesoscopic scale. To this end, we compare the experimentally determined magnetic field dependence for several vanadium tips to microscopic calculations based on the Usadel equation. For our theoretical model of a superconducting cone, we find a direct correlation between the geometry and the order of the superconducting phase transition. Increasing the opening angle of the cone changes the phase transition from first to second order. Comparing our experimental findings to the theory reveals first and second order quantum phase transitions in the vanadium STM tips. In addition, the theory also explains experimentally observed broadening effects by the specific tip geometry.

  7. A unifying phase diagram with correlation-driven superconductor-to-insulator transition for the 122 series of iron chalcogenides

    NASA Astrophysics Data System (ADS)

    Niu, X. H.; Chen, S. D.; Jiang, J.; Ye, Z. R.; Yu, T. L.; Xu, D. F.; Xu, M.; Feng, Y.; Yan, Y. J.; Xie, B. P.; Zhao, J.; Gu, D. C.; Sun, L. L.; Mao, Qianhui; Wang, Hangdong; Fang, Minghu; Zhang, C. J.; Hu, J. P.; Sun, Z.; Feng, D. L.

    2016-02-01

    The 122 series of iron chalcogenide superconductors, for example KxFe2 -ySe2 , only possesses electron Fermi pockets. Their distinctive electronic structure challenges the picture built upon iron pnictide superconductors, where both electron and hole Fermi pockets coexist. However, partly due to the intrinsic phase separation in this family of compounds, many aspects of their behavior remain elusive. In particular, the evolution of the 122 series of iron chalcogenides with chemical substitution still lacks a microscopic and unified interpretation. Using angle-resolved photoemission spectroscopy, we studied a major fraction of 122 iron chalcogenides, including the isovalently "doped" KxFe2 -ySe2 -zSz,RbxFe2 -ySe2 -zTez , and (Tl,K) xFe2 -ySe2 -zSz . We found that the bandwidths of the low energy Fe 3 d bands in these materials depend on doping; and more crucially, as the bandwidth decreases, the ground state evolves from a metal to a superconductor, and eventually to an insulator, yet the Fermi surface in the metallic phases is unaffected by the isovalent dopants. Moreover, the correlation-driven insulator found here with small band filling may be a novel insulating phase. Our study shows that almost all the known 122-series iron chalcogenides can be understood via one unifying phase diagram which implies that moderate correlation strength is beneficial for the superconductivity.

  8. The design of a linear phase superconducting filter with quasi-elliptic response

    NASA Astrophysics Data System (ADS)

    Zuo, Tao; Yan, Shaolin; Zhao, Xinjie; Yue, Hongwei; Xie, Qinglian; Fang, Lan

    2008-06-01

    This paper presents the design of a linear phase superconducting filter with quasi-elliptic response. The coupling structure of the filter contains two trisections and one quadruplet. The two trisections are applied to generate two independent transmission zeros for high selectivity and are realized by meandered open-loop microstrip resonators; the quadruplet is applied for phase equalization and realized by four novel L-shaped microstrip resonators. The filter is designed at 1950 MHz with a bandwidth of 20 MHz. It is fabricated on a LaAlO3 wafer with double-coated Tl2Ba2CaCu2O8 films. The filter shows good selectivity together with flat group delay over 80% of the passband both in the simulation and measurements.

  9. Phase diagram of hot magnetized two-flavor color-superconducting quark matter

    SciTech Connect

    Fayazbakhsh, Sh.; Sadooghi, N.

    2011-01-15

    A two-flavor color-superconducting Nambu-Jona-Lasinio model is introduced at finite temperature T, chemical potential {mu}, and in the presence of a constant magnetic field e-tildeB. The effect of (T,{mu},e-tildeB) on the formation of chiral- and color-symmetry-breaking condensates is studied. The complete phase portrait of the model in T-{mu}, {mu}-e-tildeB, and T-e-tildeB phase spaces for various fixed e-tildeB, T, and {mu} is explored. A threshold magnetic field e-tildeB{sub t}{approx_equal}0.5 GeV{sup 2} is found, above which the dynamics of the system are solely dominated by the lowest Landau level, and the effects of T and {mu} are partly compensated by e-tildeB.

  10. Possible "Magnéli" Phases and Self-Alloying in the Superconducting Sulfur Hydride.

    PubMed

    Akashi, Ryosuke; Sano, Wataru; Arita, Ryotaro; Tsuneyuki, Shinji

    2016-08-12

    We theoretically give an infinite number of metastable crystal structures for the superconducting sulfur hydride H_{x}S under pressure. Previously predicted crystalline phases of H_{2}S and H_{3}S have been thought to have important roles for experimentally observed low and high T_{c}, respectively. The newly found structures are long-period modulated crystals where slablike H_{2}S and H_{3}S regions intergrow on a microscopic scale. The extremely small formation enthalpy for the H_{2}S-H_{3}S boundary indicated by first-principles calculations suggests possible alloying of these phases through the formation of local H_{3}S regions. The modulated structures and gradual alloying transformations between them not only explain the peculiar pressure dependence of T_{c} in sulfur hydride observed experimentally, but also could prevail in the experimental samples under various compression schemes. PMID:27563975

  11. Possible "Magnéli" Phases and Self-Alloying in the Superconducting Sulfur Hydride

    NASA Astrophysics Data System (ADS)

    Akashi, Ryosuke; Sano, Wataru; Arita, Ryotaro; Tsuneyuki, Shinji

    2016-08-01

    We theoretically give an infinite number of metastable crystal structures for the superconducting sulfur hydride HxS under pressure. Previously predicted crystalline phases of H2S and H3S have been thought to have important roles for experimentally observed low and high Tc, respectively. The newly found structures are long-period modulated crystals where slablike H2S and H3S regions intergrow on a microscopic scale. The extremely small formation enthalpy for the H2S -H3S boundary indicated by first-principles calculations suggests possible alloying of these phases through the formation of local H3S regions. The modulated structures and gradual alloying transformations between them not only explain the peculiar pressure dependence of Tc in sulfur hydride observed experimentally, but also could prevail in the experimental samples under various compression schemes.

  12. Demonstration of Geometric Landau-Zener Interferometry in a Superconducting Phase Qubit

    NASA Astrophysics Data System (ADS)

    Yu, Yang; Tan, Xinsheng; Zhang, Zhentao; Zhu, Shiliang; Zhang, Danwei; Han, Siyuan

    2014-03-01

    Geometric quantum manipulation and Landau-Zener interferometry have been separately explored in many quantum systems. Here we fill this gap by combining these two approaches in the study of the dynamics of a superconducting phase qubit. We propose and then experimentally demonstrate Landau-Zener interferometry based on pure geometric phases in this solid-state qubit. We observe the interference due to geometric phases accumulated in the evolution between two consecutive Landau-Zener transitions, while the dynamical phase is eliminated by a spin-echo pulse. Our numerical simulation results using measured energy relaxation and dephasing times agree well with the experimental results. The full controllability of the qubit population as a function of intrinsically fault-tolerant geometric phases provides a promising approach to fault-tolerant quantum computation. This work is partially supported by the SKPBR of China (2011CB922104, 2011CBA00200), NSFC (91021003, 11274156,11125417), PAPD, and the PCSIRT. Han is supported in part by NSF of United States (PHY-1314861).

  13. Electronic Structure of Superconducting KC8 and Nonsuperconducting LiC6 Graphite Intercalation Compounds: Evidence for a Graphene-Sheet-Driven Superconducting State

    SciTech Connect

    Pan, Z.H.; Camacho, J.; Upton, M.H.; Fedorov, A.V.; Howard, C.A.; Ellerby, M.; Valla, T

    2011-05-06

    We have performed photoemission studies of the electronic structure in LiC{sub 6} and KC{sub 8}, a nonsuperconducting and a superconducting graphite intercalation compound, respectively. We have found that the charge transfer from the intercalant layers to graphene layers is larger in KC{sub 8} than in LiC{sub 6}, opposite of what might be expected from their chemical composition. We have also measured the strength of the electron-phonon interaction on the graphene-derived Fermi surface to carbon derived phonons in both materials and found that it follows a universal trend where the coupling strength and superconductivity monotonically increase with the filling of graphene {pi}* states. This correlation suggests that both graphene-derived electrons and graphene-derived phonons are crucial for superconductivity in graphite intercalation compounds.

  14. Superconducting and Ferromagnetic Phases Induced by Lattice Distortions in Stoichiometric SrFe2As2 Single Crystals

    NASA Astrophysics Data System (ADS)

    Saha, S. R.; Butch, N. P.; Kirshenbaum, K.; Paglione, Johnpierre; Zavalij, P. Y.

    2009-07-01

    Single crystals of SrFe2As2 grown using a self-flux solution method were characterized via x-ray, transport, and magnetization studies, revealing a superconducting phase below Tc=21K characterized by a full electrical resistivity transition and partial diamagnetic screening. The reversible destruction and reinstatement of this phase by heat treatment and mechanical deformation studies, along with single-crystal x-ray diffraction measurements, indicate that internal crystallographic strain originating from c-axis-oriented planar defects plays a central role in promoting the appearance of superconductivity under ambient-pressure conditions in ˜90% of as-grown crystals. The appearance of a ferromagnetic moment with magnitude proportional to the tunable superconducting volume fraction suggests that these phenomena are both stabilized by lattice distortion.

  15. Phase fluctuation in overdoped cuprates? Superconducting dome due to Mott-ness of the tightly bound preformed pairs

    NASA Astrophysics Data System (ADS)

    Ku, Wei; Yang, Fan

    2015-03-01

    In contrast to the current lore, we demonstrate that even the overdoped cuprates suffer from superconducting phase fluctuation in the strong binding limit. Specifically, the Mott-ness of the underlying doped holes dictates naturally a generic optimal doping around 15% and nearly complete loss of phase coherence around 25%, giving rise to a dome shape of superconducting transition temperature in excellent agreement with experimental observations of the cuprates. We verify this effect with a simple estimation using Gutzwiller approximation of the preformed pairs, obtained through variational Monte Carlo calculation. This realization suggests strongly the interesting possibility that the high-temperature superconductivity in the cuprates might be mostly described by Bose-Einstein condensation, without crossing over to amplitude fluctuating Cooper pairs. Supported by Department of Energy, Office of Basic Energy Science DE-AC02-98CH10886.

  16. Phase formation and superconducting properties of mechanically alloyed Nb3(Al1‑x Ge x ) system

    NASA Astrophysics Data System (ADS)

    Li, Pingyuan; Chen, Yongliang; Xu, Liyuan; Zhang, Yun; Pan, Xifeng; Yan, Guo; Zhang, Yong; Cheng, C. H.; Feng, Yong; Zhao, Yong

    2016-07-01

    Mechanically alloyed Nb3(Al1‑x Ge x ) compounds with nominal composition x = 0%, 10%, 15%, 20%, 25% and 30% were synthesized using high-energy ball milling. The effects of Ge content and sintering temperature on the formation of the Nb3Al superconducting phase at a relatively low temperature without the extremely high-temperature rapid heating, quenching and transformation process were studied. The results revealed that Ge doping in Nb3Al improved the formation of the A15 phase at low temperatures, enhanced the superconducting transition temperature (T c), and refined the grain structure, thus improving the overall superconducting properties. The pinning behavior was also studied for the optimized sample.

  17. Behavior of embedded phase in shock-driven two-phase flow

    NASA Astrophysics Data System (ADS)

    Kuehner, Garrett; Wayne, Patrick; Olmstead, Dell; Corbin, Clint; Bernard, Tennille; Vorobieff, Peter; Truman, C. Randall

    2013-11-01

    We present an experimental study of droplet acceleration in a shock-driven two-phase flow (air with embedded liquid droplets). The droplets (propylene glycol, diameter 0.5-3 μm) were pre-mixed with the air in the test section of a shock tube, then impulsively accelerated with planar shock wave with a Mach number of 1.7. A cross-section of the flow is illuminated with multiple pulses from Nd:YAG lasers, producing time-resolved visualizations of the seeded volume. The images are then analyzed to quantify droplet velocity and acceleration from the shock passage to about 1.5 ms after the shock. Based on the velocity measurements, we can resolve the droplet lag after the shock, when the massive droplets ``catch up'' with the flow of the surrounding air, as well as validate our earlier estimates of boundary layer growth. This research is supported by NNSA (US National Nuclear Security Agency).

  18. Macroscopic phase decomposition in block copolymers driven by thermooxidative reactions

    NASA Astrophysics Data System (ADS)

    Fan, Shaobin

    Macroscopic phase separations have been observed in a commercial styrene- block-butadiene-block-styrene (SBS) triblock copolymer (Kraton 1102), an as-synthesized SBS triblock copolymer, an as-synthesized styrene-block-butadiene (SB) diblock copolymer and a commercial styrene-block-isoprene-block-styrene (SIS) triblock copolymer (Kraton 1107) at elevated temperatures. To the best of our knowledge, this is the first report on macroscopic phase separations in neat copolymers, including block copolymers. The temporal evolution of the structure, growth dynamics, origin and mechanism of the macroscopic phase separations have been investigated. A theoretical model has been established to describe such phase separation in SB diblock copolymer and numerical simulations have been undertaken to predict the structure evolution and growth dynamics. For styrene-butadiene block copolymers, the phase transition process consists of the first and second phase separations. The origin of such phase separations is attributed to chain scission and crosslinking reactions due to thermooxidative degradation. The formation of phase separated domains is the result of separation of polystyrene-rich domains from polybutadiene-rich domains. A mechanism, termed secondary spinodal decomposition, has been proposed to explain second phase separation. It has also demonstrated that the theoretical model and numerical simulations capture the essential features of the experimental observations. Growth rate was seen to depend on phase separation as well as reaction kinetics. The universal scaling laws have been shown to be invalid in macroscopic phase separations of styrene-butadiene block copolymers. The macroscopic phase separation process is more complex in the SIS triblock copolymer. It consists of a first phase separation, phase dissolution and a second phase separation. The origin of such phase decompositions has been shown to be a progressive chain scission reaction during thermal oxidative

  19. Entanglement driven phase transitions in spin-orbital models

    NASA Astrophysics Data System (ADS)

    You, Wen-Long; Oleś, Andrzej M.; Horsch, Peter

    2015-08-01

    To demonstrate the role played by the von Neumann entropy (vNE) spectra in quantum phase transitions we investigate the one-dimensional anisotropic SU(2)\\otimes {XXZ} spin-orbital model with negative exchange parameter. In the case of classical Ising orbital interactions we discover an unexpected novel phase with Majumdar-Ghosh-like spin-singlet dimer correlations triggered by spin-orbital entanglement (SOE) and having k=π /2 orbital correlations, while all the other phases are disentangled. For anisotropic XXZ orbital interactions both SOE and spin-dimer correlations extend to the antiferro-spin/alternating-orbital phase. This quantum phase provides a unique example of two coupled order parameters which change the character of the phase transition from first-order to continuous. Hereby we have established the vNE spectral function as a valuable tool to identify the change of ground state degeneracies and of the SOE of elementary excitations in quantum phase transitions.

  20. Synthesis of submicron metastable phase of silicon using femtosecond laser-driven shock wave

    SciTech Connect

    Tsujino, Masashi; Sano, Tomokazu; Sakata, Osami; Ozaki, Norimasa; Kodama, Ryosuke; Kimura, Shigeru; Takeda, Shingo; Kobayashi, Kojiro F.; Hirose, Akio

    2011-12-15

    We measured the grain size of metastable phase of Si synthesized by shock compression. We analyzed the crystalline structures of the femtosecond laser-driven shock compressed silicon with x-ray diffraction measurements. We found that submicron grains of metastable Si-VIII exist in the silicon. We suggest that the pressure loading time is too short for the nucleated high-pressure phases to grow in case of the femtosecond laser-driven shock compression, therefore Si-VIII grains of submicron size are obtained. We are expecting to discover other unique crystalline structures induced by the femtosecond laser-driven shock wave.

  1. Effect of pressure-driven local structural rearrangement on the superconducting properties of FeSe0.5Te0.5

    NASA Astrophysics Data System (ADS)

    Bendele, M.; Guguchia, Z.; von Rohr, F.; Irifune, T.; Shinmei, T.; Kantor, I.; Pascarelli, S.; Joseph, B.; Marini, C.

    2014-11-01

    The pressure dependence of the superconducting transition temperature Tc, the local structure, and the electronic properties of the iron chalcogenide superconductor FeSe0.5Te0.5 was investigated by means of SQUID magnetometry and site-selective polarized x-ray absorption spectroscopy at the iron and selenium K -edges. The measurements reveal a discontinuous decrease of the local bond distances by crossing a tetragonal to monoclinic structural phase transition at pS˜2.7 GPa. The electronic structure, however, evolves evenly, but the superconducting properties are highly affected by changes in the local structure. These results underline the close connection of the lattice and the superconductivity in the iron-based superconductors.

  2. Cooperative Two-Quanta Phase Transitions in Quantum Optics and Superconductivity

    NASA Astrophysics Data System (ADS)

    Enaki, Nicolae

    2010-09-01

    The behavior of an electronic subsystem in strong interaction with phonon subsystem, or quantified electromagnetic field (QEF) is discussed. In this case the correlation effect between first and second order electron-phonon interaction (or atom-QEF interaction) takes place. It is shown that the temperature dependence of two-quanta exchange between Fermi sub-system and thermal reservoir gives a non-linear behavior of the order parameter in superconductivity and super-radiance, accompanied by an increase of the electron correlations with increasing temperature. The same effect is considered for two-quanta scattering processes, in which one quantum is absorbed and another is emitted. It is demonstrated, that the order parameter in such a system firstly increases with temperature achieving the maximal value. After that it decreases as in traditional phase transition effects.

  3. Single-Charge Transistor Based on the Charge-Phase Duality of a Superconducting Nanowire Circuit

    NASA Astrophysics Data System (ADS)

    Hongisto, T. T.; Zorin, A. B.

    2012-03-01

    We propose a transistorlike circuit including two serially connected segments of a narrow superconducting nanowire joint by a wider segment with a capacitively coupled gate in between. This circuit is made of amorphous NbSi film and embedded in a network of on-chip Cr microresistors ensuring a sufficiently high external electromagnetic impedance. Assuming a virtual regime of quantum phase slips (QPS) in two narrow segments of the wire, leading to quantum interference of voltages on these segments, this circuit is dual to the dc SQUID. Our samples demonstrated appreciable Coulomb blockade voltage (analog of critical current of the SQUIDs) and periodic modulation of this blockade by an electrostatic gate (analog of flux modulation in the SQUIDs). The model of this QPS transistor is discussed.

  4. Local structure and superconductivity of the Ce1-xLaxRu2 Laves phase system

    NASA Astrophysics Data System (ADS)

    Saini, N. L.; Agrestini, S.; Amato, E.; Filippi, M.; di Castro, D.; Bianconi, A.; Manfrinetti, P.; Palenzona, A.; Marcelli, A.

    2004-09-01

    We have studied local structure of the Laves phase Ce1-xLaxRu2 superconductor by Ru K-edge extended x-ray absorption fine-structure measurements focusing on the small La concentration regime where the transition temperature Tc passes through a local maximum. We find that correlated Debye-Waller factor of the Ru-Ru bonds follows Tc with the varying La concentration in the system. Although, this remarkable Tc correlation on the local atomic structure suggests important role of the electron-lattice interactions, the band-structure effects seem more likely the reason to drive the anomalous superconducting behavior and the Tc maximum in this 4f system.

  5. Isotope effect in the superconducting high-pressure simple cubic phase of calcium from first principles

    NASA Astrophysics Data System (ADS)

    Errea, Ion; Rousseau, Bruno; Bergara, Aitor

    2012-06-01

    It has been recently shown [I. Errea, B. Rousseau, and A. Bergara, Phys. Rev. Lett. 106, 165501 (2011)] that the phonons of the high-pressure simple cubic phase of calcium are stabilized by strong quantum anharmonic effects. This was obtained by a fully ab initio implementation of the self-consistent harmonic approximation including explicitly anharmonic coefficients up to fourth order. The renormalized anharmonic phonons make possible to estimate the superconducting transition temperature in this system, and a sharp agreement with experiments is found. In this work, this analysis is extended in order to study the effect of anharmonicity in the isotope effect. According to our calculations, despite the huge anharmonicity in the system, the isotope coefficient is predicted to be 0.45, close to the 0.5 value expected for a harmonic BCS superconductor.

  6. First demonstration and performance of an injection locked continuous wave magnetron to phase control a superconducting cavity

    SciTech Connect

    A.C. Dexter, G. Burt, R.G. Carter, I. Tahir, H. Wang, K. Davis, R. Rimmer

    2011-03-01

    The applications of magnetrons to high power proton and cw electron linacs are discussed. An experiment is described where a 2.45 GHz magnetron has been used to drive a single cell superconducting cavity. With the magnetron injection locked, a modest phase control accuracy of 0.95° rms has been demonstrated. Factors limiting performance have been identified.

  7. Fluctuation-driven electroweak phase transition. [in early universe

    NASA Technical Reports Server (NTRS)

    Gleiser, Marcelo; Kolb, Edward W.

    1992-01-01

    We examine the dynamics of the electroweak phase transition in the early Universe. For Higgs masses in the range 46 less than or = M sub H less than or = 150 GeV and top quark masses less than 200 GeV, regions of symmetric and asymmetric vacuum coexist to below the critical temperature, with thermal equilibrium between the two phases maintained by fluctuations of both phases. We propose that the transition to the asymmetric vacuum is completed by percolation of these subcritical fluctuations. Our results are relevant to scenarios of baryogenesis that invoke a weakly first-order phase transition at the electroweak scale.

  8. Vortex lattices in the superconducting phases of doped topological insulators and heterostructures

    NASA Astrophysics Data System (ADS)

    Hung, Hsiang-Hsuan; Ghaemi, Pouyan; Hughes, Taylor L.; Gilbert, Matthew J.

    2013-01-01

    Majorana fermions are predicted to play a crucial role in condensed matter realizations of topological quantum computation. These heretofore undiscovered quasiparticles have been predicted to exist at the cores of vortex excitations in topological superconductors and in heterostructures of superconductors and materials with strong spin-orbit coupling. In this work, we examine topological insulators with bulk s-wave superconductivity in the presence of a vortex lattice generated by a perpendicular magnetic field. Using self-consistent Bogoliubov-de Gennes calculations, we confirm that beyond the semiclassical, weak-pairing limit the Majorana vortex states appear as the chemical potential is tuned from either side of the band edge so long as the density of states is sufficient for superconductivity to form. Further, we demonstrate that the previously predicted vortex phase transition survives beyond the semiclassical limit. At chemical potential values smaller than the critical chemical potential, the vortex lattice modes hybridize within the top and bottom surfaces, giving rise to a dispersive low-energy mid-gap band. As the chemical potential is increased, the Majorana states become more localized within a single surface but spread into the bulk toward the opposite surface. Eventually, when the chemical potential is sufficiently high in the bulk bands, the Majorana modes can tunnel between surfaces and eventually a critical point is reached at which modes on opposite surfaces can freely tunnel and annihilate leading to the topological phase transition previously studied in the work of Hosur [Phys. Rev. Lett.10.1103/PhysRevLett.107.097001 107, 097001 (2011)].

  9. Fulde-Ferrell-Larkin-Ovchinnikov states in a superconducting ring with magnetic fields: Phase diagram and the first-order phase transitions

    NASA Astrophysics Data System (ADS)

    Yoshii, Ryosuke; Takada, Satoshi; Tsuchiya, Shunji; Marmorini, Giacomo; Hayakawa, Hisao; Nitta, Muneto

    2015-12-01

    We find the angular Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states (or the twisted kink crystals) in which a phase and an amplitude of a pair potential modulate simultaneously in a quasi-one-dimensional superconducting ring with a static Zeeman magnetic field applied on the ring and static Aharonov-Bohm magnetic flux penetrating the ring. The superconducting ring with magnetic flux produces a persistent current, whereas the Zeeman split of Fermi energy results in the spatial modulation of the pair potential. We show that these two magnetic fields stabilize the FFLO phase in a large parameter region of the magnetic fields. We further draw the phase diagram with the two kinds of first-order phase transitions; one corresponds to phase slips separating the Aharonov-Bohm magnetic flux, and the other separates the number of peaks of the pair amplitude for the Zeeman magnetic field.

  10. Competing magnetic double-Q phases and superconductivity-induced reentrance of C2 magnetic stripe order in iron pnictides

    NASA Astrophysics Data System (ADS)

    Gastiasoro, Maria N.; Andersen, Brian M.

    2015-10-01

    We perform a microscopic theoretical study of the generic properties of competing magnetic phases in iron pnictides. As a function of electron filling and temperature, the magnetic stripe (single-Q ) order forms a dome, but competing noncollinear and nonuniform double-Q phases exist at the foot of the dome, in agreement with recent experiments. We compute and compare the electronic properties of the different magnetic phases, investigate the role of competing superconductivity, and show how disorder may stabilize double-Q order. Superconductivity is shown to compete more strongly with double-Q magnetic phases, which can lead to reentrance of the C2 (single-Q ) order, in agreement with recent thermal expansion measurements on K-doped Ba-122 crystals.

  11. Josephson parametric phase-locked oscillator and its application to dispersive readout of superconducting qubits.

    PubMed

    Lin, Z R; Inomata, K; Koshino, K; Oliver, W D; Nakamura, Y; Tsai, J S; Yamamoto, T

    2014-01-01

    The parametric phase-locked oscillator (PPLO) is a class of frequency-conversion device, originally based on a nonlinear element such as a ferrite ring, that served as a fundamental logic element for digital computers more than 50 years ago. Although it has long since been overtaken by the transistor, there have been numerous efforts more recently to realize PPLOs in different physical systems such as optical photons, trapped atoms, and electromechanical resonators. This renewed interest is based not only on the fundamental physics of nonlinear systems, but also on the realization of new, high-performance computing devices with unprecedented capabilities. Here we realize a PPLO with Josephson-junction circuitry and operate it as a sensitive phase detector. Using a PPLO, we demonstrate the demodulation of a weak binary phase-shift keying microwave signal of the order of a femtowatt. We apply PPLO to dispersive readout of a superconducting qubit, and achieved high-fidelity, single-shot and non-destructive readout with Rabi-oscillation contrast exceeding 90%. PMID:25059992

  12. New High Field Superconducting Phase in CeCoIn5 Probed by Ultrasonic Measurements

    NASA Astrophysics Data System (ADS)

    Watanabe, T.; Kasahara, Y.; Izawa, K.; Sakakibara, T.; van der Beek, C. J.; Shishido, H.; Settai, R.; Onuki, Y.; Matsuda, Y.

    2004-03-01

    Very recent reports of heat capacity measurements in field parallel to the ab--plane of the unconventional superconductor CeCoIn5 have raised great interest, because they pointed out the possibility of the Fulde-Ferrel-Larkin-Ovchinikov (FFLO) phase. We have measured ultrasound velocity of CeCoIn5 to clarify this novel superconducting phase. Sound velocities of the transverse mode with propagation kallel[100] ([010]) and polarization uallel[010] ([100]) were measured in the magnetic field Hallel[100]. The sound velocity is strongly enhanced when it tilts the flux line lattice (FLL) from the field direction (H ⊥ u), indicating the strong coupling between FLL and crystal lattice. Our experimental results reveal an unusual structural transformation of the FLL in the vicinity of the upper critical field. These results provide a strong evidence that the high field state is the textured order parameter state, i.e. the FFLO phase, in which the order parameter is spatially modulated and has planar nodes aligned perpendicular to the vortices.

  13. Transformation of phase transitions driven by an anisotropic random field

    NASA Astrophysics Data System (ADS)

    Popa-Nita, V.; Kralj, Samo

    2005-04-01

    We carry out a comparative study of the influence of a random anisotropy field on continuous and discontinuous phase transitions. The ordered phase, which is reached via a continuous symmetry breaking phase transition, is characterized by an order parameter and by a corresponding hydrodynamic continuum field. We assume that the response of the hydrodynamic field to the imposed disorder results in a domainlike pattern of the system. For a strong enough disorder both transitions become gradual. For weaker disorder strengths the disorder converts a second order transition into a discontinuous one.

  14. Nanoscale phase separation of antiferromagnetic order and superconductivity in K0.75Fe1.75Se2

    PubMed Central

    Yuan, R. H.; Dong, T.; Song, Y. J.; Zheng, P.; Chen, G. F.; Hu, J. P.; Li, J. Q.; Wang, N. L.

    2012-01-01

    We report an in-plane optical spectroscopy study on the iron-selenide superconductor K0.75Fe1.75Se2. The measurement revealed the development of a sharp reflectance edge below Tc at frequency much smaller than the superconducting energy gap on a relatively incoherent electronic background, a phenomenon which was not seen in any other Fe-based superconductors so far investigated. Furthermore, the feature could be noticeably suppressed and shifted to lower frequency by a moderate magnetic field. Our analysis indicates that this edge structure arises from the development of a Josephson-coupling plasmon in the superconducting condensate. Together with the transmission electron microscopy analysis, our study yields compelling evidence for the presence of nanoscale phase separation between superconductivity and magnetism. The results also enable us to understand various seemingly controversial experimental data probed from different techniques. PMID:22355735

  15. Trapping control of phase development in zone melting of Bi-Sr-Ca-Cu-O superconducting fibres

    NASA Astrophysics Data System (ADS)

    Costa, F. M.; Carrasco, M. F.; Silva, R. F.; Vieira, J. M.

    2003-03-01

    Highly-texturized polycrystalline fibres of the Bi-Sr-Ca-Cu-O system have been grown by the laser floating zone technique at seven different pulling rates: (1.1, 2.2, 4.17, 8.3, 16.7, 33.3, 60.5) × 10-6 m s-1. The assessment of the cation segregation at the solid/liquid interface allowed us to calculate their equilibrium and effective distribution coefficients. The equilibrium distribution coefficients (k0,Bi = 0.55, k0,Sr = 0.97, k0,Ca = 1.67, k0,Cu = 1.10) were estimated using the Burton, Primm and Slichter (BPS) theory by taking into account the determined effective values. The effective distribution coefficients tend to unity as long as the pulling rate increases. The composition profiles along the initial transient region of the solidified fibres show a fast approach to the nominal composition as the pulling rate increases. The outstanding effect of the growth speed on superconducting phase type development is explained based on the solute trapping phenomena. The sequence of crystallization for superconducting phases ('2212' rightarrow '4413' rightarrow '2201') with pulling rate is a spontaneous effect of the system thermodynamics in order to balance the Bi trapping. This phase sequence corresponds to the smallest change of Bi chemical potential from the liquid phase to the solid phase. A diagram of free energy curves of the interdendritic superconducting phases illustrates the partitionless solidification phenomena at the highest growth speed.

  16. FAST TRACK COMMUNICATION: Magnetic excitations of Fe1 + ySexTe1 - x in magnetic and superconductive phases

    NASA Astrophysics Data System (ADS)

    Babkevich, P.; Bendele, M.; Boothroyd, A. T.; Conder, K.; Gvasaliya, S. N.; Khasanov, R.; Pomjakushina, E.; Roessli, B.

    2010-04-01

    We have used inelastic neutron scattering and muon-spin rotation to compare the low energy magnetic excitations in single crystals of superconducting Fe1.01Se0.50Te0.50 and non-superconducting Fe1.10Se0.25Te0.75. We confirm the existence of a spin resonance in the superconducting phase of Fe1.01Se0.50Te0.50, at an energy of 7 meV and a wavevector of (1/2, 1/2, 0). The non-superconducting sample exhibits two incommensurate magnetic excitations at (1/2, 1/2, 0) ± (0.18, - 0.18, 0) which rise steeply in energy, but no resonance is observed at low energies. A strongly dispersive low energy magnetic excitation is also observed in Fe1.10Se0.25Te0.75 close to the commensurate antiferromagnetic ordering wavevector (1/2 - δ, 0, 1/2), where δ≈0.03. The magnetic correlations in both samples are found to be quasi-two-dimensional in character and persist well above the magnetic (Fe1.10Se0.25Te0.75) and superconducting (Fe1.01Se0.50Te0.50) transition temperatures.

  17. RNA transcription modulates phase transition-driven nuclear body assembly

    PubMed Central

    Berry, Joel; Weber, Stephanie C.; Vaidya, Nilesh; Haataja, Mikko; Brangwynne, Clifford P.

    2015-01-01

    Nuclear bodies are RNA and protein-rich, membraneless organelles that play important roles in gene regulation. The largest and most well-known nuclear body is the nucleolus, an organelle whose primary function in ribosome biogenesis makes it key for cell growth and size homeostasis. The nucleolus and other nuclear bodies behave like liquid-phase droplets and appear to condense from the nucleoplasm by concentration-dependent phase separation. However, nucleoli actively consume chemical energy, and it is unclear how such nonequilibrium activity might impact classical liquid–liquid phase separation. Here, we combine in vivo and in vitro experiments with theory and simulation to characterize the assembly and disassembly dynamics of nucleoli in early Caenorhabditis elegans embryos. In addition to classical nucleoli that assemble at the transcriptionally active nucleolar organizing regions, we observe dozens of “extranucleolar droplets” (ENDs) that condense in the nucleoplasm in a transcription-independent manner. We show that growth of nucleoli and ENDs is consistent with a first-order phase transition in which late-stage coarsening dynamics are mediated by Brownian coalescence and, to a lesser degree, Ostwald ripening. By manipulating C. elegans cell size, we change nucleolar component concentration and confirm several key model predictions. Our results show that rRNA transcription and other nonequilibrium biological activity can modulate the effective thermodynamic parameters governing nucleolar and END assembly, but do not appear to fundamentally alter the passive phase separation mechanism. PMID:26351690

  18. RNA transcription modulates phase transition-driven nuclear body assembly.

    PubMed

    Berry, Joel; Weber, Stephanie C; Vaidya, Nilesh; Haataja, Mikko; Brangwynne, Clifford P

    2015-09-22

    Nuclear bodies are RNA and protein-rich, membraneless organelles that play important roles in gene regulation. The largest and most well-known nuclear body is the nucleolus, an organelle whose primary function in ribosome biogenesis makes it key for cell growth and size homeostasis. The nucleolus and other nuclear bodies behave like liquid-phase droplets and appear to condense from the nucleoplasm by concentration-dependent phase separation. However, nucleoli actively consume chemical energy, and it is unclear how such nonequilibrium activity might impact classical liquid-liquid phase separation. Here, we combine in vivo and in vitro experiments with theory and simulation to characterize the assembly and disassembly dynamics of nucleoli in early Caenorhabditis elegans embryos. In addition to classical nucleoli that assemble at the transcriptionally active nucleolar organizing regions, we observe dozens of "extranucleolar droplets" (ENDs) that condense in the nucleoplasm in a transcription-independent manner. We show that growth of nucleoli and ENDs is consistent with a first-order phase transition in which late-stage coarsening dynamics are mediated by Brownian coalescence and, to a lesser degree, Ostwald ripening. By manipulating C. elegans cell size, we change nucleolar component concentration and confirm several key model predictions. Our results show that rRNA transcription and other nonequilibrium biological activity can modulate the effective thermodynamic parameters governing nucleolar and END assembly, but do not appear to fundamentally alter the passive phase separation mechanism. PMID:26351690

  19. Transition to a labyrinthine phase in a driven granular medium

    NASA Astrophysics Data System (ADS)

    Merminod, Simon; Jamin, Timothée; Falcon, Eric; Berhanu, Michael

    2015-12-01

    Labyrinthine patterns arise in two-dimensional physical systems submitted to competing interactions, in fields ranging from solid-state physics to hydrodynamics. For systems of interacting particles, labyrinthine and stripe phases were studied in the context of colloidal particles confined into a monolayer, both numerically by means of Monte Carlo simulations and experimentally using superparamagnetic particles. Here we report an experimental observation of a labyrinthine phase in an out-of-equilibrium system constituted of macroscopic particles. Once sufficiently magnetized, they organize into short chains of particles in contact and randomly orientated. We characterize the transition from a granular gas state towards a solid labyrinthine phase, as a function of the ratio of the interaction strength to the kinetic agitation. The spatial local structure is analyzed by means of accurate particle tracking. Moreover, we explain the formation of these chains using a simple model.

  20. Topological phase transition driven by a spatially periodic potential

    NASA Astrophysics Data System (ADS)

    Fu, Bo; Zheng, Huaixiu; Li, Qunxiang; Shi, Qinwei; Yang, Jinlong

    2014-12-01

    We propose a simple approach to realize a topological phase transition using a spatial periodic potential. As an example, we examine the electronic structures of HgTe/CdTe quantum wells, and demonstrate that their band structures can be effectively manipulated by the periodic potential. At a critical potential, we find that a conventional band insulator undergoes a topological phase transition into a quantum spin Hall system, which is characterized by an abrupt change of the spin Chern number and emerging edge states. Our proposal provides an interesting way to dynamically turn on or off topologically protected edge states for application in switching devices.

  1. Superconducting phase with the ( d + id) order parameter in an ensemble of Hubbard fermions on the triangular lattice

    NASA Astrophysics Data System (ADS)

    Val'kov, V. V.; Val'kova, T. A.; Mitskan, V. A.

    2015-09-01

    In the framework of the t- J 1- J 2- V model, the integral equation determining the order parameter Δ( p) of the superconducting phase is derived for an ensemble of strongly correlated fermions on a triangular lattice using the diagram technique for the Hubbard operators. Taking into account the interaction between the Hubbard fermions within two coordination spheres, we demonstrate that the exact analytical solution Δ2( p) of this equation for the superconducting phase with the (( {{d_{{x^2} - {y^2}}} + i{d_{xy}}} )) symmetry can be expressed as a superposition of two chiral basis functions. This gives rise to a new set of nodal points for the complex parameter Δ2( p). Moreover, at some critical value x c of the charge carrier density, we obtain a gapless phase with six Dirac points. The passing of x through x = x c is accompanied by the topological quantum transition corresponding to the change in the topological parameter Q.

  2. Magnetic Transport Properties in GdBa2Cu3- x Ru x O7- δ Superconducting Phase

    NASA Astrophysics Data System (ADS)

    Abou-Aly, A. I.; Mahmoud, S. A.; Awad, R.; Ibrahim, I. H.; Barakat, M. Me.

    2012-04-01

    Bulk superconducting samples of type GdBa2Cu3- x Ru x O7- δ phase, Gd-123, with x ranging from 0.0 to 0.15 were prepared by the conventional solid-state reaction technique. X-ray powder diffraction (XRD) and the electrical resistivity measurements were performed in order to investigate the effect of Ru4+ ions substitution on Gd-123 phase. Enhancement of the phase formation and the superconducting transition temperature T c for GdBa2Cu3- x Ru x O7- δ phase up to x=0.05 was observed. The effect of magnetic field up to 4.4 kG on the electrical resistivity behavior of the prepared samples was studied to investigate the flux motion of this phase. The derived flux pinning energy U, based on the thermally activated flux creep TAFC model, decreased with increasing the magnetic field B. The flux pinning energy followed the exponent behavior as U( B)˜ B - β . The superconducting transition width ΔT increased as the magnetic field increased, showing the scaling relation as ΔT˜ B n . Using Ambegaokar and Halperin AH theory, the magnetic field and temperature dependence of U was found to be U( B, T)˜ ΔTB - η , η= β+ n. The critical current density J c (0) enhanced up to x=0.05, beyond which it decreased with further increase in Ru-content.

  3. Phase-matched Josephson traveling-wave parametric amplifier for superconducting qubit readout - theory

    NASA Astrophysics Data System (ADS)

    O'Brien, Kevin; Macklin, Chris; Siddiqi, Irfan; Zhang, Xiang

    2015-03-01

    Josephson parametric amplifiers approach quantum-noise-limited performance and are used in experiments requiring high-fidelity detection of single-photon-level microwave signals. Current Josephson parametric amplifiers couple the Josephson junction (a nonlinear inductor) to a resonant cavity, achieving high gain at the expense of limited instantaneous bandwidth. In contrast, Josephson traveling wave parametric amplifiers (JTWPAs) avoid this gain-bandwidth trade-off by employing long propagation lengths rather than a resonant cavity. A major challenge in JTWPA design is that optimum parametric gain is only achieved when the four-wave mixing process is phase matched. We show that by adding a series of resonant elements to the transmission line, phase matching and exponential gain can be achieved. Generation of higher harmonics is automatically suppressed due to the junction plasma resonance. We present the theory and selected results, including the gain, bandwidth, and dynamic range of the amplifier. The simultaneous achievement of high gain (greater than 20 dB), large instantaneous bandwidth (greater than 2 GHz), and high dynamic range make the JTWPA a promising device for the simultaneous readout of frequency-multiplexed superconducting qubits.

  4. Ultrafast phase-change logic device driven by melting processes

    PubMed Central

    Loke, Desmond; Skelton, Jonathan M.; Wang, Wei-Jie; Lee, Tae-Hoon; Zhao, Rong; Chong, Tow-Chong; Elliott, Stephen R.

    2014-01-01

    The ultrahigh demand for faster computers is currently tackled by traditional methods such as size scaling (for increasing the number of devices), but this is rapidly becoming almost impossible, due to physical and lithographic limitations. To boost the speed of computers without increasing the number of logic devices, one of the most feasible solutions is to increase the number of operations performed by a device, which is largely impossible to achieve using current silicon-based logic devices. Multiple operations in phase-change–based logic devices have been achieved using crystallization; however, they can achieve mostly speeds of several hundreds of nanoseconds. A difficulty also arises from the trade-off between the speed of crystallization and long-term stability of the amorphous phase. We here instead control the process of melting through premelting disordering effects, while maintaining the superior advantage of phase-change–based logic devices over silicon-based logic devices. A melting speed of just 900 ps was achieved to perform multiple Boolean algebraic operations (e.g., NOR and NOT). Ab initio molecular-dynamics simulations and in situ electrical characterization revealed the origin (i.e., bond buckling of atoms) and kinetics (e.g., discontinuouslike behavior) of melting through premelting disordering, which were key to increasing the melting speeds. By a subtle investigation of the well-characterized phase-transition behavior, this simple method provides an elegant solution to boost significantly the speed of phase-change–based in-memory logic devices, thus paving the way for achieving computers that can perform computations approaching terahertz processing rates. PMID:25197044

  5. Ultrafast phase-change logic device driven by melting processes.

    PubMed

    Loke, Desmond; Skelton, Jonathan M; Wang, Wei-Jie; Lee, Tae-Hoon; Zhao, Rong; Chong, Tow-Chong; Elliott, Stephen R

    2014-09-16

    The ultrahigh demand for faster computers is currently tackled by traditional methods such as size scaling (for increasing the number of devices), but this is rapidly becoming almost impossible, due to physical and lithographic limitations. To boost the speed of computers without increasing the number of logic devices, one of the most feasible solutions is to increase the number of operations performed by a device, which is largely impossible to achieve using current silicon-based logic devices. Multiple operations in phase-change-based logic devices have been achieved using crystallization; however, they can achieve mostly speeds of several hundreds of nanoseconds. A difficulty also arises from the trade-off between the speed of crystallization and long-term stability of the amorphous phase. We here instead control the process of melting through premelting disordering effects, while maintaining the superior advantage of phase-change-based logic devices over silicon-based logic devices. A melting speed of just 900 ps was achieved to perform multiple Boolean algebraic operations (e.g., NOR and NOT). Ab initio molecular-dynamics simulations and in situ electrical characterization revealed the origin (i.e., bond buckling of atoms) and kinetics (e.g., discontinuouslike behavior) of melting through premelting disordering, which were key to increasing the melting speeds. By a subtle investigation of the well-characterized phase-transition behavior, this simple method provides an elegant solution to boost significantly the speed of phase-change-based in-memory logic devices, thus paving the way for achieving computers that can perform computations approaching terahertz processing rates. PMID:25197044

  6. Precision phase control for the radio frequency system of K500 superconducting cyclotron at Variable Energy Cyclotron Centre, Kolkata

    SciTech Connect

    Som, Sumit; Ghosh, Surajit; Seth, Sudeshna; Mandal, Aditya; Paul, Saikat; Roy, Suprakash

    2013-11-15

    Variable Energy Cyclotron Centre (VECC) has commissioned K500 Superconducting cyclotron (SCC) based on MSU and Texas A and M university cyclotrons. The radio frequency (RF) system of SCC has been commissioned with the stringent requirement of various RF parameters. The three-phase RF system of Superconducting cyclotron has been developed in the frequency range 9–27 MHz with amplitude and phase stability of 100 ppm and ±0.1°, respectively. The phase control system has the option to change the relative phase difference between any two RF cavities and maintain the phase stability within ±0.1° during round-the-clock cyclotron operation. The said precision phase loop consists of both analogue In-phase/Quadrature modulator to achieve faster response and also Direct Digital Synthesis based phase shifter to achieve wide dynamic range as well. This paper discusses detail insights into the various issues of phase control for the K500 SCC at VECC, Kolkata.

  7. Precision phase control for the radio frequency system of K500 superconducting cyclotron at Variable Energy Cyclotron Centre, Kolkata

    NASA Astrophysics Data System (ADS)

    Som, Sumit; Ghosh, Surajit; Seth, Sudeshna; Mandal, Aditya; Paul, Saikat; Roy, Suprakash

    2013-11-01

    Variable Energy Cyclotron Centre (VECC) has commissioned K500 Superconducting cyclotron (SCC) based on MSU and Texas A&M university cyclotrons. The radio frequency (RF) system of SCC has been commissioned with the stringent requirement of various RF parameters. The three-phase RF system of Superconducting cyclotron has been developed in the frequency range 9-27 MHz with amplitude and phase stability of 100 ppm and ±0.1°, respectively. The phase control system has the option to change the relative phase difference between any two RF cavities and maintain the phase stability within ±0.1° during round-the-clock cyclotron operation. The said precision phase loop consists of both analogue In-phase/Quadrature modulator to achieve faster response and also Direct Digital Synthesis based phase shifter to achieve wide dynamic range as well. This paper discusses detail insights into the various issues of phase control for the K500 SCC at VECC, Kolkata.

  8. Topological phase transition driven by electron-phonon interaction

    NASA Astrophysics Data System (ADS)

    Saha, Kush; Garate, Ion

    2014-03-01

    We study the effect of electron-phonon interactions in the band topology of Dirac insulators, both at zero and finite temperature. Elaborating on recent theoretical work, we determine how and when phonons can drive a trivial insulator into a topological insulating phase. As an application, we evaluate the temperature-dependence of the critical thickness for the topological transition in CdTe/HgTe quantum wells.

  9. Design and test of a superconducting magnet in a linear accelerator for an Accelerator Driven Subcritical System

    NASA Astrophysics Data System (ADS)

    Peng, Quanling; Xu, Fengyu; Wang, Ting; Yang, Xiangchen; Chen, Anbin; Wei, Xiaotao; Gao, Yao; Hou, Zhenhua; Wang, Bing; Chen, Yuan; Chen, Haoshu

    2014-11-01

    A batch superconducting solenoid magnet for the ADS proton linear accelerator has been designed, fabricated, and tested in a vertical dewar in Sept. 2013. A total of ten superconducting magnets will be installed into two separate cryomodules. Each cryomodule contains six superconducting spoke RF cavities for beam acceleration and five solenoid magnets for beam focusing. The multifunction superconducting magnet contains a solenoid for beam focusing and two correctors for orbit correction. The design current for the solenoid magnet is 182 A. A quench performance test shows that the operating current of the solenoid magnet can reach above 300 A after natural quenching on three occasions during current ramping (260 A, 268 A, 308 A). The integrated field strength and leakage field at the nearby superconducting spoke cavities all meet the design requirements. The vertical test checked the reliability of the test dewar and the quench detection system. This paper presents the physical and mechanical design of the batch magnets, the quench detection technique, field measurements, and a discussion of the residual field resulting from persistent current effects.

  10. Elastically driven metamagnetic-like phase transformations of shape memory alloys

    NASA Astrophysics Data System (ADS)

    Danilevich, A. G.; L'vov, V. A.

    2016-03-01

    A theoretical model of metamagnetic-like (ferromagnetic-paramagnetic and ferromagnetic-antiferromagnetic) phase transitions is developed for the interpretation of experimental results obtained recently for the Ni-Mn-Co-X (X  =  In, Sn, Ga) shape memory alloys. The conditions of elastically driven (caused by the martensitic transformation of alloy) metamagnetic-like phase transitions are determined. These conditions are: high magnetic susceptibility of paramagnetic/antiferromagnetic phase; large (but real for some alloys) volume change during the martensitic transformation; and large value of volume magnetostriction caused by the metamagnetic-like phase transition. The magnetoelastic mechanism is proposed for the explanation of magnetic field influence on the martensitic transformation. The elastically driven ferromagnetic-paramagnetic phase transition is considered in more detail and the results of corresponding magnetic measurements are described.

  11. Theoretical predictions of novel superconducting phases of BaGe3 stable at atmospheric and high pressures.

    PubMed

    Zurek, Eva; Yao, Yansun

    2015-03-16

    A series of new superconducting binary silicides and germanides have recently been synthesized under high-pressure high-temperature conditions. A representative member of this group, BaGe3, was theoretically investigated using evolutionary structure searches coupled with structural analogies in the pressure range from 1 atm to 250 GPa, where three new phases were discovered. At 1 atm, in addition to the synthesized P63/mmc phase, we predicted two new phases, I4/mmm and Amm2, to be dynamically stable. The Amm2 structure comprises Ge clusters and triangular prisms intercalated with Ba and Ge atoms, a unique structural motif unknown to this group. The I4/mmm structure has been previously synthesized in binary silicides and is calculated to be thermodynamically stable in BaGe3 between 15.6 and 35.4 GPa. Above 35.4 GPa, two new phases of P6̅m2 and R3̅m symmetry become the global minima and remain so up to the highest pressure considered. These two phases have very similar enthalpies, and both feature layers of double Kagome nets of Ge intercalated with Ba-Ge layers. The predicted phases are suggested to be metallic with itinerant electrons and to be potentially superconducting from the considerable electron-phonon coupling strength. Density functional perturbation calculations combined with the Allen-Dynes-modified McMillan formula were used to estimate the superconducting critical temperatures (Tc) for these new phases, which, with slight pressure variations, are comparable to the experimental Tc measured for the P63/mmc phase. PMID:25731906

  12. Stripe-like nanoscale structural phase separation in superconducting BaPb1-xBixO3

    SciTech Connect

    Giraldo-Gallo, P.; Zhang, Y.; Parra, C.; Manoharan, H. C.; Beasley, M. R.; Geballe, T. H.; Kramer, M. J.; Fisher, I. R.

    2015-09-16

    The phase diagram of BaPb1-xBixO3 exhibits a superconducting dome in the proximity of a charge density wave phase. For the superconducting compositions, the material coexists as two structural polymorphs. Here we show, via high-resolution transmission electron microscopy, that the structural dimorphism is accommodated in the form of partially disordered nanoscale stripes. Identification of the morphology of the nanoscale structural phase separation enables determination of the associated length scales, which we compare with the Ginzburg–Landau coherence length. We find that the maximum Tc occurs when the superconducting coherence length matches the width of the partially disordered stripes, implying a connection between the structural phase separation and the shape of the superconducting dome.

  13. Stripe-like nanoscale structural phase separation in superconducting BaPb1-xBixO3

    SciTech Connect

    Giraldo-Gallo, P.; Zhang, Y.; Parra, C.; Manoharan, H. C.; Beasley, M. R.; Geballe, T. H.; Kramer, M. J.; Fisher, I. R.

    2015-09-16

    The phase diagram of BaPb1-xBixO3 exhibits a superconducting “dome” in the proximity of a charge density wave phase. For the superconducting compositions, the material coexists as two structural polymorphs. Here we show, via high resolution transmission electron microscopy, that the structural dimorphism is accommodated in the form of partially disordered nanoscale stripes. Identification of the morphology of the nanoscale structural phase separation enables determination of the associated length scales, which we compare to the Ginzburg-Landau coherence length. Thus, we find that the maximum Tc occurs when the superconducting coherence length matches the width of the partially disordered stripes, implying a connection between the structural phase separation and the shape of the superconducting dome.

  14. Confinement-driven phase separation of quantum liquid mixtures.

    PubMed

    Prisk, T R; Pantalei, C; Kaiser, H; Sokol, P E

    2012-08-17

    We report small-angle neutron scattering studies of liquid helium mixtures confined in Mobil Crystalline Material-41 (MCM-41), a porous silica glass with narrow cylindrical nanopores (d=3.4 nm). MCM-41 is an ideal model adsorbent for fundamental studies of gas sorption in porous media because its monodisperse pores are arranged in a 2D triangular lattice. The small-angle scattering consists of a series of diffraction peaks whose intensities are determined by how the imbibed liquid fills the pores. Pure (4)He adsorbed in the pores show classic, layer-by-layer film growth as a function of pore filling, leaving the long range symmetry of the system intact. In contrast, the adsorption of (3)He-(4)He mixtures produces a structure incommensurate with the pore lattice. Neither capillary condensation nor preferential adsorption of one helium isotope to the pore walls can provide the symmetry-breaking mechanism. The scattering is consistent with the formation of randomly distributed liquid-liquid microdomains ∼2.3 nm in size, providing evidence that confinement in a nanometer scale capillary can drive local phase separation in quantum liquid mixtures. PMID:23006380

  15. A phase diagram for fluid-driven sediment trasport

    NASA Astrophysics Data System (ADS)

    Clark, Abe

    When a fluid flows laterally over a granular bed, grains may be transported with the flow. This process shapes much of the natural world. The boundary between states with and without grain motion has been studied for decades. However, this boundary is not well understood, since the process whereby grains are transported involves the coupling of several complex phenomena: turbulent fluid flow near a rough boundary, Darcy flow through the pore structure of the granular bed, the yield strength of granular beds comprised of frictional grains with irregular shape, and inertial effects of grains that become entrained in the flow. In order to clarify the essential physics that governs the onset of granular motion, we study this process computationally by including only the minimal features and then adding complexities one by one. We start with a simple numerical model that includes only gravity, grain-grain interactions that are repulsive and frictionless, and a purely horizontal viscous fluid flow. By varying the fluid flow rate and the effective viscosity, we find behavior that is qualitatively consistent with a large collection of experimental data known as the Shields curve. Thus, our results suggest that the main features of this curve result from a competition between grain inertia and viscous damping. We find this phase diagram to be qualitatively insensitive to secondary effects, such as friction, irregular grain shape, and restitution losses. Funded by U.S. Army Research Office under Grant No. W911NF-14-1-0005.

  16. Emergence of Multiple Superconducting Phases in (NH3)yMxFeSe (M: Na and Li).

    PubMed

    Zheng, Lu; Miao, Xiao; Sakai, Yusuke; Izumi, Masanari; Goto, Hidenori; Nishiyama, Saki; Uesugi, Eri; Kasahara, Yuichi; Iwasa, Yoshihiro; Kubozono, Yoshihiro

    2015-01-01

    We previously discovered multiple superconducting phases in the ammoniated Na-doped FeSe material, (NH3)yNaxFeSe. To clarify the origin of the multiple superconducting phases, the variation of Tc was fully investigated as a function of x in (NH3)yNaxFeSe. The 32 K superconducting phase is mainly produced in the low-x region below 0.4, while only a single phase is observed at x  =  1.1, with Tc =  45 K, showing that the Tc depends significantly on x, but it changes discontinuously with x. The crystal structure of (NH3)yNaxFeSe does not change as x increases up to 1.1, i.e., the space group of I4/mmm. The lattice constants, a and c, of the low-Tc phase (Tc = 32.5 K) are 3.9120(9) and 14.145(8) Å, respectively, while a = 3.8266(7) Å and c = 17.565(9) Å for the high-Tc phase (~46 K). The c increases in the high Tc phase, implying that the Tc is directly related to c. In (NH3)yLixFeSe material, the Tc varies continuously within the range of 39 to 44 K with changing x. Thus, the behavior of Tc is different from that of (NH3)yNaxFeSe. The difference may be due to the difference in the sites that the Na and Li occupy. PMID:26239256

  17. Fabrication of Janus droplets by evaporation driven liquid-liquid phase separation.

    PubMed

    Zhang, Qingquan; Xu, Meng; Liu, Xiaojun; Zhao, Wenfeng; Zong, Chenghua; Yu, Yang; Wang, Qi; Gai, Hongwei

    2016-04-11

    We present a universal and scalable method to fabricate Janus droplets based on evaporation driven liquid-liquid phase separation. In this work, the morphologies and chemical properties of separate parts of the Janus droplets can be flexibly regulated, and more complex Janus droplets (such as core-shell Janus droplets, ternary Janus droplets, and multiple Janus droplets) can be constructed easily. PMID:26983706

  18. Design of single-phase driven screw-thread-type ultrasonic motor

    NASA Astrophysics Data System (ADS)

    Chang, Lien-Kai; Tsai, Mi-Ching

    2016-05-01

    Most screw-thread-type ultrasonic motors are designed to be two-phase driven. This paper aims to present a novel single phase driven design that generates the required wobble motion, thus significantly simplifying the driving circuit of the ultrasonic motor. The proposed single-phase driven screw-thread-type ultrasonic motor works with two orthogonal bending modes generated by an asymmetric stator design. The novel stator design can improve the vibration displacement and further enhance the performance of the single phase driven motor. The vibration characteristics of the asymmetric stator structure were analyzed by ANSYS finite element analysis software. Based on the design and analysis processes, a prototype of the desired screw-thread-type ultrasonic motor was fabricated and tested. When the operating voltage is 200 Vpp, the obtained main characteristics of the proposed motor are as follows: the working frequency is between 28.3 and 29.5 kHz; the maximum no-load velocity is approximately 4.1 mm s-1; and the thrust force is 1.6 N.

  19. Field-induced superconducting phase of FeSe in the BCS-BEC cross-over.

    PubMed

    Kasahara, Shigeru; Watashige, Tatsuya; Hanaguri, Tetsuo; Kohsaka, Yuhki; Yamashita, Takuya; Shimoyama, Yusuke; Mizukami, Yuta; Endo, Ryota; Ikeda, Hiroaki; Aoyama, Kazushi; Terashima, Taichi; Uji, Shinya; Wolf, Thomas; von Löhneysen, Hilbert; Shibauchi, Takasada; Matsuda, Yuji

    2014-11-18

    Fermi systems in the cross-over regime between weakly coupled Bardeen-Cooper-Schrieffer (BCS) and strongly coupled Bose-Einstein-condensate (BEC) limits are among the most fascinating objects to study the behavior of an assembly of strongly interacting particles. The physics of this cross-over has been of considerable interest both in the fields of condensed matter and ultracold atoms. One of the most challenging issues in this regime is the effect of large spin imbalance on a Fermi system under magnetic fields. Although several exotic physical properties have been predicted theoretically, the experimental realization of such an unusual superconducting state has not been achieved so far. Here we show that pure single crystals of superconducting FeSe offer the possibility to enter the previously unexplored realm where the three energies, Fermi energy εF, superconducting gap Δ, and Zeeman energy, become comparable. Through the superfluid response, transport, thermoelectric response, and spectroscopic-imaging scanning tunneling microscopy, we demonstrate that εF of FeSe is extremely small, with the ratio Δ/εF ~ 1(~0.3) in the electron (hole) band. Moreover, thermal-conductivity measurements give evidence of a distinct phase line below the upper critical field, where the Zeeman energy becomes comparable to εF and Δ. The observation of this field-induced phase provides insights into previously poorly understood aspects of the highly spin-polarized Fermi liquid in the BCS-BEC cross-over regime. PMID:25378706

  20. Entropy-driven formation of chiral nematic phases by computer simulations

    NASA Astrophysics Data System (ADS)

    Dussi, Simone; Dijkstra, Marjolein

    2016-04-01

    Predicting the macroscopic chiral behaviour of liquid crystals from the microscopic chirality of the particles is highly non-trivial, even when the chiral interactions are purely entropic in nature. Here we introduce a novel chiral hard-particle model, namely particles with a twisted polyhedral shape and obtain a stable fully entropy-driven cholesteric phase by computer simulations. By slightly modifying the triangular base of the particle, we are able to switch from a left-handed prolate (calamitic) to a right-handed oblate (discotic) cholesteric phase using the same right-handed twisted particle model. Furthermore, we show that not only prolate and oblate chiral nematic phases, but also other novel entropy-driven phases, namely chiral blue phases, chiral nematic phases featuring both twist and splay deformations, chiral biaxial nematic phases with one of the axes twisted, can be obtained by varying particle biaxiality and chirality. Our results allow to identify general guidelines for the stabilization of these phases.

  1. Dynamical many-body phases of the parametrically driven, dissipative Dicke model

    NASA Astrophysics Data System (ADS)

    Chitra, R.; Zilberberg, O.

    2015-08-01

    Control and manipulation of quantum engineered systems allows for the utilization of time-dependent parametric modulations for accessing novel out-of-equilibrium phenomena. In the absence of such driving, the dissipative Dicke model exhibits a fascinating out-of-equilibrium many-body phase transition as a function of a coupling between a driven photonic cavity and numerous two-level atoms. We study the effect of a parametric modulation of this coupling and discover a rich phase diagram as a function of the modulation strength. We find that in addition to the established normal and super-radiant phases, a new phase with pulsed superradiance, which we term dynamical normal phase, appears when the system is parametrically driven. Employing different methods, we characterize the different phases and the transitions between them. Specific heed is paid to the role of dissipation in determining the phase boundaries. Our analysis paves the road for the experimental study of dynamically stabilized phases of interacting light and matter.

  2. Entropy-driven formation of chiral nematic phases by computer simulations

    PubMed Central

    Dussi, Simone; Dijkstra, Marjolein

    2016-01-01

    Predicting the macroscopic chiral behaviour of liquid crystals from the microscopic chirality of the particles is highly non-trivial, even when the chiral interactions are purely entropic in nature. Here we introduce a novel chiral hard-particle model, namely particles with a twisted polyhedral shape and obtain a stable fully entropy-driven cholesteric phase by computer simulations. By slightly modifying the triangular base of the particle, we are able to switch from a left-handed prolate (calamitic) to a right-handed oblate (discotic) cholesteric phase using the same right-handed twisted particle model. Furthermore, we show that not only prolate and oblate chiral nematic phases, but also other novel entropy-driven phases, namely chiral blue phases, chiral nematic phases featuring both twist and splay deformations, chiral biaxial nematic phases with one of the axes twisted, can be obtained by varying particle biaxiality and chirality. Our results allow to identify general guidelines for the stabilization of these phases. PMID:27067806

  3. Entropy-driven formation of chiral nematic phases by computer simulations.

    PubMed

    Dussi, Simone; Dijkstra, Marjolein

    2016-01-01

    Predicting the macroscopic chiral behaviour of liquid crystals from the microscopic chirality of the particles is highly non-trivial, even when the chiral interactions are purely entropic in nature. Here we introduce a novel chiral hard-particle model, namely particles with a twisted polyhedral shape and obtain a stable fully entropy-driven cholesteric phase by computer simulations. By slightly modifying the triangular base of the particle, we are able to switch from a left-handed prolate (calamitic) to a right-handed oblate (discotic) cholesteric phase using the same right-handed twisted particle model. Furthermore, we show that not only prolate and oblate chiral nematic phases, but also other novel entropy-driven phases, namely chiral blue phases, chiral nematic phases featuring both twist and splay deformations, chiral biaxial nematic phases with one of the axes twisted, can be obtained by varying particle biaxiality and chirality. Our results allow to identify general guidelines for the stabilization of these phases. PMID:27067806

  4. Photoassociation dynamics driven by second- and third-order phase-modulated laser fields

    NASA Astrophysics Data System (ADS)

    Wang, Meng; Chen, Mao-Du; Hu, Xue-Jin; Li, Jing-Lun; Cong, Shu-Lin

    2016-05-01

    We investigate theoretically the photoassociation dynamics of ultracold 85Rb atoms driven by second- and third-order phase-modulated laser fields. The interplay between the second-order and third-order terms of the phase-modulated pulse has an obvious influence on photoassociation dynamics. The different combinations of the second-order and third-order phase coefficients lead to different pulse shapes. Most of the molecular population in the excited electronic state driven only by the third-order phase pulses can be distributed in a single vibrational level. The second-order term of the phase-modulated pulse can change the instantaneous frequency, and therefore the final population is distributed on several resonant vibrational levels, instead of concentrating on a single level. Although the second- and third-order phase-modulated pulse covers more resonant vibrational levels, the total population on the resonant vibrational levels is much smaller than that controlled only by the third-order phase pulse. In particular, the third-order term of the phase-modulated pulse can weaken the ‘multiple interaction’ to some degree.

  5. Phase relations in KxFe2-ySe2 and the structure of superconducting KxFe2Se2 via high-resolution synchrotron diffraction

    NASA Astrophysics Data System (ADS)

    Shoemaker, Daniel P.; Chung, Duck Young; Claus, Helmut; Francisco, Melanie C.; Avci, Sevda; Llobet, Anna; Kanatzidis, Mercouri G.

    2012-11-01

    Superconductivity in iron selenides has experienced a rapid growth, but not without major inconsistencies in the reported properties. For alkali-intercalated iron selenides, even the structure of the superconducting phase is a subject of debate, in part because the onset of superconductivity is affected much more delicately by stoichiometry and preparation than in cuprate or pnictide superconductors. If high-quality, pure, superconducting intercalated iron selenides are ever to be made, the intertwined physics and chemistry must be explained by systematic studies of how these materials form and by and identifying the many coexisting phases. To that end, we prepared pure K2Fe4Se5 powder and superconductors in the KxFe2-ySe2 system, and examined differences in their structures by high-resolution synchrotron and single-crystal x-ray diffraction. We found four distinct phases: semiconducting K2Fe4Se5, a metallic superconducting phase KxFe2Se2 with x ranging from 0.38 to 0.58, the phase KFe1.6Se2 with full K occupancy and no Fe vacancy ordering, and a oxidized phase K0.51(5)Fe0.70(2)Se that forms the PbClF structure upon exposure to moisture. We find that the vacancy-ordered phase K2Fe4Se5 does not become superconducting by doping, but the distinct iron-rich minority phase KxFe2Se2 precipitates from single crystals upon cooling from above the vacancy ordering temperature. This coexistence of separate metallic and semiconducting phases explains a broad maximum in resistivity around 100 K. Further studies to understand the solubility of excess Fe in the KxFe2-ySe2 structure will shed light on the maximum fraction of superconducting KxFe2Se2 that can be obtained by solid state synthesis.

  6. Quantum state transfer and controlled-phase gate on one-dimensional superconducting resonators assisted by a quantum bus.

    PubMed

    Hua, Ming; Tao, Ming-Jie; Deng, Fu-Guo

    2016-01-01

    We propose a quantum processor for the scalable quantum computation on microwave photons in distant one-dimensional superconducting resonators. It is composed of a common resonator R acting as a quantum bus and some distant resonators rj coupled to the bus in different positions assisted by superconducting quantum interferometer devices (SQUID), different from previous processors. R is coupled to one transmon qutrit, and the coupling strengths between rj and R can be fully tuned by the external flux through the SQUID. To show the processor can be used to achieve universal quantum computation effectively, we present a scheme to complete the high-fidelity quantum state transfer between two distant microwave-photon resonators and another one for the high-fidelity controlled-phase gate on them. By using the technique for catching and releasing the microwave photons from resonators, our processor may play an important role in quantum communication as well. PMID:26907366

  7. Absence of superconductivity in the collapsed tetragonal phase of KF e2A s2 under hydrostatic pressure

    NASA Astrophysics Data System (ADS)

    Wang, Bosen; Matsubayashi, Kazuyuki; Cheng, Jinguang; Terashima, Taichi; Kihou, Kunihiro; Ishida, Shigeyuki; Lee, Chul-Ho; Iyo, Akira; Eisaki, Hiroshi; Uwatoko, Yoshiya

    2016-07-01

    Temperature dependence of resistivity on KF e2A s2 single crystals down to 20 mK was measured under various hydrostatic pressures up to 17.5 GPa generated in a cubic-anvil cell. With increasing the pressure, the superconducting transition of tetragonal KF e2A s2 was suppressed gradually and disappears completely at ˜11 GPa, which was related to the weakening of electronic correlations and/or critical fluctuations under pressure. In sharp contrast to previous reports, no superconducting phase emerges upon further increasing pressures until the collapsed tetragonal KF e2A s2 forms. We argue that such a discrepancy can be attributed to the different pressure apparatus or homogeneity.

  8. Quantum state transfer and controlled-phase gate on one-dimensional superconducting resonators assisted by a quantum bus

    NASA Astrophysics Data System (ADS)

    Hua, Ming; Tao, Ming-Jie; Deng, Fu-Guo

    2016-02-01

    We propose a quantum processor for the scalable quantum computation on microwave photons in distant one-dimensional superconducting resonators. It is composed of a common resonator R acting as a quantum bus and some distant resonators rj coupled to the bus in different positions assisted by superconducting quantum interferometer devices (SQUID), different from previous processors. R is coupled to one transmon qutrit, and the coupling strengths between rj and R can be fully tuned by the external flux through the SQUID. To show the processor can be used to achieve universal quantum computation effectively, we present a scheme to complete the high-fidelity quantum state transfer between two distant microwave-photon resonators and another one for the high-fidelity controlled-phase gate on them. By using the technique for catching and releasing the microwave photons from resonators, our processor may play an important role in quantum communication as well.

  9. Quantum state transfer and controlled-phase gate on one-dimensional superconducting resonators assisted by a quantum bus

    PubMed Central

    Hua, Ming; Tao, Ming-Jie; Deng, Fu-Guo

    2016-01-01

    We propose a quantum processor for the scalable quantum computation on microwave photons in distant one-dimensional superconducting resonators. It is composed of a common resonator R acting as a quantum bus and some distant resonators rj coupled to the bus in different positions assisted by superconducting quantum interferometer devices (SQUID), different from previous processors. R is coupled to one transmon qutrit, and the coupling strengths between rj and R can be fully tuned by the external flux through the SQUID. To show the processor can be used to achieve universal quantum computation effectively, we present a scheme to complete the high-fidelity quantum state transfer between two distant microwave-photon resonators and another one for the high-fidelity controlled-phase gate on them. By using the technique for catching and releasing the microwave photons from resonators, our processor may play an important role in quantum communication as well. PMID:26907366

  10. Superconducting Memristors

    NASA Astrophysics Data System (ADS)

    Peotta, Sebastiano; Di Ventra, Massimiliano

    2014-09-01

    In his original work, Josephson predicted that a phase-dependent conductance should be present in superconducting tunnel junctions, an effect difficult to detect, mainly because it is hard to single it out from the usual nondissipative Josephson current. We propose a solution for this problem that consists of using different superconducting materials to realize the two junctions of a superconducting interferometer. According to the Ambegaokar-Baratoff relation the two junctions have different conductances if the critical currents are equal, thus the Josephson current can be suppressed by fixing the magnetic flux in the loop at half of a flux quantum without canceling the phase-dependent conductance. Our proposal can be used to study the phase-dependent conductance, an effect present in principle in all superconducting weak links. From the standpoint of nonlinear circuit theory, such a device is in fact an ideal memristor with possible applications to memories and neuromorphic computing in the framework of ultrafast and low-energy-consumption superconducting digital circuits.