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Sample records for field-tuned quantum critical

  1. Heat transport study of field-tuned quantum criticality in CeIrIn5

    NASA Astrophysics Data System (ADS)

    Shakeripour, H.; Tanatar, M. A.; Petrovic, C.; Taillefer, Louis

    2016-02-01

    The in-plane electrical resistivity, ρ , and thermal conductivity, κ , of the heavy-fermion superconductor CeIrIn5 were measured down to 40 mK in magnetic fields up to 11 T applied along the c axis. For all fields above Hc 2=4 T of filamentary superconductivity, we find that the ratio of heat and charge conductivities in the T →0 limit obeys the Wiedemann-Franz law, κ /T =L0/ρ , where L0=2.45 ×10-8 WΩ K-2 is the Sommerfeld value of the Lorenz number. The temperature-dependent parts of both the electrical and thermal resistivity, w ≡T /L0κ , follow the functional dependence expected for the Fermi liquid theory of metals with ρ -ρ0=A T2 , w -w0=B T2 , with ρ0=w0 and B ≈2 A . The coefficient B does not show a significant field dependence even upon approaching Hc 2=0.4 T of the bulk superconducting state. The weak response to the magnetic field is in stark contrast with the behavior found in the closely related CeCoIn5, in which the field-tuned quantum critical point coincides with Hc 2. The value of the electron-electron mass enhancement, as judged by the A and B coefficients, is about one order of magnitude reduced in CeIrIn5 as compared to CeCoIn5 (in spite of the fact that the zero field γ0 in CeIrIn5 is twice as large as γ0 in CeCoIn5), which suggests that the material is significantly farther away from the magnetic quantum critical point at bulk Hc 2 and at all of the studied fields. A suppressed Kadowaki-Woods ratio in CeIrIn5 compared to CeCoIn5 suggests a notably more localized nature of f electrons in the compound.

  2. Magnetic field tuned quantum criticality of heavy fermion system YbPtBi

    NASA Astrophysics Data System (ADS)

    Mun, Eundeok

    2014-03-01

    Quantum criticality triggers an emergence of new quantum phase of matters due to the critical behavior of quantum fluctuations. Heavy fermion (HF) compounds have provided the cleanest evidence for the quantum phase transition. The face-centered cubic YbPtBi is one of the few frustrated stoichiometric Yb-based HF compounds. Measurements of magnetic field and temperature dependent resistivity, specific heat, thermal expansion, Hall effect, and thermoelectric power indicate that the antiferromagnetic (AFM) order (TN ~ 0.4 K) can be suppressed by applied magnetic field of Hc ~ 4 kOe. In the H- T phase diagram of YbPtBi, three regimes of its low temperature states emerges: (I) AFM state, characterized by spin density wave (SDW) like feature, which can be suppressed to T = 0 by the relatively small magnetic field of Hc ~ 4 kOe, (II) field induced anomalous state in which the electrical resistivity follows ρ(T) ~T 1 . 5 between Hc and ~ 8 kOe, and (III) Fermi liquid (FL) state in which ρ(T) ~T2 for H >8 kOe. Regions I and II are separated at T = 0 by what appears to be a quantum critical point. Whereas region III appears to be a FL associated with the hybridized 4 f states of Yb, region II may be a manifestation of a spin liquid state. Work was supported by the US Department of Energy, Office of Basic Energy Science, Division of Materials Sciences and Engineering. Ames Laboratory is operated for the US Department of Energy by Iowa State University under Contract No. DE-AC02-07CH11358.

  3. Wiedemann-Franz law and nonvanishing temperature scale across the field-tuned quantum critical point of YbRh2Si2

    SciTech Connect

    Reid, J.-Ph.; Tanatar, Makariy; Daou, R.; Hu, Rongwei; Petrovic, C.; Taillefer, Louis

    2014-01-23

    The in-plane thermal conductivity kappa and electrical resistivity rho of the heavy-fermion metal YbRh2Si2 were measured down to 50 mK for magnetic fields H parallel and perpendicular to the tetragonal c axis, through the field-tuned quantum critical point H-c, at which antiferromagnetic order ends. The thermal and electrical resistivities, w L0T/kappa and rho, show a linear temperature dependence below 1 K, typical of the non-Fermi-liquid behavior found near antiferromagnetic quantum critical points, but this dependence does not persist down to T = 0. Below a characteristic temperature T-star similar or equal to 0.35 K, which depends weakly on H, w(T) and rho(T) both deviate downward and converge as T -> 0. We propose that T-star marks the onset of short-range magnetic correlations, persisting beyond H-c. By comparing samples of different purity, we conclude that the Wiedemann-Franz law holds in YbRh2Si2, even at H-c, implying that no fundamental breakdown of quasiparticle behavior occurs in this material. The overall phenomenology of heat and charge transport in YbRh2Si2 is similar to that observed in the heavy-fermion metal CeCoIn5, near its own field-tuned quantum critical point.

  4. Yb-based heavy fermion compounds and field tuned quantum chemistry

    SciTech Connect

    Mun, Eundeok

    2010-01-01

    The motivation of this dissertation was to advance the study of Yb-based heavy fermion (HF) compounds especially ones related to quantum phase transitions. One of the topics of this work was the investigation of the interaction between the Kondo and crystalline electric field (CEF) energy scales in Yb-based HF systems by means of thermoelectric power (TEP) measurements. In these systems, the Kondo interaction and CEF excitations generally give rise to large anomalies such as maxima in ρ(T) and as minima in S(T). The TEP data were use to determine the evolution of Kondo and CEF energy scales upon varying transition metals for YbT2Zn20 (T = Fe, Ru, Os, Ir, Rh, and Co) compounds and applying magnetic fields for YbAgGe and YbPtBi. For YbT2Zn20 and YbPtBi, the Kondo and CEF energy scales could not be well separated in S(T), presumably because of small CEF level splittings. A similar effect was observed for the magnetic contribution to the resistivity. For YbAgGe, S(T) has been successfully applied to determine the Kondo and CEF energy scales due to the clear separation between the ground state and thermally excited CEF states. The Kondo temperature, TK, inferred from the local maximum in S(T), remains finite as magnetic field increases up to 140 kOe. In this dissertation we have examined the heavy quasi-particle behavior, found near the field tuned AFM quantum critical point (QCP), with YbAgGe and YbPtBi. Although the observed nFL behaviors in the vicinity of the QCP are different between YbAgGe and YbPtBi, the constructed H-T phase diagram including the two crossovers are similar. For both YbAgGe and YbPtBi, the details of the quantum criticality turn out to be complicated. We expect that YbPtBi will provide an additional example of field tuned quantum criticality, but clearly there are further experimental investigations left and more ideas needed to understand the basic physics of field-induced quantum

  5. Quantum criticality

    NASA Astrophysics Data System (ADS)

    Coleman, Piers; Schofield, Andrew J.

    2005-01-01

    As we mark the centenary of Albert Einstein's seminal contribution to both quantum mechanics and special relativity, we approach another anniversary - that of Einstein's foundation of the quantum theory of solids. But 100 years on, the same experimental measurement that puzzled Einstein and his contemporaries is forcing us to question our understanding of how quantum matter transforms at ultra-low temperatures.

  6. Unconventional magnetic field tuned quantum ground states in the noncentrosymmetric compound Yb2Fe12P7

    NASA Astrophysics Data System (ADS)

    Baumbach, Ryan; Hamlin, James; Shu, Lei; Zocco, Diego; Maple, M. Brian; O'Brien, Jim; -Chun Ho, Pei

    2010-03-01

    Although so-called non-Fermi-liquid (NFL) behavior has been intensely investigated, there is no consensus as to its origin. A well known scenario for NFL behavior is the quantum critical point (QCP) model, where a second order phase transition (usually antiferromagnetic) is suppressed to T = 0 K by a control parameter. NFL behavior is found near the QCP, after which FL behavior is recovered for larger tuning parameter values. We will discuss the unusual phase diagram in single crystals of the noncentrosymmetric compound Yb2Fe12P7, which exhibits a crossover from a zero magnetic field NFL ground state to another distinct NFL quantum region which is stabilized with magnetic field. Interestingly, the transition between the two states coincides with the suppression of antiferromagnetism towards T = 0 K. Based on these observations, we argue that a fundamental understanding of QCP and NFL phenomena and their interrelationship has yet to be realized.

  7. Quantum criticality.

    PubMed

    Coleman, Piers; Schofield, Andrew J

    2005-01-20

    As we mark the centenary of Albert Einstein's seminal contribution to both quantum mechanics and special relativity, we approach another anniversary--that of Einstein's foundation of the quantum theory of solids. But 100 years on, the same experimental measurement that puzzled Einstein and his contemporaries is forcing us to question our understanding of how quantum matter transforms at ultra-low temperatures. PMID:15662409

  8. Quantum Critical Elasticity.

    PubMed

    Zacharias, Mario; Paul, Indranil; Garst, Markus

    2015-07-10

    We discuss elastic instabilities of the atomic crystal lattice at zero temperature. Because of long-range shear forces of the solid, at such transitions the phonon velocities vanish, if at all, only along certain crystallographic directions, and, consequently, the critical phonon fluctuations are suppressed to a lower dimensional manifold and governed by a Gaussian fixed point. In the case of symmetry-breaking elastic transitions, a characteristic critical phonon thermodynamics arises that is found, e.g., to violate Debye's T(3) law for the specific heat. We point out that quantum critical elasticity is triggered whenever a critical soft mode couples linearly to the strain tensor. In particular, this is relevant for the electronic Ising-nematic quantum phase transition in a tetragonal crystal as discussed in the context of certain cuprates, ruthenates, and iron-based superconductors. PMID:26207483

  9. Deconfined quantum critical points.

    PubMed

    Senthil, T; Vishwanath, Ashvin; Balents, Leon; Sachdev, Subir; Fisher, Matthew P A

    2004-03-01

    The theory of second-order phase transitions is one of the foundations of modern statistical mechanics and condensed-matter theory. A central concept is the observable order parameter, whose nonzero average value characterizes one or more phases. At large distances and long times, fluctuations of the order parameter(s) are described by a continuum field theory, and these dominate the physics near such phase transitions. We show that near second-order quantum phase transitions, subtle quantum interference effects can invalidate this paradigm, and we present a theory of quantum critical points in a variety of experimentally relevant two-dimensional antiferromagnets. The critical points separate phases characterized by conventional "confining" order parameters. Nevertheless, the critical theory contains an emergent gauge field and "deconfined" degrees of freedom associated with fractionalization of the order parameters. We propose that this paradigm for quantum criticality may be the key to resolving a number of experimental puzzles in correlated electron systems and offer a new perspective on the properties of complex materials.

  10. Anomalous critical fields in quantum critical superconductors.

    PubMed

    Putzke, C; Walmsley, P; Fletcher, J D; Malone, L; Vignolles, D; Proust, C; Badoux, S; See, P; Beere, H E; Ritchie, D A; Kasahara, S; Mizukami, Y; Shibauchi, T; Matsuda, Y; Carrington, A

    2014-01-01

    Fluctuations around an antiferromagnetic quantum critical point (QCP) are believed to lead to unconventional superconductivity and in some cases to high-temperature superconductivity. However, the exact mechanism by which this occurs remains poorly understood. The iron-pnictide superconductor BaFe2(As(1-x)P(x))2 is perhaps the clearest example to date of a high-temperature quantum critical superconductor, and so it is a particularly suitable system to study how the quantum critical fluctuations affect the superconducting state. Here we show that the proximity of the QCP yields unexpected anomalies in the superconducting critical fields. We find that both the lower and upper critical fields do not follow the behaviour, predicted by conventional theory, resulting from the observed mass enhancement near the QCP. Our results imply that the energy of superconducting vortices is enhanced, possibly due to a microscopic mixing of antiferromagnetism and superconductivity, suggesting that a highly unusual vortex state is realized in quantum critical superconductors. PMID:25477044

  11. Anomalous critical fields in quantum critical superconductors

    PubMed Central

    Putzke, C.; Walmsley, P.; Fletcher, J. D.; Malone, L.; Vignolles, D.; Proust, C.; Badoux, S.; See, P.; Beere, H. E.; Ritchie, D. A.; Kasahara, S.; Mizukami, Y.; Shibauchi, T.; Matsuda, Y.; Carrington, A.

    2014-01-01

    Fluctuations around an antiferromagnetic quantum critical point (QCP) are believed to lead to unconventional superconductivity and in some cases to high-temperature superconductivity. However, the exact mechanism by which this occurs remains poorly understood. The iron-pnictide superconductor BaFe2(As1−xPx)2 is perhaps the clearest example to date of a high-temperature quantum critical superconductor, and so it is a particularly suitable system to study how the quantum critical fluctuations affect the superconducting state. Here we show that the proximity of the QCP yields unexpected anomalies in the superconducting critical fields. We find that both the lower and upper critical fields do not follow the behaviour, predicted by conventional theory, resulting from the observed mass enhancement near the QCP. Our results imply that the energy of superconducting vortices is enhanced, possibly due to a microscopic mixing of antiferromagnetism and superconductivity, suggesting that a highly unusual vortex state is realized in quantum critical superconductors. PMID:25477044

  12. Quantum criticality and black holes.

    PubMed

    Sachdev, Subir; Müller, Markus

    2009-04-22

    Many condensed matter experiments explore the finite temperature dynamics of systems near quantum critical points. Often, there are no well-defined quasiparticle excitations, and so quantum kinetic equations do not describe the transport properties completely. The theory shows that the transport coefficients are not proportional to a mean free scattering time (as is the case in the Boltzmann theory of quasiparticles), but are completely determined by the absolute temperature and by equilibrium thermodynamic observables. Recently, explicit solutions of this quantum critical dynamics have become possible via the anti-de Sitter/conformal field theory duality discovered in string theory. This shows that the quantum critical theory provides a holographic description of the quantum theory of black holes in a negatively curved anti-de Sitter space, and relates its transport coefficients to properties of the Hawking radiation from the black hole. We review how insights from this connection have led to new results for experimental systems: (i) the vicinity of the superfluid-insulator transition in the presence of an applied magnetic field, and its possible application to measurements of the Nernst effect in the cuprates, (ii) the magnetohydrodynamics of the plasma of Dirac electrons in graphene and the prediction of a hydrodynamic cyclotron resonance. PMID:21825396

  13. Three studies in quantum criticality

    NASA Astrophysics Data System (ADS)

    Ramazashvili, Revaz

    This thesis has been unified by the general topic of quantum criticality, an area of active current research which draws inspiration from the ongoing experiments on a host of T = 0 transitions of various nature, such as magnetic transitions, metal-insulator and superconductor-insulator transitions, Quantum Hall plateau-to-plateau transitions, and many others. In addition to the experimental motivation, the field is being driven by the internal demands of the theory, as many fundamental questions regarding e.g. the nature of the order parameter or the effects of disorder still remain to be answered. Chapter 1, the Introduction, briefly covers the key theoretical concepts and describes relevant materials. In Chapter 2 of the thesis, it is shown that, for a superconductor with a gap which is odd with respect to reflection in the Fermi surface, it is possible to suppress the transition temperature to zero without violating either the time reversal or the translational invariance. This feature is a qualitative hallmark of such superconductors, distinguishing them from isotropic BCS superconductors as well as from superconductors with anisotropic pairing. The pair propagator is calculated dose to this quantum critical point along with several observable quantities. It is argued that experimental studies of a superconducting quantum critical point in clean materials may provide a diagnostic tool for unusual mechanisms of superconductivity. Chapter 3 of the thesis concentrates on an s-wave superconductor near a quantum critical point driven by pairbreaking disorder. The disorder average of the pair propagator is calculated diagrammatically, and the low-temperature thermodynamic and transport properties are evaluated. It is argued that, in the absence of the effects of glassiness, this description should hold equally well for a strong-coupling superconductor at a quantum critical point. Chapter 4 presents a phenomenological theory of the quantum critical point observed in

  14. Quantum critical scaling in graphene.

    PubMed

    Sheehy, Daniel E; Schmalian, Jörg

    2007-11-30

    We show that the emergent relativistic symmetry of electrons in graphene near its quantum critical point (QCP) implies a crucial importance of the Coulomb interaction. We derive scaling laws, valid near the QCP, that dictate the nontrivial magnetic and charge response of interacting graphene. Our analysis yields numerous predictions for how the Coulomb interaction will be manifested in experimental observables such as the diamagnetic response and electronic compressibility. PMID:18233313

  15. Quantum-to-classical crossover near quantum critical point

    PubMed Central

    Vasin, M.; Ryzhov, V.; Vinokur, V. M.

    2015-01-01

    A quantum phase transition (QPT) is an inherently dynamic phenomenon. However, while non-dissipative quantum dynamics is described in detail, the question, that is not thoroughly understood is how the omnipresent dissipative processes enter the critical dynamics near a quantum critical point (QCP). Here we report a general approach enabling inclusion of both adiabatic and dissipative processes into the critical dynamics on the same footing. We reveal three distinct critical modes, the adiabatic quantum mode (AQM), the dissipative classical mode [classical critical dynamics mode (CCDM)], and the dissipative quantum critical mode (DQCM). We find that as a result of the transition from the regime dominated by thermal fluctuations to that governed by the quantum ones, the system acquires effective dimension d + zΛ(T), where z is the dynamical exponent, and temperature-depending parameter Λ(T) ∈ [0, 1] decreases with the temperature such that Λ(T = 0) = 1 and Λ(T → ∞) = 0. Our findings lead to a unified picture of quantum critical phenomena including both dissipation- and dissipationless quantum dynamic effects and offer a quantitative description of the quantum-to-classical crossover. PMID:26688102

  16. Quantum-to-classical crossover near quantum critical point

    SciTech Connect

    Vasin, M.; Ryzhov, V.; Vinokur, V. M.

    2015-12-21

    A quantum phase transition (QPT) is an inherently dynamic phenomenon. However, while non-dissipative quantum dynamics is described in detail, the question, that is not thoroughly understood is how the omnipresent dissipative processes enter the critical dynamics near a quantum critical point (QCP). Here we report a general approach enabling inclusion of both adiabatic and dissipative processes into the critical dynamics on the same footing. We reveal three distinct critical modes, the adiabatic quantum mode (AQM), the dissipative classical mode [classical critical dynamics mode (CCDM)], and the dissipative quantum critical mode (DQCM). We find that as a result of the transition from the regime dominated by thermal fluctuations to that governed by the quantum ones, the system acquires effective dimension d+zΛ(T), where z is the dynamical exponent, and temperature-depending parameter Λ(T)ε[0, 1] decreases with the temperature such that Λ(T=0) = 1 and Λ(T →∞) = 0. Lastly, our findings lead to a unified picture of quantum critical phenomena including both dissipation- and dissipationless quantum dynamic effects and offer a quantitative description of the quantum-to-classical crossover.

  17. Quantum-to-classical crossover near quantum critical point

    DOE PAGESBeta

    Vasin, M.; Ryzhov, V.; Vinokur, V. M.

    2015-12-21

    A quantum phase transition (QPT) is an inherently dynamic phenomenon. However, while non-dissipative quantum dynamics is described in detail, the question, that is not thoroughly understood is how the omnipresent dissipative processes enter the critical dynamics near a quantum critical point (QCP). Here we report a general approach enabling inclusion of both adiabatic and dissipative processes into the critical dynamics on the same footing. We reveal three distinct critical modes, the adiabatic quantum mode (AQM), the dissipative classical mode [classical critical dynamics mode (CCDM)], and the dissipative quantum critical mode (DQCM). We find that as a result of the transitionmore » from the regime dominated by thermal fluctuations to that governed by the quantum ones, the system acquires effective dimension d+zΛ(T), where z is the dynamical exponent, and temperature-depending parameter Λ(T)ε[0, 1] decreases with the temperature such that Λ(T=0) = 1 and Λ(T →∞) = 0. Lastly, our findings lead to a unified picture of quantum critical phenomena including both dissipation- and dissipationless quantum dynamic effects and offer a quantitative description of the quantum-to-classical crossover.« less

  18. Universal quantum correlation close to quantum critical phenomena

    PubMed Central

    Qin, Meng; Ren, Zhong-Zhou; Zhang, Xin

    2016-01-01

    We study the ground state quantum correlation of Ising model in a transverse field (ITF) by implementing the quantum renormalization group (QRG) theory. It is shown that various quantum correlation measures and the Clauser-Horne-Shimony-Holt inequality will highlight the critical point related with quantum phase transitions, and demonstrate nonanalytic phenomena and scaling behavior when the size of the systems becomes large. Our results also indicate a universal behavior of the critical exponent of ITF under QRG theory that the critical exponent of different measures is identical, even when the quantities vary from entanglement measures to quantum correlation measures. This means that the two kinds of quantum correlation criterion including the entanglement-separability paradigm and the information-theoretic paradigm have some connections between them. These remarkable behaviors may have important implications on condensed matter physics because the critical exponent directly associates with the correlation length exponent. PMID:27189504

  19. Universal quantum correlation close to quantum critical phenomena.

    PubMed

    Qin, Meng; Ren, Zhong-Zhou; Zhang, Xin

    2016-05-18

    We study the ground state quantum correlation of Ising model in a transverse field (ITF) by implementing the quantum renormalization group (QRG) theory. It is shown that various quantum correlation measures and the Clauser-Horne-Shimony-Holt inequality will highlight the critical point related with quantum phase transitions, and demonstrate nonanalytic phenomena and scaling behavior when the size of the systems becomes large. Our results also indicate a universal behavior of the critical exponent of ITF under QRG theory that the critical exponent of different measures is identical, even when the quantities vary from entanglement measures to quantum correlation measures. This means that the two kinds of quantum correlation criterion including the entanglement-separability paradigm and the information-theoretic paradigm have some connections between them. These remarkable behaviors may have important implications on condensed matter physics because the critical exponent directly associates with the correlation length exponent.

  20. Controlling superconductivity by tunable quantum critical points.

    PubMed

    Seo, S; Park, E; Bauer, E D; Ronning, F; Kim, J N; Shim, J-H; Thompson, J D; Park, Tuson

    2015-03-04

    The heavy fermion compound CeRhIn5 is a rare example where a quantum critical point, hidden by a dome of superconductivity, has been explicitly revealed and found to have a local nature. The lack of additional examples of local types of quantum critical points associated with superconductivity, however, has made it difficult to unravel the role of quantum fluctuations in forming Cooper pairs. Here, we show the precise control of superconductivity by tunable quantum critical points in CeRhIn5. Slight tin-substitution for indium in CeRhIn5 shifts its antiferromagnetic quantum critical point from 2.3 GPa to 1.3 GPa and induces a residual impurity scattering 300 times larger than that of pure CeRhIn5, which should be sufficient to preclude superconductivity. Nevertheless, superconductivity occurs at the quantum critical point of the tin-doped metal. These results underline that fluctuations from the antiferromagnetic quantum criticality promote unconventional superconductivity in CeRhIn5.

  1. Controlling superconductivity by tunable quantum critical points.

    PubMed

    Seo, S; Park, E; Bauer, E D; Ronning, F; Kim, J N; Shim, J-H; Thompson, J D; Park, Tuson

    2015-01-01

    The heavy fermion compound CeRhIn5 is a rare example where a quantum critical point, hidden by a dome of superconductivity, has been explicitly revealed and found to have a local nature. The lack of additional examples of local types of quantum critical points associated with superconductivity, however, has made it difficult to unravel the role of quantum fluctuations in forming Cooper pairs. Here, we show the precise control of superconductivity by tunable quantum critical points in CeRhIn5. Slight tin-substitution for indium in CeRhIn5 shifts its antiferromagnetic quantum critical point from 2.3 GPa to 1.3 GPa and induces a residual impurity scattering 300 times larger than that of pure CeRhIn5, which should be sufficient to preclude superconductivity. Nevertheless, superconductivity occurs at the quantum critical point of the tin-doped metal. These results underline that fluctuations from the antiferromagnetic quantum criticality promote unconventional superconductivity in CeRhIn5. PMID:25737108

  2. Quantum Criticality and Black Holes

    SciTech Connect

    Sachdev, Subir

    2007-08-22

    I will describe the behavior of a variety of condensed matter systems in the vicinity of zero temperature quantum phase transitions. There is a remarkable analogy between the hydrodynamics of such systems and the quantum theory of black holes. I will show how insights from this analogy have shed light on recent experiments on the cuprate high temperature superconductors. Studies of new materials and trapped ultracold atoms are yielding new quantum phases, with novel forms of quantum entanglement. Some materials are of technological importance: e.g. high temperature superconductors. Exact solutions via black hole mapping have yielded first exact results for transport coefficients in interacting many-body systems, and were valuable in determining general structure of hydrodynamics. Theory of VBS order and Nernst effect in cuprates. Tabletop 'laboratories for the entire universe': quantum mechanics of black holes, quark-gluon plasma, neutrons stars, and big-bang physics.

  3. Quantum Criticality and Black Holes

    ScienceCinema

    Sachdev, Subir [Harvard University, Cambridge, Massachusetts, United States

    2016-07-12

    I will describe the behavior of a variety of condensed matter systems in the vicinity of zero temperature quantum phase transitions. There is a remarkable analogy between the hydrodynamics of such systems and the quantum theory of black holes. I will show how insights from this analogy have shed light on recent experiments on the cuprate high temperature superconductors. Studies of new materials and trapped ultracold atoms are yielding new quantum phases, with novel forms of quantum entanglement. Some materials are of technological importance: e.g. high temperature superconductors. Exact solutions via black hole mapping have yielded first exact results for transport coefficients in interacting many-body systems, and were valuable in determining general structure of hydrodynamics. Theory of VBS order and Nernst effect in cuprates. Tabletop 'laboratories for the entire universe': quantum mechanics of black holes, quark-gluon plasma, neutrons stars, and big-bang physics.

  4. Nonequilibrium critical scaling in quantum thermodynamics

    NASA Astrophysics Data System (ADS)

    Bayat, Abolfazl; Apollaro, Tony J. G.; Paganelli, Simone; De Chiara, Gabriele; Johannesson, Henrik; Bose, Sougato; Sodano, Pasquale

    2016-05-01

    The emerging field of quantum thermodynamics is contributing important results and insights into archetypal many-body problems, including quantum phase transitions. Still, the question whether out-of-equilibrium quantities, such as fluctuations of work, exhibit critical scaling after a sudden quench in a closed system has remained elusive. Here, we take a novel approach to the problem by studying a quench across an impurity quantum critical point. By performing density matrix renormalization group computations on the two-impurity Kondo model, we are able to establish that the irreversible work produced in a quench exhibits finite-size scaling at quantum criticality. This scaling faithfully predicts the equilibrium critical exponents for the crossover length and the order parameter of the model, and, moreover, implies an exponent for the rescaled irreversible work. By connecting the irreversible work to the two-impurity spin correlation function, our findings can be tested experimentally.

  5. Quantum critical behavior in heavy electron materials

    PubMed Central

    Yang, Yi-feng; Pines, David

    2014-01-01

    Quantum critical behavior in heavy electron materials is typically brought about by changes in pressure or magnetic field. In this paper, we develop a simple unified model for the combined influence of pressure and magnetic field on the effectiveness of the hybridization that plays a central role in the two-fluid description of heavy electron emergence. We show that it leads to quantum critical and delocalization lines that accord well with those measured for CeCoIn5, yields a quantitative explanation of the field and pressure-induced changes in antiferromagnetic ordering and quantum critical behavior measured for YbRh2Si2, and provides a valuable framework for describing the role of magnetic fields in bringing about quantum critical behavior in other heavy electron materials. PMID:24912172

  6. Boundary quantum critical phenomena with entanglement renormalization

    SciTech Connect

    Evenbly, G.; Pfeifer, R. N. C.; Tagliacozzo, L.; McCulloch, I. P.; Vidal, G.; Pico, V.; Iblisdir, S.

    2010-10-15

    We propose the use of entanglement renormalization techniques to study boundary critical phenomena on a lattice system. The multiscale entanglement renormalization ansatz (MERA), in its scale invariant version, offers a very compact approximation to quantum critical ground states. Here we show that, by adding a boundary to the MERA, an accurate approximation to the ground state of a semi-infinite critical chain with an open boundary is obtained, from which one can extract boundary scaling operators and their scaling dimensions. As in Wilson's renormalization-group formulation of the Kondo problem, our construction produces, as a side result, an effective chain displaying explicit separation of energy scales. We present benchmark results for the quantum Ising and quantum XX models with free and fixed boundary conditions.

  7. Anomalous quantum criticality in an itinerant ferromagnet.

    PubMed

    Huang, C L; Fuchs, D; Wissinger, M; Schneider, R; Ling, M C; Scheurer, M S; Schmalian, J; Löhneysen, H V

    2015-01-01

    The dynamics of continuous phase transitions is governed by the dynamic scaling exponent relating the correlation length and correlation time. For transitions at finite temperature, thermodynamic critical properties are independent of the dynamic scaling exponent. In contrast, at quantum phase transitions where the transition temperature becomes zero, static and dynamic properties are inherently entangled by virtue of the uncertainty principle. Consequently, thermodynamic scaling equations explicitly contain the dynamic exponent. Here we report on thermodynamic measurements (as a function of temperature and magnetic field) for the itinerant ferromagnet Sr1-xCaxRuO3 where the transition temperature becomes zero for x=0.7. We find dynamic scaling of the magnetization and specific heat with highly unusual quantum critical dynamics. We observe a small dynamic scaling exponent of 1.76 strongly deviating from current models of ferromagnetic quantum criticality and likely being governed by strong disorder in conjunction with strong electron-electron coupling. PMID:26348932

  8. Quantum criticality with two length scales.

    PubMed

    Shao, Hui; Guo, Wenan; Sandvik, Anders W

    2016-04-01

    The theory of deconfined quantum critical (DQC) points describes phase transitions at absolute temperature T = 0 outside the standard paradigm, predicting continuous transformations between certain ordered states where conventional theory would require discontinuities. Numerous computer simulations have offered no proof of such transitions, instead finding deviations from expected scaling relations that neither were predicted by the DQC theory nor conform to standard scenarios. Here we show that this enigma can be resolved by introducing a critical scaling form with two divergent length scales. Simulations of a quantum magnet with antiferromagnetic and dimerized ground states confirm the form, proving a continuous transition with deconfined excitations and also explaining anomalous scaling at T > 0. Our findings revise prevailing paradigms for quantum criticality, with potential implications for many strongly correlated materials. PMID:26989196

  9. Quantum criticality with two length scales

    NASA Astrophysics Data System (ADS)

    Shao, Hui; Guo, Wenan; Sandvik, Anders W.

    2016-04-01

    The theory of deconfined quantum critical (DQC) points describes phase transitions at absolute temperature T = 0 outside the standard paradigm, predicting continuous transformations between certain ordered states where conventional theory would require discontinuities. Numerous computer simulations have offered no proof of such transitions, instead finding deviations from expected scaling relations that neither were predicted by the DQC theory nor conform to standard scenarios. Here we show that this enigma can be resolved by introducing a critical scaling form with two divergent length scales. Simulations of a quantum magnet with antiferromagnetic and dimerized ground states confirm the form, proving a continuous transition with deconfined excitations and also explaining anomalous scaling at T > 0. Our findings revise prevailing paradigms for quantum criticality, with potential implications for many strongly correlated materials.

  10. Anomalous superfluid density in quantum critical superconductors

    PubMed Central

    Hashimoto, Kenichiro; Mizukami, Yuta; Katsumata, Ryo; Shishido, Hiroaki; Yamashita, Minoru; Ikeda, Hiroaki; Matsuda, Yuji; Schlueter, John A.; Fletcher, Jonathan D.; Carrington, Antony; Gnida, Daniel; Kaczorowski, Dariusz; Shibauchi, Takasada

    2013-01-01

    When a second-order magnetic phase transition is tuned to zero temperature by a nonthermal parameter, quantum fluctuations are critically enhanced, often leading to the emergence of unconventional superconductivity. In these “quantum critical” superconductors it has been widely reported that the normal-state properties above the superconducting transition temperature Tc often exhibit anomalous non-Fermi liquid behaviors and enhanced electron correlations. However, the effect of these strong critical fluctuations on the superconducting condensate below Tc is less well established. Here we report measurements of the magnetic penetration depth in heavy-fermion, iron-pnictide, and organic superconductors located close to antiferromagnetic quantum critical points, showing that the superfluid density in these nodal superconductors universally exhibits, unlike the expected T-linear dependence, an anomalous 3/2 power-law temperature dependence over a wide temperature range. We propose that this noninteger power law can be explained if a strong renormalization of effective Fermi velocity due to quantum fluctuations occurs only for momenta k close to the nodes in the superconducting energy gap Δ(k). We suggest that such “nodal criticality” may have an impact on low-energy properties of quantum critical superconductors. PMID:23404698

  11. Quantum criticality at the origin of life

    NASA Astrophysics Data System (ADS)

    Vattay, Gábor; Salahub, Dennis; Csabai, István; Nassimi, Ali; Kaufmann, Stuart A.

    2015-07-01

    Why life persists at the edge of chaos is a question at the very heart of evolution. Here we show that molecules taking part in biochemical processes from small molecules to proteins are critical quantum mechanically. Electronic Hamiltonians of biomolecules are tuned exactly to the critical point of the metal-insulator transition separating the Anderson localized insulator phase from the conducting disordered metal phase. Using tools from Random Matrix Theory we confirm that the energy level statistics of these biomolecules show the universal transitional distribution of the metal-insulator critical point and the wave functions are multifractals in accordance with the theory of Anderson transitions. The findings point to the existence of a universal mechanism of charge transport in living matter. The revealed bio-conductor material is neither a metal nor an insulator but a new quantum critical material which can exist only in highly evolved systems and has unique material properties.

  12. Quantum criticality in a uniaxial organic ferroelectric

    NASA Astrophysics Data System (ADS)

    Rowley, S. E.; Hadjimichael, M.; Ali, M. N.; Durmaz, Y. C.; Lashley, J. C.; Cava, R. J.; Scott, J. F.

    2015-10-01

    Tris-sarcosine calcium chloride (TSCC) is a highly uniaxial ferroelectric with a Curie temperature of approximately 130 K. By suppressing ferroelectricity with bromine substitution on the chlorine sites, pure single crystals were tuned through a ferroelectric quantum phase transition. The resulting quantum critical regime was investigated in detail and was found to persist up to temperatures of at least 30-40 K. The nature of long-range dipole interactions in uniaxial materials, which lead to non-analytical terms in the free-energy expansion in the polarization, predict a dielectric susceptibility varying as 1/T 3close to the quantum critical point. Rather than this, we find that the dielectric susceptibility varies as 1/T 2 as expected and observed in better known multi-axial systems. We explain this result by identifying the ultra-weak nature of the dipole moments in the TSCC family of crystals. Interestingly, we observe a shallow minimum in the inverse dielectric function at low temperatures close to the quantum critical point in paraelectric samples that may be attributed to the coupling of quantum polarization and strain fields. Finally, we present results of the heat capacity and electro-caloric effect and explain how the time dependence of the polarization in ferroelectrics and paraelectrics should be considered when making quantitative estimates of temperature changes induced by applied electric fields.

  13. Quantum Criticality in an Organic Magnet

    SciTech Connect

    Stone, Matthew B; Broholm, C. L.; Reich, D. H.; Tchemyshyov, O.; Vorderwisch, P.; Harrison, N.

    2006-01-01

    Exchange interactions between S=1/2 sites in piperazinium hexachlorodicuprate produce a frustrated bilayer magnet with a singlet ground state. We have determined the field-temperature phase diagram by high field magnetization and neutron scattering experiments. There are two quantum critical points: H{sub c1}=7.5 T separates a quantum paramagnet phase from a three dimensional, antiferromagnetically ordered state while H{sub c2}=37 T marks the onset of a fully polarized state. The ordered phase, which we describe as a magnon Bose-Einstein condensate (BEC), is embedded in a quantum critical regime with short range correlations. A low temperature anomaly in the BEC phase boundary indicates that additional low energy features of the material become important near H{sub c1}.

  14. Sensitive chemical compass assisted by quantum criticality

    NASA Astrophysics Data System (ADS)

    Cai, C. Y.; Ai, Qing; Quan, H. T.; Sun, C. P.

    2012-02-01

    A radical-pair-based chemical reaction might be used by birds for navigation via the geomagnetic direction. The inherent physical mechanism is that the quantum coherent transition from a singlet state to triplet states of the radical pair could respond to a weak magnetic field and be sensitive to the direction of such a field; this then results in different photopigments to be sensed by the avian eyes. Here, we propose a quantum bionic setup, inspired by the avian compass, as an ultrasensitive probe of a weak magnetic field based on the quantum phase transition of the environments of the two electrons in the radical pair. We prove that the yield of the chemical products via recombination from the singlet state is determined by the Loschmidt echo of the environments with interacting nuclear spins. Thus quantum criticality of environments could enhance the sensitivity of detection of weak magnetic fields.

  15. Quantum Critical Quasiparticle Scattering within the Superconducting State of CeCoIn5

    DOE PAGESBeta

    Paglione, Johnpierre; Tanatar, M. A.; Reid, J.-Ph.; Shakeripour, H.; Petrovic, C.; Taillefer, Louis

    2016-06-27

    The thermal conductivity κ of the heavy-fermion metal CeCoIn5 was measured in the normal and superconducting states as a function of temperature T and magnetic field H, for a current and field parallel to the [100] direction. Inside the superconducting state, when the field is lower than the upper critical field Hc2, κ/T is found to increase as T→0, just as in a metal and in contrast to the behavior of all known superconductors. This is due to unpaired electrons on part of the Fermi surface, which dominate the transport above a certain field. The evolution of κ/T with fieldmore » reveals that the electron-electron scattering (or transport mass m*) of those unpaired electrons diverges as H→Hc2 from below, in the same way that it does in the normal state as H→Hc2 from above. This shows that the unpaired electrons sense the proximity of the field-tuned quantum critical point of CeCoIn5 at H*=Hc2 even from inside the superconducting state. In conclusion, the fact that the quantum critical scattering of the unpaired electrons is much weaker than the average scattering of all electrons in the normal state reveals a k-space correlation between the strength of pairing and the strength of scattering, pointing to a common mechanism, presumably antiferromagnetic fluctuations.« less

  16. Quantum Critical Quasiparticle Scattering within the Superconducting State of CeCoIn5

    NASA Astrophysics Data System (ADS)

    Paglione, Johnpierre; Tanatar, M. A.; Reid, J.-Ph.; Shakeripour, H.; Petrovic, C.; Taillefer, Louis

    2016-07-01

    The thermal conductivity κ of the heavy-fermion metal CeCoIn5 was measured in the normal and superconducting states as a function of temperature T and magnetic field H , for a current and field parallel to the [100] direction. Inside the superconducting state, when the field is lower than the upper critical field Hc 2, κ /T is found to increase as T →0 , just as in a metal and in contrast to the behavior of all known superconductors. This is due to unpaired electrons on part of the Fermi surface, which dominate the transport above a certain field. The evolution of κ /T with field reveals that the electron-electron scattering (or transport mass m⋆) of those unpaired electrons diverges as H →Hc 2 from below, in the same way that it does in the normal state as H →Hc 2 from above. This shows that the unpaired electrons sense the proximity of the field-tuned quantum critical point of CeCoIn5 at H⋆=Hc 2 even from inside the superconducting state. The fact that the quantum critical scattering of the unpaired electrons is much weaker than the average scattering of all electrons in the normal state reveals a k -space correlation between the strength of pairing and the strength of scattering, pointing to a common mechanism, presumably antiferromagnetic fluctuations.

  17. NpCoGe, near quantum criticality?

    NASA Astrophysics Data System (ADS)

    Colineau, E.; Eloirdi, R.; Griveau, J.-C.; Gaczynski, P.; Shick, A. B.

    2013-05-01

    The magnetic and electronic properties of NpCoGe are reported. NpCoGe orders antiferromagnetically at T N ≈ 13 K with an average ordered magnetic moment < µ N p > = 0.80 µ B . The comparison with NpRhGe and uranium analogues suggests the leading role of f-d hybridization, the rather delocalized character of 5f electrons in NpCoGe and its possible proximity to a magnetic quantum critical point.

  18. Dynamic trapping near a quantum critical point

    NASA Astrophysics Data System (ADS)

    Kolodrubetz, Michael; Katz, Emanuel; Polkovnikov, Anatoli

    2015-02-01

    The study of dynamics in closed quantum systems has been revitalized by the emergence of experimental systems that are well-isolated from their environment. In this paper, we consider the closed-system dynamics of an archetypal model: spins driven across a second-order quantum critical point, which are traditionally described by the Kibble-Zurek mechanism. Imbuing the driving field with Newtonian dynamics, we find that the full closed system exhibits a robust new phenomenon—dynamic critical trapping—in which the system is self-trapped near the critical point due to efficient absorption of field kinetic energy by heating the quantum spins. We quantify limits in which this phenomenon can be observed and generalize these results by developing a Kibble-Zurek scaling theory that incorporates the dynamic field. Our findings can potentially be interesting in the context of early universe physics, where the role of the driving field is played by the inflaton or a modulus field.

  19. Critical currents of ideal quantum Hall superfluids

    NASA Astrophysics Data System (ADS)

    Abolfath, M.; MacDonald, A. H.; Radzihovsky, Leo

    2003-10-01

    Filling factor ν=1 bilayer electron systems in the quantum Hall regime have an excitonic-condensate superfluid ground state when the layer separation d is less than a critical value dc. On a quantum Hall plateau current injected and removed through one of the two layers drives a dissipationless edge current that carries parallel currents and a dissipationless bulk supercurrent that carries opposing currents in the two layers. In this paper we discuss the theory of finite supercurrent bilayer states, both in the presence and in the absence of symmetry breaking interlayer hybridization. Solutions to the microscopic mean-field equations exist at all condensate phase winding rates for zero and sufficiently weak hybridization strengths. We find, however, that collective instabilities occur when the supercurrent exceeds a critical value determined primarily by a competition between direct and exchange interlayer Coulomb interactions. The critical current is estimated using a local stability criterion and varies as (dc-d)1/2 when d approaches dc from below. For large interlayer hybridization, we find that the critical current is limited by a soliton instability of microscopic origin.

  20. Composite fermions and the field-tuned superconductor-insulator transition

    NASA Astrophysics Data System (ADS)

    Mulligan, Michael; Raghu, S.

    2016-05-01

    In several two-dimensional films that exhibit a magnetic field-tuned superconductor to insulator transition (SIT), stable metallic phases have been observed. Building on the `dirty boson' description of the SIT, we suggest that the metallic region is analogous to the composite Fermi liquid observed about half-filled Landau levels of the two-dimensional electron gas. The composite fermions here are mobile vortices attached to one flux quantum of an emergent gauge field. The composite vortex liquid is a 2D non-Fermi liquid metal, which we argue is stable to weak quenched disorder. We describe several experimental consequences of the emergent composite vortex liquid.

  1. Undercompensated kondo impurity with quantum critical point

    PubMed

    Schlottmann

    2000-02-14

    The low-temperature properties of a magnetic impurity of spin S interacting with an electron gas via anisotropic spin exchange are studied via Bethe's ansatz. For S>1/2 the impurity is only partially compensated at T = 0, leaving an effective spin that is neither integer nor half integer. The entropy has an essential singularity at H = T = 0, and the susceptibility and the specific heat follow power laws of H and T with nonuniversal exponents, which are the consequence of a quantum critical point. The results for the generalization to an arbitrary number of channels are also reported. PMID:11017567

  2. Order parameter fluctuations at a buried quantum critical point

    PubMed Central

    Feng, Yejun; Wang, Jiyang; Jaramillo, R.; van Wezel, Jasper; Haravifard, S.; Srajer, G.; Liu, Y.; Xu, Z.-A.; Littlewood, P. B.; Rosenbaum, T. F.

    2012-01-01

    Quantum criticality is a central concept in condensed matter physics, but the direct observation of quantum critical fluctuations has remained elusive. Here we present an X-ray diffraction study of the charge density wave (CDW) in 2H-NbSe2 at high pressure and low temperature, where we observe a broad regime of order parameter fluctuations that are controlled by proximity to a quantum critical point. X-rays can track the CDW despite the fact that the quantum critical regime is shrouded inside a superconducting phase; and in contrast to transport probes, allow direct measurement of the critical fluctuations of the charge order. Concurrent measurements of the crystal lattice point to a critical transition that is continuous in nature. Our results confirm the long-standing expectations of enhanced quantum fluctuations in low-dimensional systems, and may help to constrain theories of the quantum critical Fermi surface. PMID:22529348

  3. Fermion-induced quantum critical points: beyond Landau criterion

    NASA Astrophysics Data System (ADS)

    Yao, Hong; Li, Zi-Xiang; Jiang, Yi-Fan; Jian, Shao-Kai

    According to Landau criterion, phase transitions must be first-order when cubic terms of order parameters in the Landau-Ginzburg free energy are allowed by symmetry. Here, from both renormalization group analysis and sign-problem-free quantum Monte Carlo simulations, we show that second-order quantum phase transitions can occur at such putatively-first-order quantum phase transitions in strongly-interacting Dirac semimetals in two spatial dimensions. Such type of Landau-criterion-violating quantum critical points are induced by massless fermionic modes at the quantum phase transitions. We call them ``fermion-induced quantum critical points''. From Majorana-quantum-Monte-Carlo simulations and renormalization analysis, we find that the critical exponentials at the kekule valence-bond-solid transition of the Dirac fermions on the honeycomb lattice are highly-nonclassical. We also discuss experimental signatures of the kekule quantum critical point which may be realized in graphene-like systems.

  4. Quantum critical metals in 4 -ɛ dimensions

    NASA Astrophysics Data System (ADS)

    Torroba, Gonzalo; Wang, Huajia

    2014-10-01

    We study the quantum theory of a Fermi surface coupled to a gapless boson scalar in D =4 -ɛ space-time dimensions as a simple model for non-Fermi liquids (NFL) near a quantum phase transition. Our analysis takes into account the full backreaction from Landau damping of the boson, and obtains an RG flow that proceeds through three distinct stages. Above the scale of Landau damping, the Fermi velocity flows to zero, while the coupling evolves according to its classical dimension. Once damping becomes important, its backreaction leads to a crossover regime where dynamic and static damping effects compete and the fermion self-energy does not respect scaling. Below this crossover and having tuned the boson to criticality, the theory flows to a z =3 scalar interacting with an NFL. We finally analyze the IR phases of the theory with arbitrary number of flavors Nc. When Nc is small, the superconducting dome covers the NFL behavior; strikingly, for moderately large Nc, we find that NFL effects become important first, before the onset of superconductivity. A generic prediction of the theory is that the Fermi velocity and quasiparticle residue vanish with a power law ωɛ as the fixed point is approached. These features may be useful for understanding some of the phenomenology of high-Tc materials in a systematic ɛ expansion.

  5. Dynamics and conductivity near quantum criticality

    NASA Astrophysics Data System (ADS)

    Gazit, Snir; Podolsky, Daniel; Auerbach, Assa; Arovas, Daniel P.

    2013-12-01

    Relativistic O(N) field theories are studied near the quantum-critical point in two space dimensions. We compute dynamical correlations by large-scale Monte Carlo simulations and numerical analytic continuation. In the ordered side, the scalar spectral function exhibits a universal peak at the Higgs mass. For N=3 and 4, we confirm its ω3 rise at low frequency. On the disordered side, the spectral function exhibits a sharp gap. For N=2, the dynamical conductivity rises above a threshold at the Higgs mass (density gap), in the superfluid (Mott insulator) phase. For charged bosons (Josephson arrays), the power-law rise above the Higgs mass increases from two to four. Approximate charge-vortex duality is reflected in the ratio of imaginary conductivities on either side of the transition. We determine the critical conductivity to be σc*=0.3(±0.1)×4e2/h and describe a generalization of the worm algorithm to N>2. We use a singular value decomposition error analysis for the numerical analytic continuation.

  6. Fisher information in a quantum-critical environment

    SciTech Connect

    Sun Zhe; Ma Jian; Lu Xiaoming; Wang Xiaoguang

    2010-08-15

    We consider a process of parameter estimation in a spin-j system surrounded by a quantum-critical spin chain. Quantum Fisher information lies at the heart of the estimation task. We employ Ising spin chain in a transverse field as the environment which exhibits a quantum phase transition. Fisher information decays with time almost monotonously when the environment reaches the critical point. By choosing a fixed time or taking the time average, one can see the quantum Fisher information presents a sudden drop at the critical point. Different initial states of the environment are considered. The phenomenon that the quantum Fisher information, namely, the precision of estimation, changes dramatically can be used to detect the quantum criticality of the environment. We also introduce a general method to obtain the maximal Fisher information for a given state.

  7. Critical integer quantum Hall topology and the integrable Maryland model as a topological quantum critical point

    NASA Astrophysics Data System (ADS)

    Ganeshan, Sriram; Kechedzhi, K.; Das Sarma, S.

    2014-07-01

    One-dimensional tight binding models such as the Aubry-André-Harper (AAH) model (with an on-site cosine potential) and the integrable Maryland model (with an on-site tangent potential) have been the subject of extensive theoretical research in localization studies. AAH can be directly mapped onto the two-dimensional (2D) Hofstadter model which manifests the integer quantum Hall topology on a lattice. However, such a connection needs to be made for the Maryland model (MM). Here we describe a generalized model that contains AAH and MM as the limiting cases with the MM lying precisely at a topological quantum phase transition (TQPT) point. A remarkable feature of this critical point is that the one-dimensional MM retains well defined energy gaps whereas the equivalent 2D model becomes gapless, signifying the 2D nature of the TQPT.

  8. Quantum criticality in ferromagnetic single-electron transistors.

    PubMed

    Kirchner, Stefan; Zhu, Lijun; Si, Qimiao; Natelson, D

    2005-12-27

    Considerable evidence exists for the failure of the traditional theory of quantum critical points, pointing to the need to incorporate novel excitations. The destruction of Kondo entanglement and the concomitant critical Kondo effect may underlie these emergent excitations in heavy fermion metals (a prototype system for quantum criticality), but the effect remains poorly understood. Here, we show how ferromagnetic single-electron transistors can be used to study this effect. We theoretically demonstrate a gate-voltage-induced quantum phase transition. The critical Kondo effect is manifested in a fractional-power-law dependence of the conductance on temperature (T). The AC conductance and thermal noise spectrum have related power-law dependences on frequency (omega) and, in addition, show an omega/T scaling. Our results imply that the ferromagnetic nanostructure constitutes a realistic model system to elucidate magnetic quantum criticality that is central to the heavy fermions and other bulk materials with non-Fermi liquid behavior. PMID:16354834

  9. Characteristic signatures of quantum criticality driven by geometrical frustration

    PubMed Central

    Tokiwa, Yoshifumi; Stingl, Christian; Kim, Moo-Sung; Takabatake, Toshiro; Gegenwart, Philipp

    2015-01-01

    Geometrical frustration describes situations where interactions are incompatible with the lattice geometry and stabilizes exotic phases such as spin liquids. Whether geometrical frustration of magnetic interactions in metals can induce unconventional quantum critical points is an active area of research. We focus on the hexagonal heavy fermion metal CeRhSn, where the Kondo ions are located on distorted kagome planes stacked along the c axis. Low-temperature specific heat, thermal expansion, and magnetic Grüneisen parameter measurements prove a zero-field quantum critical point. The linear thermal expansion, which measures the initial uniaxial pressure derivative of the entropy, displays a striking anisotropy. Critical and noncritical behaviors along and perpendicular to the kagome planes, respectively, prove that quantum criticality is driven be geometrical frustration. We also discovered a spin flop–type metamagnetic crossover. This excludes an itinerant scenario and suggests that quantum criticality is related to local moments in a spin liquid–like state. PMID:26601165

  10. Quantum critical transport at a continuous metal-insulator transition

    NASA Astrophysics Data System (ADS)

    Haldar, P.; Laad, M. S.; Hassan, S. R.

    2016-08-01

    In contrast to the first-order correlation-driven Mott metal-insulator transition, continuous disorder-driven transitions are intrinsically quantum critical. Here, we investigate transport quantum criticality in the Falicov-Kimball model, a representative of the latter class in the strong disorder category. Employing cluster-dynamical mean-field theory, we find clear and anomalous quantum critical scaling behavior manifesting as perfect mirror symmetry of scaling curves on both sides of the MIT. Surprisingly, we find that the beta function β (g ) scales as log(g ) deep into the bad-metallic phase as well, providing a sound unified basis for these findings. We argue that such strong localization quantum criticality may manifest in real three-dimensional systems where disorder effects are more important than electron-electron interactions.

  11. Transport signatures of quantum critically in Cr at high pressure.

    SciTech Connect

    Jaramillo, R.; Feng, Y.; Wang, J.; Rosenbaum, T. F.

    2010-08-03

    The elemental antiferromagnet Cr at high pressure presents a new type of naked quantum critical point that is free of disorder and symmetry-breaking fields. Here we measure magnetotransport in fine detail around the critical pressure, P{sub c} {approx} 10 GPa, in a diamond anvil cell and reveal the role of quantum critical fluctuations at the phase transition. As the magnetism disappears and T {yields} 0, the magntotransport scaling converges to a non-mean-field form that illustrates the reconstruction of the magnetic Fermi surface, and is distinct from the critical scaling measured in chemically disordered Cr:V under pressure. The breakdown of itinerant antiferromagnetism only comes clearly into view in the clean limit, establishing disorder as a relevant variable at a quantum phase transition.

  12. Hall effect in quantum critical charge-cluster glass

    NASA Astrophysics Data System (ADS)

    Wu, Jie; Bollinger, Anthony T.; Sun, Yujie

    2016-04-01

    Upon doping, cuprates undergo a quantum phase transition from an insulator to a d-wave superconductor. The nature of this transition and of the insulating state is vividly debated. Here, we study the Hall effect in La2-xSrxCuO4 (LSCO) samples doped near the quantum critical point at x ˜ 0.06. Dramatic fluctuations in the Hall resistance appear below TCG ˜ 1.5 K and increase as the sample is cooled down further, signaling quantum critical behavior. We explore the doping dependence of this effect in detail, by studying a combinatorial LSCO library in which the Sr content is varied in extremely fine steps, Δx ˜ 0.00008. We observe that quantum charge fluctuations wash out when superconductivity emerges but can be restored when the latter is suppressed by applying a magnetic field, showing that the two instabilities compete for the ground state.

  13. Hall effect in quantum critical charge-cluster glass.

    PubMed

    Wu, Jie; Bollinger, Anthony T; Sun, Yujie; Božović, Ivan

    2016-04-19

    Upon doping, cuprates undergo a quantum phase transition from an insulator to a d-wave superconductor. The nature of this transition and of the insulating state is vividly debated. Here, we study the Hall effect in La2-xSrxCuO4(LSCO) samples doped near the quantum critical point atx∼ 0.06. Dramatic fluctuations in the Hall resistance appear belowTCG∼ 1.5 K and increase as the sample is cooled down further, signaling quantum critical behavior. We explore the doping dependence of this effect in detail, by studying a combinatorial LSCO library in which the Sr content is varied in extremely fine steps,Δx∼ 0.00008. We observe that quantum charge fluctuations wash out when superconductivity emerges but can be restored when the latter is suppressed by applying a magnetic field, showing that the two instabilities compete for the ground state. PMID:27044081

  14. Hall effect in quantum critical charge-cluster glass

    PubMed Central

    Wu, Jie; Bollinger, Anthony T.; Sun, Yujie; Božović, Ivan

    2016-01-01

    Upon doping, cuprates undergo a quantum phase transition from an insulator to a d-wave superconductor. The nature of this transition and of the insulating state is vividly debated. Here, we study the Hall effect in La2-xSrxCuO4 (LSCO) samples doped near the quantum critical point at x ∼ 0.06. Dramatic fluctuations in the Hall resistance appear below TCG ∼ 1.5 K and increase as the sample is cooled down further, signaling quantum critical behavior. We explore the doping dependence of this effect in detail, by studying a combinatorial LSCO library in which the Sr content is varied in extremely fine steps, Δx ∼ 0.00008. We observe that quantum charge fluctuations wash out when superconductivity emerges but can be restored when the latter is suppressed by applying a magnetic field, showing that the two instabilities compete for the ground state. PMID:27044081

  15. Hall effect in quantum critical charge-cluster glass.

    PubMed

    Wu, Jie; Bollinger, Anthony T; Sun, Yujie; Božović, Ivan

    2016-04-19

    Upon doping, cuprates undergo a quantum phase transition from an insulator to a d-wave superconductor. The nature of this transition and of the insulating state is vividly debated. Here, we study the Hall effect in La2-xSrxCuO4(LSCO) samples doped near the quantum critical point atx∼ 0.06. Dramatic fluctuations in the Hall resistance appear belowTCG∼ 1.5 K and increase as the sample is cooled down further, signaling quantum critical behavior. We explore the doping dependence of this effect in detail, by studying a combinatorial LSCO library in which the Sr content is varied in extremely fine steps,Δx∼ 0.00008. We observe that quantum charge fluctuations wash out when superconductivity emerges but can be restored when the latter is suppressed by applying a magnetic field, showing that the two instabilities compete for the ground state.

  16. Quantum critical behavior of the quantum Ising model on fractal lattices

    NASA Astrophysics Data System (ADS)

    Yi, Hangmo

    2015-01-01

    I study the properties of the quantum critical point of the transverse-field quantum Ising model on various fractal lattices such as the Sierpiński carpet, Sierpiński gasket, and Sierpiński tetrahedron. Using a continuous-time quantum Monte Carlo simulation method and finite-size scaling analysis, I identify the quantum critical point and investigate its scaling properties. Among others, I calculate the dynamic critical exponent and find that it is greater than one for all three structures. The fact that it deviates from one is a direct consequence of the fractal structures not being integer-dimensional regular lattices. Other critical exponents are also calculated. The exponents are different from those of the classical critical point and satisfy the quantum scaling relation, thus confirming that I have indeed found the quantum critical point. I find that the Sierpiński tetrahedron, of which the dimension is exactly 2, belongs to a different universality class than that of the two-dimensional square lattice. I conclude that the critical exponents depend on more details of the structure than just the dimension and the symmetry.

  17. Magnetic field tuned reentrant superconductivity in out-of-equilibrium aluminum nanowires

    NASA Astrophysics Data System (ADS)

    Bretz-Sullivan, Terence M.; Goldman, A. M.

    2016-05-01

    Perpendicular-to-the-plane magnetic field tuned reentrant superconductivity in out-of-equilibrium, quasi-one-dimensional (quasi-1D) planar nanowires is a novel, counterintuitive phenomenon. It was not until recently that a microscopic mechanism explaining the phenomenon as arising from the coexistence of superconductivity with phase-slip driven dissipation was developed. Here we present results on reentrance phenomena in quasi-1D aluminum nanowires with in-plane magnetic fields, transverse and longitudinal to the nanowire axis. The response to in-plane transverse magnetic fields in this geometry is qualitatively different from that previously reported for perpendicular-to-the-plane field experiments and for in-plane longitudinal field studies. The different feature in the data is an abrupt return to the superconducting state with increasing field at values of field corresponding to a single flux quantum for a short wire and a fractional flux quantum for a long wire. Since these findings are dramatically different from those involving perpendicular-to-the-plane magnetic fields, a different mechanism, as yet unidentified, may be at work.

  18. Quantum criticality in the electron doped cuprates

    NASA Astrophysics Data System (ADS)

    Dagan, Y.; Greene, R. L.

    2007-09-01

    We report transport measurements at low temperatures on the electron doped superconductor Pr 2- xCe xCuO 4- δ. Above a certain doping level we observe an abrupt change in the doping dependence of the Hall coefficient along with a significant change in the temperature dependence of the resistivity. At this doping the spin scattering channel in the magnetoresistance vanishes and the temperature dependence of the Hall angle changes. This suggests a quantum phase transition as a function of doping. This transition is most probably due to vanishing of an antiferromagnetic order persisting into the superconducting dome.

  19. Chalker-Coddington Network Model is Quantum Critical

    NASA Astrophysics Data System (ADS)

    Marston, J. B.; Tsai, Shan-Wen

    1999-06-01

    We show that the localization transition in the integer quantum Hall effect as described by the Chalker-Coddington network model is quantum critical. We first map the anisotropic network model to the problem of diagonalizing a one-dimensional non-Hermitian noncompact supersymmetric lattice Hamiltonian of interacting bosons and fermions. Its behavior is investigated numerically using the density matrix renormalization group method, and critical behavior is found at the plateau transition. This result is confirmed by a generalization of the Lieb-Schultz-Mattis theorem.

  20. Quantum Criticality in the Biased Dicke Model

    PubMed Central

    Zhu, Hanjie; Zhang, Guofeng; Fan, Heng

    2016-01-01

    The biased Dicke model describes a system of biased two-level atoms coupled to a bosonic field, and is expected to produce new phenomena that are not present in the original Dicke model. In this paper, we study the critical properties of the biased Dicke model in the classical oscillator limits. For the finite-biased case in this limit, We present analytical results demonstrating that the excitation energy does not vanish for arbitrary coupling. This indicates that the second order phase transition is avoided in the biased Dicke model, which contrasts to the original Dicke model. We also analyze the squeezing and the entanglement in the ground state, and find that a finite bias will strongly modify their behaviors in the vicinity of the critical coupling point. PMID:26786239

  1. Novel duality in disorder driven local quantum criticality.

    PubMed

    Tran, Minh-Tien; Kim, Ki-Seok

    2010-09-10

    We find that competition between random Kondo and random magnetic correlations results in a quantum phase transition from a local Fermi liquid to a spin liquid. The local charge susceptibility turns out to have exactly the same critical exponent as the local spin susceptibility, suggesting a novel duality between the Kondo singlet phase and the critical local moment state beyond the Landau-Ginzburg-Wilson symmetry breaking framework. This leads us to propose an enhanced symmetry at the local quantum critical point, described by an O(4) vector for spin and charge. The symmetry enhancement serves as a mechanism of electron fractionalization in critical impurity dynamics, where such fractionalized excitations are identified with topological excitations.

  2. Topological crossovers near a quantum critical point

    NASA Astrophysics Data System (ADS)

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

    2011-09-01

    We study the temperature evolution of the single-particle spectrum ɛ-( p) and quasiparticle momentum distribution n( p) of homogeneous strongly correlated Fermi systems beyond a point where the necessary condition for stability of the Landau state is violated, and the Fermi surface becomes multi-connected by virtue of a topological crossover. Attention is focused on the different non-Fermi-liquid temperature regimes experienced by a phase exhibiting a single additional hole pocket compared with the conventional Landau state. A critical experiment is proposed to elucidate the origin of NFL behavior in dense films of liquid 3He.

  3. Quantum clock: A critical discussion on spacetime

    NASA Astrophysics Data System (ADS)

    Burderi, Luciano; Di Salvo, Tiziana; Iaria, Rosario

    2016-03-01

    We critically discuss the measure of very short time intervals. By means of a Gedankenexperiment, we describe an ideal clock based on the occurrence of completely random events. Many previous thought experiments have suggested fundamental Planck-scale limits on measurements of distance and time. Here we present a new type of thought experiment, based on a different type of clock, that provide further support for the existence of such limits. We show that the minimum time interval Δ t that this clock can measure scales as the inverse of its size Δ r . This implies an uncertainty relation between space and time: Δ r Δ t >G ℏ/c4, where G , ℏ, and c are the gravitational constant, the reduced Planck constant, and the speed of light, respectively. We outline and briefly discuss the implications of this uncertainty conjecture.

  4. Superconducting quantum criticality in three-dimensional Luttinger semimetals

    NASA Astrophysics Data System (ADS)

    Boettcher, Igor; Herbut, Igor F.

    2016-05-01

    We study a simple model of three-dimensional fermions close to a quadratic band touching point, built from the celebrated Luttinger single-particle Hamiltonian and an attractive contact interaction between the particles. Such a system displays a quantum critical point between the semimetallic and an s -wave superconducting phase at which the low-energy "Luttinger fermions" are inextricably coupled to the order parameter fluctuations. The quantum critical point is perturbatively accessible near four spatial dimensions, where it features nontrivial scaling with dynamical exponent 1 criticality, such as oscillatory corrections to scaling and its enhanced symmetry, are discussed.

  5. Critical properties of dissipative quantum spin systems in finite dimensions

    NASA Astrophysics Data System (ADS)

    Takada, Kabuki; Nishimori, Hidetoshi

    2016-10-01

    We study the critical properties of finite-dimensional dissipative quantum spin systems with uniform ferromagnetic interactions. Starting from the transverse field Ising model coupled to a bath of harmonic oscillators with Ohmic spectral density, we generalize its classical representation to classical spin systems with O(n) symmetry and then take the large-n limit to reduce the system to a spherical model. The exact solution to the resulting spherical model with long-range interactions along the imaginary time axis shows a phase transition with static critical exponents coinciding with those of the conventional short-range spherical model in d+2 dimensions, where d is the spatial dimensionality of the original quantum system. This implies that the dynamical exponent is z = 2. These conclusions are consistent with the results of Monte Carlo simulations and renormalization group calculations for dissipative transverse field Ising and O(n) models in one and two dimensions. The present approach therefore serves as a useful tool for analytically investigating the properties of quantum phase transitions of the dissipative transverse field Ising and other related models. Our method may also offer a platform to study more complex phase transitions in dissipative finite-dimensional quantum spin systems, which have recently received renewed interest in the context of quantum annealing in a noisy environment.

  6. Stochastic Approximation of Dynamical Exponent at Quantum Critical Point

    NASA Astrophysics Data System (ADS)

    Suwa, Hidemaro; Yasuda, Shinya; Todo, Synge

    We have developed a unified finite-size scaling method for quantum phase transitions that requires no prior knowledge of the dynamical exponent z. During a quantum Monte Carlo simulation, the temperature is automatically tuned by the Robbins-Monro stochastic approximation method, being proportional to the lowest gap of the finite-size system. The dynamical exponent is estimated in a straightforward way from the system-size dependence of the temperature. As a demonstration of our novel method, the two-dimensional S = 1 / 2 quantum XY model, or equivalently the hard-core boson system, in uniform and staggered magnetic fields is investigated in the combination of the world-line quantum Monte Carlo worm algorithm. In the absence of a uniform magnetic field, we obtain the fully consistent result with the Lorentz invariance at the quantum critical point, z = 1 . Under a finite uniform magnetic field, on the other hand, the dynamical exponent becomes two, and the mean-field universality with effective dimension (2+2) governs the quantum phase transition. We will discuss also the system with random magnetic fields, or the dirty boson system, bearing a non-trivial dynamical exponent.Reference: S. Yasuda, H. Suwa, and S. Todo Phys. Rev. B 92, 104411 (2015); arXiv:1506.04837

  7. Stochastic approximation of dynamical exponent at quantum critical point

    NASA Astrophysics Data System (ADS)

    Yasuda, Shinya; Suwa, Hidemaro; Todo, Synge

    2015-09-01

    We have developed a unified finite-size scaling method for quantum phase transitions that requires no prior knowledge of the dynamical exponent z . During a quantum Monte Carlo simulation, the temperature is automatically tuned by the Robbins-Monro stochastic approximation method, being proportional to the lowest gap of the finite-size system. The dynamical exponent is estimated in a straightforward way from the system-size dependence of the temperature. As a demonstration of our novel method, the two-dimensional S =1 /2 quantum X Y model in uniform and staggered magnetic fields is investigated in the combination of the world-line quantum Monte Carlo worm algorithm. In the absence of a uniform magnetic field, we obtain the fully consistent result with the Lorentz invariance at the quantum critical point, z =1 , i.e., the three-dimensional classical X Y universality class. Under a finite uniform magnetic field, on the other hand, the dynamical exponent becomes two, and the mean-field universality with effective dimension (2 +2 ) governs the quantum phase transition.

  8. Quantum critical fluctuations in layered YFe2Al10

    PubMed Central

    Wu, L. S.; Kim, M. S.; Park, K.; Tsvelik, A. M.; Aronson, M. C.

    2014-01-01

    The absence of thermal fluctuations at T = 0 makes it possible to observe the inherently quantum mechanical nature of systems where the competition among correlations leads to different types of collective ground states. Our high precision measurements of the magnetic susceptibility, specific heat, and electrical resistivity in the layered compound YFe2Al10 demonstrate robust field-temperature scaling, evidence that this system is naturally poised without tuning on the verge of ferromagnetic order that occurs exactly at T = 0, where magnetic fields drive the system away from this quantum critical point and restore normal metallic behavior. PMID:25225377

  9. Experimental consequences of quantum critical points at high temperatures

    NASA Astrophysics Data System (ADS)

    Freitas, D. C.; Rodière, P.; Núñez, M.; Garbarino, G.; Sulpice, A.; Marcus, J.; Gay, F.; Continentino, M. A.; Núñez-Regueiro, M.

    2015-11-01

    We study the C r1 -xR ex phase diagram finding that its phase transition temperature towards an antiferromagnetic order TN follows a quantum [(xc-x ) /xc ] ψ law, with ψ =1 /2 , from the quantum critical point (QCP) at xc=0.25 up to TN≈600 K . We compare this system to others in order to understand why this elemental material is affected by the QCP up to such unusually high temperatures. We determine a general criterion for the crossover, as a function of an external parameter such as concentration, from the region controlled solely by thermal fluctuations to that where quantum effects become observable. The properties of materials with low coherence lengths will thus be altered far away from the QCP.

  10. Finite-temperature scaling of quantum coherence near criticality in a spin chain

    NASA Astrophysics Data System (ADS)

    Cheng, Weiwen; Zhang, Zhijun; Gong, Longyan; Zhao, Shengmei

    2016-06-01

    We explore quantum coherence, inherited from Wigner-Yanase skew information, to analyze quantum criticality in the anisotropic XY chain model at finite temperature. Based on the exact solutions of the Hamiltonian, the quantum coherence contained in a nearest-neighbor spin pairs reduced density matrix ρ is obtained. The first-order derivative of the quantum coherence is non-analytic around the critical point at sufficient low temperature. The finite-temperature scaling behavior and the universality are verified numerically. In particular, the quantum coherence can also detect the factorization transition in such a model at sufficient low temperature. We also show that quantum coherence contained in distant spin pairs can characterize quantum criticality and factorization phenomena at finite temperature. Our results imply that quantum coherence can serve as an efficient indicator of quantum criticality in such a model and shed considerable light on the relationships between quantum phase transitions and quantum information theory at finite temperature.

  11. Hall effect in quantum critical charge-cluster glass

    DOE PAGESBeta

    Bozovic, Ivan; Wu, Jie; Bollinger, Anthony T.; Sun, Yujie

    2016-04-04

    Upon doping, cuprates undergo a quantum phase transition from an insulator to a d-wave superconductor. The nature of this transition and of the insulating state is vividly debated. Here, we study the Hall effect in La2-xSrxCuO4 (LSCO) samples doped near the quantum critical point at x ≈ 0.06. Dramatic fluctuations in the Hall resistance appear below TCG ≈ 1.5 K and increase as the sample is cooled down further, signaling quantum critical behavior. We explore the doping dependence of this effect in detail, by studying a combinatorial LSCO library in which the Sr content is varied in extremely fine steps,more » Δx ≈ 0.00008. Furthermore, we observe that quantum charge fluctuations wash out when superconductivity emerges but can be restored when the latter is suppressed by applying a magnetic field, showing that the two instabilities compete for the ground state.« less

  12. Quantum criticality in selected uranium intermetallic and organometallic compounds

    NASA Astrophysics Data System (ADS)

    Nasreen, Farzana

    My thesis presents the studies of the bulk properties of materials that exhibit unusual low-temperature properties due to the proximity of a quantum-critical point (QCP), for which long-range magnetic order can be suppressed to 0 K as a consequence of quantum fluctuations. A material can be tuned to the QCP by variation of a non-thermal control parameter such as hydrostatic pressure, magnetic field and chemical pressure/doping. Most of my experimental studies were performed at extreme conditions, such as high magnetic fields, low temperatures and/or high pressures. Two classes of materials were studied, namely uranium intermetallics and organometallics. The investigations on uranium intermetallics were done on compounds close to the edge of magnetism, i.e. the UCu4+xAl 8-x, UCuxAl5-x and UFe1-xNixAl compounds. Several of those compounds exhibit deviations from traditional Fermi-liquid theory and show non-Fermi liquid (NFL) scaling at low temperatures. Field-induced magnetic transitions were studied for some selected uranium compounds (UNiAl, UNiGa, UNiGe and UIrGe) as well. Furthermore, a study of organometallic quantum magnet (DTN: NiCl2-4SC(NH 2)2), which exhibits field-induced quantum criticality, is presented. In DTN, the magnetic-field induced polarization shows magneto-electric couplings between the antiferromagnetic Ni spins and the soft organic lattice.

  13. Subvacuum effects in quantum critical theories from a holographic approach

    NASA Astrophysics Data System (ADS)

    Yeh, Chen-Pin; Lee, Da-Shin

    2016-06-01

    The subvacuum phenomena, induced by the squeezed vacuum of the strongly coupled quantum critical fields with a dynamical scaling z , are explored by a probe particle. The holographic description corresponds to a string moving in (4 +1 )-dimensional Lifshitz geometry with gravitational wave perturbations. The dynamics of the particle can be realized from the motion of the endpoint of the string at the boundary. We then examine the particle's velocity dispersion, influenced by the squeezed vacuum states of strongly coupled quantum critical fields. With appropriate choices of squeezing parameters, the velocity dispersion is found to be smaller than the value caused by the normal vacuum fluctuations of the fields. This leads to the subvacuum effect. We find that the large coupling constant of the quantum fields tends to counteract the effect in the reduction of velocity dispersion, though this phenomenon is in principle observable. The effect of the squeezed vacuum on the decoherence dynamics of a quantum particle is also investigated. Coherence loss can be shown to be less severe in certain squeezed vacuums than in normal vacuum. This recovery of coherence is understood as recoherence, another manifestation of the subvacuum phenomena. We make some estimates of the degree of recoherence and find that, contrary to the velocity dispersion case, the recoherence effect is enhanced by the large coupling constant. Finally we compare the findings in our earlier works when the particle is influenced by a weakly coupled relativistic field with the dynamical scaling z =1 .

  14. Quantum Critical Behavior in a Concentrated Ternary Solid Solution.

    PubMed

    Sales, Brian C; Jin, Ke; Bei, Hongbin; Stocks, G Malcolm; Samolyuk, German D; May, Andrew F; McGuire, Michael A

    2016-01-01

    The face centered cubic (fcc) alloy NiCoCrx with x ≈ 1 is found to be close to the Cr concentration where the ferromagnetic transition temperature, Tc, goes to 0. Near this composition these alloys exhibit a resistivity linear in temperature to 2 K, a linear magnetoresistance, an excess -TlnT (or power law) contribution to the low temperature heat capacity, and excess low temperature entropy. All of the low temperature electrical, magnetic and thermodynamic properties of the alloys with compositions near x ≈ 1 are not typical of a Fermi liquid and suggest strong magnetic fluctuations associated with a quantum critical region. The limit of extreme chemical disorder in this simple fcc material thus provides a novel and unique platform to study quantum critical behavior in a highly tunable system. PMID:27188715

  15. Bulk entanglement spectrum reveals quantum criticality within a topological state.

    PubMed

    Hsieh, Timothy H; Fu, Liang

    2014-09-01

    A quantum phase transition is usually achieved by tuning physical parameters in a Hamiltonian at zero temperature. Here, we show that the ground state of a topological phase itself encodes critical properties of its transition to a trivial phase. To extract this information, we introduce an extensive partition of the system into two subsystems both of which extend throughout the bulk in all directions. The resulting bulk entanglement spectrum has a low-lying part that resembles the excitation spectrum of a bulk Hamiltonian, which allows us to probe a topological phase transition from a single wave function by tuning either the geometry of the partition or the entanglement temperature. As an example, this remarkable correspondence between the topological phase transition and the entanglement criticality is rigorously established for integer quantum Hall states.

  16. Quantum Critical Behavior in a Concentrated Ternary Solid Solution

    PubMed Central

    Sales, Brian C.; Jin, Ke; Bei, Hongbin; Stocks, G. Malcolm; Samolyuk, German D.; May, Andrew F.; McGuire, Michael A.

    2016-01-01

    The face centered cubic (fcc) alloy NiCoCrx with x ≈ 1 is found to be close to the Cr concentration where the ferromagnetic transition temperature, Tc, goes to 0. Near this composition these alloys exhibit a resistivity linear in temperature to 2 K, a linear magnetoresistance, an excess –TlnT (or power law) contribution to the low temperature heat capacity, and excess low temperature entropy. All of the low temperature electrical, magnetic and thermodynamic properties of the alloys with compositions near x ≈ 1 are not typical of a Fermi liquid and suggest strong magnetic fluctuations associated with a quantum critical region. The limit of extreme chemical disorder in this simple fcc material thus provides a novel and unique platform to study quantum critical behavior in a highly tunable system. PMID:27188715

  17. Hawking Radiation and Nonequilibrium Quantum Critical Current Noise

    NASA Astrophysics Data System (ADS)

    Sonner, Julian; Green, A. G.

    2012-08-01

    The dynamical scaling of quantum critical systems in thermal equilibrium may be inherited in the driven steady state, leading to universal out-of-equilibrium behavior. This attractive notion has been demonstrated in just a few cases. We demonstrate how holography—a mapping between the quantum critical system and a gravity dual—provides an illuminating perspective and new results. Nontrivial out-of-equilibrium universality is particularly apparent in current noise, which is dual to Hawking radiation in the gravitational system. We calculate this in a two-dimensional system driven by a strong in-plane electric field and deduce a universal scaling function interpolating between previously established equilibrium and far-from-equilibrium current noise. Since this applies at all fields, out-of-equilibrium experiments no longer require very high fields for comparison with theory.

  18. Quantum Critical Behavior in a Concentrated Ternary Solid Solution

    NASA Astrophysics Data System (ADS)

    Sales, Brian C.; Jin, Ke; Bei, Hongbin; Stocks, G. Malcolm; Samolyuk, German D.; May, Andrew F.; McGuire, Michael A.

    2016-05-01

    The face centered cubic (fcc) alloy NiCoCrx with x ≈ 1 is found to be close to the Cr concentration where the ferromagnetic transition temperature, Tc, goes to 0. Near this composition these alloys exhibit a resistivity linear in temperature to 2 K, a linear magnetoresistance, an excess –TlnT (or power law) contribution to the low temperature heat capacity, and excess low temperature entropy. All of the low temperature electrical, magnetic and thermodynamic properties of the alloys with compositions near x ≈ 1 are not typical of a Fermi liquid and suggest strong magnetic fluctuations associated with a quantum critical region. The limit of extreme chemical disorder in this simple fcc material thus provides a novel and unique platform to study quantum critical behavior in a highly tunable system.

  19. Hawking radiation and nonequilibrium quantum critical current noise.

    PubMed

    Sonner, Julian; Green, A G

    2012-08-31

    The dynamical scaling of quantum critical systems in thermal equilibrium may be inherited in the driven steady state, leading to universal out-of-equilibrium behavior. This attractive notion has been demonstrated in just a few cases. We demonstrate how holography-a mapping between the quantum critical system and a gravity dual-provides an illuminating perspective and new results. Nontrivial out-of-equilibrium universality is particularly apparent in current noise, which is dual to Hawking radiation in the gravitational system. We calculate this in a two-dimensional system driven by a strong in-plane electric field and deduce a universal scaling function interpolating between previously established equilibrium and far-from-equilibrium current noise. Since this applies at all fields, out-of-equilibrium experiments no longer require very high fields for comparison with theory.

  20. Thermal conductivity at a disordered quantum critical point

    NASA Astrophysics Data System (ADS)

    Hartnoll, Sean A.; Ramirez, David M.; Santos, Jorge E.

    2016-04-01

    Strongly disordered and strongly interacting quantum critical points are difficult to access with conventional field theoretic methods. They are, however, both experimentally important and theoretically interesting. In particular, they are expected to realize universal incoherent transport. Such disordered quantum critical theories have recently been constructed holographically by deforming a CFT by marginally relevant disorder. In this paper we find additional disordered fixed points via relevant disordered deformations of a holographic CFT. Using recently developed methods in holographic transport, we characterize the thermal conductivity in both sets of theories in 1+1 dimensions. The thermal conductivity is found to tend to a constant at low temperatures in one class of fixed points, and to scale as T 0.3 in the other. Furthermore, in all cases the thermal conductivity exhibits discrete scale invariance, with logarithmic in temperature oscillations superimposed on the low temperature scaling behavior. At no point do we use the replica trick.

  1. Critical Supercurrents and Self-Organization in Quantum Hall Bilayers

    NASA Astrophysics Data System (ADS)

    Eastham, P. R.; Cooper, N. R.; Lee, D. K. K.

    2010-12-01

    We present a theory of interlayer tunneling in a disordered quantum Hall bilayer at total filling factor one, allowing for the effect of static vortices. In agreement with recent experiments [Phys. Rev. BPRBMDO1098-0121 80, 165120 (2009)10.1103/PhysRevB.80.165120; Phys. Rev. B PRBMDO1098-012178, 075302 (2008)10.1103/PhysRevB.78.075302], we find that the critical current is proportional to the sample area and is comparable in magnitude to observed values. This reflects the formation of a Bean critical state as a result of current injection at the boundary. We predict a crossover to a critical current proportional to the square-root of the area in smaller samples. We also predict a peak in the critical current as the electron density varies at fixed layer separation.

  2. Critical supercurrents and self-organization in quantum Hall bilayers.

    PubMed

    Eastham, P R; Cooper, N R; Lee, D K K

    2010-12-01

    We present a theory of interlayer tunneling in a disordered quantum Hall bilayer at total filling factor one, allowing for the effect of static vortices. In agreement with recent experiments [Phys. Rev. B 80, 165120 (2009); Phys. Rev. B 78, 075302 (2008)], we find that the critical current is proportional to the sample area and is comparable in magnitude to observed values. This reflects the formation of a Bean critical state as a result of current injection at the boundary. We predict a crossover to a critical current proportional to the square-root of the area in smaller samples. We also predict a peak in the critical current as the electron density varies at fixed layer separation.

  3. Universal scaling for a quantum discontinuity critical point and quantum quenches

    NASA Astrophysics Data System (ADS)

    Suzuki, Sei; Dutta, Amit

    2015-08-01

    We introduce the notion of a quantum version of a discontinuity critical point (DCP) in the context of a first-order quantum phase transition referred to as a quantum DCP (QDCP). We evaluate the critical exponents associated with such a QDCP using the appropriate scaling relations focusing mainly on a QDCP that is located at the boundary between a gapped phase and a gapless critical line as observed in a spin-1/2 XXZ chain while we also touch upon the conventional Ising case. We then study temporal and spatial quenches in the vicinity of the QDCP associated with the XXZ chain and propose the scaling relation for the defect density and the residual energy characterized by associated critical exponents. These predictions are numerically verified for quenches of the XXZ chain to the QDCP (or across it), thereby establishing the existence of a Kibble-Zurek scaling for such quenches given in terms of appropriate critical exponents. Finally, in the Appendix we consider a generic situation which reduces to the case when the QDCP separates two gapped phases and also to that occurring in the XXZ chain, and present detail analysis of the universality and scaling relations concerning quantum quenches.

  4. Critical fluctuations near excitation threshold of a quantum parametric oscillator

    NASA Astrophysics Data System (ADS)

    Dykman, M. I.; Nakamura, Y.; Lin, Z. R.

    A weakly damped parametrically driven oscillator has several vibrational states already for weak driving. These are stable and unstable states with twice the modulation period and also the steady state. At the critical point all states merge. We show that this leads to anomalously strong quantum fluctuations. These fluctuations are similar whether the friction, in the classical picture, is linear or nonlinear. The critical region is ~[ ℏ (2 n + 1) ] 1 / 3 along the field frequency axis and ~[ ℏ (2 n + 1) ] 2 / 3 along the field amplitude axis, where n is the Planck number. The correlation time scales as [ ℏ (2 n + 1) ] - 2 / 3. The number of photons for n = 0 scales as ℏ - 2 / 3. It is determined by the oscillator nonlinearity and decay rate. Above the threshold, quantum fluctuations induce transitions between the period-two states over the quasienergy barrier. We find the effective quantum activation energies for such transitions and their scaling with the difference of the driving amplitude from its critical value. We also present the results of relevant experimental observations obtained with a circuit QED system.

  5. Quantum Criticality in Quasi-Two-Dimensional Itinerant Antiferromagnets

    NASA Astrophysics Data System (ADS)

    Varma, C. M.

    2015-10-01

    Quasi-two-dimensional itinerant fermions in the antiferromagnetic (AFM) quantum-critical region of their phase diagram, such as in the Fe-based superconductors or in some of the heavy-fermion compounds, exhibit a resistivity varying linearly with temperature and a contribution to specific heat or thermopower proportional to T ln T . It is shown, here, that a generic model of itinerant anti-ferromagnet can be canonically transformed so that its critical fluctuations around the AFM-vector Q can be obtained from the fluctuations in the long wavelength limit of a dissipative quantum X Y model. The fluctuations of the dissipative quantum X Y model in 2D have been evaluated recently, and in a large regime of parameters, they are determined, not by renormalized spin fluctuations, but by topological excitations. In this regime, the fluctuations are separable in their spatial and temporal dependence and have a spatial correlation length which is proportional to the logarithm of the temporal correlation length, i.e., for some purposes, the effective dynamic exponent z =∞ . The time dependence gives ω /T scaling at criticality. The observed resistivity and entropy then follow. Several predictions to test the theory are also given.

  6. Hall effect indicates destruction of large Fermi surface at a heavy-fermion quantum critical point

    NASA Astrophysics Data System (ADS)

    Paschen, Silke

    2005-03-01

    Quantum critical points (QCPs) - phase transitions at absolute zero in temperature -- are of great current interest because of their singular ability to influence the finite temperature properties of materials. Recently, heavy-fermion metals have played a key role in the study of antiferromagnetic QCPs. To accommodate the heavy electrons, the Fermi surface of the heavy-fermion paramagnet is larger than that of an antiferromagnet [1]. An important unsolved question concerns whether the Fermi surface transformation at the QCP develops gradually, as expected if the magnetism is of spin density wave type [2], or suddenly as expected if the heavy electrons are abruptly localized by magnetism [3]. Here we report measurements of the low-temperature Hall coefficient (RH) -- a measure of the Fermi surface volume -- in the heavy-fermion metal YbRh2Si2 upon field-tuning it from an antiferromagnetic to a paramagnetic state. RH undergoes an increasingly rapid change near the QCP as the temperature is lowered, extrapolating to a sudden jump in the zero temperature limit. We interpret these results in terms of a collapse of the large Fermi surface and of the heavy-fermion state itself precisely at the QCP [4].[0.2cm] [1] R. M. Martin, Phys. Rev. Lett. 48, 362-- 365 (1982); P. Fulde, in Narrow-Band Phenomena -- Influence of Electrons with both Band and Localized Character (ed. Fuggle, J. C.) 27--29 (Plenum Press, New York, 1988); M. Oshikawa, Phys. Rev. Lett. 84, 3370--3373 (2000).[0.2cm] [2] J. A. Hertz, Phys. Rev. B 14, 1165--1184 (1976); A. J. Millis, Phys. Rev. B 48, 7183-- 7196 (1993).[0.2cm] [3] A. Schröder et al., Nature 407, 351- -355 (2000); P. Coleman et al., J. Phys.: Condens. Matter 13, R723--R738 (2001); Q. Si et al., Nature 413, 804--808 (2001).[0.2cm] [4] S. Paschen et al., to appear in Nature.[0.2cm] In collaboration with: T. Lühmann, S. Wirth, P. Gegenwart, O. Trovarelli, C. Geibel, F. Steglich, P. Coleman, and Q. Si.

  7. Persistent Currents and Quantum Critical Phenomena in Mesoscopic Physics

    NASA Astrophysics Data System (ADS)

    Zelyak, Oleksandr

    In this thesis, we study persistent currents and quantum critical phenomena in the systems of mesoscopic physics. As an introduction in Chapter 1 we familiarize the reader with the area of mesoscopic physics. We explain how mesoscopic systems are different from quantum systems of single atoms and molecules and bulk systems with an Avogadro number of elements. We also describe some important mesoscopic phenomena. One of the mathematical tools that we extensively use in our studies is Random Matrix Theorty. This theory is not a part of standard physics courses and for educational purposes we provide the basics of Random Matrix Theory in Chapter 2. In Chapter 3 we study the persistent current of noninteracting electrons in quantum billiards. We consider simply connected chaotic Robnik-Berry quantum billiard and its annular analog. The electrons move in the presence of a point-like magnetic flux at the center of the billiard. For the simply connected billiard, we find a large diamagnetic contribution to the persistent current at small flux, which is independent of the flux and is proportional to the number of electrons (or equivalently the density since we keep the area fixed). The size of this diamagnetic contribution is much larger than the previously studied mesoscopic fluctuations in the persistent current in the simply connected billiard. This behavior of persistent current can ultimately be traced to the response of the angular-momentum l = 0 levels (neglected in semiclassical expansions) on the unit disk to a point-like flux at its center. We observe the same behavior for the annular billiard when the inner radius is much smaller than the outer one. We also find that the usual fluctuating persistent current and Anderson-like localization due to boundary scattering are seen when the annulus tends to a one-dimensional ring. We explore the conditions for the observability of this phenomenon. In Chapter 4 we study quantum critical phenomena in a system of two

  8. Random matrix theory and critical phenomena in quantum spin chains.

    PubMed

    Hutchinson, J; Keating, J P; Mezzadri, F

    2015-09-01

    We compute critical properties of a general class of quantum spin chains which are quadratic in the Fermi operators and can be solved exactly under certain symmetry constraints related to the classical compact groups U(N),O(N), and Sp(2N). In particular we calculate critical exponents s,ν, and z, corresponding to the energy gap, correlation length, and dynamic exponent, respectively. We also compute the ground state correlators 〈σ_{i}^{x}σ_{i+n}^{x}〉_{g},〈σ_{i}^{y}σ_{i+n}^{y}〉_{g}, and 〈∏_{i=1}^{n}σ_{i}^{z}〉_{g}, all of which display quasi-long-range order with a critical exponent dependent upon system parameters. Our approach establishes universality of the exponents for the class of systems in question.

  9. Quantum Criticality in FeSc2S4

    NASA Astrophysics Data System (ADS)

    Ish, Daniel; Balents, Leon

    2015-03-01

    Despite possessing a local spin 2 moment on the iron site and a Curie-Weiss temperature of 45 K , the A site spinel FeSc2S4 does not magnetically order down to 50mK. Previous theoretical work by Chen and Balents advanced an explanation for this observation in the form of the ``J2- λ'' model which places FeSc2S4 close to a quantum critical point on the disordered side of a quantum phase transition between a Néel ordered phase and a ``Spin-Orbital Liquid'' in which spins and orbitals are entangled, quenching the magnetization. We present new theoretical studies of the optical properties of the J2- λ model, including a computation of the dispersion relation for the quasiparticle excitations and the form of the collective response to electric field. We argue that the latter directly probes a low energy excitation continuum characteristic of quantum criticality, and that our results reinforce the consistency of this model with experiment.

  10. Quantum critical behavior in a concentrated ternary solid solution

    DOE PAGESBeta

    Sales, Brian C.; Bei, Hongbin; Stocks, George Malcolm; Samolyuk, German D.; McGuire, Michael A.; Jin, Ke; May, Andrew F.

    2016-05-18

    The face centered cubic (fcc) alloy NiCoCrx with x ≈ 1 is found to be close to the Cr concentration where the ferromagnetic transition temperature, Tc, goes to 0. Near this composition these alloys exhibit a resistivity linear in temperature to 2 K, a linear magnetoresistance, an excess –TlnT (or power law) contribution to the low temperature heat capacity, and excess low temperature entropy. All of the low temperature electrical, magnetic and thermodynamic properties of the alloys with compositions near x ≈ 1 are not typical of a Fermi liquid and suggest strong magnetic fluctuations associated with a quantum criticalmore » region. Lastly, the limit of extreme chemical disorder in this simple fcc material thus provides a novel and unique platform to study quantum critical behavior in a highly tunable system.« less

  11. Novel Quantum Criticality in Two Dimensional Topological Phase transitions

    PubMed Central

    Cho, Gil Young; Moon, Eun-Gook

    2016-01-01

    Topological quantum phase transitions intrinsically intertwine self-similarity and topology of many-electron wave-functions, and divining them is one of the most significant ways to advance understanding in condensed matter physics. Our focus is to investigate an unconventional class of the transitions between insulators and Dirac semimetals whose description is beyond conventional pseudo relativistic Dirac Hamiltonian. At the transition without the long-range Coulomb interaction, the electronic energy dispersion along one direction behaves like a relativistic particle, linear in momentum, but along the other direction it behaves like a non-relativistic particle, quadratic in momentum. Various physical systems ranging from TiO2-VO2 heterostructure to organic material α-(BEDT-TTF)2I3 under pressure have been proposed to have such anisotropic dispersion relation. Here, we discover a novel quantum criticality at the phase transition by incorporating the long range Coulomb interaction. Unique interplay between the Coulomb interaction and electronic critical modes enforces not only the anisotropic renormalization of the Coulomb interaction but also marginally modified electronic excitation. In connection with experiments, we investigate several striking effects in physical observables of our novel criticality. PMID:26791803

  12. Universal quantum criticality in Hubbard models with massless Dirac dispersion

    NASA Astrophysics Data System (ADS)

    Otsuka, Yuichi; Yunoki, Seiji; Sorella, Sandro

    We investigate the metal-insulator transition of two-dimensional interacting electrons with massless Dirac-like dispersion, describe by the Hubbard models on two geometrically different lattices: honeycomb and π-flux square lattices. By performing large-scale quantum Monte Carlo simulations followed by careful finite-size scaling analyses, we find that the transition from semi-metallic to antiferromagnetic insulating phases is continuous and evaluate the critical exponents with a high degree of accuracy for the corresponding universality class, which is described in the continuous limit by the Gross-Neveu model. We furthermore discuss the fate of the quasiparticle weight and the Fermi velocity across this transition.

  13. Dimensional decoupling at continuous quantum critical Mott transitions

    NASA Astrophysics Data System (ADS)

    Zou, Liujun; Senthil, T.

    2016-09-01

    For continuous Mott metal-insulator transitions in layered two-dimensional systems, we demonstrate the phenomenon of dimensional decoupling: the system behaves as a three-dimensional metal in the Fermi-liquid side but as a stack of decoupled two-dimensional layers in the Mott insulator. We show that the dimensional decoupling happens at the Mott quantum critical point itself. We derive the temperature dependence of the interlayer electric conductivity in various crossover regimes near such a continuous Mott transition, and discuss experimental implications.

  14. Local quantum criticality of an iron-pnictide tetrahedron.

    PubMed

    Ong, T Tzen; Coleman, Piers

    2012-03-01

    Motivated by the close correlation between transition temperature (T(c)) and the tetrahedral bond angle of the As-Fe-As layer observed in the iron-based superconductors, we study the interplay between spin and orbital physics of an isolated iron-arsenide tetrahedron embedded in a metallic environment. Whereas the spin-Kondo effect is suppressed to low temperatures by Hund's coupling, the orbital degrees of freedom are expected to quantum mechanically quench at high temperatures, giving rise to an overscreened, non-Fermi liquid ground state. Translated into a dense environment, this critical state may play an important role in the superconductivity of these materials.

  15. Quantum Theory as a Critical Regime of Language Dynamics

    NASA Astrophysics Data System (ADS)

    Grinbaum, Alexei

    2015-10-01

    Some mathematical theories in physics justify their explanatory superiority over earlier formalisms by the clarity of their postulates. In particular, axiomatic reconstructions drive home the importance of the composition rule and the continuity assumption as two pillars of quantum theory. Our approach sits on these pillars and combines new mathematics with a testable prediction. If the observer is defined by a limit on string complexity, information dynamics leads to an emergent continuous model in the critical regime. Restricting it to a family of binary codes describing `bipartite systems,' we find strong evidence of an upper bound on bipartite correlations equal to 2.82537. This is measurably different from the Tsirelson bound. The Hilbert space formalism emerges from this mathematical investigation as an effective description of a fundamental discrete theory in the critical regime.

  16. Quantum-Critical Dynamics of the Skyrmion Lattice.

    NASA Astrophysics Data System (ADS)

    Green, Andrew G.

    2002-03-01

    Slightly away from exact filling of the lowest Landau level, the quantum Hall ferromagnet contains a finite density of magnetic vortices or Skyrmions[1,2]. These Skyrmions are expected to form a square lattice[3], the low energy excitations of which (translation/phonon modes and rotation/breathing modes) lead to dramatically enhanced nuclear relaxation[4,5]. Upon changing the filling fraction, the rotational modes undergo a quantum phase transition where zero-point fluctuations destroy the orientational order of the Skyrmions[4,6]. I will discuss the effect of this quantum critical point upon nuclear spin relaxation[7]. [1]S. L. Sondhi et al., Phys. Rev. B47, 16419 (1993). [2]S. E. Barrett et al., Phys. Rev. Lett. 74, 5112 (1995), A. Schmeller et al., Phys. Rev. Lett. 75, 4290 (1995). [3]L. Brey et al, Phys. Rev. Lett. 75, 2562 (1995). [4]R. Côté et al., Phys. Rev. Lett. 78, 4825 (1997). [5]R. Tycko et al., Science 268, 1460 (1995). [6]Yu V. Nazarov and A. V. Khaetskii, Phys. Rev. Lett. 80, 576 (1998). [7]A. G. Green, Phys. Rev. B61, R16 299 (2000).

  17. Critical integer quantum Hall topology in the integrable Maryland model

    NASA Astrophysics Data System (ADS)

    Ganeshan, Sriram; Kechedzhi, Kostyantyn

    2014-03-01

    One-dimensional tight binding models such as Aubry-Andre-Harper (AAH) model (with onsite cosine potential) and the integrable Maryland model (with onsite tangent potential) have been the subjects of extensive theoretical research in localization studies. AAH can be directly mapped onto the two-dimensional Hofstadter model that manifests the integer quantum Hall topology on a lattice. However, no such connection has been made for the Maryland model (MM). In this talk, we present a generalized model that contains AAH and MM as the limiting cases with the MM lying precisely at a topological quantum phase transition (TQPT) point. A remarkable feature of this critical point is that the 1D MM retains well-defined energy gaps whereas the equivalent 2D model becomes gapless, signifying the 2D nature of the TQPT. The criticality allows us to associate topological invariants with the Maryland model in a restricted mathematical sense at the special filling factors that are adiabatically connected to the spectral gaps in the 1D Aubry-Andre-Harper model. Our theory presented in this work establishes deep and unexpected mathematical connections between 2D topological models and a family of 1D incommensurate localization models. This work is supported by JQI-NSF-PFC, Microsoft Q and JQI-ARO-MU.

  18. Visualizing heavy fermions emerging in a quantum critical Kondo lattice

    NASA Astrophysics Data System (ADS)

    Aynajian, Pegor

    2013-03-01

    In solids containing elements with f orbitals, the interaction between f-electron spins and those of itinerant electrons leads to the development of low-energy fermionic excitations with a heavy effective mass. These excitations are fundamental to the appearance of unconventional superconductivity and non-Fermi-liquid behavior observed in actinide- and lanthanide-based compounds. We use spectroscopic mapping with the scanning tunneling microscope to detect the emergence of heavy excitations with lowering of temperature in a prototypical family of cerium-based heavy-fermion compounds. We demonstrate the sensitivity of the tunneling process to the composite nature of these heavy quasiparticles, which arises from quantum entanglement of itinerant conduction and f electrons. Scattering and interference of the composite quasiparticles is used to resolve their energy-momentum structure and to extract their mass enhancement, which develops with decreasing temperature. The lifetime of the emergent heavy quasiparticles reveals signatures of enhanced scattering and their spectral lineshape shows evidence of energy-temperature scaling. These findings demonstrate that proximity to a quantum critical point results in critical damping of the emergent heavy excitation of our Kondo lattice system. This work is funded by a DOE-BES grant. Partial support for instrumentation is provided by NSF-DMR, Keck Foundation, and NSF-MRSEC. PA also acknowledges support of a fellowship through the PCCM funded by NSF MERSEC.

  19. Quantum Mechanically Defined Critical Thickness in Metallic Overlayer Heteroepitaxy^1

    NASA Astrophysics Data System (ADS)

    Zhang, Zhenyu; Niu, Qian; Shih, Chih-Kang

    1997-03-01

    In a recent study of Ag film growth on GaAs(110), one startling observation was the existence of a critical thickness: an atomically flat overlayer can be formed only if the total Ag coverage exceeds a minimum value of about 7 ML.^2 Here we provide an explanation of the phenomena by invoking the quantum nature of the conduction electrons within an ultrathin metallic overlayer. We show that the discrete levels of the quantum well play a very important role in defining the overall energetics of the system. The critical thickness is found to be the minimal thickness of the film at which the conduction electrons can be truly confined without much charge spilling into the semiconductor. A quantitative comparison with the experiment is made using a thermodynamic analysis based on a simple model. ^1 Supported by DOE, NSF, and the R.A. Welch Foundation. ^2 A. R. Smith, K.-J. Chao, Q. Niu, and C. K. Shih, Science 273, 226 (1996).

  20. A magnetically induced quantum critical point in holography

    NASA Astrophysics Data System (ADS)

    Gnecchi, A.; Gursoy, U.; Papadoulaki, O.; Toldo, C.

    2016-09-01

    We investigate quantum critical points in a 2+1 dimensional gauge theory at finite chemical potential χ and magnetic field B. The gravity dual is based on 4D N = 2 Fayet-Iliopoulos gauged supergravity and the solutions we consider — that are constructed analytically — are extremal, dyonic, asymptotically AdS 4 black-branes with a nontrivial radial profile for the scalar field. We discover a line of second order fixed points at B = B c (χ) between the dyonic black brane and an extremal "thermal gas" solution with a singularity of good-type, according to the acceptability criteria of Gubser [1]. The dual field theory is a strongly coupled nonconformal field theory at finite charge and magnetic field, related to the ABJM theory [2] deformed by a triple trace operator Φ3. This line of fixed points might be useful in studying the various strongly interacting quantum critical phenomena such as the ones proposed to underlie the cuprate superconductors. We also find curious similarities between the behaviour of the VeV <Φ> under B and that of the quark condensate in 2+1 dimensional NJL models.

  1. Critical relaxation with overdamped quasiparticles in open quantum systems

    NASA Astrophysics Data System (ADS)

    Lang, Johannes; Piazza, Francesco

    2016-09-01

    We study the late-time relaxation following a quench in an open quantum many-body system. We consider the open Dicke model, describing the infinite-range interactions between N atoms and a single, lossy electromagnetic mode. We show that the dynamical phase transition at a critical atom-light coupling is characterized by the interplay between reservoir-driven and intrinsic relaxation processes in the absence of number conservation. Above the critical coupling, small fluctuations in the occupation of the dominant quasiparticle mode start to grow in time, while the quasiparticle lifetime remains finite due to losses. Near the critical interaction strength, we observe a crossover between exponential and power-law 1 /τ relaxation, the latter driven by collisions between quasiparticles. For a quench exactly to the critical coupling, the power-law relaxation extends to infinite times, but the finite lifetime of quasiparticles prevents aging from appearing in two-times response and correlation functions. We predict our results to be accessible to quench experiments with ultracold bosons in optical resonators.

  2. Fermi-surface collapse and dynamical scaling near a quantum-critical point.

    PubMed

    Friedemann, Sven; Oeschler, Niels; Wirth, Steffen; Krellner, Cornelius; Geibel, Christoph; Steglich, Frank; Paschen, Silke; Kirchner, Stefan; Si, Qimiao

    2010-08-17

    Quantum criticality arises when a macroscopic phase of matter undergoes a continuous transformation at zero temperature. While the collective fluctuations at quantum-critical points are being increasingly recognized as playing an important role in a wide range of quantum materials, the nature of the underlying quantum-critical excitations remains poorly understood. Here we report in-depth measurements of the Hall effect in the heavy-fermion metal YbRh(2)Si(2), a prototypical system for quantum criticality. We isolate a rapid crossover of the isothermal Hall coefficient clearly connected to the quantum-critical point from a smooth background contribution; the latter exists away from the quantum-critical point and is detectable through our studies only over a wide range of magnetic field. Importantly, the width of the critical crossover is proportional to temperature, which violates the predictions of conventional theory and is instead consistent with an energy over temperature, E/T, scaling of the quantum-critical single-electron fluctuation spectrum. Our results provide evidence that the quantum-dynamical scaling and a critical Kondo breakdown simultaneously operate in the same material. Correspondingly, we infer that macroscopic scale-invariant fluctuations emerge from the microscopic many-body excitations associated with a collapsing Fermi-surface. This insight is expected to be relevant to the unconventional finite-temperature behavior in a broad range of strongly correlated quantum systems.

  3. Holographic view on quantum correlations and mutual information between disjoint blocks of a quantum critical system

    NASA Astrophysics Data System (ADS)

    Molina-Vilaplana, Javier; Sodano, Pasquale

    2011-10-01

    In ( d + 1) dimensional Multiscale Entanglement Renormalization Ansatz (MERA) networks, tensors are connected so as to reproduce the discrete, ( d + 2) holographic geometry of Anti de Sitter space (AdS d+2) with the original system lying at the boundary. We analyze the MERA renormalization flow that arises when computing the quantum correlations between two disjoint blocks of a quantum critical system, to show that the structure of the causal cones characteristic of MERA, requires a transition between two different regimes attainable by changing the ratio between the size and the separation of the two disjoint blocks. We argue that this transition in the MERA causal developments of the blocks may be easily accounted by an AdS d+2 black hole geometry when the mutual information is computed using the Ryu-Takayanagi formula. As an explicit example, we use a BTZ AdS3 black hole to compute the MI and the quantum correlations between two disjoint intervals of a one dimensional boundary critical system. Our results for this low dimensional system not only show the existence of a phase transition emerging when the conformal four point ratio reaches a critical value but also provide an intuitive entropic argument accounting for the source of this instability. We discuss the robustness of this transition when finite temperature and finite size effects are taken into account.

  4. One-norm geometric quantum discord and critical point estimation in the XY spin chain

    NASA Astrophysics Data System (ADS)

    Cheng, Chang-Cheng; Wang, Yao; Guo, Jin-Liang

    2016-11-01

    In contrast with entanglement and quantum discord (QD), we investigate the thermal quantum correlation in terms of Schatten one-norm geometric quantum discord (GQD) in the XY spin chain, and analyze their capabilities in detecting the critical point of quantum phase transition. We show that the one-norm GQD can reveal more properties about quantum correlation between two spins, especially for the long-range quantum correlation at finite temperature. Under the influences of site distance, anisotropy and temperature, one-norm GQD and its first derivative make it possible to detect the critical point efficiently for a general XY spin chain.

  5. Electronic Griffiths Phases and Quantum Criticality at Disordered Mott Transitions

    NASA Astrophysics Data System (ADS)

    Dobrosavljevic, Vladimir

    2012-02-01

    The effects of disorder are investigated in strongly correlated electronic systems near the Mott metal-insulator transition. Correlation effects are foundootnotetextE. C. Andrade, E. Miranda, and V. Dobrosavljevic, Phys. Rev. Lett., 102, 206403 (2009). to lead to strong disorder screening, a mechanism restricted to low-lying electronic states, very similar to what is observed in underdoped cuprates. These results suggest, however, that this effect is not specific to disordered d-wave superconductors, but is a generic feature of all disordered Mott systems. In addition, the resulting spatial inhomogeneity rapidly increasesootnotetextE. C. Andrade, E. Miranda, and V. Dobrosavljevic, Phys. Rev. Lett., 104 (23), 236401 (2010). as the Mott insulator is approached at fixed disorder strength. This behavior, which can be described as an Electronic Griffiths Phase, displays all the features expected for disorder-dominated Infinite-Randomness Fixed Point scenario of quantum criticality.

  6. Distributed Hybridization Model for Quantum Critical Behavior in Magnetic Quasicrystals

    NASA Astrophysics Data System (ADS)

    Otsuki, Junya; Kusunose, Hiroaki

    2016-07-01

    A quantum critical behavior of the magnetic susceptibility was observed in a quasicrystal containing ytterbium. At the same time, a mixed-valence feature of Yb ions was reported, which appears to be incompatible with the magnetic instability. We derive the magnetic susceptibility by expressing the quasiperiodicity as the distributed hybridization strength between Yb 4f and conduction electrons. Assuming a wide distribution of the hybridization strength, the most f electrons behave as renormalized paramagnetic states in the Kondo or mixed-valence regime, but a small number of f moments remain unscreened. As a result, the bulk magnetic susceptibility exhibits a nontrivial power-law-like behavior, while the average f-electron occupation is that of mixed-valence systems. This model thus resolves two contradictory properties of Yb quasicrystals.

  7. Luttinger Liquid, Singular Interaction and Quantum Criticality in Cuprate Materials

    NASA Astrophysics Data System (ADS)

    di Castro, C.; Caprara, S.

    2014-10-01

    With particular reference to the role of the renormalization group (RG) approach and Ward identities (WI's), we start by recalling some old features of the one-dimensional Luttinger liquid as the prototype of non-Fermi-liquid behavior. Its dimensional crossover to the Landau normal Fermi liquid implies that a non-Fermi liquid, as, e.g., the normal phase of the cuprate high temperature superconductors, can be maintained in d > 1 only in the presence of a sufficiently singular effective interaction among the charge carriers. This is the case when, nearby an instability, the interaction is mediated by critical fluctuations. We are then led to introduce the specific case of superconductivity in cuprates as an example of avoided quantum criticality. We will disentangle the fluctuations which act as mediators of singular electron-electron interaction, enlightening the possible order competing with superconductivity and a mechanism for the non-Fermi-liquid behavior of the metallic phase. This paper is not meant to be a comprehensive review. Many important contributions will not be considered. We will also avoid using extensive technicalities and making full calculations for which we refer to the original papers and to the many good available reviews. We will here only follow one line of reasoning which guided our research activity in this field.

  8. Thermal Ising transitions in the vicinity of two-dimensional quantum critical points

    NASA Astrophysics Data System (ADS)

    Hesselmann, S.; Wessel, S.

    2016-04-01

    The scaling of the transition temperature into an ordered phase close to a quantum critical point as well as the order parameter fluctuations inside the quantum critical region provide valuable information about universal properties of the underlying quantum critical point. Here, we employ quantum Monte Carlo simulations to examine these relations in detail for two-dimensional quantum systems that exhibit a finite-temperature Ising-transition line in the vicinity of a quantum critical point that belongs to the universality class of either (i) the three-dimensional Ising model for the case of the quantum Ising model in a transverse magnetic field on the square lattice or (ii) the chiral Ising transition for the case of a half-filled system of spinless fermions on the honeycomb lattice with nearest-neighbor repulsion. While the first case allows large-scale simulations to assess the scaling predictions to a high precision in terms of the known values for the critical exponents at the quantum critical point, for the later case, we extract values of the critical exponents ν and η , related to the order parameter fluctuations, which we discuss in relation to other recent estimates from ground-state quantum Monte Carlo calculations as well as analytical approaches.

  9. Odd Viscosity in the Quantum Critical Region of a Holographic Weyl Semimetal

    NASA Astrophysics Data System (ADS)

    Landsteiner, Karl; Liu, Yan; Sun, Ya-Wen

    2016-08-01

    We study odd viscosity in a holographic model of a Weyl semimetal. The model is characterized by a quantum phase transition from a topological semimetal to a trivial semimetal state. Since the model is axisymmetric in three spatial dimensions there are two independent odd viscosities. Both odd viscosity coefficients are nonvanishing in the quantum critical region and nonzero only due to the mixed axial gravitational anomaly. It is therefore a novel example in which the mixed axial gravitational anomaly gives rise to a transport coefficient at first order in derivatives at finite temperature. In the quantum critical region, the physics of viscosities as well as conductivities is governed by the quantum critical point.

  10. Nonlinear I-V Curve at a Quantum Impurity Quantum Critical Point

    NASA Astrophysics Data System (ADS)

    Baranger, Harold; Chung, Chung-Hou; Lin, Chao-Yun; Zhang, Gu; Ke, Chung-Ting; Finkelstein, Gleb

    The nonlinear I-V curve at an interacting quantum critical point (QCP) is typically out of reach theoretically. Here, however, we provide a striking example of an analytical calculation of the full nonlinear I-V curve at the QCP. The system that we consider is a quantum dot coupled to resistive leads - a spinless resonant level interacting with an ohmic EM environment in which a QCP similar to the two-channel Kondo QCP occurs. Recent experiments studied this criticality via transport measurements: the transmission approaches unity at low temperature and applied bias when tuned exactly to the QCP (on resonance and symmetric tunnel barriers) and approaches zero in all other cases. To obtain the current at finite temperature and arbitrary bias, we write the problem as a one-dimensional field theory and transform from electrons in the left/right leads to right-going and left-going channels between which there is weak two-body backscattering. Drawing on dynamical Coulomb blockade theory, we thus obtain an analytical expression for the full I-V curve. The agreement with the experimental result is remarkable.

  11. Energy scales and magnetoresistance at a quantum critical point

    NASA Astrophysics Data System (ADS)

    Shaginyan, V. R.; Amusia, M. Ya.; Msezane, A. Z.; Popov, K. G.; Stephanovich, V. A.

    2009-03-01

    The magnetoresistance (MR) of CeCoIn 5 is notably different from that in many conventional metals. We show that a pronounced crossover from negative to positive MR at elevated temperatures and fixed magnetic fields is determined by the scaling behavior of quasiparticle effective mass. At a quantum critical point (QCP) this dependence generates kinks (crossover points from fast to slow growth) in thermodynamic characteristics (like specific heat, magnetization, etc.) at some temperatures when a strongly correlated electron system transits from the magnetic field induced Landau-Fermi liquid (LFL) regime to the non-Fermi liquid (NFL) one taking place at rising temperatures. We show that the above kink-like peculiarity separates two distinct energy scales in QCP vicinity - low temperature LFL scale and high temperature one related to NFL regime. Our comprehensive theoretical analysis of experimental data permits to reveal for the first time new MR and kinks scaling behavior as well as to identify the physical reasons for above energy scales.

  12. Unconventional Quantum Criticality in Heavy-Fermion Compounds

    NASA Astrophysics Data System (ADS)

    Stockert, O.; Steglich, F.

    2011-03-01

    We review magnetic quantum-critical points (QPCs) in heavy-fermion compounds separating at zero temperature: an antiferromagnetically ordered state and a nonordered ground state. At the magnetic instability, the Fermi-liquid (FL) description valid for normal metals breaks down, giving rise to unusual, non-Fermi-liquid (NFL) low-temperature behavior. After a short introduction to phase transitions and to T = 0 phase transitions in general as well as to the physics of heavy-fermion systems, the two main theoretical scenarios describing the physics at QPCs in these systems are presented, the conventional spin-density-wave (SDW) scenario and the unconventional Kondo-breakdown scenario. Whereas for the conventional scenario experimental data for CeCu2Si2 and Ce1-xLaxRu2Si2 are discussed only briefly, we focus in more detail on the unusual behavior of CeCu6-xAux and YbRh2Si2 at their respective QPCs and show that these systems are best described within the unconventional scenario.

  13. Energy scales and magnetoresistance at a quantum critical point

    NASA Astrophysics Data System (ADS)

    Amusia, Miron; Shaginyan, Vasiliy

    2009-05-01

    The magnetoresistance (MR) of CeCoIn55 is notably different from that in many conventional metals. We show that a pronounced crossover from negative to positive MR at elevated temperatures and fixed magnetic fields is determined by the scaling behavior of quasiparticle effective mass. At a quantum critical point (QCP) this dependence generates kinks (crossover points from fast to slow growth) in thermodynamic characteristics (like specific heat, magnetization etc) at some temperatures when a strongly correlated electron system transits from the magnetic field induced Landau Fermi liquid (LFL) regime to the non-Fermi liquid (NFL) one taking place at rising temperatures. We show that the above kink-like peculiarity separates two distinct energy scales in QCP vicinity - low temperature LFL scale and high temperature one related to NFL regime. We show that the same behavior is observed under the application of elevated magnetic field at fixed temperature. These observations are in accord with recent facts (P. Gegenwart, et. al., Science 315, 969 (2007)). Our comprehensive theoretical analysis of experimental data permits to reveal for the first time new MR and kinks scaling behavior as well as to identify the physical reasons for above energy scales.

  14. Criticality without frustration for quantum spin-1 chains.

    PubMed

    Bravyi, Sergey; Caha, Libor; Movassagh, Ramis; Nagaj, Daniel; Shor, Peter W

    2012-11-16

    Frustration-free (FF) spin chains have a property that their ground state minimizes all individual terms in the chain Hamiltonian. We ask how entangled the ground state of a FF quantum spin-s chain with nearest-neighbor interactions can be for small values of s. While FF spin-1/2 chains are known to have unentangled ground states, the case s=1 remains less explored. We propose the first example of a FF translation-invariant spin-1 chain that has a unique highly entangled ground state and exhibits some signatures of a critical behavior. The ground state can be viewed as the uniform superposition of balanced strings of left and right brackets separated by empty spaces. Entanglement entropy of one half of the chain scales as 1/2 log n+O(1), where n is the number of spins. We prove that the energy gap above the ground state is polynomial in 1/n. The proof relies on a new result concerning statistics of Dyck paths which might be of independent interest. PMID:23215521

  15. Entropic Signatures of Quantum Criticality in Itinerant Ferromagnets and Metamagnetic Systems

    NASA Astrophysics Data System (ADS)

    Wu, Jianda; Zhu, Lijun; Si, Qimiao; Rost, Andreas; MacKenzie, Andy

    2012-02-01

    We investigate the thermodynamic properties of itinerant ferromagnets near quantum critical points described by a quantum Landau-Ginzburg 4̂ theory. We show that the quartic coupling in this theory, which is dangerously irrelevant, has a singular contribution to the renormalized Gaussian free energy. We trace this singularity to some ultraviolet contributions, thereby demonstrating its unphysical nature. We introduce a procedure to regularize this singularity, and apply the prescription to calculate thermodynamic quantities across ferromagnetic quantum critical points in both two and three dimensions. Our calculation illustrates various thermodynamic signatures of quantum criticality, including the entropy accumulation at the quantum critical point which was first proposed on scaling grounds [1]. We systematically compare our theoretical results with the experimental data on entropy and specific heat as a function of magnetic field in Sr3Ru2O7 [2]. We demonstrate that the thermodynamic data are compatible with a quantum critical scenario, but the critical behavior does not agree well with the conventional itinerant ferromagnetic quantum criticality picture. [1] L. Zhu et al PRL 91, 066404 (2003). [2] A.W. Rost et al, Science 325, 1360 (2009).

  16. Magnetic transitions and quantum criticality in the three-dimensional Hubbard model

    NASA Astrophysics Data System (ADS)

    Schäfer, Thomas; Katanin, Andrey; Held, Karsten; Toschi, Alessandro

    We analyze the (quantum) critical properties of the simplest model for electronic correlations, the Hubbard model, in three spatial dimensions by means of the dynamical mean field theory (DMFT, including all local correlations) and the dynamical vertex approximation (D ΓA, including non-local correlations on all length scales). Both in the half-filled/unfrustrated and in the hole-doped system the transition temperature is significantly lowered by including non-local fluctuations.In the latter case, however, the magnetic order becomes incommensurate, eventually leading to a complete suppression of the order and giving rise to a magnetic quantum critical point (QCP) at zero temperature. We analyze the (quantum) critical properties of this QCP (e.g. critical exponents) and relate our findings to the standard theory of quantum criticality in metals, the Hertz-Millis-Moriya theory. Solids4Fun, Austrian Science Fund (FWF, Project ID 1243).

  17. Deconfined quantum criticality and conformal phase transition in two-dimensional antiferromagnets

    NASA Astrophysics Data System (ADS)

    Nogueira, Flavio S.; Sudbø, Asle

    2013-12-01

    Deconfined quantum criticality of two-dimensional SU(2) quantum antiferromagnets featuring a transition from an antiferromagnetically ordered ground state to a so-called valence-bond solid state, is governed by a non-compact CP1 model with a Maxwell term in 2+1 spacetime dimensions. We introduce a new perspective on deconfined quantum criticality within a field-theoretic framework based on an expansion in powers of \\epsilon=4-d for fixed number N of complex matter fields. We show that in the allegedly weak first-order transition regime, a so-called conformal phase transition leads to a genuine deconfined quantum critical point. In such a transition, the gap vanishes when the critical point is approached from above and diverges when it is approached from below. We also find that the spin stiffness has a universal jump at the critical point.

  18. Quantum critical scaling in beta-YbAlB4 and theoretical implications

    NASA Astrophysics Data System (ADS)

    Nevidomskyy, Andriy

    2012-02-01

    Emergent phenomena in quantum materials are subject of intense experimental and theoretical research at present. A wonderful example thereof are the sister phases of YbAlB4 - a newly discovered heavy fermion material [1]. While one phase (α-YbAlB4) is a heavy Fermi liquid, its sibling β-YbAlB4 is quantum critical, supporting an unconventional superconductivity with a tiny transition temperature of ˜80 mK. Latest experiments [2] uncover the quantum critical T/B-scaling in β-YbAlB4 and prove that superconductivity emerges from a strange metal governed by an extremely fragile quantum criticality, which apparently occurs at zero field, without any external tuning. Here, we will present a theoretical perspective on the quantum critical scaling in β-YbAlB4 and will show that the critical exponents can be derived from the nodal structure of the hybridization matrix between Yb f-band and the conduction electrons. It follows that the free energy at low temperatures can be written in a scaling form F[(kBT)^2 + (gμBB)^2]^3/4, which predicts the divergent Sommerfeld coefficient γ and quasi-particle effective mass as B->0: γ˜m^*/m B-1/2. This is indeed observed in the experiment [1,2], which places a tiny upper bound on the critical magnetic field Bc<0.2 mT. We will discuss theoritical implications of this fragile intrinsic quantum criticality in β-YbAlB4 and discuss the possibility of a quantum critical phase, rather than a quantum critical point, in this material. [1] S. Nakatsuji et al., Nature Physics 4, 603 (2008). [2] Y. Matsumoto, S. Nakatsuji, K. Kuga, Y. Karaki, Y. Shimura, T. Sakakibara, A. H. Nevidomskyy, and P. Coleman, Science 331, 316 (2011).

  19. Heavy-fermion quantum criticality and destruction of the Kondo effect in a nickel oxypnictide.

    PubMed

    Luo, Yongkang; Pourovskii, Leonid; Rowley, S E; Li, Yuke; Feng, Chunmu; Georges, Antoine; Dai, Jianhui; Cao, Guanghan; Xu, Zhu'an; Si, Qimiao; Ong, N P

    2014-08-01

    A quantum critical point arises at a continuous transformation between distinct phases of matter at zero temperature. Studies in antiferromagnetic heavy-fermion materials have revealed that quantum criticality has several classes, with an unconventional type that involves a critical destruction of the Kondo entanglement. To understand such varieties, it is important to extend the materials basis beyond the usual setting of intermetallic compounds. Here we show that a nickel oxypnictide, CeNiAsO, exhibits a heavy-fermion antiferromagnetic quantum critical point as a function of either pressure or P/As substitution. At the quantum critical point, non-Fermi-liquid behaviour appears, which is accompanied by a divergent effective carrier mass. Across the quantum critical point, the low-temperature Hall coefficient undergoes a rapid sign change, suggesting a sudden jump of the Fermi surface and a destruction of the Kondo effect. Our results imply that the enormous materials basis for the oxypnictides, which has been so crucial in the search for high-temperature superconductivity, will also play a vital role in the effort to establish the universality classes of quantum criticality in strongly correlated electron systems. PMID:24859644

  20. Multiple Metamagnetic Quantum Criticality in Sr_{3}Ru_{2}O_{7}.

    PubMed

    Tokiwa, Y; Mchalwat, M; Perry, R S; Gegenwart, P

    2016-06-01

    Bilayer strontium ruthenate Sr_{3}Ru_{2}O_{7} displays pronounced non-Fermi liquid behavior at magnetic fields around 8 T, applied perpendicular to the ruthenate planes, which previously has been associated with an itinerant metamagnetic quantum critical end point (QCEP). We focus on the magnetic Grüneisen parameter Γ_{H}, which is the most direct probe to characterize field-induced quantum criticality. We confirm quantum critical scaling due to a putative two-dimensional QCEP near 7.845(5) T, which is masked by two ordered phases A and B, identified previously by neutron scattering. In addition, we find evidence for a QCEP at 7.53(2) T and determine the quantum critical regimes of both instabilities and the effect of their superposition. PMID:27314732

  1. Quantum Critical Electron Systems: The Uncharted Sign Worlds

    NASA Astrophysics Data System (ADS)

    Zaanen, J.

    2008-02-01

    Phases of classical matter, such as solids and liquids, are ruled by emergence principles that are well understood. Although the same principles govern forms of quantum matter that have no secrets for physicists, such as the superfluids, having to deal with fermions and the associated Fermi sign problem shatters this analogy. This Perspective addresses the Fermion sign problem and describes experiments on metals undergoing quantum phase transitions exhibiting scale-invariant electronic behavior, a description of which is at odds with established quantum theory.

  2. Quantum wavepacket ab initio molecular dynamics: an approach for computing dynamically averaged vibrational spectra including critical nuclear quantum effects.

    PubMed

    Sumner, Isaiah; Iyengar, Srinivasan S

    2007-10-18

    We have introduced a computational methodology to study vibrational spectroscopy in clusters inclusive of critical nuclear quantum effects. This approach is based on the recently developed quantum wavepacket ab initio molecular dynamics method that combines quantum wavepacket dynamics with ab initio molecular dynamics. The computational efficiency of the dynamical procedure is drastically improved (by several orders of magnitude) through the utilization of wavelet-based techniques combined with the previously introduced time-dependent deterministic sampling procedure measure to achieve stable, picosecond length, quantum-classical dynamics of electrons and nuclei in clusters. The dynamical information is employed to construct a novel cumulative flux/velocity correlation function, where the wavepacket flux from the quantized particle is combined with classical nuclear velocities to obtain the vibrational density of states. The approach is demonstrated by computing the vibrational density of states of [Cl-H-Cl]-, inclusive of critical quantum nuclear effects, and our results are in good agreement with experiment. A general hierarchical procedure is also provided, based on electronic structure harmonic frequencies, classical ab initio molecular dynamics, computation of nuclear quantum-mechanical eigenstates, and employing quantum wavepacket ab initio dynamics to understand vibrational spectroscopy in hydrogen-bonded clusters that display large degrees of anharmonicities.

  3. Quantum critical scaling at a Bose-glass/superfluid transition: Theory and experiment for a model quantum magnet

    NASA Astrophysics Data System (ADS)

    Yu, Rong; Miclea, Corneliu F.; Weickert, Franziska; Movshovich, Roman; Paduan-Filho, Armando; Zapf, Vivien S.; Roscilde, Tommaso

    2012-10-01

    In this paper we investigate the quantum phase transition from magnetic Bose Glass to magnetic Bose-Einstein condensation induced by a magnetic field in NiCl2·4SC(NH2)2 (dichloro-tetrakis-thiourea-nickel, or DTN), doped with Br (Br-DTN) or site diluted. Quantum Monte Carlo simulations for the quantum phase transition of the model Hamiltonian for Br-DTN, as well as for site-diluted DTN, are consistent with conventional scaling at the quantum critical point and with a critical exponent z verifying the prediction z=d; moreover the correlation length exponent is found to be ν=0.75(10), and the order parameter exponent to be β=0.95(10). We investigate the low-temperature thermodynamics at the quantum critical field of Br-DTN both numerically and experimentally, and extract the power-law behavior of the magnetization and of the specific heat. Our results for the exponents of the power laws, as well as previous results for the scaling of the critical temperature to magnetic ordering with the applied field, are incompatible with the conventional crossover-scaling Ansatz proposed by Fisher [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.40.546 40, 546 (1989)]. However they can all be reconciled within a phenomenological Ansatz in the presence of a dangerously irrelevant operator.

  4. Dynamic sensitivity of photon-dressed atomic ensemble with quantum criticality

    SciTech Connect

    Huang Jinfeng; Kuang Leman; Li Yong; Liao Jieqiao; Sun, C. P.

    2009-12-15

    We study the dynamic sensitivity of an atomic ensemble dressed by a single-mode cavity field (called a photon-dressed atomic ensemble), which is described by the Dicke model near the quantum critical point. It is shown that when an extra atom in a pure initial state passes through the cavity, the photon-dressed atomic ensemble will experience a quantum phase transition showing an explicit sudden change in its dynamics characterized by the Loschmidt echo of this quantum critical system. With such dynamic sensitivity, the Dicke model can resemble the cloud chamber for detecting a flying particle by the enhanced trajectory due to the classical phase transition.

  5. Critical behavior of quantum magnets with long-range interactions in the thermodynamic limit

    NASA Astrophysics Data System (ADS)

    Fey, Sebastian; Schmidt, Kai Phillip

    2016-08-01

    Quasiparticle properties of quantum magnets with long-range interactions are investigated by high-order linked-cluster expansions in the thermodynamic limit. It is established that perturbative continuous unitary transformations on white graphs are a promising and flexible approach to treat long-range interactions in quantum many-body systems. We exemplify this scheme for the one-dimensional transverse-field Ising chain with long-range interactions. For this model, the elementary quasiparticle gap is determined allowing to access the quantum-critical regime including critical exponents and multiplicative logarithmic corrections for the ferro- and antiferromagnetic case.

  6. Exploring the quantum critical behaviour in a driven Tavis-Cummings circuit.

    PubMed

    Feng, M; Zhong, Y P; Liu, T; Yan, L L; Yang, W L; Twamley, J; Wang, H

    2015-05-14

    Quantum phase transitions play an important role in many-body systems and have been a research focus in conventional condensed-matter physics over the past few decades. Artificial atoms, such as superconducting qubits that can be individually manipulated, provide a new paradigm of realising and exploring quantum phase transitions by engineering an on-chip quantum simulator. Here we demonstrate experimentally the quantum critical behaviour in a highly controllable superconducting circuit, consisting of four qubits coupled to a common resonator mode. By off-resonantly driving the system to renormalize the critical spin-field coupling strength, we have observed a four-qubit nonequilibrium quantum phase transition in a dynamical manner; that is, we sweep the critical coupling strength over time and monitor the four-qubit scaled moments for a signature of a structural change of the system's eigenstates. Our observation of the nonequilibrium quantum phase transition, which is in good agreement with the driven Tavis-Cummings theory under decoherence, offers new experimental approaches towards exploring quantum phase transition-related science, such as scaling behaviours, parity breaking and long-range quantum correlations.

  7. Exploring the quantum critical behaviour in a driven Tavis–Cummings circuit

    PubMed Central

    Feng, M.; Zhong, Y.P.; Liu, T.; Yan, L.L.; Yang, W.L.; Twamley, J.; Wang, H.

    2015-01-01

    Quantum phase transitions play an important role in many-body systems and have been a research focus in conventional condensed-matter physics over the past few decades. Artificial atoms, such as superconducting qubits that can be individually manipulated, provide a new paradigm of realising and exploring quantum phase transitions by engineering an on-chip quantum simulator. Here we demonstrate experimentally the quantum critical behaviour in a highly controllable superconducting circuit, consisting of four qubits coupled to a common resonator mode. By off-resonantly driving the system to renormalize the critical spin-field coupling strength, we have observed a four-qubit nonequilibrium quantum phase transition in a dynamical manner; that is, we sweep the critical coupling strength over time and monitor the four-qubit scaled moments for a signature of a structural change of the system's eigenstates. Our observation of the nonequilibrium quantum phase transition, which is in good agreement with the driven Tavis–Cummings theory under decoherence, offers new experimental approaches towards exploring quantum phase transition-related science, such as scaling behaviours, parity breaking and long-range quantum correlations. PMID:25971985

  8. Odd Viscosity in the Quantum Critical Region of a Holographic Weyl Semimetal.

    PubMed

    Landsteiner, Karl; Liu, Yan; Sun, Ya-Wen

    2016-08-19

    We study odd viscosity in a holographic model of a Weyl semimetal. The model is characterized by a quantum phase transition from a topological semimetal to a trivial semimetal state. Since the model is axisymmetric in three spatial dimensions there are two independent odd viscosities. Both odd viscosity coefficients are nonvanishing in the quantum critical region and nonzero only due to the mixed axial gravitational anomaly. It is therefore a novel example in which the mixed axial gravitational anomaly gives rise to a transport coefficient at first order in derivatives at finite temperature. In the quantum critical region, the physics of viscosities as well as conductivities is governed by the quantum critical point. PMID:27588846

  9. Entanglement is not a critical resource for quantum metrology

    SciTech Connect

    Tilma, Todd; Nemoto, Kae; Hamaji, Shinichiro; Munro, W. J.

    2010-02-15

    We investigate high-precision measurements beyond the standard quantum limit, utilizing nonclassical states. Although entanglement was considered a resource for achieving the Heisenberg limit in measurements, we show that any advantage expected from using entanglement is dependent on the measurement in question. We investigate several measurement scenarios and illustrate the role of entanglement as a resource for quantum high-precision measurement. In particular, we demonstrate that there is a regime wherein entanglement not only does not help, but prevents the achievement of the fundamental limit.

  10. Quantum Critical Origin of the Superconducting Dome in SrTiO_{3}.

    PubMed

    Edge, Jonathan M; Kedem, Yaron; Aschauer, Ulrich; Spaldin, Nicola A; Balatsky, Alexander V

    2015-12-11

    We expand the well-known notion that quantum criticality can induce superconductivity by proposing a concrete mechanism for superconductivity due to quantum ferroelectric fluctuations. To this end, we investigate the origin of superconductivity in doped SrTiO_{3} using a combination of density functional and strong coupling theories within the framework of quantum criticality. Our density functional calculations of the ferroelectric soft mode frequency as a function of doping reveal a crossover related to quantum paraelectricity at a doping level coincident with the experimentally observed top of the superconducting dome. Thus, we suggest a model in which the soft mode fluctuations provide the pairing interaction for superconductivity carriers. Within our model, the low doping limit of the superconducting dome is explained by the emergence of the Fermi surface, and the high doping limit by departure from the quantum critical regime. We predict that the highest critical temperature will increase and shift to lower carrier doping with increasing ^{18}O isotope substitution, a scenario that is experimentally verifiable. Our model is applicable to other quantum paraelectrics, such as KTaO_{3}.

  11. Quantum Critical Origin of the Superconducting Dome in SrTiO3

    NASA Astrophysics Data System (ADS)

    Edge, Jonathan M.; Kedem, Yaron; Aschauer, Ulrich; Spaldin, Nicola A.; Balatsky, Alexander V.

    2015-12-01

    We expand the well-known notion that quantum criticality can induce superconductivity by proposing a concrete mechanism for superconductivity due to quantum ferroelectric fluctuations. To this end, we investigate the origin of superconductivity in doped SrTiO3 using a combination of density functional and strong coupling theories within the framework of quantum criticality. Our density functional calculations of the ferroelectric soft mode frequency as a function of doping reveal a crossover related to quantum paraelectricity at a doping level coincident with the experimentally observed top of the superconducting dome. Thus, we suggest a model in which the soft mode fluctuations provide the pairing interaction for superconductivity carriers. Within our model, the low doping limit of the superconducting dome is explained by the emergence of the Fermi surface, and the high doping limit by departure from the quantum critical regime. We predict that the highest critical temperature will increase and shift to lower carrier doping with increasing 18O isotope substitution, a scenario that is experimentally verifiable. Our model is applicable to other quantum paraelectrics, such as KTaO3 .

  12. Scaling of the magnetic Grüneisen ratio near quantum critical point

    NASA Astrophysics Data System (ADS)

    Tokiwa, Yoshi

    2014-03-01

    The magnetic Grüneisen ratio ΓH = (1/T)dT/dH is the most sensitive probe of quantum criticality. Its divergence signals the underlying instability. We have studied quantum criticality in the frustrated Kondo lattice system YbAgGe and the heavy fermion superconductor CeCoIn5 by high-precision magnetocaloric effect measurements. In the former, NFL behavior appears around a metamagnetic spin-flop transition between two symmetry broken phases. Previously, it was unclear how the two ordered phases are related to the NFL state. Here, we propose a novel quantum bicritical point (QBCP) scenario, which is distinct from either quantum critical end point or ordinary QCPs with single symmetry broken phase. The observed scaling behavior of ΓH and its characteristic asymmetry across the critical field are consistent with a QBCP scenario. We also report a possible violation of Wiedemann-Franz law at the QBCP in YbAgGe. In CeCoIn5 indications of a quantum critical field hidden inside the superconducting (SC) phase have been extensively debated. We show ΓH data and scaling analysis in the normal state, which surprisingly suggests a zero-field QCP. Anomalous behaviors of ΓH and specific heat within the SC state further support this conclusion.

  13. Thermodynamics of phase formation in the quantum critical metal Sr3Ru2O7

    PubMed Central

    Rost, A. W.; Grigera, S. A.; Bruin, J. A. N.; Perry, R. S.; Tian, D.; Raghu, S.; Kivelson, Steven Allan; Mackenzie, A. P.

    2011-01-01

    The behavior of matter near zero temperature continuous phase transitions, or “quantum critical points” is a central topic of study in condensed matter physics. In fermionic systems, fundamental questions remain unanswered: the nature of the quantum critical regime is unclear because of the apparent breakdown of the concept of the quasiparticle, a cornerstone of existing theories of strongly interacting metals. Even less is known experimentally about the formation of ordered phases from such a quantum critical “soup.” Here, we report a study of the specific heat across the phase diagram of the model system Sr3Ru2O7, which features an anomalous phase whose transport properties are consistent with those of an electronic nematic. We show that this phase, which exists at low temperatures in a narrow range of magnetic fields, forms directly from a quantum critical state, and contains more entropy than mean-field calculations predict. Our results suggest that this extra entropy is due to remnant degrees of freedom from the highly entropic state above Tc. The associated quantum critical point, which is “concealed” by the nematic phase, separates two Fermi liquids, neither of which has an identifiable spontaneously broken symmetry, but which likely differ in the topology of their Fermi surfaces. PMID:21933961

  14. Thermodynamics of phase formation in the quantum critical metal Sr3Ru2O7.

    PubMed

    Rost, A W; Grigera, S A; Bruin, J A N; Perry, R S; Tian, D; Raghu, S; Kivelson, Steven Allan; Mackenzie, A P

    2011-10-01

    The behavior of matter near zero temperature continuous phase transitions, or "quantum critical points" is a central topic of study in condensed matter physics. In fermionic systems, fundamental questions remain unanswered: the nature of the quantum critical regime is unclear because of the apparent breakdown of the concept of the quasiparticle, a cornerstone of existing theories of strongly interacting metals. Even less is known experimentally about the formation of ordered phases from such a quantum critical "soup." Here, we report a study of the specific heat across the phase diagram of the model system Sr(3)Ru(2)O(7), which features an anomalous phase whose transport properties are consistent with those of an electronic nematic. We show that this phase, which exists at low temperatures in a narrow range of magnetic fields, forms directly from a quantum critical state, and contains more entropy than mean-field calculations predict. Our results suggest that this extra entropy is due to remnant degrees of freedom from the highly entropic state above T(c). The associated quantum critical point, which is "concealed" by the nematic phase, separates two Fermi liquids, neither of which has an identifiable spontaneously broken symmetry, but which likely differ in the topology of their Fermi surfaces.

  15. Athermal domain-wall creep near a ferroelectric quantum critical point.

    PubMed

    Kagawa, Fumitaka; Minami, Nao; Horiuchi, Sachio; Tokura, Yoshinori

    2016-02-16

    Ferroelectric domain walls are typically stationary because of the presence of a pinning potential. Nevertheless, thermally activated, irreversible creep motion can occur under a moderate electric field, thereby underlying rewritable and non-volatile memory applications. Conversely, as the temperature decreases, the occurrence of creep motion becomes less likely and eventually impossible under realistic electric-field magnitudes. Here we show that such frozen ferroelectric domain walls recover their mobility under the influence of quantum fluctuations. Nonlinear permittivity and polarization-retention measurements of an organic charge-transfer complex reveal that ferroelectric domain-wall creep occurs via an athermal process when the system is tuned close to a pressure-driven ferroelectric quantum critical point. Despite the heavy masses of material building blocks such as molecules, the estimated effective mass of the domain wall is comparable to the proton mass, indicating the realization of a ferroelectric domain wall with a quantum-particle nature near the quantum critical point.

  16. Athermal domain-wall creep near a ferroelectric quantum critical point

    PubMed Central

    Kagawa, Fumitaka; Minami, Nao; Horiuchi, Sachio; Tokura, Yoshinori

    2016-01-01

    Ferroelectric domain walls are typically stationary because of the presence of a pinning potential. Nevertheless, thermally activated, irreversible creep motion can occur under a moderate electric field, thereby underlying rewritable and non-volatile memory applications. Conversely, as the temperature decreases, the occurrence of creep motion becomes less likely and eventually impossible under realistic electric-field magnitudes. Here we show that such frozen ferroelectric domain walls recover their mobility under the influence of quantum fluctuations. Nonlinear permittivity and polarization-retention measurements of an organic charge-transfer complex reveal that ferroelectric domain-wall creep occurs via an athermal process when the system is tuned close to a pressure-driven ferroelectric quantum critical point. Despite the heavy masses of material building blocks such as molecules, the estimated effective mass of the domain wall is comparable to the proton mass, indicating the realization of a ferroelectric domain wall with a quantum-particle nature near the quantum critical point. PMID:26880041

  17. Critical comparison of classical and quantum mechanical treatments of the phase equilibria of water

    SciTech Connect

    Wick, Collin D.; Schenter, Gregory K.

    2006-03-17

    The Gibbs ensemble Monte Carlo simulation technique was used to compare the phase equilibria of the rigid TIP4P water model [J.\\ Chem.\\ Phys.\\ {\\bf 79}, 926, (1983)] utilizing classical and quantum statistical mechanical treatments. The quantum statistical mechanical treatment generally resulted in lower liquid densities and higher vapor densities, showing a narrowing in the phase envelope. As a result, the calculated critical temperature and normal boiling point were higher from the quantum simulations than the classical by 20~and 17~K, respectively, but the critical densities were very close. A semiclassical treatment, involving a low order expansion in Plank's constant, resulted in densities and vapor pressures that fluctuated between the values for the classical and quantum statistical mechanics values, with no definite agreement with either.

  18. Ising nematic quantum critical point in a metal: a Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Lederer, Samuel

    The Ising nematic quantum critical point (QCP) associated with the zero temperature transition from a symmetric to a nematic metal is an exemplar of metallic quantum criticality. We have carried out a minus sign-free quantum Monte Carlo study of this QCP for a two dimensional lattice model with sizes up to 24 × 24 sites. The system remains non-superconducting down to the lowest accessible temperatures. The results exhibit critical scaling behavior over the accessible ranges of temperature, (imaginary) time, and distance. This scaling behavior has remarkable similarities with recently measured properties of the Fe-based superconductors proximate to their putative nematic QCP. With Yoni Schattner, Steven A. Kivelson, and Erez Berg.

  19. Gamma Ray Bursts from a Quantum Critical Surface

    SciTech Connect

    Chapline, G; Santiago, D I

    2002-11-20

    The logical inconsistency of quantum mechanics and general relativity can be avoided if the relativity principle fails for length scales smaller than the quantum coherence length for the vacuum state. Ordinarily this corresponds to energies near the Planck energy, but recently it has been pointed out that near to the event horizon of a black hole the coherence length can be much larger and Planck scale physics can take over at macroscopic distances from the event horizon. This has dramatic consequences for the phenomenology of black holes. If we assume that at the Planck scale elementary particles interact via a universal 4-point interaction and baryon number conservation is violated, then the rest mass of a star hitting the event horizon of a large black hole would be rapidly converted into a burst of gamma rays followed by a pulse of hard X-rays whose duration is on the order of the light transit time across the black hole. Predictions for the gamma ray spectra are strikingly similar to those observed for cosmic gamma ray bursts.

  20. Quantum critical fluctuations in disordered d-wave superconductors.

    PubMed

    Meyer, Julia S; Gornyi, Igor V; Altland, Alexander

    2003-03-14

    To explain the strong quasiparticle damping in the cuprates, Sachdev and collaborators proposed to couple the system to a critically fluctuating id(xy)- or is-order parameter mode. Here we generalize the approach to the presence of static disorder. In the id case, the order parameter dynamics becomes diffusive, but otherwise much of the phenomenology of the clean case remains intact. In contrast, the interplay of disorder and is-order parameter fluctuations leads to a secondary superconductor transition, with a critical temperature exponentially sensitive to the impurity concentration.

  1. Emergent Lorentz symmetry with vanishing velocity in a critical two-subband quantum wire.

    PubMed

    Sitte, M; Rosch, A; Meyer, J S; Matveev, K A; Garst, M

    2009-05-01

    We consider a quantum wire with two subbands of spin-polarized electrons in the presence of strong interactions. We focus on the quantum phase transition when the second subband starts to get filled as a function of gate voltage. Performing a one-loop renormalization group analysis of the effective Hamiltonian, we identify the critical fixed-point theory as a conformal field theory having an enhanced SU(2) symmetry and central charge 3/2. While the fixed point is Lorentz invariant, the effective "speed of light" nevertheless vanishes at low energies due to marginally irrelevant operators leading to a diverging critical specific heat coefficient.

  2. Emergent Lorentz symmetry with vanishing velocity in a critical two-subband quantum wire.

    SciTech Connect

    Sitte, M.; Rosch, A.; Meyer, J. S.; Matveev, K. A.; Garst, M.; Materials Science Division; Univ. zu Koln; Ohio State Univ.

    2009-01-01

    We consider a quantum wire with two subbands of spin-polarized electrons in the presence of strong interactions. We focus on the quantum phase transition when the second subband starts to get filled as a function of gate voltage. Performing a one-loop renormalization group analysis of the effective Hamiltonian, we identify the critical fixed-point theory as a conformal field theory having an enhanced SU(2) symmetry and central charge 3/2. While the fixed point is Lorentz invariant, the effective 'speed of light' nevertheless vanishes at low energies due to marginally irrelevant operators leading to a diverging critical specific heat coefficient.

  3. Emergent Lorentz symmetry with vanishing velocity in a critical two-subband quantum wire.

    PubMed

    Sitte, M; Rosch, A; Meyer, J S; Matveev, K A; Garst, M

    2009-05-01

    We consider a quantum wire with two subbands of spin-polarized electrons in the presence of strong interactions. We focus on the quantum phase transition when the second subband starts to get filled as a function of gate voltage. Performing a one-loop renormalization group analysis of the effective Hamiltonian, we identify the critical fixed-point theory as a conformal field theory having an enhanced SU(2) symmetry and central charge 3/2. While the fixed point is Lorentz invariant, the effective "speed of light" nevertheless vanishes at low energies due to marginally irrelevant operators leading to a diverging critical specific heat coefficient. PMID:19518804

  4. Metamagnetic quantum criticality in Sr3Ru2O7 studied by thermal expansion.

    PubMed

    Gegenwart, P; Weickert, F; Garst, M; Perry, R S; Maeno, Y

    2006-04-01

    We report low-temperature thermal expansion measurements on the bilayer ruthenate Sr3Ru2O7 as a function of magnetic field applied perpendicular to the ruthenium-oxide planes. The field dependence of the c-axis expansion coefficient indicates the accumulation of entropy close to 8 T, related to an underlying quantum critical point. The latter is masked by two first-order metamagnetic transitions which bound a regime of enhanced entropy. Outside this region the singular thermal expansion behavior is compatible with the predictions of the itinerant theory for a two-dimensional metamagnetic quantum critical end point. PMID:16712009

  5. Diagnostic for phases and quantum critical regions using deviations from the local fluctuation-dissipation theorem

    NASA Astrophysics Data System (ADS)

    Duchon, E.; Kato, Y.; Trivedi, N.

    2012-12-01

    We propose that the temperature dependence of a single quantity R=κi/δni2, the ratio of the local compressibility to the local number fluctuations, can be used to map out the finite temperature phase diagram, diagnose the critical region around a quantum phase transition, and identify critical points belonging to different universality classes. We test our proposal using state-of-the-art large-scale quantum Monte Carlo simulations of the two-dimensional Bose Hubbard model. Our results have implications for recently developed single-site imaging experiments.

  6. Critical excitation spectrum of a quantum chain with a local three-spin coupling

    SciTech Connect

    McCabe, John F.; Wydro, Tomasz

    2011-09-15

    Using the phenomenological renormalization group (PRG), we evaluate the low-energy excitation spectrum along the critical line of a quantum spin chain having a local interaction between three Ising spins and longitudinal and transverse magnetic fields, i.e., a Turban model. The low-energy excitation spectrum found with the PRG agrees with the spectrum predicted for the (D{sub 4},A{sub 4}) conformal minimal model under a nontrivial correspondence between translations at the critical line and discrete lattice translations. Under this correspondence, the measurements confirm a prediction that the critical line of this quantum spin chain and the critical point of the two-dimensional three-state Potts model are in the same universality class.

  7. Metal-insulator quantum critical point beneath the high Tc superconducting dome

    PubMed Central

    Sebastian, Suchitra E.; Harrison, N.; Altarawneh, M. M.; Mielke, C. H.; Liang, Ruixing; Bonn, D. A.; Lonzarich, G. G.; Hardy, W. N.

    2010-01-01

    An enduring question in correlated systems concerns whether superconductivity is favored at a quantum critical point (QCP) characterized by a divergent quasiparticle effective mass. Despite such a scenario being widely postulated in high Tc cuprates and invoked to explain non-Fermi liquid transport signatures, experimental evidence is lacking for a critical divergence under the superconducting dome. We use ultrastrong magnetic fields to measure quantum oscillations in underdoped YBa2Cu3O6+x, revealing a dramatic doping-dependent upturn in quasiparticle effective mass at a critical metal-insulator transition beneath the superconducting dome. Given the location of this QCP under a plateau in Tc in addition to a postulated QCP at optimal doping, we discuss the intriguing possibility of two intersecting superconducting subdomes, each centered at a critical Fermi surface instability. PMID:20304800

  8. Atomic spin-chain realization of a model for quantum criticality

    NASA Astrophysics Data System (ADS)

    Toskovic, R.; van den Berg, R.; Spinelli, A.; Eliens, I. S.; van den Toorn, B.; Bryant, B.; Caux, J.-S.; Otte, A. F.

    2016-07-01

    The ability to manipulate single atoms has opened up the door to constructing interesting and useful quantum structures from the ground up. On the one hand, nanoscale arrangements of magnetic atoms are at the heart of future quantum computing and spintronic devices; on the other hand, they can be used as fundamental building blocks for the realization of textbook many-body quantum models, illustrating key concepts such as quantum phase transitions, topological order or frustration as a function of system size. Here, we use low-temperature scanning tunnelling microscopy to construct arrays of magnetic atoms on a surface, designed to behave like spin-1/2 XXZ Heisenberg chains in a transverse field, for which a quantum phase transition from an antiferromagnetic to a paramagnetic phase is predicted in the thermodynamic limit. Site-resolved measurements on these finite-size realizations reveal a number of sudden ground state changes when the field approaches the critical value, each corresponding to a new domain wall entering the chains. We observe that these state crossings become closer for longer chains, suggesting the onset of critical behaviour. Our results present opportunities for further studies on quantum behaviour of many-body systems, as a function of their size and structural complexity.

  9. Quantum criticality on ferromagnetic systems: it is not where you think it is!

    NASA Astrophysics Data System (ADS)

    Taufour, Valentin; Kaluarachchi, Udhara; Nguyen, Manh Cuong; Kim, Stella K.; Lin, Xiao; Mun, Eun Deok; Kim, Hyunsoo; Furukawa, Yuji; Wang, Cai Zhuang; Ho, Kai Ming; Bud'Ko, Sergey L.; Canfield, Paul C.; Guguchia, Zurab; Khasanov, Rustem; Bonfa, Pietro; de Renzi, Roberto

    When a ferromagnetic-paramagnetic transition is tuned to 0 K by application of pressure in clean systems, the transition becomes of the first order at a tricritical point before disappearing. Instead of having a quantum critical point, i.e. a second order transition at 0 K, there is a quantum phase transition of the first order. The quantum phase transition can be from a ferromagnetic to a paramagnetic phase, or to a spatially modulated phase. We illustrate this case on a new material: LaCrGe3. We will present the temperature-pressure-magnetic field phase diagram of LaCrGe3 and show that quantum criticality is avoided by the appearance of a modulated phase. We will also explain how quantum criticality can be re-introduced. Work at Ames Laboratory was supported by US DOE under the Contract No. DE-AC02-07CH11358. Magnetization measurements under pressure were supported by Ames Laboratory's laboratory-directed research and development (LDRD) funding.

  10. Universal Scaling in the Fan of an Unconventional Quantum Critical Point

    SciTech Connect

    Melko, Roger G; Kaul, Ribhu

    2008-01-01

    We present the results of extensive finite-temperature Quantum Monte Carlo simulati ons on a SU(2) symmetric, $S=1/2$ quantum antiferromagnet with a frustrating four-s pin interaction -- the so-called 'JQ' model~[Sandvik, Phys. Rev. Lett. {\\bf 98}, 22 7202 (2007)]. Our simulations, which are unbiased, free of the sign-problem and car ried out on lattice sizes containing in excess of $1.6\\times 10^4$ spins, indicate that N\\'eel order is destroyed through a continuous quantum transition at a critica l value of the frustrating interaction. At larger values of this coupling the param agnetic state obtained has valence-bond solid order. The scaling behavior in the 'q uantum critical fan' above the putative critical point confirms a $z=1$ quantum pha se transition that is not in the conventional $O(3)$ universality class. Our result s are consistent with the predictions of the 'deconfined quantum criticality' scena rio.

  11. Universal Fermi liquid crossover and quantum criticality in a mesoscopic system.

    PubMed

    Keller, A J; Peeters, L; Moca, C P; Weymann, I; Mahalu, D; Umansky, V; Zaránd, G; Goldhaber-Gordon, D

    2015-10-01

    Quantum critical systems derive their finite-temperature properties from the influence of a zero-temperature quantum phase transition. The paradigm is essential for understanding unconventional high-Tc superconductors and the non-Fermi liquid properties of heavy fermion compounds. However, the microscopic origins of quantum phase transitions in complex materials are often debated. Here we demonstrate experimentally, with support from numerical renormalization group calculations, a universal crossover from quantum critical non-Fermi liquid behaviour to distinct Fermi liquid ground states in a highly controllable quantum dot device. Our device realizes the non-Fermi liquid two-channel Kondo state, based on a spin-1/2 impurity exchange-coupled equally to two independent electronic reservoirs. On detuning the exchange couplings we observe the Fermi liquid scale T*, at energies below which the spin is screened conventionally by the more strongly coupled channel. We extract a quadratic dependence of T* on gate voltage close to criticality, and validate an asymptotically exact description of the universal crossover between strongly correlated non-Fermi liquid and Fermi liquid states. PMID:26450057

  12. Quantum critical response function in quasi-two-dimensional itinerant antiferromagnets

    NASA Astrophysics Data System (ADS)

    Varma, C. M.; Zhu, Lijun; Schröder, Almut

    2015-10-01

    We reexamine the experimental results for the magnetic response function χ''(q ,E ,T ) for q around the antiferromagnetic vectors Q , in the quantum-critical region, obtained by inelastic neutron scattering, on an Fe-based superconductor and on a heavy-fermion compound. The motivation is to compare the results with a recent theory, which shows that the fluctuations in a generic antiferromagnetic model for itinerant fermions map to those in the universality class of the dissipative quantum-XY model. The quantum-critical fluctuations in this model, in a range of parameters, are given by the correlations of spatial and temporal topological defects. The theory predicts a χ''(q ,E ,T ) (i) which is a separable function of (q -Q ) and of (E ,T ) , (ii) at criticality, the energy-dependent part is ∝tanh(E /2 T ) below a cutoff energy, (iii) the correlation time departs from its infinite value at criticality on the disordered side by an essential singularity, and (iv) the correlation length depends logarithmically on the correlation time, so that the dynamical critical exponent z is ∞ . The limited existing experimental results are found to be consistent with the first two unusual predictions from which the linear dependence of the resistivity on T and the T lnT dependence of the entropy also follow. More experiments are suggested, especially to test the theory of variations on the correlation time and length on the departure from criticality.

  13. Quantum critical dynamics of a magnetic impurity in a semiconducting host

    NASA Astrophysics Data System (ADS)

    Dasari, Nagamalleswararao; Acharya, Swagata; Taraphder, A.; Moreno, Juana; Jarrell, Mark; Vidhyadhiraja, N. S.; N. S. Vidhyadhiraja Collaboration, Prof.; Mark Jarrell Collaboration, Prof.; A. Taraphder Collaboration, Prof.

    We have investigated the finite temperature dynamics of the singlet to doublet continuous quantum phase transition in the gapped Anderson impurity model using hybridization expansion continuous time quantum Monte Carlo. Using the self-energy and the longitudinal static susceptibility, we obtain a phase diagram in the temperature-gap plane. The separatrix between the low-temperature local moment phase and the high temperature generalized Fermi liquid phase is shown to be the lower bound of the critical scaling region of the zero gap interacting quantum critical point. We have computed the nuclear magnetic spin-lattice relaxation rate, the Knight shift, and the Korringa ratio, which show strong deviations for any non-zero gap from the corresponding quantities in the gapless Kondo screened impurity case. This work is supported by NSF DMR-1237565 and NSF EPSCoR Cooperative Agreement EPS-1003897 with additional support from the Louisiana Board of Regents, and by CSIR and DST, India.

  14. Matrix Product State, Quantum Entanglement, and Criticality in the One-Dimensional Dimerized Antiferromagnetic Heisenberg Model

    NASA Astrophysics Data System (ADS)

    Liu, Guang-Hua; Tian, Guang-Shan

    2012-08-01

    The matrix product state (MPS) is utilized to investigate the ground state properties and quantum phase transitions (QPTs) of the dimerized antiferromagnetic Heisenberg (DAH) model. The ground state MPS wavefunctions determined by the infinite time-evolving block decimation (iTEBD) algorithm are shown to be very efficient descriptions of DAH model. In the thermodynamic limit, the quantum entanglement, the bond energy, and the nearest-neighbor correlations are calculated. It is revealed that the singular behavior of the bipartite entanglement can detect the QPTs directly. The critical point Jc2 = 1.0 is determined evidently, and the quantum phase transition is argued to belong to the second-order category. At the critical point, logarithmic divergent character of the block entanglement is observed, and the system can be described by a free bosonic field theory.

  15. FFLO strange metal and quantum criticality in two dimensions: Theory and application to organic superconductors

    NASA Astrophysics Data System (ADS)

    Piazza, Francesco; Zwerger, Wilhelm; Strack, Philipp

    2016-02-01

    Increasing the spin imbalance in superconductors can spatially modulate the gap by forming Cooper pairs with finite momentum. For large imbalances compared to the Fermi energy, the inhomogeneous FFLO superconductor ultimately becomes a normal metal. There is mounting experimental evidence for this scenario in two-dimensional (2D) organic superconductors in large in-plane magnetic fields; this is complemented by ongoing efforts to realize this scenario in coupled tubes of atomic Fermi gases with spin imbalance. Yet, a theory for the phase transition from a metal to an FFLO superconductor has not been developed so far and the universality class has remained unknown. Here we propose and analyze a spin imbalance driven quantum critical point between a 2D metal and an FFLO phase in anisotropic electron systems. We derive the effective action for electrons and bosonic FFLO pairs at this quantum phase transition. Using this action, we predict non-Fermi-liquid behavior and the absence of quasiparticles at a discrete set of hot spots on the Fermi surfaces. This results in strange power laws in thermodynamics and response functions, which are testable with existing experimental setups on 2D organic superconductors and may also serve as signatures of the elusive FFLO phase itself. The proposed universality class is distinct from previously known quantum critical metals and, because its critical fluctuations appear already in the pairing channel, a promising candidate for naked metallic quantum criticality over extended temperature ranges.

  16. Nematic Quantum Critical Fluctuations in BaFe2 -xNix As2

    NASA Astrophysics Data System (ADS)

    Liu, Zhaoyu; Gu, Yanhong; Zhang, Wei; Gong, Dongliang; Zhang, Wenliang; Xie, Tao; Lu, Xingye; Ma, Xiaoyan; Zhang, Xiaotian; Zhang, Rui; Zhu, Jun; Ren, Cong; Shan, Lei; Qiu, Xianggang; Dai, Pengcheng; Yang, Yi-feng; Luo, Huiqian; Li, Shiliang

    2016-10-01

    We have systematically studied the nematic fluctuations in the electron-doped iron-based superconductor BaFe2 -xNix As2 by measuring the in-plane resistance change under uniaxial pressure. While the nematic quantum critical point can be identified through the measurements along the (110) direction, as studied previously, quantum and thermal critical fluctuations cannot be distinguished due to similar Curie-Weiss-like behaviors. Here we find that a sizable pressure-dependent resistivity along the (100) direction is present in all doping levels, which is against the simple picture of an Ising-type nematic model. The signal along the (100) direction becomes maximum at optimal doping, suggesting that it is associated with nematic quantum critical fluctuations. Our results indicate that thermal fluctuations from striped antiferromagnetic order dominate the underdoped regime along the (110) direction. We argue that either there is a strong coupling between the quantum critical fluctuations and the fermions, or more exotically, a higher symmetry may be present around optimal doping.

  17. Vertex functions at finite momentum: Application to antiferromagnetic quantum criticality

    NASA Astrophysics Data System (ADS)

    Wölfle, Peter; Abrahams, Elihu

    2016-02-01

    We analyze the three-point vertex function that describes the coupling of fermionic particle-hole pairs in a metal to spin or charge fluctuations at nonzero momentum. We consider Ward identities, which connect two-particle vertex functions to the self-energy, in the framework of a Hubbard model. These are derived using conservation laws following from local symmetries. The generators considered are the spin density and particle density. It is shown that at certain antiferromagnetic critical points, where the quasiparticle effective mass is diverging, the vertex function describing the coupling of particle-hole pairs to the spin density Fourier component at the antiferromagnetic wave vector is also divergent. Then we give an explicit calculation of the irreducible vertex function for the case of three-dimensional antiferromagnetic fluctuations, and show that it is proportional to the diverging quasiparticle effective mass.

  18. Quantum critical point of Dirac fermions studied using efficient continuous-time projector quantum Monte Carlo method

    NASA Astrophysics Data System (ADS)

    Wang, Lei; Iazzi, Mauro; Corboz, Philippe; Troyer, Matthias

    2015-03-01

    Quantum phase transition (QPT) of Dirac fermions is a fascinating topic both in condensed matter and in high energy physics. Besides its immediate connection to fundamental problems like mass generation and exotic phases of matter, it provides a common playground where state of the art numerical simulations can be crosschecked with various effective field theory predictions, thus deepen our understanding of both fields. The universality class of the QPT is fundamentally different from the usual bosonic field theory because of the coupling to the gapless fermionic mode at the critical point. We study lattice models with spinless and multi-flavor Dirac fermions using the newly developed efficient continuous-time projector quantum Monte Carlo method. Besides eliminating the Trotter error, the method also enables us to directly calculate derivative observables in a continuous range of interaction strengths, thus greatly enhancing the resolution of the quantum critical region. Compatible results are also obtained from infinite projected entangled-pair states calculations. We compare these numerical results with predictions of the Gross-Neveu theory and discuss their physical implications.

  19. Erratum: Quantum superconducting criticality in graphene and topological insulators [Phys. Rev. B 87, 041401(R) (2013)

    NASA Astrophysics Data System (ADS)

    Roy, Bitan; Juričić, Vladimir; Herbut, Igor F.

    2016-09-01

    We correct our previous conclusion regarding the fate of a charged quantum critical point across the superconducting transition for two dimensional massless Dirac fermion. Within the leading order $\\epsilon$ expansion, we now find that the requisite number of four-component Dirac fermion flavors ($N_f$) for the continuous phase transition through a charged critical point is $N_f>18.2699$. For $N_f\\geq1/2$, the critical number of bosonic flavors for this transition is significantly reduced as compared to the value determined in the absence of the Dirac fermions in the theory.

  20. Thermodynamic signature of quantum criticality: universally diverging Grüneisen ratio

    NASA Astrophysics Data System (ADS)

    Zhu, Lijun

    2005-03-01

    At a generic quantum critical point where pressure acts as (or couples to) the zero-temperature control parameter, the Grüneisen ratio γ (the ratio of thermal expansion to specific heat) is divergent[1]. This property provides a novel probe to quantum criticality from thermodynamics. When scaling applies, γ˜1/T^x at the critical pressure p=pc, where the exponent x measures the scaling dimension of the most singular operator coupled to pressure; in the alternative limit T ->0 and p !=pc, γ= Gr/(p-pc), where Gr is a universal combination of critical exponents. The predicted divergence has been observed near the quantum critical points of several heavy fermion metals[2]. Analyses based on specific models relevant to these experiments are also presented. [1] L. Zhu, M. Garst, A. Rosch, and Q. Si, Phys. Rev. Lett. 91, 066404 (2003). [2] R. Küchler et al., Phys. Rev. Lett. 91, 066405 (2003); ibid. 93, 096402 (2004).

  1. Superconductivity near a Quantum-Critical Point: The Special Role of the First Matsubara Frequency

    NASA Astrophysics Data System (ADS)

    Wang, Yuxuan; Abanov, Artem; Altshuler, Boris L.; Yuzbashyan, Emil A.; Chubukov, Andrey V.

    2016-10-01

    Near a quantum-critical point in a metal strong fermion-fermion interaction mediated by a soft collective boson gives rise to incoherent, non-Fermi liquid behavior. It also often gives rise to superconductivity which masks the non-Fermi liquid behavior. We analyze the interplay between the tendency to pairing and fermionic incoherence for a set of quantum-critical models with effective dynamical interaction between low-energy fermions. We argue that superconducting Tc is nonzero even for strong incoherence and/or weak interaction due to the fact that the self-energy from dynamic critical fluctuations vanishes for the two lowest fermionic Matsubara frequencies ωm=±π T . We obtain the analytic formula for Tc, which reproduces well earlier numerical results for the electron-phonon model at vanishing Debye frequency.

  2. Quantum criticality and nodal superconductivity in the FeAs-based superconductor KFe2As2.

    PubMed

    Dong, J K; Zhou, S Y; Guan, T Y; Zhang, H; Dai, Y F; Qiu, X; Wang, X F; He, Y; Chen, X H; Li, S Y

    2010-02-26

    The in-plane resistivity rho and thermal conductivity kappa of the FeAs-based superconductor KFe2As2 single crystal were measured down to 50 mK. We observe non-Fermi-liquid behavior rho(T) approximately T{1.5} at H{c{2}}=5 T, and the development of a Fermi liquid state with rho(T) approximately T{2} when further increasing the field. This suggests a field-induced quantum critical point, occurring at the superconducting upper critical field H{c{2}}. In zero field, there is a large residual linear term kappa{0}/T, and the field dependence of kappa_{0}/T mimics that in d-wave cuprate superconductors. This indicates that the superconducting gaps in KFe2As2 have nodes, likely d-wave symmetry. Such a nodal superconductivity is attributed to the antiferromagnetic spin fluctuations near the quantum critical point.

  3. Holographic antiferromagnetic quantum criticality and AdS2 scaling limit

    NASA Astrophysics Data System (ADS)

    Cai, Rong-Gen; Yang, Run-Qiu; Kusmartsev, F. V.

    2015-08-01

    A holographic description on the antiferromagnetic quantum phase transition (QPT) induced by the magnetic field and the criticality in the vicinity of the quantum critical point have been investigated numerically recently. In this paper, we show that the properties of QPT in this holographic model are governed by a CFT dual to the emergent AdS2 in the IR region, which confirms that the dual boundary theory is a strong coupling theory with dynamic exponent z =2 and logarithmic corrections appearing. We also compare them with the results from the Hertz model by solving the RG equation at its upper critical dimension and with some experimental data from pyrochlores Er2 -2 xY2 xTi2 O7 and BiCoPO5 .

  4. Weak phase stiffness and nature of the quantum critical point in underdoped cuprates

    SciTech Connect

    Yildirim, Yucel; Ku, Wei

    2015-11-02

    We demonstrate that the zero-temperature superconducting phase diagram of underdoped cuprates can be quantitatively understood in the strong binding limit, using only the experimental spectral function of the “normal” pseudogap phase without any free parameter. In the prototypical (La1–xSrx)2CuO4, a kinetics-driven d-wave superconductivity is obtained above the critical doping δc ~ 5.2%, below which complete loss of superfluidity results from local quantum fluctuation involving local p-wave pairs. Near the critical doping, an enormous mass enhancement of the local pairs is found responsible for the observed rapid decrease of phase stiffness. Lastly, a striking mass divergence is predicted at δc that dictates the occurrence of the observed quantum critical point and the abrupt suppression of the Nernst effects in the nearby region.

  5. Weak phase stiffness and nature of the quantum critical point in underdoped cuprates

    DOE PAGESBeta

    Yildirim, Yucel; Ku, Wei

    2015-11-02

    We demonstrate that the zero-temperature superconducting phase diagram of underdoped cuprates can be quantitatively understood in the strong binding limit, using only the experimental spectral function of the “normal” pseudogap phase without any free parameter. In the prototypical (La1–xSrx)2CuO4, a kinetics-driven d-wave superconductivity is obtained above the critical doping δc ~ 5.2%, below which complete loss of superfluidity results from local quantum fluctuation involving local p-wave pairs. Near the critical doping, an enormous mass enhancement of the local pairs is found responsible for the observed rapid decrease of phase stiffness. Lastly, a striking mass divergence is predicted at δc thatmore » dictates the occurrence of the observed quantum critical point and the abrupt suppression of the Nernst effects in the nearby region.« less

  6. Regularity and chaos at critical points of first-order quantum phase transitions

    NASA Astrophysics Data System (ADS)

    Macek, M.; Leviatan, A.

    2011-10-01

    We study the interplay between regular and chaotic dynamics at the critical point of a generic first-order quantum phase transition in an interacting boson model of nuclei. A classical analysis reveals a distinct behavior of the coexisting phases in a broad energy range. The dynamics is completely regular in the deformed phase and, simultaneously, strongly chaotic in the spherical phase. A quantum analysis of the spectra separates the regular states from the irregular ones, assigns them to particular phases, and discloses persisting regular rotational bands in the deformed region.

  7. Quantum size effect on the paramagnetic critical field in free-standing superconducting nanofilms.

    PubMed

    Wójcik, P; Zegrodnik, M

    2014-11-12

    The quantum size effect on the in-plane paramagnetic critical field in Pb(1 1 1) free-standing nanofilms is investigated with the use of the spin-generalized Bogoliubov-de Gennes equations. It is shown that the critical field oscillates as a function of the nanofilm thickness with the period ∼ 2 ML (even-odd oscillations), modulated by the beating effect. The calculated values of the critical field for different nanofilm thicknesses are analyzed in the context of the Clogston-Chandrasekhar limit. It is found that the critical field for superconducting nanofilms differs from this limit. This phenomena is explained in terms of quantization of the electron energy caused by the confinement of electron motion in a direction perpendicular to the film. The thermal effect and thickness-dependence of electron-phonon coupling on the value of the critical magnetic field are also studied. PMID:25318561

  8. Quantum critical behavior in three-dimensional one-band Hubbard model at half-filling

    SciTech Connect

    Karchev, Naoum

    2013-06-15

    A one-band Hubbard model with hopping parameter t and Coulomb repulsion U is considered at half-filling. By means of the Schwinger bosons and slave fermions representation of the electron operators and integrating out the spin–singlet Fermi fields an effective Heisenberg model with antiferromagnetic exchange constant is obtained for vectors which identifies the local orientation of the spin of the itinerant electrons. The amplitude of the spin vectors is an effective spin of the itinerant electrons accounting for the fact that some sites, in the ground state, are doubly occupied or empty. Accounting adequately for the magnon–magnon interaction the Néel temperature is calculated. When the ratio t/U is small enough (t/U ≤0.09) the effective model describes a system of localized electrons. Increasing the ratio increases the density of doubly occupied states which in turn decreases the effective spin and Néel temperature. The phase diagram in the plane of temperature (T{sub N})/U and parameter t/U is presented. The quantum critical point (T{sub N}=0) is reached at t/U =0.9. The magnons in the paramagnetic phase are studied and the contribution of the magnons’ fluctuations to the heat capacity is calculated. At the Néel temperature the heat capacity has a peak which is suppressed when the system approaches a quantum critical point. It is important to stress that, at half-filling, the ground state, determined by fermions, is antiferromagnetic. The magnon fluctuations drive the system to quantum criticality and when the effective spin is critically small these fluctuations suppress the magnetic order. -- Highlights: •Technique of calculation is introduced which permits us to study the magnons’ fluctuations. •Quantum critical point is obtained in the one-band 3D Hubbard model at half-filling. •The present analytical results supplement the numerical ones (see Fig. 7)

  9. Quantum critical Mott transitions in a bilayer Kondo insulator-metal model system

    NASA Astrophysics Data System (ADS)

    Sen, Sudeshna; Vidhyadhiraja, N. S.

    2016-04-01

    A bilayer system comprising a Kondo insulator coupled to a simple metal (KI-M) is considered. Employing the framework of dynamical mean-field theory, the model system is shown to exhibit a surface of quantum critical points (QCPs) that separates a Kondo screened, Fermi liquid phase from a local moment, Mott insulating phase. The quantum critical nature of these Mott transitions is characterized by the vanishing of (a) the coherence scale on the Fermi liquid side, and (b) the Mott gap on the MI side. In contrast to the usual "large-to-small" Fermi surface (FS) QCPs in heavy-fermion systems, the bilayer KI-M system exhibits a complete FS destruction.

  10. Quantum criticality in CePt1-xNixSi2

    NASA Astrophysics Data System (ADS)

    Baumbach, R. E.; Lu, X.; Ronning, F.; Thompson, J. D.; Bauer, E. D.

    2012-12-01

    We report measurements of the specific heat, electrical resistivity, and magnetic susceptibility for CePt1-xNixSi2 from which we develop a T - x phase diagram that includes a quantum critical point near xcr ≈ 0.125 and accompanying non-Fermi-liquid behavior in a "v"-shaped region. This phase diagram is strikingly similar to that of CePtSi2 under applied pressure P, suggesting that CePt1-xNixSi2 provides a model system in which a T - P - x phase diagram can be smoothly generated, thereby allowing a systematic study of the influence of disorder on quantum criticality.

  11. Field-induced magnetization jumps and quantum criticality in the 2D J-Q model

    NASA Astrophysics Data System (ADS)

    Iaizzi, Adam; Sandvik, Anders

    The J-Q model is a `designer hamiltonian' formed by adding a four spin `Q' term to the standard antiferromagnetic S = 1 / 2 Heisenberg model. The Q term drives a quantum phase transition to a valence-bond solid (VBS) state: a non-magnetic state with a pattern of local singlets which breaks lattice symmetries. The elementary excitations of the VBS are triplons, i.e. gapped S=1 quasiparticles. There is considerable interest in the quantum phase transition between the Néel and VBS states as an example of deconfined quantum criticality. Near the phase boundary, triplons deconfine into pairs of bosonic spin-1/2 excitations known as spinons. Using exact diagonalization and the stochastic series expansion quantum monte carlo method, we study the 2D J-Q model in the presence of an external magnetic field. We use the field to force a nonzero density of magnetic excitations at T=0 and look for signatures of Bose-Einstein condensation of spinons. At higher magnetic fields, there is a jump in the induced magnetization caused by the onset of an effective attractive interaction between magnons on a ferromagnetic background. We characterize the first order quantum phase transition and determine the minimum value of the coupling ratio q ≡ Q / J required to produce this jump. Funded by NSF DMR-1410126.

  12. Magneto-acoustic study near the quantum critical point of the frustrated quantum antiferromagnet Cs2CuCl4

    NASA Astrophysics Data System (ADS)

    Cong, P. T.; Postulka, L.; Wolf, B.; van Well, N.; Ritter, F.; Assmus, W.; Krellner, C.; Lang, M.

    2016-10-01

    Magneto-acoustic investigations of the frustrated triangular-lattice antiferromagnet Cs2CuCl4 were performed for the longitudinal modes c11 and c33 in magnetic fields along the a-axis. The temperature dependence of the sound velocity at zero field shows a mild softening at low temperature and displays a small kink-like anomaly at TN. Isothermal measurements at T < TN of the sound attenuation α reveal two closely spaced features of different characters on approaching the material's quantum-critical point (QCP) at Bs ≈ 8.5 T for B || a. The peak at slightly lower fields remains sharp down to the lowest temperature and can be attributed to the ordering temperature TN(B). The second anomaly, which is rounded and which becomes reduced in size upon cooling, is assigned to the material's spin-liquid properties preceding the long-range antiferromagnetic ordering with decreasing temperature. These two features merge upon cooling suggesting a coincidence at the QCP. The elastic constant at lowest temperatures of our experiment at 32 mK can be well described by a Landau free energy model with a very small magnetoelastic coupling constant G/kB ≈ 2.8 K. The applicability of this classical model indicates the existence of a small gap in the magnetic excitation spectrum which drives the system away from quantum criticality.

  13. Topology-induced anomalous defect production by crossing a quantum critical point.

    PubMed

    Bermudez, A; Patanè, D; Amico, L; Martin-Delgado, M A

    2009-04-01

    We study the influence of topology on the quench dynamics of a system driven across a quantum critical point. We show how the appearance of certain edge states, which fully characterize the topology of the system, dramatically modifies the process of defect production during the crossing of the critical point. Interestingly enough, the density of defects is no longer described by the Kibble-Zurek scaling, but determined instead by the nonuniversal topological features of the system. Edge states are shown to be robust against defect production, which highlights their topological nature.

  14. Singularity of the London Penetration Depth at Quantum Critical Points in Superconductors

    NASA Astrophysics Data System (ADS)

    Chowdhury, Debanjan; Swingle, Brian; Berg, Erez; Sachdev, Subir

    2013-10-01

    We present a general theory of the singularity in the London penetration depth at symmetry-breaking and topological quantum critical points within a superconducting phase. While the critical exponents and ratios of amplitudes on the two sides of the transition are universal, an overall sign depends upon the interplay between the critical theory and the underlying Fermi surface. We determine these features for critical points to spin density wave and nematic ordering, and for a topological transition between a superconductor with Z2 fractionalization and a conventional superconductor. We note implications for recent measurements of the London penetration depth in BaFe2(As1-xPx)2 [K. Hashimoto , Science 336, 1554 (2012)SCIEAS0036-807510.1126/science.1219821].

  15. Critical fluctuations and the rates of interstate switching near the excitation threshold of a quantum parametric oscillator.

    PubMed

    Lin, Z R; Nakamura, Y; Dykman, M I

    2015-08-01

    We study the dynamics of a nonlinear oscillator near the critical point where period-two vibrations are first excited with the increasing amplitude of parametric driving. Above the threshold, quantum fluctuations induce transitions between the period-two states over the quasienergy barrier. We find the effective quantum activation energies for such transitions and their scaling with the difference of the driving amplitude from its critical value. We also find the scaling of the fluctuation correlation time with the quantum noise parameters in the critical region near the threshold. The results are extended to oscillators with nonlinear friction.

  16. Critical fluctuations and the rates of interstate switching near the excitation threshold of a quantum parametric oscillator

    NASA Astrophysics Data System (ADS)

    Lin, Z. R.; Nakamura, Y.; Dykman, M. I.

    2015-08-01

    We study the dynamics of a nonlinear oscillator near the critical point where period-two vibrations are first excited with the increasing amplitude of parametric driving. Above the threshold, quantum fluctuations induce transitions between the period-two states over the quasienergy barrier. We find the effective quantum activation energies for such transitions and their scaling with the difference of the driving amplitude from its critical value. We also find the scaling of the fluctuation correlation time with the quantum noise parameters in the critical region near the threshold. The results are extended to oscillators with nonlinear friction.

  17. Critical fluctuations and the rates of interstate switching near the excitation threshold of a quantum parametric oscillator.

    PubMed

    Lin, Z R; Nakamura, Y; Dykman, M I

    2015-08-01

    We study the dynamics of a nonlinear oscillator near the critical point where period-two vibrations are first excited with the increasing amplitude of parametric driving. Above the threshold, quantum fluctuations induce transitions between the period-two states over the quasienergy barrier. We find the effective quantum activation energies for such transitions and their scaling with the difference of the driving amplitude from its critical value. We also find the scaling of the fluctuation correlation time with the quantum noise parameters in the critical region near the threshold. The results are extended to oscillators with nonlinear friction. PMID:26382342

  18. Scaling in driven dynamics starting in the vicinity of a quantum critical point

    NASA Astrophysics Data System (ADS)

    Yin, Shuai; Lo, Chung-Yu; Chen, Pochung

    2016-08-01

    Driven dynamics across a quantum critical point is usually described by the Kibble-Zurek scaling. Although the original Kibble-Zurek scaling requires an adiabatic initial state, it has been shown that scaling behaviors exist even when the driven dynamics is triggered from a thermal equilibrium state exactly at the critical point, in spite of the breakdown of the initial adiabaticity. In this paper, we show that the existence of the scaling behavior can be generalized to the case of the initial state being a thermal equilibrium state near the critical point. We propose a scaling theory in which the initial parameters are included as additional scaling variables due to the breakdown of the initial adiabaticity. In particular, we demonstrate that for the driven critical dynamics in a closed system, the nontrivial thermal effects are closely related to the initial distance to the critical point. We numerically confirm the scaling theory by simulating the real-time dynamics of the one-dimensional quantum Ising model at both zero and finite temperatures.

  19. Nematic quantum criticality in FeSe1-x Sx revealed by elastoresistance measurements

    NASA Astrophysics Data System (ADS)

    Hosoi, Suguru; Matsuura, Kohei; Wang, Hao; Ishida, Kousuke; Mizukami, Yuta; Watashige, Tatsuya; Kasahara, Shigeru; Matsuda, Yuji; Shibauchi, Takasada

    Electronic nematicity and its connection to the high-temperature superconductivity is one of the central issues in iron-based superconductors. Among them, FeSe is unique in that it exhibits a tetragonal-to-orthorhombic structural transition but no antiferromagnetic order, which enables us to study the nematicity without the effect of magnetism. Here we report on elastoresistance measurements in FeSe1- x Sx evidencing a nonmagnetic nematic quantum critical point near x ~ 0.2. When the Se site is substituted by the isovalent S, the structural transition temperature is reduced gradually and it vanishes above x ~ 0.2. From the changes in in-plane resistivity induced by anisotropic strain, we evaluate the nematic susceptibility which shows Curie-Weiss-like temperature dependence. We find that with increasing x the Weiss temperature changes its sign indicating a quantum critical point, while there is no sign of antiferromagnetism for all samples. The superconducting transition temperature does not show a significant change with S concentration, suggesting that the nonmagnetic nematic quantum criticality does not help to enhance superconductivity in this system.

  20. Quantum criticality and inhomogeneous magnetic order in Fe-doped α -YbAlB4

    NASA Astrophysics Data System (ADS)

    MacLaughlin, D. E.; Kuga, K.; Shu, Lei; Bernal, O. O.; Ho, P.-C.; Nakatsuji, S.; Huang, K.; Ding, Z. F.; Tan, C.; Zhang, Jian

    2016-06-01

    The intermediate-valent polymorphs α - and β -YbAlB4 exhibit quantum criticality and other novel properties not usually associated with intermediate valence. Iron doping induces quantum criticality in α -YbAlB4 and magnetic order in both compounds. We report results of muon spin relaxation (μ SR ) experiments in α -YbAl1 -xFexB4 , x =0.014 and 0.25. For x =0.014 we find no evidence for magnetic order down to 25 mK. The dynamic muon spin relaxation rate λd exhibits a power-law temperature dependence λd∝T-a , a =0.40 (4 ) , in the temperature range 100 mK-2 K, in disagreement with predictions by theories of antiferromagnetic (AFM) or valence quantum critical behavior. For x =0.25 , where AFM order develops in the temperature range 7.5-10 K, we find coexistence of meso- or macroscopically segregated paramagnetic and AFM phases, with considerable disorder in the latter down to 2 K.

  1. Quantum Criticality Beneath the Superconducting Dome in β-YbAlB4

    NASA Astrophysics Data System (ADS)

    Tomita, T.; Kuga, K.; Uwatoko, Y.; Nakatsuji, S.

    2016-02-01

    Yb-based heavy fermion superconductor β-YbAlB4 at 0 K and 0 T at ambient pressure is located near the quantum critical point with strong mixed valiancy. In this type of Yb electron system, we expect that the magnetic order connected to the quantum critical point derives from the applied pressure. We built a pressure-temperature phase diagram for β-YbAlB4 by measuring the electrical resistivity of high quality single crystal at temperatures down to 40 mK under an applied pressure. A strange metal region appeared, showing non-Fermi liquid ρab α T1.5 behavior, which is stable with applied pressure up to 0.4 GPa, even when below the superconducting dome excluded by a magnetic field of 0.1 T. By increasing of pressure above 2.5 GPa, a magnetic order is first generated. Such ambient quantum criticality/superconductivity is unconventional and is detached from the magnetic order.

  2. Field-induced magnetic instability and quantum criticality in the antiferromagnet CeCu2Ge2

    NASA Astrophysics Data System (ADS)

    Liu, Yi; Xie, Donghua; Wang, Xiaoying; Zhu, Kangwei; Yang, Ruilong

    2016-01-01

    The magnetic quantum criticality in strongly correlated electron systems has been considered to be closely related with the occurrence of unconventional superconductivity. Control parameters such as magnetic field, pressure or chemical doping are frequently used to externally tune the quantum phase transition for a deeper understanding. Here we report the research of a field-induced quantum phase transition using conventional bulk physical property measurements in the archetypal antiferromagnet CeCu2Ge2, which becomes superconductive under a pressure of about 10 GPa with Tc ~ 0.64 K. We offer strong evidence that short-range dynamic correlations start appearing above a magnetic field of about 5 T. Our demonstrations of the magnetic instability and the field-induced quantum phase transition are crucial for the quantum criticality, which may open a new route in experimental investigations of the quantum phase transition in heavy-fermion systems.

  3. Field-induced magnetic instability and quantum criticality in the antiferromagnet CeCu2Ge2

    PubMed Central

    Liu, Yi; Xie, Donghua; Wang, Xiaoying; Zhu, Kangwei; Yang, Ruilong

    2016-01-01

    The magnetic quantum criticality in strongly correlated electron systems has been considered to be closely related with the occurrence of unconventional superconductivity. Control parameters such as magnetic field, pressure or chemical doping are frequently used to externally tune the quantum phase transition for a deeper understanding. Here we report the research of a field-induced quantum phase transition using conventional bulk physical property measurements in the archetypal antiferromagnet CeCu2Ge2, which becomes superconductive under a pressure of about 10 GPa with Tc ~ 0.64 K. We offer strong evidence that short-range dynamic correlations start appearing above a magnetic field of about 5 T. Our demonstrations of the magnetic instability and the field-induced quantum phase transition are crucial for the quantum criticality, which may open a new route in experimental investigations of the quantum phase transition in heavy-fermion systems. PMID:26758347

  4. Bi-layer ^3He: a simple two dimensional heavy fermion system with quantum criticality

    NASA Astrophysics Data System (ADS)

    Saunders, John

    2008-03-01

    Two dimensional helium films provide simple model systems for the investigation of quantum phase transitions in two dimensions. Monolayer ^3He absorbed on graphite, with various pre-platings, behaves as a two dimensional Mott-Hubbard system, complete with a density driven ``metal-insulator'' transition [1, 2] into what appears to be a gapless spin-liquid. In two dimensions the corrections to the temperature dependence of the fluid heat capacity, beyond the term linear in T, are anomalous and attributed to quasi-1D scattering [3]. On the other hand, bi-layer ^3He films adsorbed on the surface of graphite show evidence of two-band heavy-fermion behavior and quantum criticality [4, 5]. The relevant control parameter is the total density of the ^3He film. The ^3He bilayer system can be driven toward a quantum critical point (QCP) at which the effective mass appears to diverge, the effective inter-band hybridization vanishes, and a local moment state appears. A theoretical model in terms of a ``Kondo breakdown selective Mott transition'' has recently been suggested [6]. * In collaboration with: A Casey, M Neumann, J Nyeki, B Cowan. [1] Evidence for a Mott-Hubbard Transition in a Two-Dimensional ^3He Fluid Monolayer, A. Casey, H. Patel, J. Ny'eki, B. P. Cowan, and J. Saunders Phys. Rev. Lett. 90, 115301 (2003) [2] D Tsuji et al. J. Low Temp. Phys. 134, 31 (2004) [3] A V Chubukov et al. Phys. Rev. B71, 205112 (2005) [4] Bilayer ^3He; a simple two dimensional heavy fermion system with quantum criticality, Michael Neumann, Jan Nyeki, Brian Cowan, John Saunders. Science 317, 1356 (2007) [5] Heavy fermions in the original Fermi liquid. Christopher A Hooley and Andrew P Mackenzie. Science 317, 1332 (2007) [6] C Pepin, Phys. Rev. Lett. 98, 206401 (2007) and A Benlagra and C Pepin, arXiv: 0709.0354

  5. Field-induced quantum critical route to a Fermi liquid in high-temperature superconductors

    PubMed Central

    Shibauchi, Takasada; Krusin-Elbaum, Lia; Hasegawa, Masashi; Kasahara, Yuichi; Okazaki, Ryuji; Matsuda, Yuji

    2008-01-01

    In high-transition-temperature (Tc) superconductivity, charge doping is a natural tuning parameter that takes copper oxides from the antiferromagnet to the superconducting region. In the metallic state above Tc, the standard Landau's Fermi-liquid theory of metals as typified by the temperature squared (T2) dependence of resistivity appears to break down. Whether the origin of the non-Fermi-liquid behavior is related to physics specific to the cuprates is a fundamental question still under debate. We uncover a transformation from the non-Fermi-liquid state to a standard Fermi-liquid state driven not by doping but by magnetic field in the overdoped high-Tc superconductor Tl2Ba2CuO6+x. From the c-axis resistivity measured up to 45 T, we show that the Fermi-liquid features appear above a sufficiently high field that decreases linearly with temperature and lands at a quantum critical point near the superconductivity's upper critical field—with the Fermi-liquid coefficient of the T2 dependence showing a power-law diverging behavior on the approach to the critical point. This field-induced quantum criticality bears a striking resemblance to that in quasi-two-dimensional heavy-Fermion superconductors, suggesting a common underlying spin-related physics in these superconductors with strong electron correlations. PMID:18480261

  6. Low Temperature Properties and Quantum Criticality of CrAs1-x Px single crystal

    NASA Astrophysics Data System (ADS)

    Luo, Jianlin; Institute of Physics, Chinese Academy of Sciences Team

    We report a systematically study of resistivity and specific heat on phosphorus doped CrAs1-xPx single crystals with x =0 to 0.2. With the increasing of phosphorus doping concentration x, the magnetic and structural transition temperature TN is suppressed. Non-fermi liquid behavior and quantum criticality phenomenon are observed from low temperature resistivity around critical doping with xc ~0.05 where the long-range antiferromagnetic ordering is completely suppressed. The low temperature specific heat of CrAs1-xPx is contributed by the thermal excitation of phonons and electrons. The electronic specific heat coefficient γ, which reflects the effective mass of quasi-particles, shows maximum around xc ~0.05, also indicating the existence of quantum critical phenomenon around the critical doping. The value of Kadowaki-Woods ratio of CrAs1-xPx shows no significant different from that of CrAs. Work is done in collaboration with Fukun Lin, Wei Wu, Ping Zheng, Guozhi Fan, Jinguang Cheng.

  7. Universal Quantum Criticality in the Metal-Insulator Transition of Two-Dimensional Interacting Dirac Electrons

    NASA Astrophysics Data System (ADS)

    Otsuka, Yuichi; Yunoki, Seiji; Sorella, Sandro

    2016-01-01

    The metal-insulator transition has been a subject of intense research since Mott first proposed that the metallic behavior of interacting electrons could turn to an insulating one as electron correlations increase. Here, we consider electrons with massless Dirac-like dispersion in two spatial dimensions, described by the Hubbard models on two geometrically different lattices, and perform numerically exact calculations on unprecedentedly large systems that, combined with a careful finite-size scaling analysis, allow us to explore the quantum critical behavior in the vicinity of the interaction-driven metal-insulator transition. Thereby, we find that the transition is continuous, and we determine the quantum criticality for the corresponding universality class, which is described in the continuous limit by the Gross-Neveu model, a model extensively studied in quantum field theory. Furthermore, we discuss a fluctuation-driven scenario for the metal-insulator transition in the interacting Dirac electrons: The metal-insulator transition is triggered only by the vanishing of the quasiparticle weight, not by the Dirac Fermi velocity, which instead remains finite near the transition. This important feature cannot be captured by a simple mean-field or Gutzwiller-type approximate picture but is rather consistent with the low-energy behavior of the Gross-Neveu model.

  8. Theory of excitations and dielectric response at a spin-orbital quantum critical point

    NASA Astrophysics Data System (ADS)

    Ish, Daniel; Balents, Leon

    2015-09-01

    Despite possessing a local spin-2 moment on the iron site and a Curie-Weiss temperature of 45 K, the A-site spinel FeSc2S4 does not magnetically order down to 50 mK. Previous theoretical work advanced an explanation for this observation in the form of the "J2-λ " model, which places FeSc2S4 close to a quantum critical point on the disordered side of a quantum phase transition between a Néel ordered phase and a "spin-orbital liquid" in which spins and orbitals are entangled, quenching the magnetization. We present new theoretical studies of the optical properties of the J2-λ model, including a computation of the dispersion relation for the quasiparticle excitations and the form of the collective response to electric field. We argue that the latter directly probes a low energy excitation continuum characteristic of quantum criticality, and that our results reinforce the consistency of this model with experiment.

  9. Field-induced quadrupolar quantum criticality in PrV2Al20

    NASA Astrophysics Data System (ADS)

    Shimura, Yasuyuki; Tsujimoto, Masaki; Zeng, Bin; Balicas, Luis; Sakai, Akito; Nakatsuji, Satoru

    2015-06-01

    PrV2Al20 is a heavy-fermion superconductor based on the cubic Γ3 doublet that exhibits nonmagnetic quadrupolar ordering below ˜0.6 K. Our magnetotransport study on PrV2Al20 reveals field-induced quadrupolar quantum criticality at μ0Hc˜11 T applied along the [111] direction. Near the critical field μ0Hc required to suppress the quadrupolar state, we find a marked enhancement of the resistivity ρ (H ,T ) , a divergent quasiparticle effective mass and concomitant non-Fermi-liquid (NFL) behavior [i.e., ρ (T ) ∝Tn with n ≤0.5 ]. We also observe the Shubnikov-de Haas effect above μ0Hc , indicating effective mass enhancement or m*/m0˜10 . This reveals the competition between the nonmagnetic Kondo effect and the intersite quadrupolar coupling which leads to pronounced NFL behavior in an extensive region of T and μ0H emerging from the quantum-critical point.

  10. Origin of Quantum Criticality in Yb-Al-Au Approximant Crystal and Quasicrystal

    NASA Astrophysics Data System (ADS)

    Watanabe, Shinji; Miyake, Kazumasa

    2016-06-01

    To get insight into the mechanism of emergence of unconventional quantum criticality observed in quasicrystal Yb15Al34Au51, the approximant crystal Yb14Al35Au51 is analyzed theoretically. By constructing a minimal model for the approximant crystal, the heavy quasiparticle band is shown to emerge near the Fermi level because of strong correlation of 4f electrons at Yb. We find that charge-transfer mode between 4f electron at Yb on the 3rd shell and 3p electron at Al on the 4th shell in Tsai-type cluster is considerably enhanced with almost flat momentum dependence. The mode-coupling theory shows that magnetic as well as valence susceptibility exhibits χ ˜ T-0.5 for zero-field limit and is expressed as a single scaling function of the ratio of temperature to magnetic field T/B over four decades even in the approximant crystal when some condition is satisfied by varying parameters, e.g., by applying pressure. The key origin is clarified to be due to strong locality of the critical Yb-valence fluctuation and small Brillouin zone reflecting the large unit cell, giving rise to the extremely-small characteristic energy scale. This also gives a natural explanation for the quantum criticality in the quasicrystal corresponding to the infinite limit of the unit-cell size.

  11. Time-domain pumping a quantum-critical charge density wave ordered material

    NASA Astrophysics Data System (ADS)

    Matveev, O. P.; Shvaika, A. M.; Devereaux, T. P.; Freericks, J. K.

    2016-09-01

    We determine the exact time-resolved photoemission spectroscopy for a nesting driven charge density wave (described by the spinless Falicov-Kimball model within dynamical mean-field theory). The pump-probe experiment involves two light pulses: the first is an ultrashort intense pump pulse that excites the system into nonequilibrium, and the second is a lower amplitude, higher frequency probe pulse that photoexcites electrons. We examine three different cases: the strongly correlated metal, the quantum-critical charge density wave, and the critical Mott insulator. Our results show that the quantum critical charge density wave has an ultraefficient relaxation channel that allows electrons to be de-excited during the pump pulse, resulting in little net excitation. In contrast, the metal and the Mott insulator show excitations that are closer to what one expects from these systems. In addition, the pump field produces spectral band narrowing, peak sharpening, and a spectral gap reduction, all of which rapidly return to their field free values after the pump is over.

  12. Zeeman-Field-Tuned Topological Phase Transitions in a Two-Dimensional Class-DIII Superconductor

    PubMed Central

    Deng, W. Y.; Geng, H.; Luo, W.; Sheng, L.; Xing, D. Y.

    2016-01-01

    We investigate the topological phase transitions in a two-dimensional time-reversal invariant topological superconductor in the presence of a Zeeman field. Based on the spin Chern number theory, we find that the system exhibits a number of topologically distinct phases with changing the out-of-plane component of the Zeeman field, including a quantum spin Hall-like phase, quantum anomalous Hall-like phases with total Chern number C = −2, −1, 1 and 2, and a topologically trivial superconductor phase. The BdG band gap closes at each boundary of the phase transitions. Furthermore, we demonstrate that the zero bias conductance provides clear transport signatures of the different topological phases, which are robust against symmetry-breaking perturbations. PMID:27148675

  13. Zeeman-Field-Tuned Topological Phase Transitions in a Two-Dimensional Class-DIII Superconductor.

    PubMed

    Deng, W Y; Geng, H; Luo, W; Sheng, L; Xing, D Y

    2016-01-01

    We investigate the topological phase transitions in a two-dimensional time-reversal invariant topological superconductor in the presence of a Zeeman field. Based on the spin Chern number theory, we find that the system exhibits a number of topologically distinct phases with changing the out-of-plane component of the Zeeman field, including a quantum spin Hall-like phase, quantum anomalous Hall-like phases with total Chern number C = -2, -1, 1 and 2, and a topologically trivial superconductor phase. The BdG band gap closes at each boundary of the phase transitions. Furthermore, we demonstrate that the zero bias conductance provides clear transport signatures of the different topological phases, which are robust against symmetry-breaking perturbations.

  14. CRITIC2: A program for real-space analysis of quantum chemical interactions in solids

    NASA Astrophysics Data System (ADS)

    Otero-de-la-Roza, A.; Johnson, Erin R.; Luaña, Víctor

    2014-03-01

    We present CRITIC2, a program for the analysis of quantum-mechanical atomic and molecular interactions in periodic solids. This code, a greatly improved version of the previous CRITIC program (Otero-de-la Roza et al., 2009), can: (i) find critical points of the electron density and related scalar fields such as the electron localization function (ELF), Laplacian, … (ii) integrate atomic properties in the framework of Bader’s Atoms-in-Molecules theory (QTAIM), (iii) visualize non-covalent interactions in crystals using the non-covalent interactions (NCI) index, (iv) generate relevant graphical representations including lines, planes, gradient paths, contour plots, atomic basins, … and (v) perform transformations between file formats describing scalar fields and crystal structures. CRITIC2 can interface with the output produced by a variety of electronic structure programs including WIEN2k, elk, PI, abinit, Quantum ESPRESSO, VASP, Gaussian, and, in general, any other code capable of writing the scalar field under study to a three-dimensional grid. CRITIC2 is parallelized, completely documented (including illustrative test cases) and publicly available under the GNU General Public License. Catalogue identifier: AECB_v2_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AECB_v2_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: yes No. of lines in distributed program, including test data, etc.: 11686949 No. of bytes in distributed program, including test data, etc.: 337020731 Distribution format: tar.gz Programming language: Fortran 77 and 90. Computer: Workstations. Operating system: Unix, GNU/Linux. Has the code been vectorized or parallelized?: Shared-memory parallelization can be used for most tasks. Classification: 7.3. Catalogue identifier of previous version: AECB_v1_0 Journal reference of previous version: Comput. Phys. Comm. 180 (2009) 157 Nature of problem: Analysis of quantum

  15. Quantum critical origin of the superconducting dome and the isotope effect in SrTiO3

    NASA Astrophysics Data System (ADS)

    Kedem, Yaron; Edge, Jonathan; Aschauer, Ulrich; Spaldin, Nicola; Balatsky, Alexander

    We expand the notion that quantum criticality can induce superconductivity, by proposing a concrete mechanism for superconductivity due to quantum ferroelectric fluctuations. To this end, we investigate the origin of superconductivity in doped SrTiO3 (STO) using a combination of density functional and strong coupling theories within the framework of quantum criticality. Our density functional calculations of the ferroelectric soft mode frequency as a function of doping reveal a crossover related to quantum paraelectricity at a doping level coincident with the experimentally observed top of the superconducting dome. Thus, we suggest a model in which the soft mode fluctuations provide the pairing interaction for superconductivity carriers. Within our model, the low doping limit of the superconducting dome is explained by the emergence of the Fermi surface, and the high doping limit by departure from the quantum critical regime. This results in a prediction that the highest critical temperature will increase and shift to lower carrier doping with increasing 18O isotope substitution, a scenario that is experimentally verifiable. In addition we show a connection between the isotope exponent of superconductivity and the critical exponent pertaining to quantum phase transition. This work was supported by US DOE BES E304, by the ETH Zürich (NAS and UA) and by the ERC Advanced Grant Program, No. 291151 (NAS and UA), No321031, KAW and LDRD (YK).

  16. Spin S=1 ``Quantum spin liquid'': quantum criticality in 6H-B-Ba3NiSb2O9

    NASA Astrophysics Data System (ADS)

    Chen, Gang; Hermele, Michael; Radzihovsky, Leo

    2012-02-01

    We present a minimal model for a recently discovered material 6H-B-Ba3NiSb2O9 which was proposed as a candidate for S=1 quantum spin liquid on a triangular lattice. Our spin-1 model lies on a stacked multilayer triangular lattice. In our minimal model, we point out the competition between Heisenberg exchange interactions, which favor magnetic ordering, and the easy-plane single-ion anisotropy, which favors a uniform quantum paramagnetic state with S^z =0 state at each site. We argue that the system is close to the quantum critical point separating these two phases and on the quantum paramagnetic phase side. Viewing the system as a three dimensional multilayer structure, we find that the frustrated interlayer and intralayer exchange interaction induces nodal lines of low energy spin excitations at the quantum critical point. Moreover, due to the quasi-2D nature of the system and proximity to the quantum critical point, we show there exists a broad intermediate temperature regime with linear temperature dependence of specific heat. Various other predictions and suggestions for experiments are discussed.

  17. Fermion-Parity Anomaly of the Critical Supercurrent in the Quantum Spin-Hall Effect

    NASA Astrophysics Data System (ADS)

    Beenakker, C. W. J.; Pikulin, D. I.; Hyart, T.; Schomerus, H.; Dahlhaus, J. P.

    2013-01-01

    The helical edge state of a quantum spin-Hall insulator can carry a supercurrent in equilibrium between two superconducting electrodes (separation L, coherence length ξ). We calculate the maximum (critical) current Ic that can flow without dissipation along a single edge, going beyond the short-junction restriction L≪ξ of earlier work, and find a dependence on the fermion parity of the ground state when L becomes larger than ξ. Fermion-parity conservation doubles the critical current in the low-temperature, long-junction limit, while for a short junction Ic is the same with or without parity constraints. This provides a phase-insensitive, dc signature of the 4π-periodic Josephson effect.

  18. Sub-THz dielectric resonance in single crystal yttrium iron garnet and magnetic field tuning of the modes

    NASA Astrophysics Data System (ADS)

    Popov, M. A.; Zavislyak, I. V.; Srinivasan, G.

    2011-07-01

    The observation of dielectric resonance over the frequency range 40-110 GHz in single crystal yttrium iron garnet (YIG) and its magnetic field tuning characteristics are reported. The dimensions of YIG are appropriately chosen in order to have the dielectric resonance occur at a much higher frequency than the ferromagnetic resonance and avoid any hybrid spin-electromagnetic modes. The dielectric modes are magnetically tunable by 1 GHz with a magnetic field of ˜1.75 kOe. The tuning range and required bias magnetic fields, however, can be controlled with the sample dimensions (or the demagnetization factor Nzz). Theoretical calculations on magnetic field tuning characteristics for the dielectric modes are in reasonable agreement with the data. The theory also predicts a similar magnetic tuning of the dielectric modes in the sub-THz frequency range as well. The dielectric modes that can be tuned with a magnetic field are of importance for the realization of low-loss tunable devices, including resonators, isolators, and phase shifters operating in the sub-THz region.

  19. Electric Field Tuned Crossover from Classical to Weakly Localized Quantum Transport in Electron Doped SrTiO3

    SciTech Connect

    Ngai, J.H.; Segal, Y.; Su, D.; Zhu, Y.; Walker, F.J.; Ismail-Beigi, S.; Le Hur, K.; Ahn, C.H.

    2010-06-21

    Electron gases created by modulating the charge density near interfaces and surfaces of insulating SrTiO{sub 3} offer a wide range of tunable behavior. Here, we utilize the nonlinear dielectric response of SrTiO{sub 3} to electrostatically manipulate the spatial confinement of an electron gas relative to an interface, where scattering is enhanced. Magnetotransport measurements reveal that the electron gas can be tuned from weakly localized to classical transport regimes. This crossover in transport demonstrates that elastic scattering can be electrostatically controlled, providing another degree of tunability for electron gases in SrTiO{sub 3}.

  20. Universal conductivity in a two-dimensional superfluid-to-insulator quantum critical system.

    PubMed

    Chen, Kun; Liu, Longxiang; Deng, Youjin; Pollet, Lode; Prokof'ev, Nikolay

    2014-01-24

    We compute the universal conductivity of the (2+1)-dimensional XY universality class, which is realized for a superfluid-to-Mott insulator quantum phase transition at constant density. Based on large-scale Monte Carlo simulations of the classical (2+1)-dimensional J-current model and the two-dimensional Bose-Hubbard model, we can precisely determine the conductivity on the quantum critical plateau, σ(∞) = 0.359(4)σQ with σQ the conductivity quantum. The universal conductivity curve is the standard example with the lowest number of components where the bottoms-up AdS/CFT correspondence from string theory can be tested and made to use [R. C. Myers, S. Sachdev, and A. Singh, Phys. Rev. D 83, 066017 (2011)]. For the first time, the shape of the σ(iω(n)) - σ(∞) function in the Matsubara representation is accurate enough for a conclusive comparison and establishes the particlelike nature of charge transport. We find that the holographic gauge-gravity duality theory for transport properties can be made compatible with the data if temperature of the horizon of the black brane is different from the temperature of the conformal field theory. The requirements for measuring the universal conductivity in a cold gas experiment are also determined by our calculation. PMID:24484123

  1. Heavy fermions, quantum criticality, and unconventional superconductivity in filled skutterudites and related materials

    SciTech Connect

    Andraka, Bohdan

    2015-05-14

    The main goal of this program was to explore the possibility of novel states and behaviors in Pr-based system exhibiting quantum critical behavior, PrOs₄Sb₁₂. Upon small changes of external parameter, such as magnetic field, physical properties of PrOs₄Sb₁₂ are drastically altered from those corresponding to a superconductor, to heavy fermion, to field-induced ordered phase with primary quadrupolar order parameter. All these states are highly unconventional and not understood in terms of current theories thus offer an opportunity to expand our knowledge and understanding of condensed matter. At the same time, these novel states and behaviors are subjects to intense international controversies. In particular, two superconducting phases with different transition temperatures were observed in some samples and not observed in others leading to speculations that sample defects might be partially responsible for these exotic behaviors. This work clearly established that crystal disorder is important consideration, but contrary to current consensus this disorder suppresses exotic behavior. Superconducting properties imply unconventional inhomogeneous state that emerges from unconventional homogeneous normal state. Comprehensive structural investigations demonstrated that upper superconducting transition is intrinsic, bulk, and unconventional. The high quality of in-house synthesized single crystals was indirectly confirmed by de Haas-van Alphen quantum oscillation measurements. These measurements, for the first time ever reported, spanned several different phases, offering unprecedented possibility of studying quantum oscillations across phase boundaries.

  2. Quantum entanglement and criticality of the antiferromagnetic Heisenberg model in an external field.

    PubMed

    Liu, Guang-Hua; Li, Ruo-Yan; Tian, Guang-Shan

    2012-06-27

    By Lanczos exact diagonalization and the infinite time-evolving block decimation (iTEBD) technique, the two-site entanglement as well as the bipartite entanglement, the ground state energy, the nearest-neighbor correlations, and the magnetization in the antiferromagnetic Heisenberg (AFH) model under an external field are investigated. With increasing external field, the small size system shows some distinct upward magnetization stairsteps, accompanied synchronously with some downward two-site entanglement stairsteps. In the thermodynamic limit, the two-site entanglement, as well as the bipartite entanglement, the ground state energy, the nearest-neighbor correlations, and the magnetization are calculated, and the critical magnetic field h(c) = 2.0 is determined exactly. Our numerical results show that the quantum entanglement is sensitive to the subtle changing of the ground state, and can be used to describe the magnetization and quantum phase transition. Based on the discontinuous behavior of the first-order derivative of the entanglement entropy and fidelity per site, we think that the quantum phase transition in this model should belong to the second-order category. Furthermore, in the magnon existence region (h < 2.0), a logarithmically divergent behavior of block entanglement which can be described by a free bosonic field theory is observed, and the central charge c is determined to be 1.

  3. Universal conductivity in a two-dimensional superfluid-to-insulator quantum critical system.

    PubMed

    Chen, Kun; Liu, Longxiang; Deng, Youjin; Pollet, Lode; Prokof'ev, Nikolay

    2014-01-24

    We compute the universal conductivity of the (2+1)-dimensional XY universality class, which is realized for a superfluid-to-Mott insulator quantum phase transition at constant density. Based on large-scale Monte Carlo simulations of the classical (2+1)-dimensional J-current model and the two-dimensional Bose-Hubbard model, we can precisely determine the conductivity on the quantum critical plateau, σ(∞) = 0.359(4)σQ with σQ the conductivity quantum. The universal conductivity curve is the standard example with the lowest number of components where the bottoms-up AdS/CFT correspondence from string theory can be tested and made to use [R. C. Myers, S. Sachdev, and A. Singh, Phys. Rev. D 83, 066017 (2011)]. For the first time, the shape of the σ(iω(n)) - σ(∞) function in the Matsubara representation is accurate enough for a conclusive comparison and establishes the particlelike nature of charge transport. We find that the holographic gauge-gravity duality theory for transport properties can be made compatible with the data if temperature of the horizon of the black brane is different from the temperature of the conformal field theory. The requirements for measuring the universal conductivity in a cold gas experiment are also determined by our calculation.

  4. Exotic quantum critical point on the surface of three-dimensional topological insulator

    NASA Astrophysics Data System (ADS)

    Bi, Zhen; You, Yi-Zhuang; Xu, Cenke

    2016-07-01

    In the last few years a lot of exotic and anomalous topological phases were constructed by proliferating the vortexlike topological defects on the surface of the 3 d topological insulator (TI) [Fidkowski et al., Phys. Rev. X 3, 041016 (2013), 10.1103/PhysRevX.3.041016; Chen et al., Phys. Rev. B 89, 165132 (2014), 10.1103/PhysRevB.89.165132; Bonderson et al., J. Stat. Mech. (2013) P09016, 10.1088/1742-5468/2013/09/P09016; Wang et al., Phys. Rev. B 88, 115137 (2013), 10.1103/PhysRevB.88.115137; Metlitski et al., Phys. Rev. B 92, 125111 (2015), 10.1103/PhysRevB.92.125111]. In this work, rather than considering topological phases at the boundary, we will study quantum critical points driven by vortexlike topological defects. In general, we will discuss a (2 +1 )d quantum phase transition described by the following field theory: L =ψ ¯γμ(∂μ-i aμ) ψ +| (∂μ-i k aμ) ϕ| 2+r|ϕ | 2+g |ϕ| 4 , with tuning parameter r , arbitrary integer k , Dirac fermion ψ , and complex scalar bosonic field ϕ , which both couple to the same (2 +1 )d dynamical noncompact U(1) gauge field aμ. The physical meaning of these quantities/fields will be explained in the text. Making use of the new duality formalism developed in [Metlitski et al., Phys. Rev. B 93, 245151 (2016), 10.1103/PhysRevB.93.245151; Wang et al., Phys. Rev. X 5, 041031 (2015), 10.1103/PhysRevX.5.041031; Wang et al., Phys. Rev. B 93, 085110 (2016), 10.1103/PhysRevB.93.085110; D. T. Son, Phys. Rev. X 5, 031027 (2015), 10.1103/PhysRevX.5.031027], we demonstrate that this quantum critical point has a quasi-self-dual nature. And at this quantum critical point, various universal quantities such as the electrical conductivity and scaling dimension of gauge-invariant operators, can be calculated systematically through a 1 /k2 expansion, based on the observation that the limit k →+∞ corresponds to an ordinary 3 d X Y transition.

  5. Microscopic investigation of electronic inhomogeneity induced by substitutions in quantum critical CeCoIn5

    NASA Astrophysics Data System (ADS)

    Ronning, Filip; Sakai, Hironori; Zhu, Jianxin; Wakeham, Nicholas; Yasuoka, Hiroshi; Tokunaga, Yo; Kambe, Shin; Bauer, Eric; Thompson, Joe

    In Cd-doped CeCoIn5 magnetic order can be suppressed by pressure giving rise to a dome of superconductivity surrounding a quantum critical point (QCP). However, the typical non-Fermi liquid (NFL) signatures expected at this QCP are absent. In contrast, in Sn-doped CeRhIn5, pressure also suppresses magnetism giving rise to a dome of superconductivity, but in this case, the NFL signatures ARE observed at the QCP. We presents results using nuclear quadrupole resonance to probe microscopically the response of the prototypical quantum-critical metal CeCoIn5 to substitutions of small amounts of Sn and Cd for In. These substituents induce very different local electronic environments as observed by site dependent spin lattice relaxation rates 1/T1. Cd-doped samples generate a much more inhomogeneous spin environment than observed in Sn-doped samples. This difference naturally explains the presence and absence of NFL signatures at the respective QCPs mentioned above. The effects found here illustrate the need for care in general when interpreting NFL properties determined by macroscopic measurements achieved by chemical substitutions.

  6. Non-Fermi liquid phase and non-Gaussian itinerant quantum criticality of Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Goswami, Pallab

    A Weyl semimetal is a gapless topological phase in three dimensions, for which the touching points between two nondegenerate bands act as monopoles and antimonopoles of Abelian Berry curvature, with monopole strength m. Such a gapless phase can support m Fermi arcs as the protected, zero energy surface states. We consider the stability of a generalized Weyl semimetal with m > 1 in the presence of interaction and disorder by employing a renormalization group analysis, which is controlled by the parameter ɛ = 1 -1/m . For any m > 1 , we show how the long range Coulomb interaction gives rise to an infra-red stable, non-Fermi liquid phase without any sharp quasiparticle pole. In the presence of sufficiently strong short range interactions, the non-Fermi liquid can transform into a translational symmetry breaking, axionic insulator. We demonstrate that the associated itinerant quantum critical point possesses non-Gaussian scaling properties. We establish the stability of the emergent non-Fermi liquid phase and the itinerant quantum critical point against weak disorder. Finally, we discuss the scaling properties of physical quantities, the fate of the Fermi arcs, and the experimental relevance of our results for some candidate materials. NSF.

  7. Hetero-junction of two quantum wires: Critical line and duality

    NASA Astrophysics Data System (ADS)

    Lee, Taejin

    2016-08-01

    Applying the Fermi-Bose equivalence and the boundary state formulation, we study the hetero-junction of two quantum wires. Two quantum wires are described by using Tomonaga-Luttinger (TL) liquids with different TL parameters, and electron transport between the two wires is depicted by using a simple hopping interaction. We calculate the radiative corrections to the hopping interaction and obtain the renormalization (RG) exponent, making use of perturbation theory based on the boundary state formulation. The model exhibits a phase transition at zero temperature. We discuss the critical line that defines the phase boundary on the two-dimensional parameter space. The model also exhibits the particle-kink duality, which maps the strong coupling region of the model onto the weak coupling region of the dual model. The strong coupling region of the model is found to match exactly the weak coupling region of the dual model. This model is also important to study the critical behaviors of two-dimensional dissipative systems with anisotropic friction coefficients.

  8. Evolution of Quantum Critical Behavior In A Concentrated Ternary Solid Solution: NiCoCrx

    NASA Astrophysics Data System (ADS)

    Sales, Brian; Jin, Ke; Bei, Hongbin; Stocks, Malcolm; Samolyuk, German; May, Andrew; McGuire, Michael

    The face centered cubic (fcc) alloy NiCoCrx with x near 1 is found to be close to the Cr concentration where the ferromagnetic transition temperature, Tc goes to 0. Near this composition these alloys exhibit a resistivity linear in temperature to 2 K, a perfectly linear magnetoresistance, and an excess -TlnT contribution to the low temperature heat capacity. As the Cr concentration is decreased from 1, the Curie temperature and the saturation magnetization, M0, both increase exponentially with x. For x = 0.5, Tc ~ 217 K, but M0 is only 0.26 Bohr magnetons/atom, indicating highly itinerant ferromagnets for 0.5 quantum critical region. This new class of concentrated solid solution fcc alloys are ideal model systems to study the effects of chemical disorder on emergent properties near a quantum critical point. Research supported by the DOE Office of Science, Materials Science and Engineering Division, and the Energy Dissipation to Defect Evolution EFRC.

  9. Robustness of quantum critical pairing against disorder in iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Kang, Jian; Fernandes, Rafael

    Several experiments in iron pnictides and cuprates reveal a superconducting (SC) state remarkably robust against non-magnetic disorder -- at least when compared to the simple extension of the Abrikosov-Gor'kov formalism to dirty unconventional superconductors. Motivated by the fact that most of these SC states appear in proximity to a magnetic instability, here we study the impact of non-magnetic disorder on the SC state promoted by quantum critical magnetic fluctuations. We go beyond the weak coupling approach by applying a variational formalism of the Eliashberg equations of the spin-fermion model, taking into account the effects of disorder on both fermionic and bosonic degrees of freedom. We find that the reduced fermionic coherent spectral weight near the magnetic quantum critical point strongly decreases the suppression rate of Tc by weak disorder, as compared to the Abrikosov-Gor'kov universal value. Furthermore, because the bosons promoting the Cooper pairs emerge as collective modes of the fermions, they are also impacted by disorder, giving rise to an additional reduction of the suppression rate of Tc by weak disorder. Our results qualitatively agree with experiments, shedding new light on why unconventional superconductors are robust against disorder. This work is supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award Number DE-SC0012336.

  10. Evidence of f-electron localization at a heavy-fermion quantum critical point

    NASA Astrophysics Data System (ADS)

    Steglich, Frank

    2014-03-01

    The prototypical heavy-fermion compound YbRh2Si2 exhibits a magnetic-field (B) induced antiferromagnetic quantum critical point (QCP) at Bc (⊥c) ~ 60 mT. As inferred from transport and thermodynamic measurements a quantum-critical energy scale, kB T *(B) , indicating a crossover of the Fermi surface, has been established for this system. Upon extrapolating finite-temperature (T) data to T = 0, one concludes (i) a vanishing of T*(B) and (ii) an abrupt drop in the (normal) Hall coefficient RH(B) at B =Bc , verifying the proposal of a Kondo destroying QCP. The dynamical processes underlying this apparent break-up of the Kondo singlets have been explored by studying the Lorenz ratio L/L0 as a function of Tand B. Here, L = ρ / w is the ratio of the electrical (ρ) and thermal (w = L0 T / κ) resistivities, with κ being the thermal conductivity and L0 = (πkB)2 /3e2 Sommerfeld's constant. By properly taking care of bosonic (magnon/paramagnon) contributions to the heat current which exist at finite temperature only, extrapolation of the measured data to T = 0 yields a purely electronic Lorenz ratio L/L0 = 1 at B ≠Bc . At B = Bc, we extrapolate L/L0 ~ 0.9. Therefore, the Wiedemann Franz (WF) law holds at any value of the control parameter B, except for the field-induced QCP, as is also illustrated by a pronounced heating of the sample when measuring the low - T electrical resistivity in the vicinity of the critical magnetic field. This violation of the WF law is ascribed to scatterings of the electronic heat carriers from fermionic quantum-critical fluctuations, namely those of the Fermi surface. Work done in collaboration with H. Pfau, S. Lausberg, P. Sun, U. Stockert, M. Brando, S. Friedemann, C. Krellner, C. Geibel, S. Wirth, S. Kirchner, E. Abrahams and Q. Si.

  11. Coexistence of Order and Chaos at Critical Points of First-Order Quantum Phase Transitions in Nuclei

    NASA Astrophysics Data System (ADS)

    Macek, M.; Leviatan, A.

    2013-03-01

    We study the interplay between ordered and chaotic dynamics at the critical point of a generic first-order quantum phase transition in the interacting boson model of nuclei. Classical and quantum analyses reveal a distinct behaviour of the coexisting phases. While the dynamics in the deformed phase is robustly regular, the spherical phase shows strongly chaotic behavior in the same energy intervals. The effect of collective rotations on the dynamics is investigated.

  12. Ferromagnetic Quantum Critical Point Avoided by the Appearance of Another Magnetic Phase in LaCrGe3 under Pressure

    NASA Astrophysics Data System (ADS)

    Taufour, Valentin; Kaluarachchi, Udhara S.; Khasanov, Rustem; Nguyen, Manh Cuong; Guguchia, Zurab; Biswas, Pabitra Kumar; Bonfà, Pietro; De Renzi, Roberto; Lin, Xiao; Kim, Stella K.; Mun, Eun Deok; Kim, Hyunsoo; Furukawa, Yuji; Wang, Cai-Zhuang; Ho, Kai-Ming; Bud'ko, Sergey L.; Canfield, Paul C.

    2016-07-01

    The temperature-pressure phase diagram of the ferromagnet LaCrGe3 is determined for the first time from a combination of magnetization, muon-spin-rotation, and electrical resistivity measurements. The ferromagnetic phase is suppressed near 2.1 GPa, but quantum criticality is avoided by the appearance of a magnetic phase, likely modulated, AFMQ . Our density functional theory total energy calculations suggest a near degeneracy of antiferromagnetic states with small magnetic wave vectors Q allowing for the potential of an ordering wave vector evolving from Q =0 to finite Q , as expected from the most recent theories on ferromagnetic quantum criticality. Our findings show that LaCrGe3 is a very simple example to study this scenario of avoided ferromagnetic quantum criticality and will inspire further study on this material and other itinerant ferromagnets.

  13. Ferromagnetic Quantum Critical Point Avoided by the Appearance of Another Magnetic Phase in LaCrGe_{3} under Pressure.

    PubMed

    Taufour, Valentin; Kaluarachchi, Udhara S; Khasanov, Rustem; Nguyen, Manh Cuong; Guguchia, Zurab; Biswas, Pabitra Kumar; Bonfà, Pietro; De Renzi, Roberto; Lin, Xiao; Kim, Stella K; Mun, Eun Deok; Kim, Hyunsoo; Furukawa, Yuji; Wang, Cai-Zhuang; Ho, Kai-Ming; Bud'ko, Sergey L; Canfield, Paul C

    2016-07-15

    The temperature-pressure phase diagram of the ferromagnet LaCrGe_{3} is determined for the first time from a combination of magnetization, muon-spin-rotation, and electrical resistivity measurements. The ferromagnetic phase is suppressed near 2.1 GPa, but quantum criticality is avoided by the appearance of a magnetic phase, likely modulated, AFM_{Q}. Our density functional theory total energy calculations suggest a near degeneracy of antiferromagnetic states with small magnetic wave vectors Q allowing for the potential of an ordering wave vector evolving from Q=0 to finite Q, as expected from the most recent theories on ferromagnetic quantum criticality. Our findings show that LaCrGe_{3} is a very simple example to study this scenario of avoided ferromagnetic quantum criticality and will inspire further study on this material and other itinerant ferromagnets. PMID:27472137

  14. Investigation of quantum criticality in the new heavy fermion compound Ce2PdAl7Ge4

    NASA Astrophysics Data System (ADS)

    Bauer, Eric; Wakeham, N. A.; Kim, D.; Ghimire, N. J.; Ronning, F.; Movshovich, R.; Thompson, J. D.

    Ce-based intermetallic compounds exhibit a variety of interesting ground states including magnetic order, heavy fermion behavior, unconventional superconductivity, and non-Fermi liquid behavior. When magnetic order is suppressed to T = 0 K, or quantum critical point, by chemical substitution, pressure, or magnetic field, a dome of unconventional superconductivity is often found. Close to the quantum critical point, non-Fermi liquid temperature dependencies of the thermodynamic and transport properties are observed. Recently, a new family of tetragonal Ce2MAl7Ge4 (M =Co, Ni, Pd, Ir) compounds was discovered. While the Ce2MAl7Ge4 (M =Co, Ir, Ni) materials order magnetically between Tm = 0.8 - 1.6 K, Ce2PdAl7Ge4 exhibits non-Fermi liquid behavior at low temperature. Here, we discuss the quantum criticality in Ce2PdAl7Ge4.

  15. Ferromagnetic quantum critical point avoided by the appearance of another magnetic phase in LaCrGe3 under pressure

    DOE PAGESBeta

    Taufour, Valentin; Kaluarachchi, Udhara S.; Khasanov, Rustem; Nguyen, Manh Cuong; Guguchia, Zurab; Biswas, Pabitra Kumar; Bonfa, Pietro; De Renzi, Roberto; Lin, Xiao; Kim, Stella K.; et al

    2016-07-13

    Here, the temperature-pressure phase diagram of the ferromagnet LaCrGe3 is determined for the first time from a combination of magnetization, muon-spin-rotation, and electrical resistivity measurements. The ferromagnetic phase is suppressed near 2.1 GPa, but quantum criticality is avoided by the appearance of a magnetic phase, likely modulated, AFMQ. Our density functional theory total energy calculations suggest a near degeneracy of antiferromagnetic states with small magnetic wave vectors Q allowing for the potential of an ordering wave vector evolving from Q=0 to finite Q, as expected from the most recent theories on ferromagnetic quantum criticality. Our findings show that LaCrGe3 ismore » a very simple example to study this scenario of avoided ferromagnetic quantum criticality and will inspire further study on this material and other itinerant ferromagnets.« less

  16. Entropy excess in strongly correlated Fermi systems near a quantum critical point

    SciTech Connect

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

    2012-12-15

    A system of interacting, identical fermions described by standard Landau Fermi-liquid (FL) theory can experience a rearrangement of its Fermi surface if the correlations grow sufficiently strong, as occurs at a quantum critical point where the effective mass diverges. As yet, this phenomenon defies full understanding, but salient aspects of the non-Fermi-liquid (NFL) behavior observed beyond the quantum critical point are still accessible within the general framework of the Landau quasiparticle picture. Self-consistent solutions of the coupled Landau equations for the quasiparticle momentum distribution n(p) and quasiparticle energy spectrum {epsilon}(p) are shown to exist in two distinct classes, depending on coupling strength and on whether the quasiparticle interaction is regular or singular at zero momentum transfer. One class of solutions maintains the idempotency condition n{sup 2}(p)=n(p) of standard FL theory at zero temperature T while adding pockets to the Fermi surface. The other solutions are characterized by a swelling of the Fermi surface and a flattening of the spectrum {epsilon}(p) over a range of momenta in which the quasiparticle occupancies lie between 0 and 1 even at T=0. The latter, non-idempotent solution is revealed by analysis of a Poincare mapping associated with the fundamental Landau equation connecting n(p) and {epsilon}(p) and validated by solution of a variational condition that yields the symmetry-preserving ground state. Significantly, this extraordinary solution carries the burden of a large temperature-dependent excess entropy down to very low temperatures, threatening violation of the Nernst Theorem. It is argued that certain low-temperature phase transitions, notably those involving Cooper-pair formation, offer effective mechanisms for shedding the entropy excess. Available measurements in heavy-fermion compounds provide concrete support for such a scenario. - Highlights: Black-Right-Pointing-Pointer Extension of Landau

  17. Hilbert-Glass Transition: New Universality of Temperature-Tuned Many-Body Dynamical Quantum Criticality

    NASA Astrophysics Data System (ADS)

    Pekker, David; Refael, Gil; Altman, Ehud; Demler, Eugene; Oganesyan, Vadim

    2014-01-01

    We study a new class of unconventional critical phenomena that is characterized by singularities only in dynamical quantities and has no thermodynamic signatures. One example of such a transition is the recently proposed many-body localization-delocalization transition, in which transport coefficients vanish at a critical temperature with no singularities in thermodynamic observables. Describing this purely dynamical quantum criticality is technically challenging as understanding the finite-temperature dynamics necessarily requires averaging over a large number of matrix elements between many-body eigenstates. Here, we develop a real-space renormalization group method for excited states that allows us to overcome this challenge in a large class of models. We characterize a specific example: the 1 D disordered transverse-field Ising model with generic interactions. While thermodynamic phase transitions are generally forbidden in this model, using the real-space renormalization group method for excited states we find a finite-temperature dynamical transition between two localized phases. The transition is characterized by nonanalyticities in the low-frequency heat conductivity and in the long-time (dynamic) spin correlation function. The latter is a consequence of an up-down spin symmetry that results in the appearance of an Edwards-Anderson-like order parameter in one of the localized phases.

  18. Emergent Lorentz symmetry near fermionic quantum critical points in two and three dimensions

    NASA Astrophysics Data System (ADS)

    Roy, Bitan; Juričić, Vladimir; Herbut, Igor F.

    2016-04-01

    We study the renormalization group flow of the velocities in the field theory describing the coupling of the massless quasi-relativistic fermions to the bosons through the Yukawa coupling, as well as with both bosons and fermions coupled to a fluctuating U(1) gauge field in two and three spatial dimensions. Different versions of this theory describe quantum critical behavior of interacting Dirac fermions in various condensed-matter systems. We perform an analysis using one-loop ɛ-expansion about three spatial dimensions, which is the upper critical dimension in the problem. In two dimensions, we find that velocities of both charged fermions and bosons ultimately flow to the velocity of light, independently of the initial conditions, the number of fermionic and bosonic flavors, and the value of the couplings at the critical point. In three dimensions, due to the analyticity of the gauge field propagator, both the U(1) charge and the velocity of light flow, which leads to a richer behavior than in two dimensions. We show that all three velocities ultimately flow to a common terminal velocity, which is non-universal and different from the original velocity of light. Therefore, emergence of the Lorentz symmetry in the ultimate infrared regime seems to be a rather universal feature of this class of theories in both two and three dimensions.

  19. Strain-Driven Approach to Quantum Criticality in A Fe2 As2 with A =K , Rb, and Cs

    NASA Astrophysics Data System (ADS)

    Eilers, Felix; Grube, Kai; Zocco, Diego A.; Wolf, Thomas; Merz, Michael; Schweiss, Peter; Heid, Rolf; Eder, Robert; Yu, Rong; Zhu, Jian-Xin; Si, Qimiao; Shibauchi, Takasada; Löhneysen, Hilbert v.

    2016-06-01

    The iron-based superconductors A Fe2 As2 with A =K , Rb, Cs exhibit large Sommerfeld coefficients approaching those of heavy-fermion systems. We have investigated the magnetostriction and thermal expansion of this series to shed light on this unusual behavior. Quantum oscillations of the magnetostriction allow identifying the band-specific quasiparticle masses which by far exceed the band-structure derived masses. The divergence of the Grüneisen ratio derived from thermal expansion indicates that with increasing volume along the series a quantum critical point is approached. The critical fluctuations responsible for the enhancement of the quasiparticle masses appear to weaken the superconducting state.

  20. Strain-Driven Approach to Quantum Criticality in AFe_{2}As_{2} with A=K, Rb, and Cs.

    PubMed

    Eilers, Felix; Grube, Kai; Zocco, Diego A; Wolf, Thomas; Merz, Michael; Schweiss, Peter; Heid, Rolf; Eder, Robert; Yu, Rong; Zhu, Jian-Xin; Si, Qimiao; Shibauchi, Takasada; Löhneysen, Hilbert V

    2016-06-10

    The iron-based superconductors AFe_{2}As_{2} with A=K, Rb, Cs exhibit large Sommerfeld coefficients approaching those of heavy-fermion systems. We have investigated the magnetostriction and thermal expansion of this series to shed light on this unusual behavior. Quantum oscillations of the magnetostriction allow identifying the band-specific quasiparticle masses which by far exceed the band-structure derived masses. The divergence of the Grüneisen ratio derived from thermal expansion indicates that with increasing volume along the series a quantum critical point is approached. The critical fluctuations responsible for the enhancement of the quasiparticle masses appear to weaken the superconducting state. PMID:27341252

  1. Magnetic field-tuned Fermi liquid formation in Mn0.75 Fe0.25 Si

    NASA Astrophysics Data System (ADS)

    Samatham, S. Shanmukharao; Yadam, Sankararao; Singh, Durgesh; Ganesan, V.

    2016-11-01

    Low temperature ground state properties of Mn0.75 Fe0.25 Si are investigated based on temperature and magnetic field dependent behavior of specific heat and resistivity. Paramagnon spin fluctuations assisted non-Fermi liquid is suppressed by magnetic fields and gradual evolution of Fermi liquid is demonstrated. The tendency of magnetic field-induced crossover from non-Fermi to Fermi liquid behavior is illustrated by suitable magneto-specific heat scaling which reveals unusual quantum critical phenomenon in a 3d transition metal derived paramagnetic compound. In the absence of magnetic fields, Kadowaki-Wood's Ratio (KWR) A /γ2 is about 8.5 μΩcmmol2K2J-2 which is 85% close to the originally proposed KWR and reaches 100% under the moderate magnetic fields of 0.7 T.

  2. Quantum oscillations of the critical current and high-field superconducting proximity in ballistic graphene

    NASA Astrophysics Data System (ADS)

    Ben Shalom, M.; Zhu, M. J.; Fal'Ko, V. I.; Mishchenko, A.; Kretinin, A. V.; Novoselov, K. S.; Woods, C. R.; Watanabe, K.; Taniguchi, T.; Geim, A. K.; Prance, J. R.

    2016-04-01

    Graphene-based Josephson junctions provide a novel platform for studying the proximity effect due to graphene’s unique electronic spectrum and the possibility to tune junction properties by gate voltage. Here we describe graphene junctions with a mean free path of several micrometres, low contact resistance and large supercurrents. Such devices exhibit pronounced Fabry-Pérot oscillations not only in the normal-state resistance but also in the critical current. The proximity effect is mostly suppressed in magnetic fields below 10 mT, showing the conventional Fraunhofer pattern. Unexpectedly, some proximity survives even in fields higher than 1 T. Superconducting states randomly appear and disappear as a function of field and carrier concentration, and each of them exhibits a supercurrent carrying capacity close to the universal quantum limit. We attribute the high-field Josephson effect to mesoscopic Andreev states that persist near graphene edges. Our work reveals new proximity regimes that can be controlled by quantum confinement and cyclotron motion.

  3. Classical Behavior of Two-Dimensional Liquid 3He Near a Quantum Critical Point

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

    Non-Fermi-liquid (NFL) behavior of the specific heat C(T) of two-dimensional (2D) liquid 3He, first uncovered in measurements almost 20 years ago, is explained in terms of intrinsic properties of this system that emerge when its density rises and the liquid becomes strongly correlated. The occurrence of a T-independent β term in C(T) is attributed to satisfaction of the conditions for Dulong-Petit behavior by the boson part of the free energy. This unexpected classicality stems from softening of the transverse zero-sound mode (TZSM) in the density region where the anomaly in C(T), associated with a quantum critical point (QCP), is observed.

  4. General properties of CePd1-xRhx at quantum critical point

    NASA Astrophysics Data System (ADS)

    Shaginyan, V. R.; Popov, K. G.

    2009-10-01

    The heavy-fermion metal CePd1-xRhx evolves from ferromagnetism at x=0 to a non-magnetic state at some critical concentration xc. Utilizing the quasiparticle picture and the concept of fermion condensation quantum phase transition (FCQPT), we address the non-Fermi liquid (NFL) behavior of ferromagnet CePd1-xRhx and show that it coincides with that of antiferromagnets YbRh2(Si0.95Ge0.05)2 and CeCoIn 5, paramagnets CeRu 2Si 2 and CeNi 2Ge 2 and 2D 3He. We show that the NFL behavior is independent of the peculiarities of specific alloy and universal. Our study of the NFL behavior allows us to calculate the magnetoresistance of CeCoIn 5. Obtained results are in good agreement with facts and reveal a new scaling behavior of magnetoresistance.

  5. Fate of the Wiedemann-Franz Law near Quantum Critical Points of Electron Systems in Solids

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    We introduce and analyze two different scenarios for violation of the Wiedemann-Franz law in strongly correlated electron systems of solids, close to a topological quantum critical point (TQCP) where the density of states N(0) diverges. The first, applicable to the Fermi-liquid (FL) side of the TQCP, involves a transverse zero-sound collective mode that opens a new channel for the thermal conductivity, thereby enhancing the Lorenz number L(0) relative to the value L0 =π2 k B 2/3 e 2 dictated by conventional FL theory. The second mechanism for violation of the WF law, relevant to the non-Fermi-liquid (NFL) side of the TQCP, involves the formation of a flat band and leads instead to a reduction of the Lorenz number.

  6. Evidence for proximity of YFe2Si2 to a magnetic quantum critical point

    NASA Astrophysics Data System (ADS)

    Singh, David J.

    2016-06-01

    Calculations of the electronic and magnetic properties of the nonmagnetic metallic compound YFe2Si2 are reported. These predict at the density functional level a magnetic state involving ordering along the c axis. This predicted ground state contrasts with experiment, which does not show magnetic order. The electronic structure is three dimensional, and is similar to that of the unconventional superconductor YFe2Ge2 as well as that of the high-pressure collapsed tetragonal phase of KFe2As2 , which is also a superconductor. Based on the results in relation to experiment, we infer that properties of YFe2Si2 are strongly influenced by a nearby antiferromagnetic quantum critical point.

  7. Transport anomalies and quantum criticality in electron-doped cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Zhang, Xu; Yu, Heshan; He, Ge; Hu, Wei; Yuan, Jie; Zhu, Beiyi; Jin, Kui

    2016-06-01

    Superconductivity research is like running a marathon. Three decades after the discovery of high-Tc cuprates, there have been mass data generated from transport measurements, which bring fruitful information. In this review, we give a brief summary of the intriguing phenomena reported in electron-doped cuprates from the aspect of electrical transport as well as the complementary thermal transport. We attempt to sort out common features of the electron-doped family, e.g. the strange metal, negative magnetoresistance, multiple sign reversals of Hall in mixed state, abnormal Nernst signal, complex quantum criticality. Most of them have been challenging the existing theories, nevertheless, a unified diagram certainly helps to approach the nature of electron-doped cuprates.

  8. Quantum Critical Dynamics of Bose-Einstein Condensates in a Shaken Optical Lattice

    NASA Astrophysics Data System (ADS)

    Clark, Logan W.; Feng, Lei; Ha, Li-Chung; Chin, Cheng

    2016-05-01

    From condensed matter to cosmology, systems which cross a continuous, symmetry-breaking phase transition are expected to generate topological defects whose density scales universally with the rate at which the phase transition is crossed. We experimentally test the application of this universal Kibble-Zurek scaling prediction to quantum phase transitions by studying ultracold bosons in a shaken optical lattice. When the lattice shaking amplitude crosses a critical threshold, an ordinary Bose condensate transitions to an effectively ferromagnetic pseudo-spinor condensate with discrete, magnetized regions separated by domain walls. We appraise the dynamic scaling laws for both the time at which the domain structure forms and the typical size of the domains by varying the quench rate across the transition. We explore the regime in which the universal prediction applies, as well as potential deviations at extreme quench rates.

  9. Band structure and itinerant magnetism in quantum critical NbFe2

    SciTech Connect

    Subedi, A. P.; Singh, David J

    2010-01-01

    We report first-principles calculations of the band structure and magnetic ordering in the C14 Laves phase compound NbFe{sub 2}. The magnetism is itinerant in the sense that the moments are highly dependent on ordering. We find an overestimation of the magnetic tendency within the local spin-density approximation, similar to other metals near magnetic quantum critical points. We also find a competition between different magnetic states due to band-structure effects. These lead to competing magnetic tendencies due to competing interlayer interactions, one favoring a ferrimagnetic solution and the other an antiferromagnetic state. While the structure contains Kagome lattice sheets, which could, in principle, lead to strong magnetic frustration, the calculations do not show dominant nearest-neighbor antiferromagnetic interactions within these sheets. These results are discussed in relation to experimental observations.

  10. Grüneisen parameter studies on heavy fermion quantum criticality

    NASA Astrophysics Data System (ADS)

    Gegenwart, Philipp

    2016-11-01

    The Grüneisen parameter, experimentally determined from the ratio of thermal expansion to specific heat, quantifies the pressure dependence of characteristic energy scales of matter. It is highly enhanced for Kondo lattice systems, whose properties are strongly dependent on the pressure sensitive antiferromagnetic exchange interaction between f- and conduction electrons. In this review, we focus on the divergence of the Grüneisen parameter and its magnetic analogue, the adiabatic magnetocaloric effect, for heavy-fermion metals near quantum critical points. We compare experimental results with current theoretical models, including the effect of strong geometrical frustration. We also discuss the possibility of using materials with the divergent magnetic Grüneisen parameter for adiabatic demagnetization cooling to very low temperatures.

  11. Shock waves, rarefaction waves, and nonequilibrium steady states in quantum critical systems

    NASA Astrophysics Data System (ADS)

    Lucas, Andrew; Schalm, Koenraad; Doyon, Benjamin; Bhaseen, M. J.

    2016-07-01

    We reexamine the emergence of a universal nonequilibrium steady state following a local quench between quantum critical heat baths in spatial dimensions greater than one. We show that energy transport proceeds by the formation of an instantaneous shock wave and a broadening rarefaction wave on either side of the interface, and not by two shock waves as previously proposed. For small temperature differences the universal steady state energy currents of the two-shock and rarefaction-shock solutions coincide. Over a broad range of parameters, the difference in the energy flow across the interface between these two solutions is at the level of 2%. The properties of the energy flow remain fully universal and independent of the microscopic theory. We briefly discuss the width of the shock wave in a viscous fluid, the effects of momentum relaxation, and the generalization to charged fluids.

  12. Quantum Criticality and Superconductivity in β-YbAlB4

    NASA Astrophysics Data System (ADS)

    Nakatsuji, Satoru

    2009-03-01

    Heavy fermion systems have provided a number of prototypical compounds to study unconventional superconductivity and non-Fermi-liquid (NFL) states. A long standing issue in the research of heavy fermion superconductivity in 4f intermetallics is the dramatically different behavior between the electron like Ce (4f^1) and hole like Yb (4f^13) compounds. While superconductivity has been found in a number of Ce based heavy fermion compounds, no superconductivity has been reported for the corresponding Yb systems. In this talk, I present our recent finding of the superconductivity in the new heavy fermion system β-YbAlB4 [1-3]. The superconducting transition temperature is 80 mK, and above it, the system exhibits pronounced NFL behavior in the transport and thermodynamic properties [2,3]. Furthermore, the magnetic field dependence of the NFL behavior indicates that the system is a rare example of a pure metal that displays quantum criticality at ambient pressure and under zero magnetic field. Using our latest results, we discuss the detailed properties of superconductivity and quantum criticality. This is the work performed in collaboration with K. Kuga, Y. Matsumoto, T. Tomita, Y. Machida, T. Tayama, T. Sakakibara, Y. Karaki, H. Ishimoto, S. Yonezawa, Y. Maeno, E. Pearson, G. G. Lonzarich, L.Balicas, H. Lee, and Z. Fisk. [4pt] [1] Robin T. Macaluso, Satoru Nakatsuji, Kentaro Kuga, Evan Lyle Thomas, Yo Machida, Yoshiteru Maeno, Zachary Fisk, and Julia Y. Chan, Chem. Mater. 19 1918 (2007). [0pt] [2] S. Nakatsuji, K.Kuga, Y. Machida, T. Tayama, T. Sakakibara, Y. Karaki, H. Ishimoto, S. Yonezawa, Y. Maeno, E. Pearson, G. G. Lonzarich, L.Balicas, H. Lee, and Z. Fisk, Nature Phys 4, 603-607 (2008). [0pt] [3] K. Kuga, Y. Karaki, Y. Matsumoto, Y. Machida, and S. Nakatsuji, Phys. Rev. Lett. 101, 137004 (2008).

  13. Entropy excess in strongly correlated Fermi systems near a quantum critical point

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    A system of interacting, identical fermions described by standard Landau Fermi-liquid (FL) theory can experience a rearrangement of its Fermi surface if the correlations grow sufficiently strong, as occurs at a quantum critical point where the effective mass diverges. As yet, this phenomenon defies full understanding, but salient aspects of the non-Fermi-liquid (NFL) behavior observed beyond the quantum critical point are still accessible within the general framework of the Landau quasiparticle picture. Self-consistent solutions of the coupled Landau equations for the quasiparticle momentum distribution n(p) and quasiparticle energy spectrum ɛ(p) are shown to exist in two distinct classes, depending on coupling strength and on whether the quasiparticle interaction is regular or singular at zero momentum transfer. One class of solutions maintains the idempotency condition n2(p)=n(p) of standard FL theory at zero temperature T while adding pockets to the Fermi surface. The other solutions are characterized by a swelling of the Fermi surface and a flattening of the spectrum ɛ(p) over a range of momenta in which the quasiparticle occupancies lie between 0 and 1 even at T=0. The latter, non-idempotent solution is revealed by analysis of a Poincaré mapping associated with the fundamental Landau equation connecting n(p) and ɛ(p) and validated by solution of a variational condition that yields the symmetry-preserving ground state. Significantly, this extraordinary solution carries the burden of a large temperature-dependent excess entropy down to very low temperatures, threatening violation of the Nernst Theorem. It is argued that certain low-temperature phase transitions, notably those involving Cooper-pair formation, offer effective mechanisms for shedding the entropy excess. Available measurements in heavy-fermion compounds provide concrete support for such a scenario.

  14. Degenerate Fermi and non-Fermi liquids near a quantum critical phase transition

    NASA Astrophysics Data System (ADS)

    Kambe, S.; Sakai, H.; Tokunaga, Y.; Lapertot, G.; Matsuda, T. D.; Knebel, G.; Flouquet, J.; Walstedt, R. E.

    2014-11-01

    Recently there is renewed interest in quantum critical phase transitions (QCPT) at T = 0 K in metallic strongly correlated electron systems. From early experimental results, the QCPT in the Kondo-lattice compound YbRh2Si2 is not a case of the ordinary spin density wave (SDW) instability observed in Ce-based Kondo lattices, but a candidate for a novel locally critical case. Here, we observe that coexisting, static Fermi liquid (FL) and non-Fermi liquid (NFL) states are a key feature of the QCPT in YbRh2Si2. By means of nuclear magnetic resonance (NMR) spin-lattice relaxation time (T1) measurements on a single-crystalline sample, we find that the FL and NFL states are invariant, whereas their ratio in a crossover is field dependent near the QCPT. Such a pair of states has remained hidden in Ce compounds, owing presumably to the short lifetimes of the two states. We derive a scaling law for the occupation ratio of the two states, which could be widely applicable to Kondo-lattice systems.

  15. Uncovering the hidden quantum critical point in disordered massless Dirac and Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Pixley, J. H.; Huse, David A.; Das Sarma, S.

    2016-09-01

    We study the properties of the avoided or hidden quantum critical point (AQCP) in three-dimensional Dirac and Weyl semimetals in the presence of short range potential disorder. By computing the averaged density of states (along with its second and fourth derivative at zero energy) with the kernel polynomial method (KPM) we systematically tune the effective length scale that eventually rounds out the transition and leads to an AQCP. We show how to determine the strength of the avoidance, establishing that it is not controlled by the long wavelength component of the disorder. Instead, the amount of avoidance can be adjusted via the tails of the probability distribution of the local random potentials. A binary distribution with no tails produces much less avoidance than a Gaussian distribution. We introduce a double Gaussian distribution to interpolate between these two limits. As a result we are able to make the length scale of the avoidance sufficiently large so that we can accurately study the properties of the underlying transition (that is eventually rounded out), unambiguously identify its location, and provide accurate estimates of the critical exponents ν =1.01 ±0.06 and z =1.50 ±0.04 . We also show that the KPM expansion order introduces an effective length scale that can also round out the transition in the scaling regime near the AQCP.

  16. The infinite-range quantum transverse Ising spin glass: new estimate of the critical line via thermo-field method

    NASA Astrophysics Data System (ADS)

    Kopeć, T. K.; Büttner, G.; Usadel, K. D.

    1990-10-01

    The infinite-range quantum Ising spin glass in a transverse field Γ is studied by means of the thermo-field dynamics as a substitute for the n-replica trick. A new estimate of the critical line Tc(Γ) is obtained by the improved treatment of the dynamic self-interaction - in considerable agreement with the Trotter-Suzuki method.

  17. Pressure-tuned quantum criticality in the antiferromagnetic Kondo semimetal CeNi2-δAs2.

    PubMed

    Luo, Yongkang; Ronning, F; Wakeham, N; Lu, Xin; Park, Tuson; Xu, Z-A; Thompson, J D

    2015-11-01

    The easily tuned balance among competing interactions in Kondo-lattice metals allows access to a zero-temperature, continuous transition between magnetically ordered and disordered phases, a quantum-critical point (QCP). Indeed, these highly correlated electron materials are prototypes for discovering and exploring quantum-critical states. Theoretical models proposed to account for the strange thermodynamic and electrical transport properties that emerge around the QCP of a Kondo lattice assume the presence of an indefinitely large number of itinerant charge carriers. Here, we report a systematic transport and thermodynamic investigation of the Kondo-lattice system CeNi2-δAs2 (δ ≈ 0.28) as its antiferromagnetic order is tuned by pressure and magnetic field to zero-temperature boundaries. These experiments show that the very small but finite carrier density of ~0.032 E-/formular unit in CeNi2-δAs2 leads to unexpected transport signatures of quantum criticality and the delayed development of a fully coherent Kondo-lattice state with decreasing temperature. The small carrier density and associated semimetallicity of this Kondo-lattice material favor an unconventional, local-moment type of quantum criticality and raises the specter of the Nozières exhaustion idea that an insufficient number of conduction-electron spins to separately screen local moments requires collective Kondo screening. PMID:26483465

  18. Contradiction between the results of observations of resistance and critical current quantum oscillations in asymmetric superconducting rings

    SciTech Connect

    Gurtovoi, V. L.; Dubonos, S. V.; Karpii, S. V.; Nikulov, A. V. Tulin, V. A.

    2007-07-15

    Magnetic field dependences of critical current, resistance, and rectified voltage of asymmetric (half circles of different widths) and symmetrical (half circles of equal widths) aluminum rings close to the super-conducting transition were measured. All these dependences are periodic magnetic field functions with periods corresponding to the flux quantum in the ring. The periodic dependences of critical current measured in opposite directions were found to be close to each other for symmetrical rings and shifted with respect to each other by half the flux quantum in asymmetric rings with ratios between half circle widths of from 1.25 to 2. This shift of the dependences by a quarter of the flux quantum as the ring becomes asymmetric makes critical current anisotropic, which explains the effect of alternating current rectification observed for asymmetric rings. Shifts of the extrema of the periodic dependences of critical current by a quarter of the flux quantum directly contradict the results obtained by measuring asymmetric ring resistance oscillations, whose extrema are, as for symmetrical rings, observed at magnetic fluxes equal to an integer and a half of flux quanta.

  19. Pressure-tuned quantum criticality in the antiferromagnetic Kondo semimetal CeNi2−δAs2

    PubMed Central

    Luo, Yongkang; Ronning, F.; Wakeham, N.; Lu, Xin; Park, Tuson; Xu, Z.-A.; Thompson, J. D.

    2015-01-01

    The easily tuned balance among competing interactions in Kondo-lattice metals allows access to a zero-temperature, continuous transition between magnetically ordered and disordered phases, a quantum-critical point (QCP). Indeed, these highly correlated electron materials are prototypes for discovering and exploring quantum-critical states. Theoretical models proposed to account for the strange thermodynamic and electrical transport properties that emerge around the QCP of a Kondo lattice assume the presence of an indefinitely large number of itinerant charge carriers. Here, we report a systematic transport and thermodynamic investigation of the Kondo-lattice system CeNi2−δAs2 (δ ≈ 0.28) as its antiferromagnetic order is tuned by pressure and magnetic field to zero-temperature boundaries. These experiments show that the very small but finite carrier density of ∼0.032 e−/formular unit in CeNi2−δAs2 leads to unexpected transport signatures of quantum criticality and the delayed development of a fully coherent Kondo-lattice state with decreasing temperature. The small carrier density and associated semimetallicity of this Kondo-lattice material favor an unconventional, local-moment type of quantum criticality and raises the specter of the Nozières exhaustion idea that an insufficient number of conduction-electron spins to separately screen local moments requires collective Kondo screening. PMID:26483465

  20. Pressure-tuned quantum criticality in the antiferromagnetic Kondo semimetal CeNi2–δAs2

    DOE PAGESBeta

    Luo, Yongkang; Ronning, F.; Wakeham, N.; Lu, Xin; Park, Tuson; Xu, Z. -A.; Thompson, J. D.

    2015-10-19

    The easily tuned balance among competing interactions in Kondo-lattice metals allows access to a zero-temperature, continuous transition between magnetically ordered and disordered phases, a quantum-critical point (QCP). Indeed, these highly correlated electron materials are prototypes for discovering and exploring quantum-critical states. Theoretical models proposed to account for the strange thermodynamic and electrical transport properties that emerge around the QCP of a Kondo lattice assume the presence of an indefinitely large number of itinerant charge carriers. Here, we report a systematic transport and thermodynamic investigation of the Kondo-lattice system CeNi2–δAs2 (δ ≈ 0.28) as its antiferromagnetic order is tuned by pressuremore » and magnetic field to zero-temperature boundaries. These experiments show that the very small but finite carrier density of ~0.032 e–/formular unit in CeNi2–δAs2 leads to unexpected transport signatures of quantum criticality and the delayed development of a fully coherent Kondo-lattice state with decreasing temperature. Here, the small carrier density and associated semimetallicity of this Kondo-lattice material favor an unconventional, local-moment type of quantum criticality and raises the specter of the Nozières exhaustion idea that an insufficient number of conduction-electron spins to separately screen local moments requires collective Kondo screening.« less

  1. How Far can a Pragmatist GO Into Quantum Theory? a Critical View of Our Current Understanding of Quantum Phenomena

    NASA Astrophysics Data System (ADS)

    Sanz, A. S.

    2015-06-01

    To date, quantum mechanics has proven to be our most successful theoretical model. However, it is still surrounded by a "mysterious halo", which can be summarized in a simple but challenging question: Why quantum phenomena are not understood under the same logic as classical ones? Although this is an open question (probably without an answer), from a pragmatist's point of view there is still room enough to further explore the quantum world, marveling ourselves with new physical insights. We just need to look back in the historical evolution of the quantum theory and thoroughly reconsider three key issues: (1) how this theory has developed since its early stages at a conceptual level, (2) what kind of experiments can be performed at present in a laboratory, and (3) what nonstandard conceptual models are available to extract some extra information. This contribution is aimed at providing some answers (and, perhaps, also raising some issues) to these questions through one of such models, namely Bohmian mechanics, a hydrodynamic formulation of the quantum theory, which is currently trying to open new pathways of understanding. Specifically, the Chapter constitutes a brief and personal overview on the historic and contextual evolution of this quantum formulation, its physical meaning and interest (leaving aside metaphysical issues), and how it may help to overcome some preconceived paradoxical aspects of the quantum theory.

  2. Quantum Critical Behavior in Heavy-Fermion Iron Oxypnictide Ce(Ru1-xFex) PO

    NASA Astrophysics Data System (ADS)

    Ishida, Kenji

    2014-03-01

    Quantum phase transition in itinerant ferromagnets is one of the major topics in a strongly correlated electron system, since it has been suggested to be always first order when the ferromagnetic (FM) order is suppressed by pressure or chemical doping. In order to obtain universal features of the FM quantum criticality, we have studied the two-dimensional heavy-fermion (HF) system Ce(Ru1-xFex) PO from microscopic 31P-NMR measurements. A HF ferromagnet CeRuPO turns into a HF paramagnet by an isovalent Fe substitution for Ru. We found that Ce(Ru0.15Fe0.85) PO shows critical fluctuations down to ~ 0.3 K, as well as the continuous suppression of Curie temperature and the ordered moments by the Fe substitution. These experimental results suggest the presence of a FM quantum critical point (QCP) at around x = 0.86, which is a rare example among itinerant ferromagnets. In addition, we point out that the critical behaviors in Ce(Ru0.15Fe0.85) PO share a similarity with those in YbRh2Si2, where the local criticality of f electrons has been discussed. We reveal that Ce(Ru1-xFex) PO is a new system to study FM quantum criticality in HF compound. This work has been done in collaboration with Shunsaku Kitagawa in Kyoto Univ. and T, Nakamura, M. Matoba, and Y. Kamihara, in Department of Applied Physics and Physico-informatics, Keio University.

  3. Fermionic quantum criticality in honeycomb and π -flux Hubbard models: Finite-size scaling of renormalization-group-invariant observables from quantum Monte Carlo

    NASA Astrophysics Data System (ADS)

    Parisen Toldin, Francesco; Hohenadler, Martin; Assaad, Fakher F.; Herbut, Igor F.

    2015-04-01

    We numerically investigate the critical behavior of the Hubbard model on the honeycomb and the π -flux lattice, which exhibits a direct transition from a Dirac semimetal to an antiferromagnetically ordered Mott insulator. We use projective auxiliary-field quantum Monte Carlo simulations and a careful finite-size scaling analysis that exploits approximately improved renormalization-group-invariant observables. This approach, which is successfully verified for the three-dimensional XY transition of the Kane-Mele-Hubbard model, allows us to extract estimates for the critical couplings and the critical exponents. The results confirm that the critical behavior for the semimetal to Mott insulator transition in the Hubbard model belongs to the Gross-Neveu-Heisenberg universality class on both lattices.

  4. Evolution of quantum criticality in the system CeNi9Ge4

    NASA Astrophysics Data System (ADS)

    Michor, H.; Adroja, D. T.; Hillier, A. D.; Koza, M. M.; Manalo, S.; Gold, C.; Peyker, L.; Scheidt, E.-W.

    2012-03-01

    The heavy fermion system CeNi9Ge4 exhibits a paramagnetic ground state with remarkable features such as: a record value of the electronic specific heat coefficient in systems with a paramagnetic ground state, γ = C/T simeq 5.5 J/molK2 at 80 mK, a temperature-dependent Sommerfeld-Wilson ratio, R = χ/γ, below 1 K and an approximate single ion scaling of the 4f-magnetic specific heat and susceptibility. These features are related to a rather small Kondo energy scale of a few Kelvin in combination with a quasi-quartet crystal field ground state. Tuning the system towards long range magnetic order is accomplished by replacing a few at.% of Ni by Cu or Co. Specific heat, susceptibility and resistivity studies reveal TN ~ 0.2 K for CeNi8CuGe4 and TN ~ 1K for CeNi8CoGe4. To gain insight whether the transition from the paramagnetic NFL state to the magnetically ordered ground state is connected with a heavy fermion quantum critical point we performed specific heat and ac susceptibility studies and utilized the μSR technique and quasi-elastic neutron scattering.

  5. Unconventional Quantum Criticality in β-YbAlB4 Detached from Its Magnetically Ordered Phase

    NASA Astrophysics Data System (ADS)

    Tomita, Takahiro; Kuga, Kentaro; Uwatoko, Yoshiya; Coleman, Piers; Nakatsuji, Satoru

    We studied the effect of pressure on the Yb-based heavy-fermion superconductor β-YbAlB4 (Tc=80 mK) near its quantum critical point (QCP) at ambient pressure. Here, the electrical resistivity ρ(T) of the high-quality single crystal (RRR = 300) is measured under hydrostatic pressure P ≃ 2.7 GPa at low temperatures down to 70 mK. The superconducting transition Tc gradually decreases with the application of pressure and disappears near 0.9 GPa. However, the non-Fermi liquid (NFL) behavior is found to be robust over a broad range of pressure 0 ≤ P ≤ 0.5 GPa. The NFL state above Tc gradually changes to the Fermi liquid state with the application of pressure above P ≃ 0.5 GPa. The magnetic order transition is first observed at 50 mK and Pc = 2.7 GPa. The P -T phase diagram indicates that the QCP lying beneath the superconductivity dome is detached from the magnetically ordered phase.

  6. Is U3Ni3Sn4 best described as near a quantum critical point?

    SciTech Connect

    Booth, C.H.; Shlyk, L.; Nenkov, K.; Huber, J.G.; De Long, L.E.

    2003-04-08

    Although most known non-Fermi liquid (NFL) materials are structurally or chemically disordered, the role of this disorder remains unclear. In particular, very few systems have been discovered that may be stoichiometric and well ordered. To test whether U{sub 3}Ni{sub 3}Sn{sub 4} belongs in this latter class, we present measurements of the x-ray absorption fine structure (XAFS) of polycrystalline and single-crystal U{sub 3}Ni{sub 3}Sn{sub 4} samples that are consistent with no measurable local atomic disorder. We also present temperature-dependent specific heat data in applied magnetic fields as high as 8 T that show features that are inconsistent with the antiferromagnetic Griffiths' phase model, but do support the conclusion that a Fermi liquid/NFL crossover temperature increases with applied field. These results are inconsistent with theoretical explanations that require strong disorder effects, but do support the view that U{sub 3}Ni{sub 3}Sn{sub 4} is a stoichoiometric, ordered material that exhibits NFL behavior, and is best described as being near an antiferromagnetic quantum critical point.

  7. Nematic quantum critical point without magnetism in FeSe1-xSx superconductors.

    PubMed

    Hosoi, Suguru; Matsuura, Kohei; Ishida, Kousuke; Wang, Hao; Mizukami, Yuta; Watashige, Tatsuya; Kasahara, Shigeru; Matsuda, Yuji; Shibauchi, Takasada

    2016-07-19

    In most unconventional superconductors, the importance of antiferromagnetic fluctuations is widely acknowledged. In addition, cuprate and iron-pnictide high-temperature superconductors often exhibit unidirectional (nematic) electronic correlations, including stripe and orbital orders, whose fluctuations may also play a key role for electron pairing. In these materials, however, such nematic correlations are intertwined with antiferromagnetic or charge orders, preventing the identification of the essential role of nematic fluctuations. This calls for new materials having only nematicity without competing or coexisting orders. Here we report systematic elastoresistance measurements in FeSe1-xSx superconductors, which, unlike other iron-based families, exhibit an electronic nematic order without accompanying antiferromagnetic order. We find that the nematic transition temperature decreases with sulfur content x; whereas, the nematic fluctuations are strongly enhanced. Near [Formula: see text], the nematic susceptibility diverges toward absolute zero, revealing a nematic quantum critical point. The obtained phase diagram for the nematic and superconducting states highlights FeSe1-xSx as a unique nonmagnetic system suitable for studying the impact of nematicity on superconductivity. PMID:27382157

  8. Nematic quantum critical point without magnetism in FeSe1-xSx superconductors.

    PubMed

    Hosoi, Suguru; Matsuura, Kohei; Ishida, Kousuke; Wang, Hao; Mizukami, Yuta; Watashige, Tatsuya; Kasahara, Shigeru; Matsuda, Yuji; Shibauchi, Takasada

    2016-07-19

    In most unconventional superconductors, the importance of antiferromagnetic fluctuations is widely acknowledged. In addition, cuprate and iron-pnictide high-temperature superconductors often exhibit unidirectional (nematic) electronic correlations, including stripe and orbital orders, whose fluctuations may also play a key role for electron pairing. In these materials, however, such nematic correlations are intertwined with antiferromagnetic or charge orders, preventing the identification of the essential role of nematic fluctuations. This calls for new materials having only nematicity without competing or coexisting orders. Here we report systematic elastoresistance measurements in FeSe1-xSx superconductors, which, unlike other iron-based families, exhibit an electronic nematic order without accompanying antiferromagnetic order. We find that the nematic transition temperature decreases with sulfur content x; whereas, the nematic fluctuations are strongly enhanced. Near [Formula: see text], the nematic susceptibility diverges toward absolute zero, revealing a nematic quantum critical point. The obtained phase diagram for the nematic and superconducting states highlights FeSe1-xSx as a unique nonmagnetic system suitable for studying the impact of nematicity on superconductivity.

  9. Quantum criticality in the 122 iron pnictide superconductors emerging from orbital-selective Mottness

    NASA Astrophysics Data System (ADS)

    Das, S. D.; Laad, M. S.; Craco, L.; Gillett, J.; Tripathi, V.; Sebastian, S. E.

    2015-10-01

    The twin issues of the nature of the "normal" state and competing order(s) in the iron arsenides are central to understanding their unconventional, high-Tc superconductivity. We use a combination of transport anisotropy measurements on detwinned Sr (Fe1-xCox) 2As2 single crystals and local density approximation plus dynamical mean field theory (LDA + DMFT) calculations to revisit these issues. The peculiar resistivity anisotropy and its evolution with x are naturally interpreted in terms of an underlying orbital-selective Mott transition (OSMT) that gaps out the dx z or dy z states. Further, we use a Landau-Ginzburg approach using LDA + DMFT input to rationalize a wide range of anomalies seen up to optimal doping, providing strong evidence for secondary electronic nematic order. These findings suggest that strong dynamical fluctuations linked to a marginal quantum-critical point associated with this OSMT and a secondary electronic nematic order constitute an intrinsically electronic pairing mechanism for superconductivity in Fe arsenides.

  10. Quantum anomalous Hall effect with field-tunable Chern number near Z2 topological critical point

    NASA Astrophysics Data System (ADS)

    Duong, Le Quy; Lin, Hsin; Tsai, Wei-Feng; Feng, Yuan Ping

    We study the practicability of achieving quantum anomalous Hall (QAH) effect with field-tunable Chern number in a magnetically doped, topologically trivial insulating thin film. Specifically in a candidate material, TlBi(S1-δSeδ)2, we demonstrate that the QAH phases with different Chern numbers can be achieved by means of tuning the exchange field strength or the sample thickness near the Z2 topological critical point. Our physics scenario successfully reduces the necessary exchange coupling strength for a targeted Chern number. This QAH mechanism differs from the traditional QAH picture with a magnetic topological insulating thin film, where the ``surface'' states must involve and sometimes complicate the realization issue. Furthermore, we find that a given Chern number can also be tuned by a perpendicular electric field, which naturally occurs when a substrate is present. High-Chern number QAH phase obtained from magnetically doped topological crystalline insulator thin films will also be discussed. Support by the Singapore National Research Foundation under NRF Award No. NRF-NRFF2013-03 is acknowledged.

  11. Quantum criticality and fractional charge excitations in itinerant ice-rule systems

    NASA Astrophysics Data System (ADS)

    Udagawa, Masafumi; Ishizuka, Hiroaki; Motome, Yukitoshi

    2013-03-01

    ``Ice rule'' is a configurational constraint on Ising-type variables defined on tetrahedron-based lattices, such as a pyrochlore lattice, so that two out of the four sites on a tetrahedron are in the opposite state to the other two. This concept plays an important role in many systems, such as water ice Ih, magnetite Fe3O4, and spin ice materials Ho(Dy)2Ti2O7. Under the ice-rule constraint, the ground state is disordered and retains macroscopic degeneracy. Nevertheless, the ice-rule configuration is not completely random but has a peculiar spatial structure with quasi-long-range correlation. It is interesting to ask how itinerant electrons change their properties by coupling to this anomalous spatial structure. To answer this problem, we adopt an extended Falicov-Kimball model as a minimal model, in which itinerant electrons interact with localized charge degrees of freedom under the ice rule. We exactly solve this model on a loop-less variant of the tetrahedron-based lattices, a tetrahedron Husimi cactus and clarify the ground-state phase diagram. The exact solution reveals a quantum critical point separating two insulating phases, where a novel non-Fermi-liquid behavior emerges. We also discuss the nature of fractional excitations breaking the ice-rule manifold.

  12. Upper critical field and quantum oscillations in tetragonal superconducting FeS

    NASA Astrophysics Data System (ADS)

    Terashima, Taichi; Kikugawa, Naoki; Lin, Hai; Zhu, Xiyu; Wen, Hai-Hu; Nomoto, Takuya; Suzuki, Katsuhiro; Ikeda, Hiroaki; Uji, Shinya

    2016-09-01

    The magnetoresistance and magnetic torque of FeS are measured in magnetic fields B of up to 18 T down to a temperature of 0.03 K. The superconducting transition temperature is found to be Tc=4.1 K , and the anisotropy ratio of the upper critical field Bc 2 at Tc is estimated from the initial slopes to be Γ (Tc)=6.9 . Bc 2(0 ) is estimated to be 2.2 and 0.36 T for B ∥a b and c , respectively. Quantum oscillations are observed in both the resistance and torque. Two frequencies F =0.15 and 0.20 kT are resolved and assigned to a quasi-two-dimensional Fermi surface cylinder. The carrier density and Sommerfeld coefficient associated with this cylinder are estimated to be 5.8 ×10-3 carriers/Fe and 0.48 mJ /(K2mol ) , respectively. Other Fermi surface pockets still remain to be found. Band-structure calculations are performed and compared to the experimental results.

  13. Nematic quantum critical point without magnetism in FeSe1‑xSx superconductors

    NASA Astrophysics Data System (ADS)

    Hosoi, Suguru; Matsuura, Kohei; Ishida, Kousuke; Wang, Hao; Mizukami, Yuta; Watashige, Tatsuya; Kasahara, Shigeru; Matsuda, Yuji; Shibauchi, Takasada

    2016-07-01

    In most unconventional superconductors, the importance of antiferromagnetic fluctuations is widely acknowledged. In addition, cuprate and iron-pnictide high-temperature superconductors often exhibit unidirectional (nematic) electronic correlations, including stripe and orbital orders, whose fluctuations may also play a key role for electron pairing. In these materials, however, such nematic correlations are intertwined with antiferromagnetic or charge orders, preventing the identification of the essential role of nematic fluctuations. This calls for new materials having only nematicity without competing or coexisting orders. Here we report systematic elastoresistance measurements in FeSe1‑xSx superconductors, which, unlike other iron-based families, exhibit an electronic nematic order without accompanying antiferromagnetic order. We find that the nematic transition temperature decreases with sulfur content x; whereas, the nematic fluctuations are strongly enhanced. Near x0.17x≈0.17, the nematic susceptibility diverges toward absolute zero, revealing a nematic quantum critical point. The obtained phase diagram for the nematic and superconducting states highlights FeSe1‑xSx as a unique nonmagnetic system suitable for studying the impact of nematicity on superconductivity.

  14. Signatures of a quantum Griffiths phase in a d-metal alloy close to its ferromagnetic quantum critical point.

    PubMed

    Schroeder, Almut; Ubaid-Kassis, Sara; Vojta, Thomas

    2011-03-01

    We report magnetization measurements close to the ferromagnetic quantum phase transition of the d-metal alloy Ni(1 - x)V(x) at a vanadium concentration of x(c)≈11.4%. In the diluted regime (x > x(c)), the temperature (T) and magnetic field (H) dependences of the magnetization are characterized by nonuniversal power laws and display H/T scaling in a wide temperature and field range. The exponents vary strongly with x and follow the predictions of a quantum Griffiths phase. We also discuss the deviations and limits of the quantum Griffiths phase as well as the phase boundaries due to bulk and cluster physics. PMID:21339558

  15. Signature of a continuous quantum phase transition in non-equilibrium energy absorption: Footprints of criticality on higher excited states

    PubMed Central

    Bhattacharyya, Sirshendu; Dasgupta, Subinay; Das, Arnab

    2015-01-01

    Understanding phase transitions in quantum matters constitutes a significant part of present day condensed matter physics. Quantum phase transitions concern ground state properties of many-body systems, and hence their signatures are expected to be pronounced in low-energy states. Here we report signature of a quantum critical point manifested in strongly out-of-equilibrium states with finite energy density with respect to the ground state and extensive (subsystem) entanglement entropy, generated by an external pulse. These non-equilibrium states are evidently completely disordered (e.g., paramagnetic in case of a magnetic ordering transition). The pulse is applied by switching a coupling of the Hamiltonian from an initial value (λI) to a final value (λF) for sufficiently long time and back again. The signature appears as non-analyticities (kinks) in the energy absorbed by the system from the pulse as a function of λF at critical-points (i.e., at values of λF corresponding to static critical-points of the system). As one excites higher and higher eigenstates of the final Hamiltonian H(λF) by increasing the pulse height , the non-analyticity grows stronger monotonically with it. This implies adding contributions from higher eigenstates help magnifying the non-analyticity, indicating strong imprint of the critical-point on them. Our findings are grounded on exact analytical results derived for Ising and XY chains in transverse field. PMID:26568306

  16. Anomalous behaviour of critical fields near a superconducting quantum critical point in BaFe2(As1-xPx)2

    NASA Astrophysics Data System (ADS)

    Putzke, C.; Carrington, A.; Walmsley, P.; Malone, L.; Fletcher, J. D.; See, P.; Vignolles, D.; Proust, C.; Badoux, S.; Kasahara, S.; Mazukami, Y.; Shibauchi, T.; Matsuda, Y.

    2014-03-01

    BaFe2(As1-xPx)2 presents one of the cleanest and clearest systems in which to study the influence of quantum critical fluctuations on high temperature superconductivity. In this material a sharp maximum in the magnetic penetration depth has been found at the quantum critical point (QCP x = 0 . 3) where Tc is maximal1. Specific heat and de Haas-van Alphen effect measurements2 show that this peak is driven by a corresponding increase in the quasiparticle effective mass. Based on these previous results a simple one-band theory would suggest that at the QCP we should expect a large increase in Hc 2 and a corresponding dip in Hc 1 . Actual measurements of these critical fields, which we present here, shows quite different behavior which we suggest is caused by an anomalous enhancement in the vortex core energy close to the QCP. 1 K.Hashimoto et.al., Science 336, 1554 (2012) 2 P.Walmsley, C.Putzke et.al., Phys. Rev. Lett. 110, 257002 (2013) This work was supported by the Engineering and Physical Sciences Research Council, EuroMagNET II, and KAKENHI from JSPS.

  17. Ferromagnetic quantum critical behavior in heavy-fermion compounds CeTi1‑x Ni x Ge3

    NASA Astrophysics Data System (ADS)

    Khan, Rajwali; Yang, Jinhu; Wang, Hangdong; Mao, Qianhui; Du, Jianhua; Xu, Binjie; Zhou, Yuxing; Zhang, Yannan; Chen, Bin; Fang, Minghu

    2016-10-01

    The measurements on magnetization (M), resistivity (ρ) and specific heat (C) were carried out for the ferromagnetic CeTi{}1-x Ni x Ge3 (0.0 ≤slant x ≤slant 0.45) system. It was found that the Curie temperature, T C, decreases with increasing Ni content, x, and reaches zero kelvin near a critical content x cr = 0.44. A new phase diagram is constructed based on these measurements. The non-Fermi liquid (nFL) behavior in ρ(T), and {log}(T 0/T) relationship in C/T in the samples near x cr, demonstrate that strong spin fluctuation emerges in these samples, indicating that they are near a quantum critical point (QCP). Our results indicate that CeTi{}1-x Ni x Ge3 may provide another platform to study exotic quantum phenomena near ferromagnetic QCP.

  18. Finite-temperature scaling at the quantum critical point of the Ising chain in a transverse field

    NASA Astrophysics Data System (ADS)

    Haelg, Manuel; Huvonen, Dan; Guidi, Tatiana; Quintero-Castro, Diana Lucia; Boehm, Martin; Regnault, Louis-Pierre; Zheludev, Andrey

    2015-03-01

    Inelastic neutron scattering is used to study the finite-temperature scaling behavior of spin correlations at the quantum critical point in an experimental realization of the one-dimensional Ising model in a transverse field. The target compound is the well-characterized, anisotropic and bond-alternating Heisenberg spin-1 chain material NTENP. The validity and the limitations of the dynamic structure factor scaling are tested, discussed and compared to theoretical predictions. For this purpose neutron data have been collected on the three-axes spectrometers IN14 at ILL and FLEXX at HZB as well as on the time of flight multi-chopper spectrometer LET at ISIS. In addition to the general statement about quantum criticality and universality, present study also reveals new insight into the properties of the spin chain compound NTENP in particular.

  19. Quasi-one-dimensional quantum spin liquid in the Cu(C4H4N2)(NO3)2 insulator

    NASA Astrophysics Data System (ADS)

    Shaginyan, V. R.; Stephanovich, V. A.; Popov, K. G.; Kirichenko, E. V.

    2016-01-01

    We analyze measurements of the magnetization, differential susceptibility and specific heat of quasi-onedimensional insulator Cu(C4H4N2)(NO3)2 (CuPzN) subjected to magnetic fields. We show that the thermodynamic properties are defined by quantum spin liquid formed with spinons, with the magnetic field tuning the insulator CuPzN towards quantum critical point related to fermion condensation quantum phase transition (FCQPT) at which the spinon effective mass diverges kinematically. We show that the FCQPT concept permits to reveal and explain the scaling behavior of thermodynamic characteristics. For the first time, we construct the schematic T-H (temperature-magnetic field) phase diagram of CuPzN that contains Landau-Fermi-liquid, crossover and non-Fermi liquid parts, thus resembling that of heavy-fermion compounds.

  20. Manifestation of magnetic quantum fluctuations in the dielectric properties of a multiferroic

    NASA Astrophysics Data System (ADS)

    Kim, Jae Wook; Khim, Seunghyun; Chun, Sae Hwan; Jo, Y.; Balicas, L.; Yi, H. T.; Cheong, S.-W.; Harrison, N.; Batista, C. D.; Hoon Han, Jung; Hoon Kim, Kee

    2014-07-01

    Insulating magnets can display novel signatures of quantum fluctuations as similar to the case of metallic magnets. However, their weak spin-lattice coupling has made such observations challenging. Here we find that antiferromagnetic (AF) quantum fluctuations manifest in the dielectric properties of multiferroic Ba2CoGe2O7, where a ferroelectric polarization develops concomitant to an AF ordering. Upon application of a magnetic field (H), dielectric constant shows a characteristic power-law dependence near absolute zero temperature and close to the critical field Hc=37.1 T due to enhanced AF quantum fluctuations. When H>Hc, the dielectric constant shows the temperature-dependent anomalies that reflect a crossover from a field-tuned quantum critical to a gapped spin-polarized state. We uncover theoretically that a linear relation between AF susceptibility and dielectric constant stems from the generic magnetoelectric coupling and directly explains the experimental findings, opening a new pathway for studying quantum criticality in condensed matter.

  1. Lévy flights and multifractality in quantum critical diffusion and in classical random walks on fractals.

    PubMed

    Kravtsov, V E; Yevtushenko, O M; Snajberk, P; Cuevas, E

    2012-08-01

    We employ the method of virial expansion to compute the retarded density correlation function (generalized diffusion propagator) in the critical random matrix ensemble in the limit of strong multifractality. We find that the long-range nature of the Hamiltonian is a common root of both multifractality and Lévy flights, which show up in the power-law intermediate- and long-distance behaviors, respectively, of the density correlation function. We review certain models of classical random walks on fractals and show the similarity of the density correlation function in them to that for the quantum problem described by the random critical long-range Hamiltonians.

  2. Critical scaling in the large-N O (N ) model in higher dimensions and its possible connection to quantum gravity

    NASA Astrophysics Data System (ADS)

    Mati, P.

    2016-09-01

    The critical scaling of the large-N O (N ) model in higher dimensions using the exact renormalization group equations has been studied, motivated by the recently found nontrivial fixed point in 4 critical potential. Particular attention is paid to the case of d =5 where the scaling exponent ν has the value 1 /3 , which coincides with the scaling exponent of quantum gravity in one fewer dimensions. Convincing results show that this relation could be generalized to arbitrary number of dimensions above five. Some aspects of AdS/CFT correspondence are also discussed.

  3. Memory-preserving equilibration after a quantum quench in a one-dimensional critical model

    NASA Astrophysics Data System (ADS)

    Sotiriadis, Spyros

    2016-09-01

    One of the fundamental principles of statistical physics is that only partial information about a system's state is required for its macroscopic description. This is not only true for thermal ensembles, but also for the unconventional ensemble, known as generalized Gibbs ensemble (GGE), that is expected to describe the relaxation of integrable systems after a quantum quench. By analytically studying the quench dynamics in a prototypical one-dimensional critical model, the massless free bosonic field theory, we find evidence of a novel type of equilibration characterized by the preservation of an enormous amount of memory of the initial state that is accessible by local measurements. In particular, we show that the equilibration retains memory of non-Gaussian initial correlations, in contrast to the case of massive free evolution which erases all such memory. The GGE in its standard form, being a Gaussian ensemble, fails to predict correctly the equilibrium values of local observables, unless the initial state is Gaussian itself. Our findings show that the equilibration of a broad class of quenches whose evolution is described by Luttinger liquid theory with an initial state that is non-Gaussian in terms of the bosonic field, is not correctly captured by the corresponding bosonic GGE, raising doubts about the validity of the latter in general one-dimensional gapless integrable systems such as the Lieb-Liniger model. We also propose that the same experiment by which the GGE was recently observed [Langen et al., Science 348, 207 (2015), 10.1126/science.1257026] can also be used to observe its failure, simply by starting from a non-Gaussian initial state.

  4. Evidence of a quantum critical point in Ce1-xYbxCoIn5 alloys at high Yb doping

    NASA Astrophysics Data System (ADS)

    Singh, Y. P.; Haney, D. J.; Huang, X. Y.; White, B. D.; Maple, M. B.; Dzero, M.; Almasan, C. C.

    2015-03-01

    We performed this study on single crystals of Ce1-xYbxCoIn5 alloys with the motivation to further explore some of the previously reported unusual behaviors such as robust coherence and superconductivity, non-Fermi liquid (NFL) behavior, and the possibility of quantum criticality in higher Yb doping. Our specific heat and electronic magneto-transport measurements on the alloy with x = 0.75 nominal doping down to temperatures (T) as low as 0.5 K and magnetic fields (H) as high as 14 T. Our analysis of both specific heat and resistivity data unveils the presence of a crossover from NFL behavior at high temperatures to Fermi-liquid (FL) behavior at lower temperatures. Our analysis also indicates that the origin of the NFL behavior is a result of quantum fluctuations of unknown origin. The H-T phase diagram extracted from resistivity and specific heat shows that the crossover from NFL to FL behavior at zero temperature occurs at H = 0. This implies that the alloy with x = 0.75 Yb concentration is quantum critical, i.e., xc = 0.75. This result of zero field quantum critical point at x = 0.75 is also confirmed from our analysis of magneto-resistance data. This work was supported by the National Science Foundation (Grant NSF DMR-1006606) and Ohio Board of Regents (Grant OBR-RIP-220573) at KSU, and by the U.S. Department of Energy (Grant DE-FG02- 04ER46105) at UCSD.

  5. Quantum correlation dynamics subjected to critical spin environment with short-range anisotropic interaction

    NASA Astrophysics Data System (ADS)

    Guo, J. L.; Zhang, X. Z.

    2016-09-01

    Short-range interaction among the spins can not only results in the rich phase diagram but also brings about fascinating phenomenon both in the contexts of quantum computing and information. In this paper, we investigate the quantum correlation of the system coupled to a surrounding environment with short-range anisotropic interaction. It is shown that the decay of quantum correlation of the central spins measured by pairwise entanglement and quantum discord can serve as a signature of quantum phase transition. In addition, we study the decoherence factor of the system when the environment is in the vicinity of the phase transition point. In the strong coupling regime, the decay of the decoherence factor exhibits Gaussian envelop in the time domain. However, in weak coupling limit, the quantum correlation of the system is robust against the disturbance of the magnetic field through optimal control of the anisotropic short-range interaction strength. Based on this, the effects of the short-range anisotropic interaction on the sudden transition from classical to quantum decoherence are also presented.

  6. Quantum correlation dynamics subjected to critical spin environment with short-range anisotropic interaction.

    PubMed

    Guo, J L; Zhang, X Z

    2016-01-01

    Short-range interaction among the spins can not only results in the rich phase diagram but also brings about fascinating phenomenon both in the contexts of quantum computing and information. In this paper, we investigate the quantum correlation of the system coupled to a surrounding environment with short-range anisotropic interaction. It is shown that the decay of quantum correlation of the central spins measured by pairwise entanglement and quantum discord can serve as a signature of quantum phase transition. In addition, we study the decoherence factor of the system when the environment is in the vicinity of the phase transition point. In the strong coupling regime, the decay of the decoherence factor exhibits Gaussian envelop in the time domain. However, in weak coupling limit, the quantum correlation of the system is robust against the disturbance of the magnetic field through optimal control of the anisotropic short-range interaction strength. Based on this, the effects of the short-range anisotropic interaction on the sudden transition from classical to quantum decoherence are also presented. PMID:27596050

  7. Quantum correlation dynamics subjected to critical spin environment with short-range anisotropic interaction

    PubMed Central

    Guo, J. L.; Zhang, X. Z.

    2016-01-01

    Short-range interaction among the spins can not only results in the rich phase diagram but also brings about fascinating phenomenon both in the contexts of quantum computing and information. In this paper, we investigate the quantum correlation of the system coupled to a surrounding environment with short-range anisotropic interaction. It is shown that the decay of quantum correlation of the central spins measured by pairwise entanglement and quantum discord can serve as a signature of quantum phase transition. In addition, we study the decoherence factor of the system when the environment is in the vicinity of the phase transition point. In the strong coupling regime, the decay of the decoherence factor exhibits Gaussian envelop in the time domain. However, in weak coupling limit, the quantum correlation of the system is robust against the disturbance of the magnetic field through optimal control of the anisotropic short-range interaction strength. Based on this, the effects of the short-range anisotropic interaction on the sudden transition from classical to quantum decoherence are also presented. PMID:27596050

  8. Strong Coupling Superconductivity in the Vicinity of the Structural Quantum Critical Point in (CaxSr1 -x)3Rh4Sn13

    NASA Astrophysics Data System (ADS)

    Yu, Wing Chi; Cheung, Yiu Wing; Saines, Paul J.; Imai, Masaki; Matsumoto, Takuya; Michioka, Chishiro; Yoshimura, Kazuyoshi; Goh, Swee K.

    2015-11-01

    The family of the superconducting quasiskutterudites (CaxSr1 -x)3Rh4Sn13 features a structural quantum critical point at xc=0.9 , around which a dome-shaped variation of the superconducting transition temperature Tc is found. Using specific heat, we probe the normal and the superconducting states of the entire series straddling the quantum critical point. Our analysis indicates a significant lowering of the effective Debye temperature on approaching xc, which we interpret as a result of phonon softening accompanying the structural instability. Furthermore, a remarkably large enhancement of 2 Δ /kBTc and Δ C /γ Tc beyond the Bardeen-Cooper-Schrieffer values is found in the vicinity of the structural quantum critical point. The phase diagram of (CaxSr1 -x)3Rh4Sn13 thus provides a model system to study the interplay between structural quantum criticality and strong electron-phonon coupling superconductivity.

  9. Phase diagram of quantum critical system via local convertibility of ground state

    PubMed Central

    Liu, Si-Yuan; Quan, Quan; Chen, Jin-Jun; Zhang, Yu-Ran; Yang, Wen-Li; Fan, Heng

    2016-01-01

    We investigate the relationship between two kinds of ground-state local convertibility and quantum phase transitions in XY model. The local operations and classical communications (LOCC) convertibility is examined by the majorization relations and the entanglement-assisted local operations and classical communications (ELOCC) via Rényi entropy interception. In the phase diagram of XY model, LOCC convertibility and ELOCC convertibility of ground-states are presented and compared. It is shown that different phases in the phase diagram of XY model can have different LOCC or ELOCC convertibility, which can be used to detect the quantum phase transition. This study will enlighten extensive studies of quantum phase transitions from the perspective of local convertibility, e.g., finite-temperature phase transitions and other quantum many-body models. PMID:27381284

  10. Phase diagram of quantum critical system via local convertibility of ground state.

    PubMed

    Liu, Si-Yuan; Quan, Quan; Chen, Jin-Jun; Zhang, Yu-Ran; Yang, Wen-Li; Fan, Heng

    2016-01-01

    We investigate the relationship between two kinds of ground-state local convertibility and quantum phase transitions in XY model. The local operations and classical communications (LOCC) convertibility is examined by the majorization relations and the entanglement-assisted local operations and classical communications (ELOCC) via Rényi entropy interception. In the phase diagram of XY model, LOCC convertibility and ELOCC convertibility of ground-states are presented and compared. It is shown that different phases in the phase diagram of XY model can have different LOCC or ELOCC convertibility, which can be used to detect the quantum phase transition. This study will enlighten extensive studies of quantum phase transitions from the perspective of local convertibility, e.g., finite-temperature phase transitions and other quantum many-body models.

  11. Uniaxial ferroelectric quantum criticality in multiferroic hexaferrites BaFe12O19 and SrFe12O19.

    PubMed

    Rowley, S E; Chai, Yi-Sheng; Shen, Shi-Peng; Sun, Young; Jones, A T; Watts, B E; Scott, J F

    2016-05-17

    BaFe12O19 is a popular M-type hexaferrite with a Néel temperature of 720 K and is of enormous commercial value ($3 billion/year). It is an incipient ferroelectric with an expected ferroelectric phase transition extrapolated to lie at 6 K but suppressed due to quantum fluctuations. The theory of quantum criticality for such uniaxial ferroelectrics predicts that the temperature dependence of the electric susceptibility χ diverges as 1/T(3), in contrast to the 1/T(2) dependence found in pseudo-cubic materials such as SrTiO3 or KTaO3. In this paper we present evidence of the susceptibility varying as 1/T(3), i.e. with a critical exponent γ = 3. In general γ = (d + z - 2)/z, where the dynamical exponent for a ferroelectric z = 1 and the dimension is increased by 1 from deff = 3 + z to deff = 4 + z due to the effect of long-range dipole interactions in uniaxial as opposed to multiaxial ferroelectrics. The electric susceptibility of the incipient ferroelectric SrFe12O19, which is slightly further from the quantum phase transition is also found to vary as 1/T(3).

  12. Uniaxial ferroelectric quantum criticality in multiferroic hexaferrites BaFe12O19 and SrFe12O19

    PubMed Central

    Rowley, S. E.; Chai, Yi-Sheng; Shen, Shi-Peng; Sun, Young; Jones, A. T.; Watts, B. E.; Scott, J. F.

    2016-01-01

    BaFe12O19 is a popular M-type hexaferrite with a Néel temperature of 720 K and is of enormous commercial value ($3 billion/year). It is an incipient ferroelectric with an expected ferroelectric phase transition extrapolated to lie at 6 K but suppressed due to quantum fluctuations. The theory of quantum criticality for such uniaxial ferroelectrics predicts that the temperature dependence of the electric susceptibility χ diverges as 1/T3, in contrast to the 1/T2 dependence found in pseudo-cubic materials such as SrTiO3 or KTaO3. In this paper we present evidence of the susceptibility varying as 1/T3, i.e. with a critical exponent γ = 3. In general γ = (d + z – 2)/z, where the dynamical exponent for a ferroelectric z = 1 and the dimension is increased by 1 from deff = 3 + z to deff = 4 + z due to the effect of long-range dipole interactions in uniaxial as opposed to multiaxial ferroelectrics. The electric susceptibility of the incipient ferroelectric SrFe12O19, which is slightly further from the quantum phase transition is also found to vary as 1/T3. PMID:27185343

  13. Uniaxial ferroelectric quantum criticality in multiferroic hexaferrites BaFe12O19 and SrFe12O19.

    PubMed

    Rowley, S E; Chai, Yi-Sheng; Shen, Shi-Peng; Sun, Young; Jones, A T; Watts, B E; Scott, J F

    2016-01-01

    BaFe12O19 is a popular M-type hexaferrite with a Néel temperature of 720 K and is of enormous commercial value ($3 billion/year). It is an incipient ferroelectric with an expected ferroelectric phase transition extrapolated to lie at 6 K but suppressed due to quantum fluctuations. The theory of quantum criticality for such uniaxial ferroelectrics predicts that the temperature dependence of the electric susceptibility χ diverges as 1/T(3), in contrast to the 1/T(2) dependence found in pseudo-cubic materials such as SrTiO3 or KTaO3. In this paper we present evidence of the susceptibility varying as 1/T(3), i.e. with a critical exponent γ = 3. In general γ = (d + z - 2)/z, where the dynamical exponent for a ferroelectric z = 1 and the dimension is increased by 1 from deff = 3 + z to deff = 4 + z due to the effect of long-range dipole interactions in uniaxial as opposed to multiaxial ferroelectrics. The electric susceptibility of the incipient ferroelectric SrFe12O19, which is slightly further from the quantum phase transition is also found to vary as 1/T(3). PMID:27185343

  14. Uniaxial ferroelectric quantum criticality in multiferroic hexaferrites BaFe12O19 and SrFe12O19

    NASA Astrophysics Data System (ADS)

    Rowley, S. E.; Chai, Yi-Sheng; Shen, Shi-Peng; Sun, Young; Jones, A. T.; Watts, B. E.; Scott, J. F.

    2016-05-01

    BaFe12O19 is a popular M-type hexaferrite with a Néel temperature of 720 K and is of enormous commercial value ($3 billion/year). It is an incipient ferroelectric with an expected ferroelectric phase transition extrapolated to lie at 6 K but suppressed due to quantum fluctuations. The theory of quantum criticality for such uniaxial ferroelectrics predicts that the temperature dependence of the electric susceptibility χ diverges as 1/T3, in contrast to the 1/T2 dependence found in pseudo-cubic materials such as SrTiO3 or KTaO3. In this paper we present evidence of the susceptibility varying as 1/T3, i.e. with a critical exponent γ = 3. In general γ = (d + z – 2)/z, where the dynamical exponent for a ferroelectric z = 1 and the dimension is increased by 1 from deff = 3 + z to deff = 4 + z due to the effect of long-range dipole interactions in uniaxial as opposed to multiaxial ferroelectrics. The electric susceptibility of the incipient ferroelectric SrFe12O19, which is slightly further from the quantum phase transition is also found to vary as 1/T3.

  15. Field-induced quantum critical point in the pressure-induced superconductor CeRhIn5

    SciTech Connect

    Bauer, Eric D; Park, Tuson; Tokiwa, Yoshifumi; Ronning, Filip; Lee, Han O; Movshovich, Roman; Thompson, Joe D

    2009-01-01

    When subjected to pressure, the prototypical heavy-fermion antiferromagnet CeRhIn{sub 5} becomes superconducting, forming a broad dome of superconductivity centered around 2.35 GPa (=P2) with maximal T{sub c} of 2.3 K. Above the superconducting dome, the normal state shows strange metallic behaviors, including a divergence in the specific heat and a sub-T-linear electrical resistivity. The discovery of a field-induced magnetic phase that coexists with superconductivity for a range of pressures P {le} P2 has been interpreted as evidence for a quantum phase transition, which could explain the non-Fenni liquid behavior observed in the normal state. Here we report electrical resistivity measurements of CeRhIn{sub 5} under magnetic field at P2, where the resistivity is sub-T-linear for fields less than H{sub c2}(0) and a T{sup 2}-coefficient A found above H{sub c2}(0) diverges as H{sub c2} is approached. These results are similar to the field-induced quantum critical compound Ce-CoIn{sub 5} and confirm the presence of a quantum critical point in the pressure-induced superconductor CeRhIn{sub 5}.

  16. Supersolid phase accompanied by a quantum critical point in the intermediate coupling regime of the Holstein model.

    PubMed

    Murakami, Yuta; Werner, Philipp; Tsuji, Naoto; Aoki, Hideo

    2014-12-31

    We reveal that electron-phonon systems described by the Holstein model on a bipartite lattice exhibit, away from half filling, a supersolid (SS) phase characterized by coexisting charge order (CO) and superconductivity (SC), and an accompanying quantum critical point (QCP). The SS phase, demonstrated by the dynamical mean-field theory with a quantum Monte Carlo impurity solver, emerges in the intermediate-coupling regime, where the peak of the Tc dome is located and the metal-insulator crossover occurs. On the other hand, in the weak- and strong-coupling regimes the CO-SC boundary is of first order with no intervening SS phases. The QCP is associated with the continuous transition from SS to SC and characterized by a reentrant behavior of the SS around it. We further show that the SS-SC transition is hallmarked by diverging charge fluctuations and a kink (peak) in the superfluid density. PMID:25615362

  17. Quantum oscillations in the heavy-fermion compound YbPtBi

    SciTech Connect

    Mun, E.; Bud'ko, S. L.; Lee, Y.; Martin, C.; Tanatar, M. A.; Prozorov, R.; Canfield, P. C.

    2015-08-01

    We present quantum oscillations observed in the heavy-fermion compound YbPtBi in magnetic fields far beyond its field-tuned, quantum critical point. Quantum oscillations are observed in magnetic fields as low as 60 kOe at 60 mK and up to temperatures as high as 3 K, which confirms the very high quality of the samples as well as the small effective mass of the conduction carriers far from the quantum critical point. Although the electronic specific heat coefficient of YbPtBi reaches ~7.4 J/molK2 in zero field, which is one of the highest effective mass values among heavy-fermion systems, we suppress it quickly by an applied magnetic field. The quantum oscillations were used to extract the quasiparticle effective masses of the order of the bare electron mass, which is consistent with the behavior observed in specific heat measurements. Furthermore, such small effective masses at high fields can be understood by considering the suppression of Kondo screening.

  18. Quantum oscillations in the heavy-fermion compound YbPtBi

    DOE PAGESBeta

    Mun, E.; Bud'ko, S. L.; Lee, Y.; Martin, C.; Tanatar, M. A.; Prozorov, R.; Canfield, P. C.

    2015-08-01

    We present quantum oscillations observed in the heavy-fermion compound YbPtBi in magnetic fields far beyond its field-tuned, quantum critical point. Quantum oscillations are observed in magnetic fields as low as 60 kOe at 60 mK and up to temperatures as high as 3 K, which confirms the very high quality of the samples as well as the small effective mass of the conduction carriers far from the quantum critical point. Although the electronic specific heat coefficient of YbPtBi reaches ~7.4 J/molK2 in zero field, which is one of the highest effective mass values among heavy-fermion systems, we suppress it quicklymore » by an applied magnetic field. The quantum oscillations were used to extract the quasiparticle effective masses of the order of the bare electron mass, which is consistent with the behavior observed in specific heat measurements. Furthermore, such small effective masses at high fields can be understood by considering the suppression of Kondo screening.« less

  19. Disorder-induced enhancement and critical scaling of spontaneous magnetization in random-field quantum spin systems

    NASA Astrophysics Data System (ADS)

    Bera, Anindita; Rakshit, Debraj; Lewenstein, Maciej; SenDe, Aditi; Sen, Ujjwal; Wehr, Jan

    2016-07-01

    We investigate the effect of a unidirectional quenched random field on the anisotropic quantum spin-1/2 X Y model, which magnetizes spontaneously in the absence of the random field. We adopt a mean-field approach for this analysis. In general, the models considered have Ising symmetry, and as such they exhibit ferromagnetic order in two and three dimensions in the presence of not too large disorder. Even in the special case when the model without disorder has U(1 ) symmetry, a small U(1 ) -symmetry-breaking random field induces ferromagnetic long-range order in two dimensions. The mean-field approach, consequently, provides a rather good qualitative and even quantitative description when applied not too close to the criticality. We show that spontaneous magnetization persists even in the presence of the random field, but the magnitude of magnetization gets suppressed due to disorder, and the system magnetizes in the directions parallel and transverse to the random field. Our results are obtained via analytical calculations within a perturbative framework and by numerical simulations. Interestingly, we show that it is possible to enhance a component of magnetization in the presence of the disorder field provided that we apply an additional constant field in the X Y plane. Moreover, we derive generalized expressions for the critical temperature and the scalings of the magnetization near the critical point for the X Y spin system with arbitrary fixed quantum spin angular momentum.

  20. Percolation theory and quantum critical systems: A new description of the critical behavior in Ce(Ru{sub 0.24}Fe{sub 0.76}){sub 2}Ge{sub 2}

    SciTech Connect

    Gaddy, John; Heitmann, Tom; Montfrooij, Wouter

    2014-05-07

    The onset of ordering in quantum critical systems is characterized by a competition between the Kondo shielding of magnetic moments and the ordering of these moments. We show how a distribution of Kondo shielding temperatures—resulting from chemical doping—leads to critical behavior whose main characteristics are given by percolation physics. With the aid of Monte Carlo computer simulations, we are able to infer the low temperature part of the distribution of shielding temperatures in heavily doped quantum critical Ce(Ru{sub 0.24}Fe{sub 0.76}){sub 2}Ge{sub 2}. Based on this distribution, we show that the ordering dynamics—such as the growth of the correlation length upon cooling—can be understood by the spawning of magnetic clusters. Our findings explain why the search for universal exponents in quantum critical systems has been unsuccessful: the underlying percolation network associated with the chemical doping of quantum critical systems has to be incorporated in the modeling of these quantum critical systems.

  1. Quantum criticality and coexistence of spontaneous ferromagnetism and field- induced metamagnetism in triple-layered Sr4Ru3O10

    NASA Astrophysics Data System (ADS)

    Chikara, Shalinee; Durairaj, Vinobalan; Cao, Gang; Brill, Joseph W.; Schlottmann, Pedro

    2007-03-01

    Results of a thermodynamic and transport study of Sr4Ru3O10 as a function of temperature and magnetic field are presented. The central results of this work include growing specific heat C with increasing field B, divergent magnetic contribution to C at low temperatures, an abrupt jump and a peak in C/T at B=2.90 T and =7 T for B||ab-plane and B||c-axis, respectively, and corresponding changes in the power law of resistivity. All results provide not only strong evidence for metamagnetic quantum criticality but also quantum fluctuations in a spontaneously ferromagnetic state. The novelty of this work lies in the fact that the quantum criticality occurs in a system that shows both intralayer metamagnetism and interlayer spontaneous ferromagnetism, a feature characteristically different from all other relevant systems involving quantum criticality.

  2. Microscopic investigation of electronic inhomogeneity induced by substitutions in a quantum critical metal CeCoIn5

    NASA Astrophysics Data System (ADS)

    Sakai, H.; Ronning, F.; Zhu, J.-X.; Wakeham, N.; Yasuoka, H.; Tokunaga, Y.; Kambe, S.; Bauer, E. D.; Thompson, J. D.

    2015-09-01

    Chemical substitutions are used commonly to tune a magnetic transition to zero temperature, but the resulting non-Fermi-liquid (NFL) behavior is nonuniversal. We have used nuclear quadrupole resonance to probe microscopically the response of a prototypical quantum critical metal CeCoIn5 to substitutions of small amounts of Sn and Cd for In. These substituents induce very different local electronic environments as observed by site-dependent spin lattice relaxation rates 1 /T1 that influence the NFL behavior. The effects found here illustrate the need for care in interpreting NFL properties determined by macroscopic measurements.

  3. Pairing interaction near a nematic quantum critical point of a three-band CuO2 model

    DOE PAGESBeta

    Maier, Thomas A.; Scalapino, Douglas J.

    2014-11-21

    In this paper, we calculate the pairing interaction and the k dependence of the gap function associated with the nematic charge fluctuations of a CuO2 model.We find that the nematic pairing interaction is attractive for small momentum transfer and that it gives rise to d-wave pairing. Finally, as the doping p approaches a quantum critical point, the strength of this pairing increases and higher d-wave harmonics contribute to the k dependence of the superconducting gap function, reflecting the longer range nature of the nematic fluctuations.

  4. Pairing interaction near a nematic quantum critical point of a three-band CuO2 model

    SciTech Connect

    Maier, Thomas A.; Scalapino, Douglas J.

    2014-11-21

    In this paper, we calculate the pairing interaction and the k dependence of the gap function associated with the nematic charge fluctuations of a CuO2 model.We find that the nematic pairing interaction is attractive for small momentum transfer and that it gives rise to d-wave pairing. Finally, as the doping p approaches a quantum critical point, the strength of this pairing increases and higher d-wave harmonics contribute to the k dependence of the superconducting gap function, reflecting the longer range nature of the nematic fluctuations.

  5. Scrutinizing Hall Effect in Mn1 -xFex Si : Fermi Surface Evolution and Hidden Quantum Criticality

    NASA Astrophysics Data System (ADS)

    Glushkov, V. V.; Lobanova, I. I.; Ivanov, V. Yu.; Voronov, V. V.; Dyadkin, V. A.; Chubova, N. M.; Grigoriev, S. V.; Demishev, S. V.

    2015-12-01

    Separating between the ordinary Hall effect and anomalous Hall effect in the paramagnetic phase of Mn1 -xFex Si reveals an ordinary Hall effect sign inversion associated with the hidden quantum critical (QC) point x*˜0.11 . The effective hole doping at intermediate Fe content leads to verifiable predictions in the field of fermiology, magnetic interactions, and QC phenomena in Mn1 -xFex Si . The change of electron and hole concentrations is considered as a "driving force" for tuning the QC regime in Mn1 -xFex Si via modifying the Ruderman-Kittel-Kasuya-Yosida exchange interaction within the Heisenberg model of magnetism.

  6. Classical-to-quantum crossover in the critical behavior of the transverse-field Sherrington-Kirkpatrick spin glass model

    NASA Astrophysics Data System (ADS)

    Mukherjee, Sudip; Rajak, Atanu; Chakrabarti, Bikas K.

    2015-10-01

    We study the critical behavior of the Sherrington-Kirkpatrick model in transverse field (at finite temperature) using Monte Carlo simulation and exact diagonalization (at zero temperature). We determine the phase diagram of the model by estimating the Binder cumulant. We also determine the correlation length exponent from the collapse of the scaled data. Our numerical studies here indicate that critical Binder cumulant (indicating the universality class of the transition behavior) and the correlation length exponent cross over from their "classical" to "quantum" values at a finite temperature (unlike the cases of pure systems, where such crossovers occur at zero temperature). We propose a qualitative argument supporting such an observation, employing a simple tunneling picture.

  7. Quantum-critical fluctuations in 2D metals: strange metals and superconductivity in antiferromagnets and in cuprates.

    PubMed

    Varma, Chandra M

    2016-08-01

    The anomalous transport and thermodynamic properties in the quantum-critical region, in the cuprates, and in the quasi-two dimensional Fe-based superconductors and heavy-fermion compounds, have the same temperature dependences. This can occur only if, despite their vast microscopic differences, a common statistical mechanical model describes their phase transitions. The antiferromagnetic (AFM)-ic models for the latter two, just as the loop-current model for the cuprates, map to the dissipative XY model. The solution of this model in (2+1)D reveals that the critical fluctuations are determined by topological excitations, vortices and a variety of instantons, and not by renormalized spin-wave theories of the Landau-Ginzburg-Wilson type, adapted by Moriya, Hertz and others for quantum-criticality. The absorptive part of the fluctuations is a separable function of momentum [Formula: see text], measured from the ordering vector, and of the frequency ω and the temperature T which scale as [Formula: see text] at criticality. Direct measurements of the fluctuations by neutron scattering in the quasi-two-dimensional heavy fermion and Fe-based compounds, near their antiferromagnetic quantum critical point, are consistent with this form. Such fluctuations, together with the vertex coupling them to fermions, lead to a marginal fermi-liquid, with the imaginary part of the self-energy [Formula: see text] for all momenta, a resistivity [Formula: see text], a [Formula: see text] contribution to the specific heat, and other singular fermi-liquid properties common to these diverse compounds, as well as to d-wave superconductivity. This is explicitly verified, in the cuprates, by analysis of the pairing and the normal self-energy directly extracted from the recent high resolution angle resolved photoemission measurements. This reveals, in agreement with the theory, that the frequency dependence of the attractive irreducible particle-particle vertex in the d-wave channel is the same

  8. Quantum-critical fluctuations in 2D metals: strange metals and superconductivity in antiferromagnets and in cuprates

    NASA Astrophysics Data System (ADS)

    Varma, Chandra M.

    2016-08-01

    The anomalous transport and thermodynamic properties in the quantum-critical region, in the cuprates, and in the quasi-two dimensional Fe-based superconductors and heavy-fermion compounds, have the same temperature dependences. This can occur only if, despite their vast microscopic differences, a common statistical mechanical model describes their phase transitions. The antiferromagnetic (AFM)-ic models for the latter two, just as the loop-current model for the cuprates, map to the dissipative XY model. The solution of this model in (2+1)D reveals that the critical fluctuations are determined by topological excitations, vortices and a variety of instantons, and not by renormalized spin-wave theories of the Landau–Ginzburg–Wilson type, adapted by Moriya, Hertz and others for quantum-criticality. The absorptive part of the fluctuations is a separable function of momentum \\mathbf{q} , measured from the ordering vector, and of the frequency ω and the temperature T which scale as \\tanh (ω /2T) at criticality. Direct measurements of the fluctuations by neutron scattering in the quasi-two-dimensional heavy fermion and Fe-based compounds, near their antiferromagnetic quantum critical point, are consistent with this form. Such fluctuations, together with the vertex coupling them to fermions, lead to a marginal fermi-liquid, with the imaginary part of the self-energy \\propto \\text{max}(ω,T) for all momenta, a resistivity \\propto T , a T\\ln T contribution to the specific heat, and other singular fermi-liquid properties common to these diverse compounds, as well as to d-wave superconductivity. This is explicitly verified, in the cuprates, by analysis of the pairing and the normal self-energy directly extracted from the recent high resolution angle resolved photoemission measurements. This reveals, in agreement with the theory, that the frequency dependence of the attractive irreducible particle–particle vertex in the d-wave channel is the same as the irreducible

  9. Quantum-critical fluctuations in 2D metals: strange metals and superconductivity in antiferromagnets and in cuprates.

    PubMed

    Varma, Chandra M

    2016-08-01

    The anomalous transport and thermodynamic properties in the quantum-critical region, in the cuprates, and in the quasi-two dimensional Fe-based superconductors and heavy-fermion compounds, have the same temperature dependences. This can occur only if, despite their vast microscopic differences, a common statistical mechanical model describes their phase transitions. The antiferromagnetic (AFM)-ic models for the latter two, just as the loop-current model for the cuprates, map to the dissipative XY model. The solution of this model in (2+1)D reveals that the critical fluctuations are determined by topological excitations, vortices and a variety of instantons, and not by renormalized spin-wave theories of the Landau-Ginzburg-Wilson type, adapted by Moriya, Hertz and others for quantum-criticality. The absorptive part of the fluctuations is a separable function of momentum [Formula: see text], measured from the ordering vector, and of the frequency ω and the temperature T which scale as [Formula: see text] at criticality. Direct measurements of the fluctuations by neutron scattering in the quasi-two-dimensional heavy fermion and Fe-based compounds, near their antiferromagnetic quantum critical point, are consistent with this form. Such fluctuations, together with the vertex coupling them to fermions, lead to a marginal fermi-liquid, with the imaginary part of the self-energy [Formula: see text] for all momenta, a resistivity [Formula: see text], a [Formula: see text] contribution to the specific heat, and other singular fermi-liquid properties common to these diverse compounds, as well as to d-wave superconductivity. This is explicitly verified, in the cuprates, by analysis of the pairing and the normal self-energy directly extracted from the recent high resolution angle resolved photoemission measurements. This reveals, in agreement with the theory, that the frequency dependence of the attractive irreducible particle-particle vertex in the d-wave channel is the same

  10. Quantum-critical fluctuations in 2D metals: strange metals and superconductivity in antiferromagnets and in cuprates

    NASA Astrophysics Data System (ADS)

    Varma, Chandra M.

    2016-08-01

    The anomalous transport and thermodynamic properties in the quantum-critical region, in the cuprates, and in the quasi-two dimensional Fe-based superconductors and heavy-fermion compounds, have the same temperature dependences. This can occur only if, despite their vast microscopic differences, a common statistical mechanical model describes their phase transitions. The antiferromagnetic (AFM)-ic models for the latter two, just as the loop-current model for the cuprates, map to the dissipative XY model. The solution of this model in (2+1)D reveals that the critical fluctuations are determined by topological excitations, vortices and a variety of instantons, and not by renormalized spin-wave theories of the Landau-Ginzburg-Wilson type, adapted by Moriya, Hertz and others for quantum-criticality. The absorptive part of the fluctuations is a separable function of momentum \\mathbf{q} , measured from the ordering vector, and of the frequency ω and the temperature T which scale as \\tanh (ω /2T) at criticality. Direct measurements of the fluctuations by neutron scattering in the quasi-two-dimensional heavy fermion and Fe-based compounds, near their antiferromagnetic quantum critical point, are consistent with this form. Such fluctuations, together with the vertex coupling them to fermions, lead to a marginal fermi-liquid, with the imaginary part of the self-energy \\propto \\text{max}(ω,T) for all momenta, a resistivity \\propto T , a T\\ln T contribution to the specific heat, and other singular fermi-liquid properties common to these diverse compounds, as well as to d-wave superconductivity. This is explicitly verified, in the cuprates, by analysis of the pairing and the normal self-energy directly extracted from the recent high resolution angle resolved photoemission measurements. This reveals, in agreement with the theory, that the frequency dependence of the attractive irreducible particle-particle vertex in the d-wave channel is the same as the irreducible

  11. Neutron, Electron and X-ray Scattering Investigation of Cr1-xVx Near Quantum Criticality

    SciTech Connect

    Sokolov, D A; Aronson, Meigan C.; Wu, Lijun; Zhu, Yimei; Nelson, C.; Mansfield, J. F.; Sun, K.; Erwin, R.; Lynn, J. W.; Lumsden, Mark D; Nagler, Stephen E

    2014-01-01

    The weakness of electron-electron correlations in the itinerant antiferromagnet Cr doped with V has long been considered the reason that neither new collective electronic states or even non Fermi liquid behaviour are observed when antiferromagnetism in Cr1 xVx is suppressed to zero temperature. We present the results of neutron and electron diffraction measurements of several lightly doped single crystals of Cr1 xVx in which the archtypal spin density wave instability is progressively suppressed as the V content increases, freeing the nesting-prone Fermi surface for a new striped charge instability that occurs at xc=0.037. This novel nesting driven instability relieves the entropy accumulation associated with the suppression of the spin density wave and avoids the formation of a quantum critical point by stabilising a new type of charge order at temperatures in excess of 400 K. Restructuring of the Fermi surface near quantum critical points is a feature found in materials as diverse as heavy fermions, high temperature copper oxide superconductors and now even elemental metals such as Cr.

  12. Zero-point term and quantum effects in the Johnson noise of resistors: a critical appraisal

    NASA Astrophysics Data System (ADS)

    Kish, Laszlo B.; Niklasson, Gunnar A.; Granqvist, Claes G.

    2016-05-01

    There is a longstanding debate about the zero-point term in the Johnson noise voltage of a resistor. This term originates from a quantum-theoretical treatment of the fluctuation-dissipation theorem (FDT). Is the zero-point term really there, or is it only an experimental artifact, due to the uncertainty principle, for phase-sensitive amplifiers? Could it be removed by renormalization of theories? We discuss some historical measurement schemes that do not lead to the effect predicted by the FDT, and we analyse new features that emerge when the consequences of the zero-point term are measured via the mean energy and force in a capacitor shunting the resistor. If these measurements verify the existence of a zero-point term in the noise, then two types of perpetual motion machines can be constructed. Further investigation with the same approach shows that, in the quantum limit, the Johnson-Nyquist formula is also invalid under general conditions even though it is valid for a resistor-antenna system. Therefore we conclude that in a satisfactory quantum theory of the Johnson noise, the FDT must, as a minimum, include also the measurement system used to evaluate the observed quantities. Issues concerning the zero-point term may also have implications for phenomena in advanced nanotechnology.

  13. Zero-point term and quantum effects in the Johnson noise of resistors: a critical appraisal

    NASA Astrophysics Data System (ADS)

    Kish, Laszlo B.; Niklasson, Gunnar A.; Granqvist, Claes G.

    2016-05-01

    There is a longstanding debate about the zero-point term in the Johnson noise voltage of a resistor. This term originates from a quantum-theoretical treatment of the fluctuation-dissipation theorem (FDT). Is the zero-point term really there, or is it only an experimental artifact, due to the uncertainty principle, for phase-sensitive amplifiers? Could it be removed by renormalization of theories? We discuss some historical measurement schemes that do not lead to the effect predicted by the FDT, and we analyse new features that emerge when the consequences of the zero-point term are measured via the mean energy and force in a capacitor shunting the resistor. If these measurements verify the existence of a zero-point term in the noise, then two types of perpetual motion machines can be constructed. Further investigation with the same approach shows that, in the quantum limit, the Johnson–Nyquist formula is also invalid under general conditions even though it is valid for a resistor-antenna system. Therefore we conclude that in a satisfactory quantum theory of the Johnson noise, the FDT must, as a minimum, include also the measurement system used to evaluate the observed quantities. Issues concerning the zero-point term may also have implications for phenomena in advanced nanotechnology.

  14. Unconventional quantum criticality emerging as a new common language of transition-metal compounds, heavy-fermion systems, and organic conductors

    NASA Astrophysics Data System (ADS)

    Imada, Masatoshi; Misawa, Takahiro; Yamaji, Youhei

    2010-04-01

    We analyze and overview some of the different types of unconventional quantum criticalities by focusing on two origins. One origin of the unconventionality is the proximity to first-order transitions. The border between the first-order and continuous transitions is described by a quantum tricritical point (QTCP) for symmetry breaking transitions. One of the characteristic features of the quantum tricriticality is the concomitant divergence of an order parameter and uniform fluctuations, in contrast to the conventional quantum critical point (QCP). The interplay of these two fluctuations generates unconventionality. Several puzzling non-Fermi-liquid properties in experiments are taken to be accounted for by the resultant universality, as in the cases of Y bRh2Si2, CeRu2Si2 and β-Y bAlB4. Another more dramatic unconventionality appears again at the border of the first-order and continuous transitions, but in this case for topological transitions such as metal-insulator and Lifshitz transitions. This border, the marginal quantum critical point (MQCP), belongs to an unprecedented universality class with diverging uniform fluctuations at zero temperature. The Ising universality at the critical end point of the first-order transition at nonzero temperatures transforms to the marginal quantum criticality when the critical temperature is suppressed to zero. The MQCP has a unique feature with a combined character of symmetry breaking and topological transitions. In the metal-insulator transitions, the theoretical results are supported by experimental indications for V2 - xCrxO3 and an organic conductor κ-(ET)2Cu[N(CN)2]Cl. Identifying topological transitions also reveals how non-Fermi liquid appears as a phase in metals. The theory also accounts for the criticality of a metamagnetic transition in ZrZn2, by interpreting it as an interplay of Lifshitz transition and correlation effects. We discuss the common underlying physics in these examples.

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

    NASA Astrophysics Data System (ADS)

    Wölfle, Peter; Abrahams, Elihu

    2015-10-01

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

  16. Field-controlled spin-density-wave order and quantum critically in Sr3 Ru2 O7

    NASA Astrophysics Data System (ADS)

    Hayden, Stephen

    The quasi-2D metamagnetic perovskite metal Sr3Ru2O7 has been an enigma for the last decade. The application of a large magnetic field of 8T parallel to the c-axis creates a new phase at low temperatures. This phase shows ``electronic nematic'' properties in that strong anisotropy its resistivity can be created by tilting the field away from the c-axis. In addition, measurement of transport and thermodynamic properties suggest that the phase is at the centre of a quantum critical region. Here we use neutron scattering to show that the magnetic field actually induces spin-density-wave magnetic order in the proximity of a metamagnetic critical endpoint. In fact, Sr3Ru2O7 can be tuned through two magnetically-ordered SDW states which exist over relatively small ranges in field (< 0.4 T). Their origin is probably due to the electronic fine structure near the Fermi energy. The magnetic field direction is shown to control the SDW domain populations which naturally explains the strong resistivity anisotropy or ''electronic nematic'' behaviour observed in this material. We find that Sr3Ru2O7 is also unique in that its the quantum critical region is controlled by overdamped incommensurate low-energy spin fluctuations with a diverging relaxation time. The low-energy electronic properties reflect the presence of these fluctuations and, in particular, the field-dependent low-temperature specific heat is proportional to the spin relaxation rate. [Based on C. Lester, S. Ramos, R. S. Perry at el. Natural Materials 14, 373 (2015).

  17. Ferromagnetic resonance in a single crystal of iron borate and magnetic field tuning of hybrid oscillations in a composite structure with a dielectric: Experiment and theory

    NASA Astrophysics Data System (ADS)

    Popov, M. A.; Zavislyak, I. V.; Chumak, H. L.; Strugatsky, M. B.; Yagupov, S. V.; Srinivasan, G.

    2015-07-01

    The high-frequency properties of a composite resonator comprised single crystal iron borate (FeBO3), a canted antiferromagnet with a weak ferromagnetic moment, and a polycrystalline dielectric were investigated at 9-10 GHz. Ferromagnetic resonance in this frequency range was observed in FeBO3 for bias magnetic fields of ˜250 Oe. In the composite resonator, the magnetic mode in iron borate and dielectric mode are found to hybridize strongly. It is shown that the hybrid mode can be tuned with a static magnetic field. Our studies indicate that coupling between the magnetic mode and the dielectric resonance can be altered from maximum hybridization to a minimum by adjusting the position of resonator inside the waveguide. Magnetic field tuning of the resonance frequency by a maximum of 145 MHz and a change in the transmitted microwave power by as much as 16 dB have been observed for a bias field of 250 Oe. A model is discussed for the magnetic field tuning of the composite resonator and theoretical estimates are in reasonable agreement with the data. The composite resonator with a weak ferromagnet and a dielectric is of interest for application in frequency agile devices with electronically tunable electrodynamic characteristics for the mm and sub-mm wave bands.

  18. Ferromagnetic resonance in a single crystal of iron borate and magnetic field tuning of hybrid oscillations in a composite structure with a dielectric: Experiment and theory

    SciTech Connect

    Popov, M. A.; Zavislyak, I. V.; Chumak, H. L.; Strugatsky, M. B.; Yagupov, S. V.; Srinivasan, G.

    2015-07-07

    The high-frequency properties of a composite resonator comprised single crystal iron borate (FeBO{sub 3}), a canted antiferromagnet with a weak ferromagnetic moment, and a polycrystalline dielectric were investigated at 9–10 GHz. Ferromagnetic resonance in this frequency range was observed in FeBO{sub 3} for bias magnetic fields of ∼250 Oe. In the composite resonator, the magnetic mode in iron borate and dielectric mode are found to hybridize strongly. It is shown that the hybrid mode can be tuned with a static magnetic field. Our studies indicate that coupling between the magnetic mode and the dielectric resonance can be altered from maximum hybridization to a minimum by adjusting the position of resonator inside the waveguide. Magnetic field tuning of the resonance frequency by a maximum of 145 MHz and a change in the transmitted microwave power by as much as 16 dB have been observed for a bias field of 250 Oe. A model is discussed for the magnetic field tuning of the composite resonator and theoretical estimates are in reasonable agreement with the data. The composite resonator with a weak ferromagnet and a dielectric is of interest for application in frequency agile devices with electronically tunable electrodynamic characteristics for the mm and sub-mm wave bands.

  19. Simultaneously optimizing fluorescent and paramagnetic properties of bifunctional NaGdF{sub 4}:Yb{sup 3+}/Er{sup 3+} nanocrystals by crystal field tuning

    SciTech Connect

    Wu, Xiaofeng; Hu, Shigang; Tan, Congbing; Liu, Yunxin

    2015-04-15

    Graphical abstract: Crystal field tuning is a powerful approach for simultaneously enhancing the optical and magnetic properties of lanthanide-doped NaGdF{sub 4} bi-functional nanocrystals. - Abstract: Here, we show the simultaneous enhancement of fluorescent and paramagnetic properties in bifunctional NaGdF{sub 4}:Yb{sup 3+}/Er{sup 3+} nanocrystals by crystal field tuning. The energy level splitting calculation indicates, that lanthanide ionic pairs La{sup 3+}/Lu{sup 3+} introduced into the NaGdF{sub 4} host can modify the crystal field around emitters (e.g., Er{sup 3+} and Tm{sup 3+}) and sensitizers (e.g., Yb{sup 3+}) that result in the broadening of crystal field splitting of energy levels and the abundant multi-site distribution of upconversion luminescence. The optimization of the paramagnetic properties in NaGdF{sub 4} doped with emitters and sensitizers is ascribed to the lowering of anti-ferromagnetic coupling.

  20. Ambient pressure structural quantum critical point in the phase diagram of (Ca(x)Sr(1-x))(3)Rh(4)Sn(13).

    PubMed

    Goh, S K; Tompsett, D A; Saines, P J; Chang, H C; Matsumoto, T; Imai, M; Yoshimura, K; Grosche, F M

    2015-03-01

    The quasiskutterudite superconductor Sr_{3}Rh_{4}Sn_{13} features a pronounced anomaly in electrical resistivity at T^{*}∼138  K. We show that the anomaly is caused by a second-order structural transition, which can be tuned to 0 K by applying physical pressure and chemical pressure via the substitution of Ca for Sr. A broad superconducting dome is centered around the structural quantum critical point. Detailed analysis of the tuning parameter dependence of T^{*} as well as insights from lattice dynamics calculations strongly support the existence of a structural quantum critical point at ambient pressure when the fraction of Ca is 0.9 (i.e., x_{c}=0.9). This establishes the (Ca_{x}Sr_{1-x})_{3}Rh_{4}Sn_{13} series as an important system for exploring the physics of structural quantum criticality without the need of applying high pressures. PMID:25793843

  1. Magnetocaloric effects, quantum critical points, and the Berezinsky-Kosterlitz-Thouless transition in two-dimensional coupled spin-dimer systems

    NASA Astrophysics Data System (ADS)

    Straßel, Dominik; Kopietz, Peter; Eggert, Sebastian

    2015-04-01

    Spin-dimer systems are a versatile playground for the detailed study of quantum phase transitions. Using the magnetic field as the tuning parameter, it is possible to observe a crossover from the characteristic scaling near critical points to the behavior of a finite-temperature phase transition. In this work we study two-dimensional coupled spin-dimer systems by comparing numerical quantum Monte Carlo simulations with analytical calculations of the susceptibility, the magnetocaloric effect, and the helicity modulus. The magnetocaloric behavior of the magnetization with temperature can be used to determine the critical fields with high accuracy, but the critical scaling does not show the expected logarithmic corrections. The zeros of the cooling rate are an excellent indicator of the competition between quantum criticality and vortex physics, but they are not directly associated with the quantum phase transition or the finite-temperature Berezinsky-Kosterlitz-Thouless transition. The results give a unified picture of the full quantum and finite-temperature phase diagram.

  2. Stability of a spin-triplet nematic state near to a quantum critical point

    NASA Astrophysics Data System (ADS)

    Hannappel, G.; Pedder, C. J.; Krüger, F.; Green, A. G.

    2016-06-01

    We analyze a model of itinerant electrons interacting through a quadrupole density-density repulsion in three dimensions. At the mean-field level, the interaction drives a continuous Pomeranchuk instability towards d -wave, spin-triplet nematic order, which simultaneously breaks the SU(2) spin-rotation and spatial-rotation symmetries. This order is characterized by spin-antisymmetric, elliptical deformations of the Fermi surfaces of up and down spins. We show that the effects of quantum fluctuations are similar to those in metallic ferromagnets, rendering the nematic transition first order at low temperatures. Using the fermionic quantum order-by-disorder approach to self-consistently calculate fluctuations around possible modulated states, we show that the first-order transition is preempted by the formation of a helical spin-triplet d -density wave. Such a state is closely related to d -wave bond density wave order in square-lattice systems. Moreover, we show that it may coexist with a modulated, p -wave superconducting state.

  3. Critical velocity of a mobile impurity in one-dimensional quantum liquids.

    PubMed

    Schecter, M; Kamenev, A; Gangardt, D M; Lamacraft, A

    2012-05-18

    We study the notion of superfluid critical velocity in one spatial dimension. It is shown that, for heavy impurities with mass M exceeding a critical mass Mc, the dispersion develops periodic metastable branches resulting in dramatic changes of dynamics in the presence of an external driving force. In contrast to smooth Bloch oscillations for M

  4. Non-Fermi liquid behavior with and without quantum criticality in Ce1-xYbxCoIn5

    NASA Astrophysics Data System (ADS)

    Singh, Y. P.; Hu, T.; Shu, L.; Janoschek, M.; Dzero, M.; Maple, M. B.; Almasan, C. C.

    2013-03-01

    In a growing number of f-electron systems the non-Fermi liquid (NFL) behavior occurs in the absence of an obvious quantum phase transition (QPT), which takes place at a quantum critical point (QCP). An intriguing candidate is Ce1-xYbxCoIn5 that exhibits an unconventional T - x phase diagram without an apparent QCP. Therefore, it is important to elucidate the nature of the NFL behavior and to search for possible QCPs in this system Here we reveal a field induced QCP (HQCP) through normal state magneto-resistivity measurements and find its evolution with x. The full suppression of HQCP for x > 0.2 has surprisingly little effect on the Kondo lattice coherence. At low Yb concentrations, resistivity consists of two contributions with linear and sub-linear temperature dependences, while at higher concentrations only the sub-linear term is present. These results imply that the NFL behavior could be a new state of matter in its own right rather than a consequence of the underlying QPT. This work was supported by NSF (DMR-1006606 and DMR- 0844115), ICAM Branches Cost Sharing Fund from Institute for Complex Adaptive Matter, and Ohio Board of Regents (Grant OBR-RIP-220573) at KSU, and DOE (DE-FG02-04ER46105) at UCSD.

  5. Heat capacity peak at the quantum critical point of the transverse Ising magnet CoNb2O6

    PubMed Central

    Liang, Tian; Koohpayeh, S. M.; Krizan, J. W.; McQueen, T. M.; Cava, R. J.; Ong, N. P.

    2015-01-01

    The transverse Ising magnet Hamiltonian describing the Ising chain in a transverse magnetic field is the archetypal example of a system that undergoes a transition at a quantum critical point (QCP). The columbite CoNb2O6 is the closest realization of the transverse Ising magnet found to date. At low temperatures, neutron diffraction has observed a set of discrete collective spin modes near the QCP. Here, we ask if there are low-lying spin excitations distinct from these relatively high-energy modes. Using the heat capacity, we show that a significant band of gapless spin excitations exists. At the QCP, their spin entropy rises to a prominent peak that accounts for 30% of the total spin degrees of freedom. In a narrow field interval below the QCP, the gapless excitations display a fermion-like, temperature-linear heat capacity below 1 K. These novel gapless modes are the main spin excitations participating in, and affected by, the quantum transition. PMID:26146018

  6. Crystal growth by Bridgman and Czochralski method of the ferromagnetic quantum critical material YbNi4P2

    NASA Astrophysics Data System (ADS)

    Kliemt, K.; Krellner, C.

    2016-09-01

    The tetragonal YbNi4P2 is one of the rare examples of compounds that allow the investigation of a ferromagnetic quantum critical point. We report in detail on two different methods which have been used to grow YbNi4P2 single crystals from a self-flux. The first, a modified Bridgman method, using a closed crucible system yields needle-shaped single crystals oriented along the [001]-direction. The second method, the Czochralski growth from a levitating melt, yields large single crystals which can be cut in any desired orientation. With this crucible-free method, samples without flux inclusions and a resistivity ratio at 1.8 K of RR1.8K = 17 have been grown.

  7. Electric-field tuning of the surface band structure of topological insulator Sb2Te3 thin films.

    PubMed

    Zhang, Tong; Ha, Jeonghoon; Levy, Niv; Kuk, Young; Stroscio, Joseph

    2013-08-01

    We measured the response of the surface state spectrum of epitaxial Sb(2)Te(3) thin films to applied gate electric fields by low temperature scanning tunneling microscopy. The gate dependent shift of the Fermi level and the screening effect from bulk carriers vary as a function of film thickness. We observed a gap opening at the Dirac point for films thinner than four quintuple layers, due to the coupling of the top and bottom surfaces. Moreover, the top surface state band gap of the three quintuple layer films was found to be tunable by a back gate, indicating the possibility of observing a topological phase transition in this system. Our results are well explained by an effective model of 3D topological insulator thin films with structure inversion asymmetry, indicating that three quintuple layer Sb(2)Te(3) films are topologically nontrivial and belong to the quantum spin Hall insulator class.

  8. Critical Examination of Incoherent Operations and a Physically Consistent Resource Theory of Quantum Coherence

    NASA Astrophysics Data System (ADS)

    Chitambar, Eric; Gour, Gilad

    2016-07-01

    Considerable work has recently been directed toward developing resource theories of quantum coherence. In this Letter, we establish a criterion of physical consistency for any resource theory. This criterion requires that all free operations in a given resource theory be implementable by a unitary evolution and projective measurement that are both free operations in an extended resource theory. We show that all currently proposed basis-dependent theories of coherence fail to satisfy this criterion. We further characterize the physically consistent resource theory of coherence and find its operational power to be quite limited. After relaxing the condition of physical consistency, we introduce the class of dephasing-covariant incoherent operations as a natural generalization of the physically consistent operations. Necessary and sufficient conditions are derived for the convertibility of qubit states using dephasing-covariant operations, and we show that these conditions also hold for other well-known classes of incoherent operations.

  9. Cooling through quantum criticality and many-body effects in condensed matter and cold gases

    NASA Astrophysics Data System (ADS)

    Wolf, Bernd; Honecker, Andreas; Hofstetter, Walter; Tutsch, Ulrich; Lang, Michael

    2014-10-01

    This article reviews some recent developments for new cooling technologies in the fields of condensed matter physics and cold gases, both from an experimental and theoretical point of view. The main idea is to make use of distinct many-body interactions of the system to be cooled which can be some cooling stage or the material of interest itself, as is the case in ultracold gases. For condensed matter systems, we discuss magnetic cooling schemes based on a large magnetocaloric effect as a result of a nearby quantum phase transition and consider effects of geometrical frustration. For ultracold gases, we review many-body cooling techniques, such as spin-gradient and Pomeranchuk cooling, which can be applied in the presence of an optical lattice. We compare the cooling performance of these new techniques with that of conventional approaches and discuss state-of-the-art applications.

  10. Critical issues in the formation of quantum computer test structures by ion implantation

    SciTech Connect

    Schenkel, T.; Lo, C. C.; Weis, C. D.; Schuh, A.; Persaud, A.; Bokor, J.

    2009-04-06

    The formation of quantum computer test structures in silicon by ion implantation enables the characterization of spin readout mechanisms with ensembles of dopant atoms and the development of single atom devices. We briefly review recent results in the characterization of spin dependent transport and single ion doping and then discuss the diffusion and segregation behaviour of phosphorus, antimony and bismuth ions from low fluence, low energy implantations as characterized through depth profiling by secondary ion mass spectrometry (SIMS). Both phosphorus and bismuth are found to segregate to the SiO2/Si interface during activation anneals, while antimony diffusion is found to be minimal. An effect of the ion charge state on the range of antimony ions, 121Sb25+, in SiO2/Si is also discussed.

  11. Critical issues in the formation of quantum computer test structures by ion implantation

    NASA Astrophysics Data System (ADS)

    Schenkel, T.; Lo, C. C.; Weis, C. D.; Schuh, A.; Persaud, A.; Bokor, J.

    2009-08-01

    The formation of quantum computer test structures in silicon by ion implantation enables the characterization of spin readout mechanisms with ensembles of dopant atoms and the development of single atom devices. We briefly review recent results in the characterization of spin dependent transport and single ion doping and then discuss the diffusion and segregation behaviour of phosphorus, antimony and bismuth ions from low fluence, low energy implantations as characterized through depth profiling by secondary ion mass spectrometry (SIMS). Both phosphorus and bismuth are found to segregate to the SiO 2/Si interface during activation anneals, while antimony diffusion is found to be minimal. An effect of the ion charge state on the range of antimony ions, 121Sb 25+, in SiO 2/Si is also discussed.

  12. Critical Examination of Incoherent Operations and a Physically Consistent Resource Theory of Quantum Coherence.

    PubMed

    Chitambar, Eric; Gour, Gilad

    2016-07-15

    Considerable work has recently been directed toward developing resource theories of quantum coherence. In this Letter, we establish a criterion of physical consistency for any resource theory. This criterion requires that all free operations in a given resource theory be implementable by a unitary evolution and projective measurement that are both free operations in an extended resource theory. We show that all currently proposed basis-dependent theories of coherence fail to satisfy this criterion. We further characterize the physically consistent resource theory of coherence and find its operational power to be quite limited. After relaxing the condition of physical consistency, we introduce the class of dephasing-covariant incoherent operations as a natural generalization of the physically consistent operations. Necessary and sufficient conditions are derived for the convertibility of qubit states using dephasing-covariant operations, and we show that these conditions also hold for other well-known classes of incoherent operations.

  13. Real-time dynamics induced by quenches across the quantum critical points in gapless Fermi systems with a magnetic impurity

    NASA Astrophysics Data System (ADS)

    Kleine, Christian; Mußhoff, Julian; Anders, Frithjof B.

    2014-12-01

    The energy-dependent scattering of fermions from a localized orbital at an energy-dependent rate Γ (ɛ ) ∝|ɛ| r gives rise to quantum critical points (QCPs) in the pseudogap single-impurity Anderson model separating a local moment phase with an unscreened spin moment from a strong-coupling phase which slightly deviates from the screened phase of standard Kondo problem. Using the time-dependent numerical renormalization group (TD-NRG) approach we show that local dynamic properties always equilibrate towards a steady-state value even for quenches across the QCP but with systematic deviations from the thermal equilibrium depending on the distance to the critical coupling. Local nonequilibrium properties are presented for interaction quenches and hybridization quenches. We augment our numerical data by an analytical calculation that becomes exact at short times and find excellent agreement between the numerics and the analytical theory. For interaction quenches within the screened phase we find a universal function for the time-dependent local double occupancy. We trace back the discrepancy between our results and the data obtained by a time-dependent Gutzwiller variational approach to restrictions of the wave-function ansatz in the Gutzwiller theory: while the NRG ground states properly account for the formation of an extended spin moment which decouples from the system in the unscreened phase, the Gutzwiller ansatz only allows the formation of the spin moment on the local impurity orbital.

  14. About the physical meaning of the critical temperature for catastrophic optical damage in high power quantum well laser diodes

    NASA Astrophysics Data System (ADS)

    Souto, J.; Pura, J. L.; Jiménez, J.

    2016-02-01

    It is usually assumed that the catastrophic optical damage of high power laser diodes is launched when a critical local temperature (T c) is reached; temperatures ranging from 120 °C to 200 °C were experimentally reported. However, the physical meaning of T c in the degradation process is still unclear. In this work we show that, in the presence of a local heat source in the active region, the temperature of the laser structure, calculated using finite element methods, is widely inhomogeneously distributed among the different layers forming the device. This is due to the impact that the low dimensionality and the thermal boundary resistances have on the thermal transport across the laser structure. When these key factors are explicitly considered, the quantum well (QW) temperature can be several hundred degrees higher than the temperature of the guides and cladding layers. Due to the size of the experimental probes, the measured critical temperature is a weighted average over the QW, guides, and claddings. We show the existence of a large difference between the calculated average temperature, equivalent to the experimentally measured temperature, and the peak temperature localized in the QW. A parallel study on double heterostructure lasers is also included for comparison.

  15. Strong enhancement of s -wave superconductivity near a quantum critical point of Ca3Ir4Sn13

    NASA Astrophysics Data System (ADS)

    Biswas, P. K.; Guguchia, Z.; Khasanov, R.; Chinotti, M.; Li, L.; Wang, Kefeng; Petrovic, C.; Morenzoni, E.

    2015-11-01

    We report microscopic studies by muon spin rotation/relaxation as a function of pressure of the Ca3Ir4Sn13 and Sr3Ir4Sn13 cubic compounds, which are members of the (Ca1-xSrx)3Ir4Sn13 system displaying superconductivity and a structural phase transition associated with the formation of a charge density wave (CDW). We find a strong enhancement of the superfluid density and a dramatic increase of the pairing strength above a pressure of ≈1.6 GPa, giving direct evidence of the presence of a quantum critical point separating a superconducting phase coexisting with CDW from a pure superconducting phase. The superconducting order parameter in both phases has the same s -wave symmetry. In spite of the conventional phonon-mediated BCS character of the weakly correlated (Ca1-xSrx)3Ir4Sn13 system, the dependence of the effective superfluid density on the critical temperature puts this compound in the "Uemura" plot close to unconventional superconductors. This system exemplifies that conventional BCS superconductors in the presence of competing orders or multiband structure can also display characteristics of unconventional superconductors.

  16. The Hilbert-glass transitions: new universality of temperature-tuned many-body dynamical quantum criticality

    NASA Astrophysics Data System (ADS)

    Pekker, David; Refael, Gil; Altman, Ehud; Demler, Eugene; Oganesyan, Vadim

    2014-03-01

    We study a new class of unconventional critical phenomena that is characterized by singularities only in dynamical quantities and has no thermodynamic signatures. Describing this purely dynamical quantum criticality is technically challenging as understanding the finite-temperature dynamics necessarily requires averaging over a large number of matrix elements between many-body eigenstates. Here we develop a real-space renormalization group method for excited state (RSRG-X) that allows us to overcome this challenge in a large class of models. We characterize a specific example: the 1D disordered transverse field Ising model with generic interactions. While thermodynamic phase transitions are generally forbidden in this model, using RSRG-X we find a finite-temperature dynamical transition between two localized phases. The transition is characterized by non-analyticities in the low frequency heat conductivity and in the long-time (dynamic) spin correlation function. The latter is a consequence of an up-down spin symmetry that results in the appearance of an Edwards-Anderson-like order parameter in one of the localized phases.

  17. RSOS quantum chains associated with off-critical minimal models and {\\boldsymbol{{Z}}}_{{{\\tssabi n}}} parafermions

    NASA Astrophysics Data System (ADS)

    Bianchini, Davide; Ercolessi, Elisa; Pearce, Paul A.; Ravanini, Francesco

    2015-03-01

    We consider the φ1,3 off-critical perturbation {M}(m,m\\prime;t) of the general non-unitary minimal models where 2 ⩽ m ⩽ m‧ and m, m‧ are coprime and t measures the departure from criticality corresponding to the φ1,3 integrable perturbation. We view these models as the continuum scaling limit in the ferromagnetic Regime III of the Forrester-Baxter Restricted Solid-On-Solid (RSOS) models on the square lattice. We also consider the RSOS models in the antiferromagnetic Regime II related in the continuum scaling limit to {Z}n parfermions with n = m‧ - 2. Using an elliptic Yang-Baxter algebra of planar tiles encoding the allowed face configurations, we obtain the Hamiltonians of the associated quantum chains defined as the logarithmic derivative of the transfer matrices with periodic boundary conditions. The transfer matrices and Hamiltonians act on a vector space of paths on the Am‧-1 Dynkin diagram whose dimension is counted by generalized Fibonacci numbers.

  18. Strong enhancement of s -wave superconductivity near a quantum critical point of Ca3Ir4Sn13

    DOE PAGESBeta

    Biswas, P. K.; Guguchia, Z.; Khasanov, R.; Chinotti, M.; Li, L.; Wang, Kefeng; Petrovic, C.; Morenzoni, E.

    2015-11-11

    We repormore » t microscopic studies by muon spin rotation/relaxation as a function of pressure of the Ca3Ir4Sn13 and Sr3Ir4Sn13 system displaying superconductivity and a structural phase transition associated with the formation of a charge density wave (CDW). Our findings show a strong enhancement of the superfluid density and a dramatic increase of the pairing strength above a pressure of ≈ 1.6 GPa giving direct evidence of the presence of a quantum critical point separating a superconducting phase coexisting with CDW from a pure superconducting phase. The superconducting order parameter in both phases has the same s-wave symmetry. In spite of the conventional phonon-mediated BCS character of the weakly correlated (Ca1-xSrx)3Ir4Sn13 system the dependence of the effective superfluid density on the critical temperature puts this compound in the “Uemura” plot close to unconventional superconductors. This system exemplifies that conventional BCS superconductors in the presence of competing orders or multi-band structure can also display characteristics of unconventional superconductors.« less

  19. Nonadiabatic analysis of the Josephson critical current influenced by quantum phase fluctuations

    SciTech Connect

    Geigenmueller, U. ); Ueda, M. Nippon Telegraph and Telephone Basic Research Laboratories, Morinosato Wakamiya, Atsugi, Kanagawa 342-01 )

    1994-10-01

    The influence of the electromagnetic environment on the dc Josephson current is studied allowing for nonadiabatic motion of the phase difference across a junction. The critical current is evaluated nonperturbatively within mean-field theory, fully taking into account the nonlocal kernels in the Ambegaokar-Eckern-Schoen effective action. It turns out that the adiabatic approximation, which can be justified when the superconducting energy gap exceeds the charging energy, yields [ital qualitatively] correct results even for the opposite case, although [ital quantitative] deviations from the adiabatic approximation are found to be substantial in some experimentally accessible regions.

  20. Pressure-tuned quantum criticality in the antiferromagnetic Kondo semimetal CeNi2–δAs2

    SciTech Connect

    Luo, Yongkang; Ronning, F.; Wakeham, N.; Lu, Xin; Park, Tuson; Xu, Z. -A.; Thompson, J. D.

    2015-10-19

    The easily tuned balance among competing interactions in Kondo-lattice metals allows access to a zero-temperature, continuous transition between magnetically ordered and disordered phases, a quantum-critical point (QCP). Indeed, these highly correlated electron materials are prototypes for discovering and exploring quantum-critical states. Theoretical models proposed to account for the strange thermodynamic and electrical transport properties that emerge around the QCP of a Kondo lattice assume the presence of an indefinitely large number of itinerant charge carriers. Here, we report a systematic transport and thermodynamic investigation of the Kondo-lattice system CeNi2–δAs2 (δ ≈ 0.28) as its antiferromagnetic order is tuned by pressure and magnetic field to zero-temperature boundaries. These experiments show that the very small but finite carrier density of ~0.032 e/formular unit in CeNi2–δAs2 leads to unexpected transport signatures of quantum criticality and the delayed development of a fully coherent Kondo-lattice state with decreasing temperature. Here, the small carrier density and associated semimetallicity of this Kondo-lattice material favor an unconventional, local-moment type of quantum criticality and raises the specter of the Nozières exhaustion idea that an insufficient number of conduction-electron spins to separately screen local moments requires collective Kondo screening.

  1. Ghost spins and quantum critical behavior in a spin chain with local bond deformation

    NASA Astrophysics Data System (ADS)

    Dai, Jianhui; Wang, Yupeng; Eckern, U.

    1999-09-01

    We study the impurity-induced critical behavior in an integrable SU(2)-invariant model consisting of an open spin chain of arbitrary spin S (Takhatajian-Babujian model) interacting with an impurity of spin S-->' located at one of the boundaries. For S=1/2 or S'=1/2, the impurity interaction takes a very simple form JS-->1.S-->' that describes the deformed boundary bond between the impurity S-->' and the first bulk spin S-->1 with an arbitrary coupling strength J. For a weak coupling 0S, and S'=J0/[(S+S')2-1/4], the impurity spin is split into two ghost spins. Their cooperative effect leads to a variety of new critical behaviors with different values of \\|S'-S\\|.

  2. Quantum criticality in the ferromagnetic superconductor UCoGe under pressure and magnetic field

    NASA Astrophysics Data System (ADS)

    Bastien, Gaël; Braithwaite, Daniel; Aoki, Dai; Knebel, Georg; Flouquet, Jacques

    2016-09-01

    The pressure-temperature phase diagram of the orthorhombic ferromagnetic superconductor UCoGe was determined by resistivity measurements up to 10.5 GPa . The Curie temperature TC is suppressed with pressure and vanishes at the critical pressure pc≈1 GPa . Superconductivity is observed in both the ferromagnetic state at low pressure, and in the paramagnetic state above pc up to about 4 GPa . Non-Fermi-liquid behavior appears in a large pressure range. The resistivity varies linearly with temperature around pc and evolves continuously with pressure to a T2 Fermi-liquid behavior for p ⪆5 GPa. The residual resistivity as a function of pressure shows a maximum far above pc at p=7.2 GPa and the amplitude of the inelastic scattering term of the resistivity decreases by more than one order in magnitude at p, which appears to mark the entrance into a weakly correlated regime. The pressure dependence of the upper critical field for magnetic field applied along the b and c axis illustrates the drastic difference in the field dependence of the ferromagnetic superconducting pairing. While for H ∥b axis Hc 2(T ) is driven by the suppression of the ferromagnetic order, it is dominated by the strong initial suppression of the ferromagnetic fluctuations for a field applied in the easy magnetization axis c .

  3. Growth of etiolated barley plants in weak static and 50 Hz electromagnetic fields tuned to calcium ion cyclotron resonance

    PubMed Central

    Pazur, Alexander; Rassadina, Valentina; Dandler, Jörg; Zoller, Jutta

    2006-01-01

    retardation of the originally Ca2+-ICR exposed plants compared to control cultures lasting several weeks, with an increased tendency for dehydration. Conclusion A direct influence of the applied MF and EMF is discussed affecting Ca2+ levels via the ICR mechanism. It influences the available Ca2+ and thereby regulatory processes. Theoretical considerations on molecular level focus on ionic interactions with water related to models using quantum electrodynamics. PMID:16457719

  4. Multiband nodeless superconductivity near the charge-density-wave quantum critical point in ZrTe3-x Se x

    NASA Astrophysics Data System (ADS)

    Shan, Cui; Lan-Po, He; Xiao-Chen, Hong; Xiang-De, Zhu; Cedomir, Petrovic; Shi-Yan, Li

    2016-07-01

    It was found that selenium doping can suppress the charge-density-wave (CDW) order and induce bulk superconductivity in ZrTe3. The observed superconducting dome suggests the existence of a CDW quantum critical point (QCP) in ZrTe3-x Se x near x ≈ 0.04. To elucidate the superconducting state near the CDW QCP, we measure the thermal conductivity of two ZrTe3-x Se x single crystals (x = 0.044 and 0.051) down to 80 mK. For both samples, the residual linear term κ 0/T at zero field is negligible, which is a clear evidence for nodeless superconducting gap. Furthermore, the field dependence of κ 0/T manifests a multigap behavior. These results demonstrate multiple nodeless superconducting gaps in ZrTe3-x Se x , which indicates conventional superconductivity despite of the existence of a CDW QCP. Project supported by the National Basic Research Program of China (Grant Nos. 2012CB821402 and 2015CB921401), the National Natural Science Foundation of China (Grant Nos. 91421101, 11422429, and 11204312), the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning, China, and STCSM of China (Grant No. 15XD1500200). Work at Brookhaven National Laboratory was supported by the US DOE under Contract No. DESC00112704.

  5. Emergent Non-Fermi-Liquid at the Quantum Critical Point of a Topological Phase Transition in Two Dimensions.

    PubMed

    Isobe, Hiroki; Yang, Bohm-Jung; Chubukov, Andrey; Schmalian, Jörg; Nagaosa, Naoto

    2016-02-19

    We study the effects of Coulomb interaction between 2D Weyl fermions with anisotropic dispersion which displays relativistic dynamics along one direction and nonrelativistic dynamics along the other. Such a dispersion can be realized in phosphorene under electric field or strain, in TiO_{2}/VO_{2} superlattices, and, more generally, at the quantum critical point between a nodal semimetal and an insulator in systems with a chiral symmetry. Using the one-loop renormalization group approach in combination with the large-N expansion, we find that the system displays interaction-driven non-Fermi liquid behavior in a wide range of intermediate frequencies and marginal Fermi liquid behavior at the smallest frequencies. In the non-Fermi liquid regime, the quasiparticle residue Z at energy E scales as Z∝E^{a} with a>0, and the parameters of the fermionic dispersion acquire anomalous dimensions. In the marginal Fermi-liquid regime, Z∝(|logE|)^{-b} with universal b=3/2. PMID:26943551

  6. Spin dynamics near a putative antiferromagnetic quantum critical point in Cu-substituted BaFe2As2 and its relation to high-temperature superconductivity

    NASA Astrophysics Data System (ADS)

    Kim, M. G.; Wang, M.; Tucker, G. S.; Valdivia, P. N.; Abernathy, D. L.; Chi, Songxue; Christianson, A. D.; Aczel, A. A.; Hong, T.; Heitmann, T. W.; Ran, S.; Canfield, P. C.; Bourret-Courchesne, E. D.; Kreyssig, A.; Lee, D. H.; Goldman, A. I.; McQueeney, R. J.; Birgeneau, R. J.

    2015-12-01

    We present the results of elastic and inelastic neutron scattering measurements on nonsuperconducting Ba (Fe 0.957Cu 0.043) 2As 2 , a composition close to a quantum critical point between antiferromagnetic (AFM) ordered and paramagnetic phases. By comparing these results with the spin fluctuations in the low-Cu composition as well as the parent compound BaFe2As2 and superconducting Ba (Fe1-xNix) 2As2 compounds, we demonstrate that paramagnon-like spin fluctuations are evident in the antiferromagnetically ordered state of Ba (Fe0.957Cu0.043)2As2 , which is distinct from the AFM-like spin fluctuations in the superconducting compounds. Our observations suggest that Cu substitution decouples the interaction between quasiparticles and the spin fluctuations. We also show that the spin-spin correlation length ξ (T ) increases rapidly as the temperature is lowered and find ω /T scaling behavior, the hallmark of quantum criticality, at an antiferromagnetic quantum critical point.

  7. Ambient Pressure Structural Quantum Critical Point in the Phase Diagram of (CaxSr1-x)3Rh4Sn13

    NASA Astrophysics Data System (ADS)

    Goh, Swee K.; Tompsett, D. A.; Saines, P. J.; Chang, H. C.; Matsumoto, T.; Imai, M.; Yoshimura, K.; Grosche, F. M.

    The quasiskutterudite superconductor Sr3Rh4Sn13 features a pronounced anomaly in electrical resistivity at T* ~ 138 K. The anomaly is caused by a second-order structural transition, which can be tuned to 0 K by applying physical pressure and chemical pressure via the substitution of Ca for Sr. A broad superconducting dome is centered around the structural quantum critical point. Detailed analysis of the tuning parameter dependence of T* as well as insights from lattice dynamics calculations strongly support the existence of a structural quantum critical point at ambient pressure when the fraction of Ca is 0.9 (xc=0.9). This establishes the (CaxSr1-x)3Rh4Sn13 series as an important system for exploring the physics of structural quantum criticality and its interplay with the superconductivity, without the need of applying high pressures. This work was supported by CUHK (Startup Grant, Direct Grant No. 4053071), UGC Hong Kong (ECS/24300214), Trinity College (Cam- bridge), Grants-in-Aid from MEXT (No. 22350029 and 23550152) and Glasstone Bequest (Oxford).

  8. Strong Coupling Superconductivity in the Vicinity of the Structural Quantum Critical Point in (CaxSr1-x)3Rh4Sn13

    NASA Astrophysics Data System (ADS)

    Yu, Wing Chi; Cheung, Yiu Wing; Saines, Paul J.; Imai, Masaki; Matsumoto, Takuya; Michioka, Chishiro; Yoshimura, Kazuyoshi; Goh, Swee K.

    The family of the superconducting quasiskutterudites (CaxSr1-x)3Rh4Sn13 features a structural quantum critical point at xc = 0 . 9 , around which a dome-shaped variation of the superconducting transition temperature Tc is found. In this talk, we present the specific heat data for the normal and the superconducting states of the entire series straddling the quantum critical point. Our analysis indicates a significant lowering of the effective Debye temperature on approaching xc, which we interpret as a result of phonon softening accompanying the structural instability. Furthermore, a remarkably large enhancement of 2 Δ /kBTc and ΔC / γTc beyond the Bardeen-Cooper-Schrieffer values is found in the vicinity of the structural quantum critical point. Reference: Wing Chi Yu et al. Phys. Rev. Lett. (in press, 2015) This work was supported by the CUHK (Startup Grant, Direct Grant No. 4053071), UGC Hong Kong (ECS/24300214), Grants-in-Aid from MEXT (22350029 and 23550152), and Glasstone Bequest, Oxford.

  9. Spin dynamics near a putative antiferromagnetic quantum critical point in Cu-substituted BaFe2As2 and its relation to high-temperature superconductivity

    DOE PAGESBeta

    Kim, M. G.; Wang, M.; Tucker, G. S.; Valdivia, P. N.; Abernathy, D. L.; Chi, Songxue; Christianson, A. D.; Aczel, A. A.; Hong, T.; Heitmann, T. W.; et al

    2015-12-02

    We present the results of elastic and inelastic neutron scattering measurements on nonsuperconducting Ba(Fe0.957Cu0.043)2As2, a composition close to a quantum critical point between antiferromagnetic (AFM) ordered and paramagnetic phases. By comparing these results with the spin fluctuations in the low-Cu composition as well as the parent compound BaFe2As2 and superconducting Ba(Fe1–xNix)2As2 compounds, we demonstrate that paramagnon-like spin fluctuations are evident in the antiferromagnetically ordered state of Ba(Fe0.957Cu0.043)2As2, which is distinct from the AFM-like spin fluctuations in the superconducting compounds. Our observations suggest that Cu substitution decouples the interaction between quasiparticles and the spin fluctuations. In addition, we show that themore » spin-spin correlation length ξ(T) increases rapidly as the temperature is lowered and find ω/T scaling behavior, the hallmark of quantum criticality, at an antiferromagnetic quantum critical point.« less

  10. Frustrated Quantum Critical Theory of Putative Spin-Liquid Phenomenology in 6H-B-Ba3NiSb2O9

    NASA Astrophysics Data System (ADS)

    Chen, G.; Hermele, M.; Radzihovsky, L.

    2012-07-01

    A recently discovered material, 6H-B-Ba3NiSb2O9 was found to display unusual low-temperature phenomenology, interpreted as a quantum spin liquid with spin S=1 on a triangular lattice. We study a spin S=1 exchange model on an AB stacked triangular lattice near its quantum paramagnet-to-spiral transition, driven by easy-plane single-ion anisotropy. We demonstrate that the frustrated inter- and intralayer exchanges induce contour lines of low-energy excitations that lead to a broad crossover regime of linear-temperature dependence of the specific heat. Based on this and various other predictions, we argue that the observed phenomenology can be understood in terms of a conventional picture of a proximity to this frustrated critical point.

  11. Frustrated quantum critical theory of putative spin-liquid phenomenology in 6H-B-Ba(3)NiSb(2)O(9).

    PubMed

    Chen, G; Hermele, M; Radzihovsky, L

    2012-07-01

    A recently discovered material, 6H-B-Ba(3)NiSb(2)O(9) was found to display unusual low-temperature phenomenology, interpreted as a quantum spin liquid with spin S=1 on a triangular lattice. We study a spin S=1 exchange model on an AB stacked triangular lattice near its quantum paramagnet-to-spiral transition, driven by easy-plane single-ion anisotropy. We demonstrate that the frustrated inter- and intralayer exchanges induce contour lines of low-energy excitations that lead to a broad crossover regime of linear-temperature dependence of the specific heat. Based on this and various other predictions, we argue that the observed phenomenology can be understood in terms of a conventional picture of a proximity to this frustrated critical point. PMID:23031118

  12. Parameter Tuning Patterns for Random Graph Coloring with Quantum Annealing

    PubMed Central

    Titiloye, Olawale; Crispin, Alan

    2012-01-01

    Quantum annealing is a combinatorial optimization technique inspired by quantum mechanics. Here we show that a spin model for the k-coloring of large dense random graphs can be field tuned so that its acceptance ratio diverges during Monte Carlo quantum annealing, until a ground state is reached. We also find that simulations exhibiting such a diverging acceptance ratio are generally more effective than those tuned to the more conventional pattern of a declining and/or stagnating acceptance ratio. This observation facilitates the discovery of solutions to several well-known benchmark k-coloring instances, some of which have been open for almost two decades. PMID:23166818

  13. Quantum criticality of a spin-1 XY model with easy-plane single-ion anisotropy via a two-time Green function approach avoiding the Anderson-Callen decoupling

    NASA Astrophysics Data System (ADS)

    Mercaldo, M. T.; Rabuffo, I.; De Cesare, L.; Caramico D'Auria, A.

    2016-04-01

    In this work we study the quantum phase transition, the phase diagram and the quantum criticality induced by the easy-plane single-ion anisotropy in a d-dimensional quantum spin-1 XY model in absence of an external longitudinal magnetic field. We employ the two-time Green function method by avoiding the Anderson-Callen decoupling of spin operators at the same sites which is of doubtful accuracy. Following the original Devlin procedure we treat exactly the higher order single-site anisotropy Green functions and use Tyablikov-like decouplings for the exchange higher order ones. The related self-consistent equations appear suitable for an analysis of the thermodynamic properties at and around second order phase transition points. Remarkably, the equivalence between the microscopic spin model and the continuous O(2) -vector model with transverse-Ising model (TIM)-like dynamics, characterized by a dynamic critical exponent z=1, emerges at low temperatures close to the quantum critical point with the single-ion anisotropy parameter D as the non-thermal control parameter. The zero-temperature critic anisotropy parameter Dc is obtained for dimensionalities d > 1 as a function of the microscopic exchange coupling parameter and the related numerical data for different lattices are found to be in reasonable agreement with those obtained by means of alternative analytical and numerical methods. For d > 2, and in particular for d=3, we determine the finite-temperature critical line ending in the quantum critical point and the related TIM-like shift exponent, consistently with recent renormalization group predictions. The main crossover lines between different asymptotic regimes around the quantum critical point are also estimated providing a global phase diagram and a quantum criticality very similar to the conventional ones.

  14. Critical-Point Boundary for the Nuclear Quantum Phase Transition Near A=100 from Mass Measurements of {sup 96,97}Kr

    SciTech Connect

    Naimi, S.; Audi, G.; Lunney, D.; Beck, D.; Herfurth, F.; Blaum, K.; Boehm, Ch.; Borgmann, Ch.; George, S.; Kowalska, M.; Kreim, S.; Breitenfeldt, M.; Rosenbusch, M.; Schweikhard, L.; Herlert, A.; Neidherr, D.; Schwarz, S.; Zuber, K.

    2010-07-16

    Mass measurements of {sup 96,97}Kr using the ISOLTRAP Penning-trap spectrometer at CERN-ISOLDE are reported, extending the mass surface beyond N=60 for Z=36. These new results show behavior in sharp contrast to the heavier neighbors where a sudden and intense deformation is present. We interpret this as the establishment of a nuclear quantum phase transition critical-point boundary. The new masses confirm findings from nuclear mean-square charge-radius measurements up to N=60 but are at variance with conclusions from recent gamma-ray spectroscopy.

  15. Switching of the magnetic order in CeRhIn5-xSnx in the vicinity of its quantum critical point

    NASA Astrophysics Data System (ADS)

    Raymond, S.; Buhot, J.; Ressouche, E.; Bourdarot, F.; Knebel, G.; Lapertot, G.

    2014-07-01

    We report neutron diffraction experiments performed in the tetragonal antiferromagnetic heavy fermion system CeRhIn5-xSnx in its (x,T) phase diagram up to the vicinity of the critical concentration xc ≈0.40, where long range magnetic order is suppressed. The propagation vector of the magnetic structure is found to be kIC=(1/2,1/2,kl) with kl increasing from kl=0.298 to kl=0.410 when x increases from x =0 to x =0.26. Surprisingly, for x =0.30, the order has changed drastically and a commensurate antiferromagnetism with kC=(1/2,1/2,0) is found. This concentration is located in the proximity of the quantum critical point where superconductivity is expected.

  16. Proceedings of the 2nd International Conference on Semiconductor Quantum Dots (QD2002): physica status solidi (c) - conferences and critical reviews, Vol. 0, No. 4

    NASA Astrophysics Data System (ADS)

    Arakawa, Yasuhiko; Tarucha, Seigo

    2005-10-01

    physica status solidi (c) conferences and critical reviews publishes conference proceedings, ranging from large international meetings to specialized topical workshops as well as collections of topical reviews on various areas of current solid state physics research. The International Conference on Semiconductor Quantum Dots (QD2002) was held at Komaba Campus of University of Tokyo, Japan, from Monday 30 September through Thursday 3 October 2002. The purpose of the QD2002 was to bring together scientists from different fields of physics and chemistry to discuss topics of common interest and significance in such growing areas including semiconductur quantum dots, nanocrystals, and clusters. The conference was focused on the optical and electronic properties of three-dimensionally confined nanostructures grown both by epitaxial methods and chemical preparation routes. The QD2002 was the second in a series which started in Munich, Germany, in 2000. The scope of QD2002 covered various research fields including novel fabrication techniques of nanoheterostructures, electronic structures, optical properties, electronic properties/single electron tunneling processes, molecular dots, nanocrystals, device applications such as lasers and memories, coherent processes/quantum computations, and biomedical applications.

  17. Small Atomic Orbital Basis Set First-Principles Quantum Chemical Methods for Large Molecular and Periodic Systems: A Critical Analysis of Error Sources.

    PubMed

    Sure, Rebecca; Brandenburg, Jan Gerit; Grimme, Stefan

    2016-04-01

    In quantum chemical computations the combination of Hartree-Fock or a density functional theory (DFT) approximation with relatively small atomic orbital basis sets of double-zeta quality is still widely used, for example, in the popular B3LYP/6-31G* approach. In this Review, we critically analyze the two main sources of error in such computations, that is, the basis set superposition error on the one hand and the missing London dispersion interactions on the other. We review various strategies to correct those errors and present exemplary calculations on mainly noncovalently bound systems of widely varying size. Energies and geometries of small dimers, large supramolecular complexes, and molecular crystals are covered. We conclude that it is not justified to rely on fortunate error compensation, as the main inconsistencies can be cured by modern correction schemes which clearly outperform the plain mean-field methods. PMID:27308221

  18. Small Atomic Orbital Basis Set First-Principles Quantum Chemical Methods for Large Molecular and Periodic Systems: A Critical Analysis of Error Sources.

    PubMed

    Sure, Rebecca; Brandenburg, Jan Gerit; Grimme, Stefan

    2016-04-01

    In quantum chemical computations the combination of Hartree-Fock or a density functional theory (DFT) approximation with relatively small atomic orbital basis sets of double-zeta quality is still widely used, for example, in the popular B3LYP/6-31G* approach. In this Review, we critically analyze the two main sources of error in such computations, that is, the basis set superposition error on the one hand and the missing London dispersion interactions on the other. We review various strategies to correct those errors and present exemplary calculations on mainly noncovalently bound systems of widely varying size. Energies and geometries of small dimers, large supramolecular complexes, and molecular crystals are covered. We conclude that it is not justified to rely on fortunate error compensation, as the main inconsistencies can be cured by modern correction schemes which clearly outperform the plain mean-field methods.

  19. Small Atomic Orbital Basis Set First‐Principles Quantum Chemical Methods for Large Molecular and Periodic Systems: A Critical Analysis of Error Sources

    PubMed Central

    Sure, Rebecca; Brandenburg, Jan Gerit

    2015-01-01

    Abstract In quantum chemical computations the combination of Hartree–Fock or a density functional theory (DFT) approximation with relatively small atomic orbital basis sets of double‐zeta quality is still widely used, for example, in the popular B3LYP/6‐31G* approach. In this Review, we critically analyze the two main sources of error in such computations, that is, the basis set superposition error on the one hand and the missing London dispersion interactions on the other. We review various strategies to correct those errors and present exemplary calculations on mainly noncovalently bound systems of widely varying size. Energies and geometries of small dimers, large supramolecular complexes, and molecular crystals are covered. We conclude that it is not justified to rely on fortunate error compensation, as the main inconsistencies can be cured by modern correction schemes which clearly outperform the plain mean‐field methods. PMID:27308221

  20. Quantum Phase Transitions across a p-Wave Feshbach Resonance

    NASA Astrophysics Data System (ADS)

    Gurarie, V.; Radzihovsky, L.; Andreev, A. V.

    2005-06-01

    We study a single-species polarized Fermi gas tuned across a narrow p-wave Feshbach resonance. We show that in the course of a Bose-Einstein condensation (BEC)-BCS crossover, the system can undergo a magnetic-field-tuned quantum phase transition from a px-wave to a px+ipy-wave superfluid. The latter state, that spontaneously breaks time-reversal symmetry, furthermore undergoes a topological px+ipy to px+ipy transition at zero chemical potential μ. In two dimensions, for μ>0 it is characterized by a Pfaffian ground state exhibiting topological order and non-Abelian excitations familiar from fractional quantum Hall systems.

  1. Tensor-product state approach to spin-1/2 square J1-J2 antiferromagnetic Heisenberg model: Evidence for deconfined quantum criticality

    NASA Astrophysics Data System (ADS)

    Wang, Ling; Gu, Zheng-Cheng; Verstraete, Frank; Wen, Xiao-Gang

    2016-08-01

    The ground state phase of a spin-1/2 J1-J2 antiferromagnetic Heisenberg model on a square lattice around the maximally frustrated regime (J2˜0.5 J1 ) has been debated for decades. Here we study this model using the cluster update algorithm for tensor-product states (TPSs). The ground state energies at finite sizes and in the thermodynamic limit (with finite size scaling) are in good agreement with exact diagonalization study. Through finite size scaling of the spin correlation function, we find the critical point J2c1=0.572 (5 ) J1 and critical exponents ν =0.50 (8 ) ,ηs=0.28 (6 ) . In the range of 0.572 quantum critical point at J2c1. Remarkably, all the observed critical exponents are consistent with the J -Q model.

  2. Towards ferromagnetic quantum criticality in FeGa3 -xGex :71Ga NQR as a zero-field microscopic probe

    NASA Astrophysics Data System (ADS)

    Majumder, M.; Wagner-Reetz, M.; Cardoso-Gil, R.; Gille, P.; Steglich, F.; Grin, Y.; Baenitz, M.

    2016-02-01

    71Ga NQR, magnetization, and specific-heat measurements have been performed on polycrystalline Ge-doped FeGa3 samples. A crossover from an insulator to a correlated local moment metal in the low-doping regime and the evolution of itinerant ferromagnet upon further doping is found. For the nearly critical concentration at the threshold of ferromagnetic order, xC=0.15, 71(1 /T1T ) exhibits a pronounced T-4 /3 power law over two orders of magnitude in temperature, which indicates three-dimensional quantum critical ferromagnetic fluctuations. Furthermore, for the ordered x =0.2 sample (TC≈6 K), 71(1 /T1T ) could be fitted well in the frame of Moriya's self-consistent renormalization theory for weakly ferromagnetic systems with 1 /T1T ˜χ . In contrast to this, the low-doping regime nicely displays local moment behavior where 1 /T1T ˜χ2 is valid. For T →0 , the Sommerfeld ratio γ =(C /T ) is enhanced (70 mJ /mole K2 for x =0.1 ) , which indicates the formation of heavy 3 d electrons.

  3. Putative quantum criticality in the (Cr{sub 90}Ir{sub 10}){sub 100−y}V{sub y} alloy system

    SciTech Connect

    Fernando, P. R.; Prinsloo, A. R. E. Sheppard, C. J.; Lodya, L.

    2014-05-07

    Quantum criticality (QC) in spin-density-wave antiferromagnetic Cr and Cr alloy systems is a topic of current interest. In the present study, V was used as a tuning parameter to drive the Néel transition temperature (T{sub N}) of the (Cr{sub 90}Ir{sub 10}){sub 100−y}V{sub y} alloy series with 0 ≤ y ≤ 14.3 to zero and search for effects of QC in the process. The magnetic properties and possible QC behaviour (QCB) in this alloy system were investigated through electrical resistivity (ρ), specific heat (C{sub p}), and susceptibility (χ) measurements as a function of temperature (T), indicating that T{sub N} is suppressed to zero at a critical concentration y{sub c} ≈ 9. The Sommerfeld coefficient (γ) is considered a key indicator of QCB and a peak is observed in γ(y) at y{sub c} on decreasing y through this concentration, followed by a sharp decreasing trend. This behaviour is reminiscent of that observed for γ of the prototypical Cr{sub 100−x}V{sub x} QC system and allows for the classification of y{sub c} in the (Cr{sub 90}Ir{sub 10}){sub 100−y}V{sub y} alloy system as a possible QC point.

  4. Hall and transverse even effects in the vicinity of a quantum critical point in Tm{sub 1-x}Yb{sub x}B{sub 12}

    SciTech Connect

    Sluchanko, N. E. Azarevich, A. N.; Bogach, A. V.; Glushkov, V. V.; Demishev, S. V.; Anisimov, M. A.; Levchenko, A. V.; Filipov, V. B.; Shitsevalova, N. Yu.

    2012-09-15

    The angular, temperature, and magnetic field dependences of the resistance recorded in the Hall effect geometry are studied for the rare-earth dodecaboride Tm{sub 1-x}Yb{sub x}B{sub 12} solid solutions where the metal-insulator and antiferromagnetic-paramagnetic phase transitions are observed in the vicinity of the quantum critical point x{sub c} Almost-Equal-To 0.3. The measurements performed on high-quality single crystals in the temperature range 1.9-300 K for the first time have revealed the appearance of the second harmonic contribution, a transverse even effect in these fcc compounds near the quantum critical point. This contribution a is found to increase drastically both under the Tm-to-ytterbium substitution in the range x > x{sub c} and with an increase in the external magnetic field. Moreover, as the Yb concentration x increases, a negative peak of a significant amplitude appears on the temperature dependences of the Hall coefficient R{sub H}(T) for the Tm{sup 1-x}Yb{sub x}B{sub 12} compounds, in contrast to the invariable behavior R{sub H}(T) Almost-Equal-To const found for TmB{sub 12}. The complicated activation-type behavior of the Hall coefficient is observed at intermediate temperatures for x {>=} 0.5 with activation energies E{sub g}/k{sub B} Almost-Equal-To 200 K and E{sub a}/k{sub B} 55-75 K, and the sign inversion of R{sub H}(T) is detected at liquid-helium temperatures in the coherent regime. Renormalization effects in the electron density of states induced by variation of the Yb concentration are analyzed. The anomalies of the charge transport in Tm{sub 1-x}Yb{sub x}B{sub 12} solid solutions in various regimes (charge gap formation, intra-gap many-body resonance, and coherent regime) are discussed in detail and the results are interpreted in terms of the electron phase separation effects in combination with the formation of nanosize clusters of rare earth ions in the cage-glass state of the studied dodecaborides. The data obtained allow

  5. Star junctions and watermelons of pure or random quantum Ising chains: finite-size properties of the energy gap at criticality

    NASA Astrophysics Data System (ADS)

    Monthus, Cécile

    2015-06-01

    We consider M  ⩾  2 pure or random quantum Ising chains of N spins when they are coupled via a single star junction at their origins or when they are coupled via two star junctions at the their two ends leading to the watermelon geometry. The energy gap is studied via a sequential self-dual real-space renormalization procedure that can be explicitly solved in terms of Kesten variables containing the initial couplings and and the initial transverse fields. In the pure case at criticality, the gap is found to decay as a power-law {ΔM}\\propto {{N}-z(M)} with the dynamical exponent z(M)=\\frac{M}{2} for the single star junction (the case M   =   2 corresponds to z   =   1 for a single chain with free boundary conditions) and z(M)   =   M  -  1 for the watermelon (the case M   =   2 corresponds to z   =   1 for a single chain with periodic boundary conditions). In the random case at criticality, the gap follows the Infinite Disorder Fixed Point scaling \\ln {ΔM}=-{{N}\\psi}g with the same activated exponent \\psi =\\frac{1}{2} as the single chain corresponding to M   =   2, and where g is an O(1) random positive variable, whose distribution depends upon the number M of chains and upon the geometry (star or watermelon).

  6. Charge redistribution and a shortening of the Fe--As bond at the quantum critical point of SmO1-xFxFeAs.

    PubMed

    Cheng, Jie; Dong, Peng; Xu, Wei; Liu, Shengli; Chu, Wangsheng; Chen, Xianhui; Wu, Ziyu

    2015-07-01

    Many researchers have pointed out that there is a quantum critical point (QCP) in the F-doped SmOFeAs system. In this paper, the electronic structure and local structure of the superconductive FeAs layer in SmO(1-x)FxFeAs as a function of the F-doping concentration have been investigated using Fe and As K-edge X-ray absorption spectroscopy. Experiments performed on the X-ray absorption near-edge structure showed that in the vicinity of the QCP the intensity of the pre-edge feature at the Fe-edge decreases continuously, while there is a striking rise of the shoulder-peak at the As edge, suggesting the occurrence of charge redistribution near the QCP. Further analysis on the As K-edge extended X-ray absorption fine structure demonstrated that the charge redistribution originates mostly from a shortening of the Fe-As bond at the QCP. An evident relationship between the mysterious QCP and the fundamental Fe-As bond was established, providing new insights on the interplay between QCP, charge dynamics and the local structural Fe-As bond in Fe-based superconductors.

  7. Multiband nodeless superconductivity near the charge-density-wave quantum critical point in ZrTe3‑x Se x

    NASA Astrophysics Data System (ADS)

    Shan, Cui; Lan-Po, He; Xiao-Chen, Hong; Xiang-De, Zhu; Cedomir, Petrovic; Shi-Yan, Li

    2016-07-01

    It was found that selenium doping can suppress the charge-density-wave (CDW) order and induce bulk superconductivity in ZrTe3. The observed superconducting dome suggests the existence of a CDW quantum critical point (QCP) in ZrTe3‑x Se x near x ≈ 0.04. To elucidate the superconducting state near the CDW QCP, we measure the thermal conductivity of two ZrTe3‑x Se x single crystals (x = 0.044 and 0.051) down to 80 mK. For both samples, the residual linear term κ 0/T at zero field is negligible, which is a clear evidence for nodeless superconducting gap. Furthermore, the field dependence of κ 0/T manifests a multigap behavior. These results demonstrate multiple nodeless superconducting gaps in ZrTe3‑x Se x , which indicates conventional superconductivity despite of the existence of a CDW QCP. Project supported by the National Basic Research Program of China (Grant Nos. 2012CB821402 and 2015CB921401), the National Natural Science Foundation of China (Grant Nos. 91421101, 11422429, and 11204312), the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning, China, and STCSM of China (Grant No. 15XD1500200). Work at Brookhaven National Laboratory was supported by the US DOE under Contract No. DESC00112704.

  8. Quantum critical point in SmO(1-x)F(x)FeAs and oxygen vacancy induced by high fluorine dopant.

    PubMed

    Cheng, Jie; Chu, Shengqi; Chu, Wangsheng; Xu, Wei; Zhou, Jing; Zhang, Linjuan; Zhao, Haifeng; Liu, Ronghua; Chen, Xianhui; Marcelli, Augusto; Wu, Ziyu

    2011-09-01

    The local lattice and electronic structure of the high-T(c) superconductor SmO(1-x)F(x)FeAs as a function of F-doping have been investigated by Sm L(3)-edge X-ray absorption near-edge structure and multiple-scattering calculations. Experiments performed at the L(3)-edge show that the white line (WL) is very sensitive to F-doping. In the under-doped region (x ≤ 0.12) the WL intensity increases with doping and then it suddenly starts decreasing at x = 0.15. Meanwhile, the trend of the WL linewidth versus F-doping levels is just contrary to that of the intensity. The phenomenon is almost coincident with the quantum critical point occurring in SmO(1-x)F(x)FeAs at x ≃ 0.14. In the under-doped region the increase of the intensity is related to the localization of Sm-5d states, while theoretical calculations show that both the decreasing intensity and the consequent broadening of linewidth at high F-doping are associated with the content and distribution of oxygen vacancies.

  9. A ferromagnetic quantum critical point in heavy-fermion iron oxypnictide CeFe{sub 1−x}Cr{sub x}PO

    SciTech Connect

    Okano, T.; Matoba, M.; Kamihara, Y.; Kitao, S.; Seto, M.; Atou, T.; Itoh, M.

    2015-05-07

    We report crystallographic and magnetic properties of layered iron oxypnictide CeFe{sub 1−x}Cr{sub x}PO (x = 0.000–0.692). Interlayer distances between Ce{sub 2}O{sub 2} and (Fe{sub 1−x}Cr{sub x}){sub 2}P{sub 2} layers increase as a function of x, suggesting suppression of Kondo coupling among hybridized conducting orbitals and localized Ce 4f orbitals. CeFe{sub 1−x}Cr{sub x}PO (x = 0.100–0.384) exhibits finite ferromagnetic transition temperatures (T{sub curie}) obtained by Arrott plots, although {sup 57}Fe Mössbauer spectra reveal paramagnetic Fe sublattice at T ≥ 4.2 K. These results indicate that the ferromagnetic phase transitions of samples are mainly due to Ce sublattice. For the samples with x ≥ 0.500, no ferromagnetic order is observed down to 2 K. These results verify that ferromagnetic quantum critical points of CeFe{sub 1−x}Cr{sub x}PO appear at 0.045 ≤ x ≤ 0.100 and 0.384 ≤ x ≤ 0.500.

  10. Quantum criticality in single crystalline YFe2 Al10 determined from zero-field and longitudinal-field muon spin relaxation

    NASA Astrophysics Data System (ADS)

    Huang, Kevin; Tan, Cheng; Zhang, Jian; Ding, Zhaofeng; Maclaughlin, Douglas; Bernal, Oscar; Ho, Pei-Chun; Wu, Liusuo; Aronson, Meigan; Shu, Lei

    Muon spin relaxation (μSR) measurements were performed on single crystalline YFe2Al10 down to 19 mK and in magnetic fields up to ~100 Oe. Zero-field- μSR measurements showed no evidence of magnetic order down to 19 mK, consistent with previous measurements. However, we also find that the depolarization rate Λ is temperature independent above 1 K but increases in an exponential behavior for T < 1 K. Longitudinal-field μSR measurements also reveals a time-field scaling where G (t , H) = G (t /Hγ), with γ = 0.67. This is further confirmed from the magnetic field dependence of Λ, which finds Λ (H) ~H0. 67 at 19 mK. This is further evidence that single crystalline YFe2Al10 is in close proximity to a ferromagnetic quantum critical point. The research performed in this study was supported by the National NSF of China under Grant No. 11474060 and STCSM of China (No. 15XD1500200). Work at CSULA funded by NSF/DMR-1105380. Research at CSU-Fresno is supported by NSF DMR-1506677.

  11. Quantum critical fluctuations in the heavy fermion compound Ce(Ni0.935Pd0.065)2Ge2

    DOE PAGESBeta

    Wang, C. H.; Poudel, L.; Taylor, Alice E.; Lawrence, J M.; Christianson, Andrew D.; Chang, S.; Rodriguez-Rivera, J. A.; Lynn, J. W.; Podlesnyak, Andrey A.; Ehlers, G.; et al

    2014-12-03

    Electric resistivity, specific heat, magnetic susceptibility, and inelastic neutron scattering experiments were performed on a single crystal of the heavy fermion compound Ce(Ni0.935Pd0.065)2Ge2 in order to research the spin fluctuations near an antiferromagnetic (AF) quantum critical point (QCP). The resistivity and the specific heat coefficient for T ≤ 1 K exhibit the power law behavior expected for a 3D itinerant AF QCP (ρ(T) ~ T3/2 and γ(T) ~ γ0 - bT1/2). However, for 2 ≤ T ≤ 10 K, the susceptibility and specific heat vary as log T and the resistivity varies linearly with temperature. In addition, despite the factmore » that the resistivity and specific heat exhibit the non-Fermi liquid behavior expected at a QCP, the correlation length, correlation time, and staggered susceptibility of the spin fluctuations remain finite at low temperature. In conclusion, we suggest that these deviations from the divergent behavior expected for a QCP may result from alloy disorder.« less

  12. A theoretical study of soft mode behavior and ferroelectric phase transition in 18O-isotope exchanged SrTiO3: evidence of phase coexistence at the quantum critical point

    NASA Astrophysics Data System (ADS)

    Mkam Tchouobiap, S. E.

    2014-02-01

    Motivated by recent experiments, the dynamics of the ferroelectric soft mode and the ferroelectric phase transition mechanism in 18O isotope exchanged systems SrTi(16O1-x18Ox)3 (abbreviated as STO18-x) are reinvestigated as a function of the 18O isotope exchange rate x, within a quasiharmonic model (QHM) for quantum ferroelectric modes in double-Morse local potential with mean-field approximation interactions between modes. The approach was realized within the framework of the variational principle method at finite temperature through the quantum mean-field approximation and by taking into account the effect of isotope replacement through the predominant mass effect, the cell volume effect, homogeneity of the composition throughout the material and the concentration-dependent ferroelectric mode distortion effect. The dynamics of the lowest-frequency soft phonon mode clearly presents an increased softening phenomenon with increasing x and a complete one at the corresponding phase transition temperature Tc, demonstrating the perfect soft-mode-type quantum ferroelectric phase transition for x ⩾ xc. Also, a ferroelectric-paraelectric phase coexistence state has been found near the quantum critical point xc and its origin is discussed. The ferroelectric phase transition mechanism is analyzed and its nature discussed, where a second-order phase transition close to the tricritical point is predicted. In addition, the effect of quantum fluctuations on the soft mode dynamics is discussed which reveals its reduction with increasing x and the crossover of the soft mode dynamics from the quantum to the classic one at the full 18O exchange limit x = 1, for which the origin seems to lie in the new homogeneity associated with the direct reduction of quantum fluctuations effects on the soft mode behavior. Within the QHM, consistent agreement with some of the previous experimental results and theoretical predictions of quantum ferroelectricity throughout the full range of x are

  13. Quantum Error Correction

    NASA Astrophysics Data System (ADS)

    Lidar, Daniel A.; Brun, Todd A.

    2013-09-01

    Prologue; Preface; Part I. Background: 1. Introduction to decoherence and noise in open quantum systems Daniel Lidar and Todd Brun; 2. Introduction to quantum error correction Dave Bacon; 3. Introduction to decoherence-free subspaces and noiseless subsystems Daniel Lidar; 4. Introduction to quantum dynamical decoupling Lorenza Viola; 5. Introduction to quantum fault tolerance Panos Aliferis; Part II. Generalized Approaches to Quantum Error Correction: 6. Operator quantum error correction David Kribs and David Poulin; 7. Entanglement-assisted quantum error-correcting codes Todd Brun and Min-Hsiu Hsieh; 8. Continuous-time quantum error correction Ognyan Oreshkov; Part III. Advanced Quantum Codes: 9. Quantum convolutional codes Mark Wilde; 10. Non-additive quantum codes Markus Grassl and Martin Rötteler; 11. Iterative quantum coding systems David Poulin; 12. Algebraic quantum coding theory Andreas Klappenecker; 13. Optimization-based quantum error correction Andrew Fletcher; Part IV. Advanced Dynamical Decoupling: 14. High order dynamical decoupling Zhen-Yu Wang and Ren-Bao Liu; 15. Combinatorial approaches to dynamical decoupling Martin Rötteler and Pawel Wocjan; Part V. Alternative Quantum Computation Approaches: 16. Holonomic quantum computation Paolo Zanardi; 17. Fault tolerance for holonomic quantum computation Ognyan Oreshkov, Todd Brun and Daniel Lidar; 18. Fault tolerant measurement-based quantum computing Debbie Leung; Part VI. Topological Methods: 19. Topological codes Héctor Bombín; 20. Fault tolerant topological cluster state quantum computing Austin Fowler and Kovid Goyal; Part VII. Applications and Implementations: 21. Experimental quantum error correction Dave Bacon; 22. Experimental dynamical decoupling Lorenza Viola; 23. Architectures Jacob Taylor; 24. Error correction in quantum communication Mark Wilde; Part VIII. Critical Evaluation of Fault Tolerance: 25. Hamiltonian methods in QEC and fault tolerance Eduardo Novais, Eduardo Mucciolo and

  14. Survival of time-evolved quantum correlations depending on whether quenching is across a critical point in an X Y spin chain

    NASA Astrophysics Data System (ADS)

    Mishra, Utkarsh; Rakshit, Debraj; Prabhu, R.

    2016-04-01

    The time dynamics of quantum correlations in the quantum transverse anisotropic X Y spin chain of infinite length is studied at zero and finite temperatures. The evolution occurs due to the instantaneous quenching of the coupling constant between the nearest-neighbor spins of the model, which is performed either within the same phase or across the quantum phase-transition point connecting the order-disorder phases of the model. We characterize the time-evolved quantum correlations, viz., entanglement and quantum discord, which exhibit varying behavior depending on the initial state and the quenching scheme. We show that the system is endowed with enhanced nearest-neighbor bipartite quantum correlations compared to that of the initial state, when quenched from the ordered to the deep disordered phase. However, nearest-neighbor quantum correlations are almost washed out when the system is quenched from the disordered to the ordered phase with the initial state being at the zero temperature. We also identify the condition for the occurrence of enhanced bipartite correlations when the system is quenched within the same phase. Moreover, we investigate the bipartite quantum correlations when the initial state is a thermal equilibrium state with finite temperature, which reveals the effects of thermal fluctuation on the phenomena observed at zero temperature. Finally, an analogous analysis is carried out for zero-temperature next-nearest-neighbor quantum correlations.

  15. Quantum Critical Behavior in the Heavy Fermion Single Crystal Ce(Ni0.935Pd0.065)2Ge2

    SciTech Connect

    Wang, Cuihuan; Lawrence, J M; Christianson, Andrew D; Chang, S; Bauer, E D; Gofryk, K; Ronning, F; Thompson, J D; McClellan, K J; Rodriguez-Rivera, J A; Lynn, J W

    2011-01-01

    We have performed magnetic susceptibility, specific heat, resistivity, and inelastic neutron scattering measurements on a single crystal of the heavy Fermion compound Ce(Ni{sub 0.935}Pd{sup 0.065}){sub 2}Ge{sub 2}, which is believed to be close to a quantum critical point (QCP) at T = 0. At lowest temperature (1.8--3.5 K), the magnetic susceptibility behaves as {chi}(T)-{chi} (0) {proportional_to} T{sup -1/6} with {chi} (0) = 0.032 x 10{sup -6} m{sup 3}/mole (0.0025 emu/mole). For T < 1 K, the specific heat can be fit to the formula {Delta} C/T = {gamma}{sub 0} - T{sup 1/2} with {gamma}{sub 0} of order 700 mJ/mole-K{sup 2}. The resistivity behaves as {rho} = {rho}{sub 0} + AT{sup 3/2} for temperatures below 2 K. This low temperature behavior for {gamma} (T) and {rho} (T) is in accord with the SCR theory of Moriya and Takimoto. The inelastic neutron scattering spectra show a broad peak near 1.5 meV that appears to be independent of Q; we interpret this as Kondo scattering with T{sub K} = 17 K. In addition, the scattering is enhanced near Q=(1/2, 1/2, 0) with maximum scattering at {Delta} E = 0.45 meV{sup -}; we interpret this as scattering from antiferromagnetic fluctuations near the antiferromagnetic QCP.

  16. Electron-electron interaction and the universality of critical indices for quantum Hall effect plateau-plateau transitions in n-InGaAs/GaAs nanostructures with double quantum wells

    SciTech Connect

    Arapov, Yu. G.; Gudina, S. V. Klepikova, A. S.; Neverov, V. N.; Shelushinina, N. G.; Yakunin, M. V.

    2015-02-15

    The dependences of the longitudinal and Hall resistances on a magnetic field in the integer quantum Hall effect regime in n-InGaAs/GaAs heterostructures with a double quantum well are measured in the range of magnetic fields B = 0–16 T and temperatures T = 0.05–4.2 K, before and after infrared illumination. Analysis of the temperature dependence of the width of transitions between plateaus of the quantum Hall effect is performed in the scope of the scaling hypothesis allowing for electron-electron interaction effects.

  17. Work and quantum phase transitions: quantum latency.

    PubMed

    Mascarenhas, E; Bragança, H; Dorner, R; França Santos, M; Vedral, V; Modi, K; Goold, J

    2014-06-01

    We study the physics of quantum phase transitions from the perspective of nonequilibrium thermodynamics. For first-order quantum phase transitions, we find that the average work done per quench in crossing the critical point is discontinuous. This leads us to introduce the quantum latent work in analogy with the classical latent heat of first order classical phase transitions. For second order quantum phase transitions the irreversible work is closely related to the fidelity susceptibility for weak sudden quenches of the system Hamiltonian. We demonstrate our ideas with numerical simulations of first, second, and infinite order phase transitions in various spin chain models.

  18. Buckley Prize Talk: Bosons on the Boundaries: The magnetic field driven superconductor-insulator quantum phase transition

    NASA Astrophysics Data System (ADS)

    Hebard, Arthur

    2015-03-01

    Experiments probing the competition between superconductivity and disorder in two-dimensional (2D) thin-film systems have provided fascinating glimpses into the physics of superconductor-insulator (S-I) quantum phase transitions (QPTs). This talk will address the use of externally applied magnetic fields to tune through the S-I transition of amorphous composite indium oxide (α-InOx) thin films prepared at different stages of disorder. Air-stable α-InOx films are particularly advantageous for these studies: the disorder parameter as measured by the sheet resistance can be reproducibly controlled during deposition and the films are uniformly homogeneous out to macroscopic length scales. Temperature-dependent resistance and current-voltage measurements confirm the power-law decay of the order-parameter correlation function appropriate to a Kosterlitz-Thouless description of phase transitions in 2D systems. Accordingly, the superconducting phase transition temperature Tc is related to the unbinding of vortex-antivortex pairs either by temperature and/or disorder. The application of magnetic fields unveils fundamentally different physics in which, rather than a vortex unbinding transition, a field-tuned QPT emerges with the signature of a disorder-dependent critical field Bc that identifies the delocalization and Bose condensation of field-induced vortices. The concomitant pronounced divergence in resistance, which becomes increasing sharp as the temperature is lowered, marks the boundary between a superconductor harboring both Bose condensed Cooper pairs and localized vortices and an insulator harboring both Bose condensed vortices and localized Cooper pairs. The data for this putative QPT are well described by finite temperature scaling theory with critical exponent values accurately determined. At higher fields there is a second critical field where the transverse resistance appears to diverge, signaling the unbinding of pairs with the superconducting energy gap

  19. Anti-Kibble-Zurek Behavior in Crossing the Quantum Critical Point of a Thermally Isolated System Driven by a Noisy Control Field.

    PubMed

    Dutta, Anirban; Rahmani, Armin; Del Campo, Adolfo

    2016-08-19

    We show that a thermally isolated system driven across a quantum phase transition by a noisy control field exhibits anti-Kibble-Zurek behavior, whereby slower driving results in higher excitations. We characterize the density of excitations as a function of the ramping rate and the noise strength. The optimal driving time to minimize excitations is shown to scale as a universal power law of the noise strength. Our findings reveal the limitations of adiabatic protocols such as quantum annealing and demonstrate the universality of the optimal ramping rate. PMID:27588838

  20. Anti-Kibble-Zurek Behavior in Crossing the Quantum Critical Point of a Thermally Isolated System Driven by a Noisy Control Field

    NASA Astrophysics Data System (ADS)

    Dutta, Anirban; Rahmani, Armin; del Campo, Adolfo

    2016-08-01

    We show that a thermally isolated system driven across a quantum phase transition by a noisy control field exhibits anti-Kibble-Zurek behavior, whereby slower driving results in higher excitations. We characterize the density of excitations as a function of the ramping rate and the noise strength. The optimal driving time to minimize excitations is shown to scale as a universal power law of the noise strength. Our findings reveal the limitations of adiabatic protocols such as quantum annealing and demonstrate the universality of the optimal ramping rate.

  1. Evolution of Transport and Magnetic Properties near the Ferromagnetic Quantum Critical Point in the Series CaxSr1−xRuO3

    SciTech Connect

    Khalifah, Peter; Okubo, Isao; Christen, Hans M; Mandrus, David

    2004-01-01

    A series of epitaxial films were grown across the solid solution Ca{sub x}Sr{sub 1-x}RuO{sub 3} in order to pinpoint the ferromagnetic to paramagnetic quantum phase transition in this system and to study the evolution of transport and magnetic properties in its vicinity. The ferromagnetic T{sub c} of SrRuO{sub 3} was found to decrease linearly with Ca doping levels up to 70%. Further doping resulted in the abrupt elimination of ferromagnetic order, and the onset of low temperature (<10 K) non-Fermi-liquid (NFL) resistivity of the form {rho} {proportional_to} {rho}{sub 0} + AT{sup 1.5} for samples with x-0.75-1.0. The resistivity exponent of 1.5 matches that previously observed for intermetallic alloys (such as MnSi) at their ferromagnetic quantum critical points, indicating the possible universality of this NFL behavior. Field-dependent specific heat measurements on bulk samples at compositions near the quantum phase transition provide additional evidence for NFL behavior (C/T {proportional_to} log{sub 10} T) and show the conditions under which spin fluctuations contribute to the specific heat.

  2. Quantum rendering

    NASA Astrophysics Data System (ADS)

    Lanzagorta, Marco O.; Gomez, Richard B.; Uhlmann, Jeffrey K.

    2003-08-01

    In recent years, computer graphics has emerged as a critical component of the scientific and engineering process, and it is recognized as an important computer science research area. Computer graphics are extensively used for a variety of aerospace and defense training systems and by Hollywood's special effects companies. All these applications require the computer graphics systems to produce high quality renderings of extremely large data sets in short periods of time. Much research has been done in "classical computing" toward the development of efficient methods and techniques to reduce the rendering time required for large datasets. Quantum Computing's unique algorithmic features offer the possibility of speeding up some of the known rendering algorithms currently used in computer graphics. In this paper we discuss possible implementations of quantum rendering algorithms. In particular, we concentrate on the implementation of Grover's quantum search algorithm for Z-buffering, ray-tracing, radiosity, and scene management techniques. We also compare the theoretical performance between the classical and quantum versions of the algorithms.

  3. Quantum wave turbulence

    NASA Astrophysics Data System (ADS)

    Haeri, M. B.; Putterman, S. J.; Garcia, A.; Roberts, P. H.

    1993-01-01

    The nonlinear quantum kinetic equation for the interaction of sound waves is solved via analytic and numerical techniques. In the classical regime energy cascades to higher frequency (ω) according to the steady-state power law ω-3/2. In the quantum limit, the system prefers a reverse cascade of energy which follows the power law ω-6. Above a critical flux, a new type of spectrum appears which is neither self-similar nor close to equilibrium. This state of nonlinear quantum wave turbulence represents a flow of energy directly from the classical source to the quantum degrees of freedom.

  4. Quantum phase transitions across a p-wave Feshbach resonance.

    PubMed

    Gurarie, V; Radzihovsky, L; Andreev, A V

    2005-06-17

    We study a single-species polarized Fermi gas tuned across a narrow p-wave Feshbach resonance. We show that in the course of a Bose-Einstein condensation (BEC)-BCS crossover, the system can undergo a magnetic-field-tuned quantum phase transition from a px-wave to a px+ipy-wave superfluid. The latter state, that spontaneously breaks time-reversal symmetry, furthermore undergoes a topological px+ipy to px+ipy transition at zero chemical potential mu. In two dimensions, for mu > 0 it is characterized by a Pfaffian ground state exhibiting topological order and non-Abelian excitations familiar from fractional quantum Hall systems. PMID:16090447

  5. 2D quantum gravity from quantum entanglement.

    PubMed

    Gliozzi, F

    2011-01-21

    In quantum systems with many degrees of freedom the replica method is a useful tool to study the entanglement of arbitrary spatial regions. We apply it in a way that allows them to backreact. As a consequence, they become dynamical subsystems whose position, form, and extension are determined by their interaction with the whole system. We analyze, in particular, quantum spin chains described at criticality by a conformal field theory. Its coupling to the Gibbs' ensemble of all possible subsystems is relevant and drives the system into a new fixed point which is argued to be that of the 2D quantum gravity coupled to this system. Numerical experiments on the critical Ising model show that the new critical exponents agree with those predicted by the formula of Knizhnik, Polyakov, and Zamolodchikov.

  6. Quantum computing

    PubMed Central

    Li, Shu-Shen; Long, Gui-Lu; Bai, Feng-Shan; Feng, Song-Lin; Zheng, Hou-Zhi

    2001-01-01

    Quantum computing is a quickly growing research field. This article introduces the basic concepts of quantum computing, recent developments in quantum searching, and decoherence in a possible quantum dot realization. PMID:11562459

  7. Quantum memories: emerging applications and recent advances

    PubMed Central

    Heshami, Khabat; England, Duncan G.; Humphreys, Peter C.; Bustard, Philip J.; Acosta, Victor M.; Nunn, Joshua; Sussman, Benjamin J.

    2016-01-01

    Quantum light–matter interfaces are at the heart of photonic quantum technologies. Quantum memories for photons, where non-classical states of photons are mapped onto stationary matter states and preserved for subsequent retrieval, are technical realizations enabled by exquisite control over interactions between light and matter. The ability of quantum memories to synchronize probabilistic events makes them a key component in quantum repeaters and quantum computation based on linear optics. This critical feature has motivated many groups to dedicate theoretical and experimental research to develop quantum memory devices. In recent years, exciting new applications, and more advanced developments of quantum memories, have proliferated. In this review, we outline some of the emerging applications of quantum memories in optical signal processing, quantum computation and non-linear optics. We review recent experimental and theoretical developments, and their impacts on more advanced photonic quantum technologies based on quantum memories.

  8. Quantum memories: emerging applications and recent advances

    NASA Astrophysics Data System (ADS)

    Heshami, Khabat; England, Duncan G.; Humphreys, Peter C.; Bustard, Philip J.; Acosta, Victor M.; Nunn, Joshua; Sussman, Benjamin J.

    2016-11-01

    Quantum light-matter interfaces are at the heart of photonic quantum technologies. Quantum memories for photons, where non-classical states of photons are mapped onto stationary matter states and preserved for subsequent retrieval, are technical realizations enabled by exquisite control over interactions between light and matter. The ability of quantum memories to synchronize probabilistic events makes them a key component in quantum repeaters and quantum computation based on linear optics. This critical feature has motivated many groups to dedicate theoretical and experimental research to develop quantum memory devices. In recent years, exciting new applications, and more advanced developments of quantum memories, have proliferated. In this review, we outline some of the emerging applications of quantum memories in optical signal processing, quantum computation and non-linear optics. We review recent experimental and theoretical developments, and their impacts on more advanced photonic quantum technologies based on quantum memories.

  9. Quantum memories: emerging applications and recent advances

    PubMed Central

    Heshami, Khabat; England, Duncan G.; Humphreys, Peter C.; Bustard, Philip J.; Acosta, Victor M.; Nunn, Joshua; Sussman, Benjamin J.

    2016-01-01

    Quantum light–matter interfaces are at the heart of photonic quantum technologies. Quantum memories for photons, where non-classical states of photons are mapped onto stationary matter states and preserved for subsequent retrieval, are technical realizations enabled by exquisite control over interactions between light and matter. The ability of quantum memories to synchronize probabilistic events makes them a key component in quantum repeaters and quantum computation based on linear optics. This critical feature has motivated many groups to dedicate theoretical and experimental research to develop quantum memory devices. In recent years, exciting new applications, and more advanced developments of quantum memories, have proliferated. In this review, we outline some of the emerging applications of quantum memories in optical signal processing, quantum computation and non-linear optics. We review recent experimental and theoretical developments, and their impacts on more advanced photonic quantum technologies based on quantum memories. PMID:27695198

  10. Nodal structure and quantum critical point beneath the superconducting dome of BaFe2(As1-xPx)2

    NASA Astrophysics Data System (ADS)

    Matsuda, Yuji

    2012-02-01

    Among BaFe2As2 based materials , the isovalent pnictogen substituted system BaFe2(As1-xPx)2 appears to be the most suitable system to discuss many physical properties, because BaFe2(As1-xPx)2 can be grown with very clean and homogeneous, as evidenced by the quantum oscillations observed over a wide doping range even in the superconducting dome giving detailed knowledge on the electronic structure. We investigate the structure of the superconducting order parameter in BaFe2(As0.67P0.33)2 (Tc=31,) with line nodes by the angle-resolved thermal conductivity measurements in magnetic field. The experimental results are most consistent with the closed nodal loops located at the flat part of the electron Fermi surface with high Fermi velocity. The doping evolution of the penetration depth indicates that nodal loop is robust against P-doping. Moreover, the magnitude of the zero temperature penetration depth exhibits a sharp peak at x=0.3, indicating the presence of a quantum phase transition deep inside the superconducting dome.[4pt] This work has been done in collaboration with T. Shibauchi, K. Hashimoto, S. Kasahara, M. Yamashita, T. Terashima, H. Ikeda (Kyoto), A. Carrington (Bristol), K. Cho, R. Prozorov, M. Tanatar (Ames), A.B. Vorontsov (Montana) and I.Vekhter (Louisiana).

  11. Quantum Mechanics

    NASA Astrophysics Data System (ADS)

    Auletta, Gennaro; Fortunato, Mauro; Parisi, Giorgio

    2014-01-01

    Introduction; Part I. Basic Features of Quantum Mechanics: 1. From classical mechanics to quantum mechanics; 2. Quantum observable and states; 3. Quantum dynamics; 4. Examples of quantum dynamics; 5. Density matrix; Part II. More Advanced Topics: 6. Angular momentum and spin; 7. Identical particles; 8. Symmetries and conservation laws; 9. The measurement problem; Part III. Matter and Light: 10. Perturbations and approximation methods; 11. Hydrogen and helium atoms; 12. Hydrogen molecular ion; 13. Quantum optics; Part IV. Quantum Information: State and Correlations: 14. Quantum theory of open systems; 15. State measurement in quantum mechanics; 16. Entanglement: non-separability; 17. Entanglement: quantum information; References; Index.

  12. Quantum information approach to the azurite mineral frustrated quantum magnet

    NASA Astrophysics Data System (ADS)

    Batle, J.; Ooi, C. H. Raymond; Abutalib, M.; Farouk, Ahmed; Abdalla, S.

    2016-07-01

    Quantum correlations are almost impossible to address in bulk systems. Quantum measures extended only to a few number of parties can be discussed in practice. In the present work, we study nonlocality for a cluster of spins belonging to a mineral whose structure is that of a quantum magnet. We reproduce at a much smaller scale the experimental outcomes, and then, we study the role of quantum correlations there. A macroscopic entanglement witness has been introduced in order to reveal nonlocal quantum correlations between individual constituents of the azurite mineral at nonzero temperatures. The critical point beyond which entanglement is zero is found at T_c < 1 K.

  13. Origin of the low critical observing temperature of the quantum anomalous Hall effect in V-doped (Bi, Sb)2Te3 film.

    PubMed

    Li, W; Claassen, M; Chang, Cui-Zu; Moritz, B; Jia, T; Zhang, C; Rebec, S; Lee, J J; Hashimoto, M; Lu, D-H; Moore, R G; Moodera, J S; Devereaux, T P; Shen, Z-X

    2016-09-07

    The experimental realization of the quantum anomalous Hall (QAH) effect in magnetically-doped (Bi, Sb)2Te3 films stands out as a landmark of modern condensed matter physics. However, ultra-low temperatures down to few tens of mK are needed to reach the quantization of Hall resistance, which is two orders of magnitude lower than the ferromagnetic phase transition temperature of the films. Here, we systematically study the band structure of V-doped (Bi, Sb)2Te3 thin films by angle-resolved photoemission spectroscopy (ARPES) and show unambiguously that the bulk valence band (BVB) maximum lies higher in energy than the surface state Dirac point. Our results demonstrate clear evidence that localization of BVB carriers plays an active role and can account for the temperature discrepancy.

  14. Origin of the low critical observing temperature of the quantum anomalous Hall effect in V-doped (Bi, Sb)2Te3 film.

    PubMed

    Li, W; Claassen, M; Chang, Cui-Zu; Moritz, B; Jia, T; Zhang, C; Rebec, S; Lee, J J; Hashimoto, M; Lu, D-H; Moore, R G; Moodera, J S; Devereaux, T P; Shen, Z-X

    2016-01-01

    The experimental realization of the quantum anomalous Hall (QAH) effect in magnetically-doped (Bi, Sb)2Te3 films stands out as a landmark of modern condensed matter physics. However, ultra-low temperatures down to few tens of mK are needed to reach the quantization of Hall resistance, which is two orders of magnitude lower than the ferromagnetic phase transition temperature of the films. Here, we systematically study the band structure of V-doped (Bi, Sb)2Te3 thin films by angle-resolved photoemission spectroscopy (ARPES) and show unambiguously that the bulk valence band (BVB) maximum lies higher in energy than the surface state Dirac point. Our results demonstrate clear evidence that localization of BVB carriers plays an active role and can account for the temperature discrepancy. PMID:27599406

  15. Origin of the low critical observing temperature of the quantum anomalous Hall effect in V-doped (Bi, Sb)2Te3 film

    PubMed Central

    Li, W.; Claassen, M.; Chang, Cui-Zu; Moritz, B.; Jia, T.; Zhang, C.; Rebec, S.; Lee, J. J.; Hashimoto, M.; Lu, D.-H.; Moore, R. G.; Moodera, J. S.; Devereaux, T. P.; Shen, Z.-X.

    2016-01-01

    The experimental realization of the quantum anomalous Hall (QAH) effect in magnetically-doped (Bi, Sb)2Te3 films stands out as a landmark of modern condensed matter physics. However, ultra-low temperatures down to few tens of mK are needed to reach the quantization of Hall resistance, which is two orders of magnitude lower than the ferromagnetic phase transition temperature of the films. Here, we systematically study the band structure of V-doped (Bi, Sb)2Te3 thin films by angle-resolved photoemission spectroscopy (ARPES) and show unambiguously that the bulk valence band (BVB) maximum lies higher in energy than the surface state Dirac point. Our results demonstrate clear evidence that localization of BVB carriers plays an active role and can account for the temperature discrepancy. PMID:27599406

  16. Competing ground states in transition metal oxides: Behavior of itinerant Sr1- x Ca x RuO3 close to the classical and quantum critical ferromagnetic phase transition

    NASA Astrophysics Data System (ADS)

    Fuchs, D.; Huang, C. L.; Schmalian, J.; Wissinger, M.; Schuppler, S.; Grube, K.; Löhneysen, H. v.

    2015-07-01

    The ferromagnetic (FM) phase transition of the itinerant electron-system Sr1- x Ca x RuO3 can be tuned by chemical composition resulting in a quantum critical point (QCP) at the critical concentration x c ≈ 0.7. Applying epitaxial pressure at constant x leads to a reduction of the Curie temperature T C which is found to be proportional to the shrinkage of the unit-cell volume V uc , shifting x c to higher values for tensile strained films. Surprisingly, the tetragonal distortion seems to play here only a minor role. With increasing x the critical scaling of the order parameter shows unusual behavior. The magnetic critical exponents β, γ, and δ change systematically from typical mean-field values at x = 0 with increasing x towards β = 1, γ = 0.9 and δ = 1.6 at x = 0.7. The results are discussed with respect to a crossover from mean-field-like behavior at x = 0 to a line of fixed points that might emerge in the strong-disorder limit as the system approaches the QCP at or near x c . Magnetic inhomogeneities are indeed suggested by a non-vanishing magnetic moment at x c and the evidence of a Griffiths phase as well as glass-like behavior close to x c . Although spin fluctuations certainly play an important role around x c as proposed previously, our highly accurate data of the magnetization M( T, B) and specific heat C( T, B) for x = 0.7 suggest dynamic scaling with an unusual dynamic exponent z = 1.8, incompatible with standard spin-fluctuation theories at a ferromagnetic QCP.

  17. Turbocharging Quantum Tomography

    SciTech Connect

    Blume-Kohout, Robin J.; Gamble, John King; Nielsen, Erik; Maunz, Peter Lukas Wilhelm; Scholten, Travis L.; Rudinger, Kenneth Michael

    2015-01-01

    Quantum tomography is used to characterize quantum operations implemented in quantum information processing (QIP) hardware. Traditionally, state tomography has been used to characterize the quantum state prepared in an initialization procedure, while quantum process tomography is used to characterize dynamical operations on a QIP system. As such, tomography is critical to the development of QIP hardware (since it is necessary both for debugging and validating as-built devices, and its results are used to influence the next generation of devices). But tomography suffers from several critical drawbacks. In this report, we present new research that resolves several of these flaws. We describe a new form of tomography called gate set tomography (GST), which unifies state and process tomography, avoids prior methods critical reliance on precalibrated operations that are not generally available, and can achieve unprecedented accuracies. We report on theory and experimental development of adaptive tomography protocols that achieve far higher fidelity in state reconstruction than non-adaptive methods. Finally, we present a new theoretical and experimental analysis of process tomography on multispin systems, and demonstrate how to more effectively detect and characterize quantum noise using carefully tailored ensembles of input states.

  18. Strong enhancement of s-wave superconductivity near a quantum critical point of (Ca1-xSrx)3Ir4Sn13 and (Ca1-xSrx)3Rh4Sn13

    NASA Astrophysics Data System (ADS)

    Morenzoni, Elvezio; Biswas, Pabitra; Guguchia, Zurab; Khasanov, Rustem; Chinotti, Manuel; Krieger, Jonas; Li, L.; Wang, Kefeng; Petrovic, Cedomir; Pomjakushina, Ekaterina

    We report microscopic studies by muon spin rotation as a function of pressure of the (Ca1-xSrx)3Ir4Sn13 and (Ca1-xSrx)3Rh4Sn13 cubic compounds, which display superconductivity and a structural phase transition associated with the formation of a charge density wave (CDW). In Ca3Ir4Sn13 we find a strong enhancement of the superfluid density and a dramatic increase of the pairing strength above a pressure of ~ 1 . 6 GPa giving direct evidence of the presence of a quantum critical point separating a superconducting phase coexisting with CDW from a pure superconducting phase. The superconducting order parameter in both phases has the same s-wave symmetry. Similar behavior is found in the other family. In spite of the conventional phonon-mediated BCS character of these weakly correlated 3-4-13 systems, the dependence of the effective superfluid density on the critical temperature put these compounds in the ``Uemura'' plot close to unconventional superconductors. These systems exemplify that conventional BCS superconductors can also display characteristics of unconventional superconductors. Supported by the Swiss National Science Foundation and by the U.S. DOE under Contract No. DE-SC00112704.

  19. Quantum memory Quantum memory

    NASA Astrophysics Data System (ADS)

    Le Gouët, Jean-Louis; Moiseev, Sergey

    2012-06-01

    Interaction of quantum radiation with multi-particle ensembles has sparked off intense research efforts during the past decade. Emblematic of this field is the quantum memory scheme, where a quantum state of light is mapped onto an ensemble of atoms and then recovered in its original shape. While opening new access to the basics of light-atom interaction, quantum memory also appears as a key element for information processing applications, such as linear optics quantum computation and long-distance quantum communication via quantum repeaters. Not surprisingly, it is far from trivial to practically recover a stored quantum state of light and, although impressive progress has already been accomplished, researchers are still struggling to reach this ambitious objective. This special issue provides an account of the state-of-the-art in a fast-moving research area that makes physicists, engineers and chemists work together at the forefront of their discipline, involving quantum fields and atoms in different media, magnetic resonance techniques and material science. Various strategies have been considered to store and retrieve quantum light. The explored designs belong to three main—while still overlapping—classes. In architectures derived from photon echo, information is mapped over the spectral components of inhomogeneously broadened absorption bands, such as those encountered in rare earth ion doped crystals and atomic gases in external gradient magnetic field. Protocols based on electromagnetic induced transparency also rely on resonant excitation and are ideally suited to the homogeneous absorption lines offered by laser cooled atomic clouds or ion Coulomb crystals. Finally off-resonance approaches are illustrated by Faraday and Raman processes. Coupling with an optical cavity may enhance the storage process, even for negligibly small atom number. Multiple scattering is also proposed as a way to enlarge the quantum interaction distance of light with matter. The

  20. Quantum Communication

    NASA Astrophysics Data System (ADS)

    Weinfurter, Harald; Zeilinger, Anton

    Quantum entanglement lies at the heart of the new field of quantum communication and computation. For a long time, entanglement was seen just as one of those fancy features which make quantum mechanics so counterintuitive. But recently, quantum information theory has shown the tremendous importance of quantum correlations for the formulation of new methods of information transfer and for algorithms exploiting the capabilities of quantum computers.This chapter describes the first experimental realizations of quantum communication schemes using entangled photon pairs. We show how to make communication secure against eavesdropping using entanglement-based quantum cryptography, how to increase the information capacity of a quantum channel by quantum dense coding and, finally, how to communicate quantum information itself in the process of quantum teleportation.

  1. String theory, quantum phase transitions, and the emergent Fermi liquid.

    PubMed

    Cubrović, Mihailo; Zaanen, Jan; Schalm, Koenraad

    2009-07-24

    A central problem in quantum condensed matter physics is the critical theory governing the zero-temperature quantum phase transition between strongly renormalized Fermi liquids as found in heavy fermion intermetallics and possibly in high-critical temperature superconductors. We found that the mathematics of string theory is capable of describing such fermionic quantum critical states. Using the anti-de Sitter/conformal field theory correspondence to relate fermionic quantum critical fields to a gravitational problem, we computed the spectral functions of fermions in the field theory. By increasing the fermion density away from the relativistic quantum critical point, a state emerges with all the features of the Fermi liquid.

  2. Stark spectroscopy of CdTe and CdMnTe quantum dots embedded in n-i-p diodes

    SciTech Connect

    Kłopotowski, Ł. Fronc, K.; Wojnar, P.; Wiater, M.; Wojtowicz, T.; Karczewski, G.

    2014-05-28

    We investigate charging effects in CdTe and Cd{sub 1−x}Mn{sub x}Te quantum dots embedded in n-i-p diodes. The tunneling of holes out of the dots at reverse bias and hole injection at forward bias control the dot charge state and allow for its electric field tuning. Furthermore, we analyze the Stark shifts of the photoluminescence transitions and evaluate the effect of the electric field on the binding of the observed excitonic complexes. We find that the binding can be strengthened or weakened depending on the zero-field alignment of the electron and hole wavefunctions.

  3. Stark spectroscopy of CdTe and CdMnTe quantum dots embedded in n-i-p diodes

    NASA Astrophysics Data System (ADS)

    Kłopotowski, Ł.; Fronc, K.; Wojnar, P.; Wiater, M.; Wojtowicz, T.; Karczewski, G.

    2014-05-01

    We investigate charging effects in CdTe and Cd1-xMnxTe quantum dots embedded in n-i-p diodes. The tunneling of holes out of the dots at reverse bias and hole injection at forward bias control the dot charge state and allow for its electric field tuning. Furthermore, we analyze the Stark shifts of the photoluminescence transitions and evaluate the effect of the electric field on the binding of the observed excitonic complexes. We find that the binding can be strengthened or weakened depending on the zero-field alignment of the electron and hole wavefunctions.

  4. On the quantum Zeno effect

    NASA Astrophysics Data System (ADS)

    Nakazato, Hiromichi; Namiki, Mikio; Pascazio, Saverio; Rauch, Helmut

    1995-02-01

    The limit of infinitely frequent measurements (continuous observation), yielding the quantum Zeno paradox, is critically analyzed and shown to be unphysical. A specific example involving neutron spin is considered and some practical estimates are given.

  5. Quantum simulation

    NASA Astrophysics Data System (ADS)

    Georgescu, I. M.; Ashhab, S.; Nori, Franco

    2014-01-01

    Simulating quantum mechanics is known to be a difficult computational problem, especially when dealing with large systems. However, this difficulty may be overcome by using some controllable quantum system to study another less controllable or accessible quantum system, i.e., quantum simulation. Quantum simulation promises to have applications in the study of many problems in, e.g., condensed-matter physics, high-energy physics, atomic physics, quantum chemistry, and cosmology. Quantum simulation could be implemented using quantum computers, but also with simpler, analog devices that would require less control, and therefore, would be easier to construct. A number of quantum systems such as neutral atoms, ions, polar molecules, electrons in semiconductors, superconducting circuits, nuclear spins, and photons have been proposed as quantum simulators. This review outlines the main theoretical and experimental aspects of quantum simulation and emphasizes some of the challenges and promises of this fast-growing field.

  6. Critical dynamics and decoherence

    SciTech Connect

    Damski, Bogdan; Quan, Haitao T; Zurek, Wojciech H

    2009-01-01

    We study dynamics of decoherence in a generic model where the environment is driven and undergoes a quantum phase transition. We model the environment by the Ising chain in the transverse field, and assume that the decohering system is a central spin-1/2. We found that when the environment is quenched slowly through the critical point, the decoherence factor of the central spin undergoes rapid decay that encodes the critical exponents of the environment. We also found that decoherence in a non-equilibrated, kink-contaminated, environment can be stronger than in a vacuum one. We derived a remarkably simple analytical expression that describes post-transition decoherence and predicts periodicities involving all system parameters. This research connects the fields of decoherence, quantum phase transitions, and Kibble-Zurek non-equilibrium dynamics.

  7. Karl Popper's Quantum Ghost

    NASA Astrophysics Data System (ADS)

    Shields, William

    2004-05-01

    Karl Popper, though not trained as a physicist and embarrassed early in his career by a physics error pointed out by Einstein and Bohr, ultimately made substantial contributions to the interpretation of quantum mechanics. As was often the case, Popper initially formulated his position by criticizing the views of others - in this case Niels Bohr and Werner Heisenberg. Underlying Popper's criticism was his belief that, first, the "standard interpretation" of quantum mechanics, sometimes called the Copenhagen interpretation, abandoned scientific realism and second, the assertion that quantum theory was "complete" (an assertion rejected by Einstein among others) amounted to an unfalsifiable claim. Popper insisted that the most basic predictions of quantum mechanics should continue to be tested, with an eye towards falsification rather than mere adding of decimal places to confirmatory experiments. His persistent attacks on the Copenhagen interpretation were aimed not at the uncertainty principle itself and the formalism from which it was derived, but at the acceptance by physicists of an unclear epistemology and ontology that left critical questions unanswered. In 1999, physicists at the University of Maryland conducted a version of Popper's Experiment, re-igniting the debate over quantum predictions and the role of locality in physics.

  8. Analysis of limiting information characteristics of quantum-cryptography protocols

    SciTech Connect

    Sych, D V; Grishanin, Boris A; Zadkov, Viktor N

    2005-01-31

    The problem of increasing the critical error rate of quantum-cryptography protocols by varying a set of letters in a quantum alphabet for space of a fixed dimensionality is studied. Quantum alphabets forming regular polyhedra on the Bloch sphere and the continual alphabet equally including all the quantum states are considered. It is shown that, in the absence of basis reconciliation, a protocol with the tetrahedral alphabet has the highest critical error rate among the protocols considered, while after the basis reconciliation, a protocol with the continual alphabet possesses the highest critical error rate. (quantum optics and quantum computation)

  9. Supersymmetric extension of the quantum spherical model

    NASA Astrophysics Data System (ADS)

    Gomes, Pedro R. S.; Bienzobaz, P. F.; Gomes, M.

    2012-06-01

    In this work, we present a supersymmetric extension of the quantum spherical model, both in components and also in the superspace formalisms. We find the solution for short- and long-range interactions through the imaginary time formalism path integral approach. The existence of critical points (classical and quantum) is analyzed and the corresponding critical dimensions are determined.

  10. Quantum ontologies

    SciTech Connect

    Stapp, H.P.

    1988-12-01

    Quantum ontologies are conceptions of the constitution of the universe that are compatible with quantum theory. The ontological orientation is contrasted to the pragmatic orientation of science, and reasons are given for considering quantum ontologies both within science, and in broader contexts. The principal quantum ontologies are described and evaluated. Invited paper at conference: Bell's Theorem, Quantum Theory, and Conceptions of the Universe, George Mason University, October 20-21, 1988. 16 refs.

  11. Quantum critical fluctuations in the heavy fermion compound Ce(Ni0.935 Pd0.065)2Ge2

    SciTech Connect

    Wang, C. H.; Poudel, L.; Taylor, A. E.; Lawrence, J. M.; Christianson, A. D.; Chang, S.; Rodriguez-Rivera, J. A.; Lynn, J. W.; Podlesnyak, A. A.; Ehlers, G.; Baumbach, R. E.; Bauer, E. D.; Gofryk, K.; Ronning, F.; McClellan, K. J.; Thompson, J. D.

    2015-01-14

    Electric resistivity, specific heat, magnetic susceptibility, and inelastic neutron scattering experi- ments were performed on a single crystal of the heavy fermion compound Ce(Ni0.935 Pd0.065)2Ge2 in order to study the spin fluctuations near an antiferromagnetic (AF) quantum critical point (QCP). The resistivity and the specific heat coefficient for T ≤ 1 K exhibit the power law behavior expected for a 3D itinerant AF QCP (ρ(T) ~ T3/2 and γ(T) ~ γ0 - bT1/2). However, for 2 ≤ T ≤ 10 K, the susceptibility and specific heat vary as log T and the resistivity varies linearly with temperature. Furthermore, despite the fact that the resistivity and specific heat exhibit the non-Fermi liquid behavior expected at a QCP, the correlation length, correlation time, and staggered susceptibility of the spin fluctuations remain finite at low temperature. We suggest that these deviations from the divergent behavior expected for a QCP may result from alloy disorder.

  12. Poisoning effect of Mn in LaFe1-xMnxAsO0.89F0.11: Unveiling a quantum critical point in the phase diagram of iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Hammerath, F.; Bonfà, P.; Sanna, S.; Prando, G.; De Renzi, R.; Kobayashi, Y.; Sato, M.; Carretta, P.

    2014-04-01

    A superconducting-to-magnetic transition is reported for LaFeAsO0.89F0.11 where a per-thousand amount of Mn impurities is dispersed. By employing local spectroscopic techniques like muon spin rotation (μSR) and nuclear quadrupole resonance (NQR) on compounds with Mn contents ranging from x =0.025% to x =0.75%, we find that the electronic properties are extremely sensitive to the Mn impurities. In fact, a small amount of Mn as low as 0.2% suppresses superconductivity completely. Static magnetism, involving the FeAs planes, is observed to arise for x >0.1% and becomes further enhanced upon increasing Mn substitution. Also a progressive increase of low-energy spin fluctuations, leading to an enhancement of the NQR spin-lattice relaxation rate T1-1, is observed upon Mn substitution. The analysis of T1-1 for the sample closest to the crossover between superconductivity and magnetism (x =0.2%) points toward the presence of an antiferromagnetic quantum critical point around that doping level.

  13. Quantum critical fluctuations in the heavy fermion compound Ce(Ni0.935Pd0.065)2Ge2

    SciTech Connect

    Wang, C. H.; Poudel, L.; Taylor, Alice E.; Lawrence, J M.; Christianson, Andrew D.; Chang, S.; Rodriguez-Rivera, J. A.; Lynn, J. W.; Podlesnyak, Andrey A.; Ehlers, G.; Baumbach, R. E.; Bauer, E. D.; Gofryk, Krzysztof; Ronning, F.; Mcclellan, K. J.; Thompson, J. D.

    2014-12-03

    Electric resistivity, specific heat, magnetic susceptibility, and inelastic neutron scattering experiments were performed on a single crystal of the heavy fermion compound Ce(Ni0.935Pd0.065)2Ge2 in order to research the spin fluctuations near an antiferromagnetic (AF) quantum critical point (QCP). The resistivity and the specific heat coefficient for T ≤ 1 K exhibit the power law behavior expected for a 3D itinerant AF QCP (ρ(T) ~ T3/2 and γ(T) ~ γ0 - bT1/2). However, for 2 ≤ T ≤ 10 K, the susceptibility and specific heat vary as log T and the resistivity varies linearly with temperature. In addition, despite the fact that the resistivity and specific heat exhibit the non-Fermi liquid behavior expected at a QCP, the correlation length, correlation time, and staggered susceptibility of the spin fluctuations remain finite at low temperature. In conclusion, we suggest that these deviations from the divergent behavior expected for a QCP may result from alloy disorder.

  14. Magnetic short-range correlations and quantum critical scattering in the non-Fermi liquid regime of URu{sub 2-x}Re{sub x}Si{sub 2} (x = 0.2-0.6).

    SciTech Connect

    Krishnamurthy, V. V.; Adroja, D. T.; Butch, N. P.; Osborn, R.; Sinha, S. K.; Robertson, J. L.; Aronson, M. C.; Nagler, S. E.; Maple, M. B.; ORNL; Rutherford Appleton Lab.; Univ. California at San Diego; Univ. Michigan

    2008-01-01

    The spin dynamics of uranium ions in the non-Fermi liquid compounds URu{sub 2-x}Re{sub x}Si{sub 2}, for x=0.2 to 0.6, have been investigated using inelastic neutron scattering. The wave vector (q) dependence of the magnetic scattering provides evidence of short-range antiferromagnetic correlations at low temperatures for x=0.2,0.25, but the scattering is nearly q independent at x=0.35,0.6. The magnetic response, {bar S}({omega}), obtained from the q-independent part of neutron scattering, varies as {omega}{sup -{alpha}} with a composition-dependent exponent {alpha} = 0.2-0.5. The dynamic magnetic susceptibility {chi}{double_prime}(q,{omega}) of the q-independent part exhibits {omega}/T scaling for the energy transfer {bar h}{omega} between 3.5 and 17 meV in the temperature (T) range of 5-300 K at all the compositions. This scaling, which indicates local quantum criticality, breaks down in the q range, 0.6-1.1 {angstrom}{sup -1} at x = 0.2 and 0.25, that is dominated by short-range antiferromagnetic correlations. The appearance of power laws in the magnetic response measured by inelastic neutron scattering over a wide Re doping region indicates a disorder driven non-Fermi liquid mechanism for the low-temperature physical properties in these compounds.

  15. Global quantum discord in multipartite systems

    SciTech Connect

    Rulli, C. C.; Sarandy, M. S.

    2011-10-15

    We propose a global measure for quantum correlations in multipartite systems, which is obtained by suitably recasting the quantum discord in terms of relative entropy and local von Neumann measurements. The measure is symmetric with respect to subsystem exchange and is shown to be nonnegative for an arbitrary state. As an illustration, we consider tripartite correlations in the Werner-GHZ (Greenberger-Horne-Zeilinger) state and multipartite correlations at quantum criticality. In particular, in contrast with the pairwise quantum discord, we show that the global quantum discord is able to characterize the infinite-order quantum phase transition in the Ashkin-Teller spin chain.

  16. Quantum biology on the edge of quantum chaos.

    PubMed

    Vattay, Gabor; Kauffman, Stuart; Niiranen, Samuli

    2014-01-01

    We give a new explanation for why some biological systems can stay quantum coherent for a long time at room temperature, one of the fundamental puzzles of quantum biology. We show that systems with the right level of complexity between chaos and regularity can increase their coherence time by orders of magnitude. Systems near Critical Quantum Chaos or Metal-Insulator Transition (MIT) can have long coherence times and coherent transport at the same time. The new theory tested in a realistic light harvesting system model can reproduce the scaling of critical fluctuations reported in recent experiments. Scaling of return probability in the FMO light harvesting complex shows the signs of universal return probability decay observed at critical MIT. The results may open up new possibilities to design low loss energy and information transport systems in this Poised Realm hovering reversibly between quantum coherence and classicality.

  17. Quantum Computer Games: Quantum Minesweeper

    ERIC Educational Resources Information Center

    Gordon, Michal; Gordon, Goren

    2010-01-01

    The computer game of quantum minesweeper is introduced as a quantum extension of the well-known classical minesweeper. Its main objective is to teach the unique concepts of quantum mechanics in a fun way. Quantum minesweeper demonstrates the effects of superposition, entanglement and their non-local characteristics. While in the classical…

  18. Quantum memristors

    PubMed Central

    Pfeiffer, P.; Egusquiza, I. L.; Di Ventra, M.; Sanz, M.; Solano, E.

    2016-01-01

    Technology based on memristors, resistors with memory whose resistance depends on the history of the crossing charges, has lately enhanced the classical paradigm of computation with neuromorphic architectures. However, in contrast to the known quantized models of passive circuit elements, such as inductors, capacitors or resistors, the design and realization of a quantum memristor is still missing. Here, we introduce the concept of a quantum memristor as a quantum dissipative device, whose decoherence mechanism is controlled by a continuous-measurement feedback scheme, which accounts for the memory. Indeed, we provide numerical simulations showing that memory effects actually persist in the quantum regime. Our quantization method, specifically designed for superconducting circuits, may be extended to other quantum platforms, allowing for memristor-type constructions in different quantum technologies. The proposed quantum memristor is then a building block for neuromorphic quantum computation and quantum simulations of non-Markovian systems. PMID:27381511

  19. Quantum memristors.

    PubMed

    Pfeiffer, P; Egusquiza, I L; Di Ventra, M; Sanz, M; Solano, E

    2016-01-01

    Technology based on memristors, resistors with memory whose resistance depends on the history of the crossing charges, has lately enhanced the classical paradigm of computation with neuromorphic architectures. However, in contrast to the known quantized models of passive circuit elements, such as inductors, capacitors or resistors, the design and realization of a quantum memristor is still missing. Here, we introduce the concept of a quantum memristor as a quantum dissipative device, whose decoherence mechanism is controlled by a continuous-measurement feedback scheme, which accounts for the memory. Indeed, we provide numerical simulations showing that memory effects actually persist in the quantum regime. Our quantization method, specifically designed for superconducting circuits, may be extended to other quantum platforms, allowing for memristor-type constructions in different quantum technologies. The proposed quantum memristor is then a building block for neuromorphic quantum computation and quantum simulations of non-Markovian systems. PMID:27381511

  20. Quantum memristors.

    PubMed

    Pfeiffer, P; Egusquiza, I L; Di Ventra, M; Sanz, M; Solano, E

    2016-07-06

    Technology based on memristors, resistors with memory whose resistance depends on the history of the crossing charges, has lately enhanced the classical paradigm of computation with neuromorphic architectures. However, in contrast to the known quantized models of passive circuit elements, such as inductors, capacitors or resistors, the design and realization of a quantum memristor is still missing. Here, we introduce the concept of a quantum memristor as a quantum dissipative device, whose decoherence mechanism is controlled by a continuous-measurement feedback scheme, which accounts for the memory. Indeed, we provide numerical simulations showing that memory effects actually persist in the quantum regime. Our quantization method, specifically designed for superconducting circuits, may be extended to other quantum platforms, allowing for memristor-type constructions in different quantum technologies. The proposed quantum memristor is then a building block for neuromorphic quantum computation and quantum simulations of non-Markovian systems.

  1. Quantum memristors

    NASA Astrophysics Data System (ADS)

    Pfeiffer, P.; Egusquiza, I. L.; di Ventra, M.; Sanz, M.; Solano, E.

    2016-07-01

    Technology based on memristors, resistors with memory whose resistance depends on the history of the crossing charges, has lately enhanced the classical paradigm of computation with neuromorphic architectures. However, in contrast to the known quantized models of passive circuit elements, such as inductors, capacitors or resistors, the design and realization of a quantum memristor is still missing. Here, we introduce the concept of a quantum memristor as a quantum dissipative device, whose decoherence mechanism is controlled by a continuous-measurement feedback scheme, which accounts for the memory. Indeed, we provide numerical simulations showing that memory effects actually persist in the quantum regime. Our quantization method, specifically designed for superconducting circuits, may be extended to other quantum platforms, allowing for memristor-type constructions in different quantum technologies. The proposed quantum memristor is then a building block for neuromorphic quantum computation and quantum simulations of non-Markovian systems.

  2. Quantum Teardrops

    NASA Astrophysics Data System (ADS)

    Brzeziński, Tomasz; Fairfax, Simon A.

    2012-11-01

    Algebras of functions on quantum weighted projective spaces are introduced, and the structure of quantum weighted projective lines or quantum teardrops is described in detail. In particular the presentation of the coordinate algebra of the quantum teardrop in terms of generators and relations and classification of irreducible *-representations are derived. The algebras are then analysed from the point of view of Hopf-Galois theory or the theory of quantum principal bundles. Fredholm modules and associated traces are constructed. C*-algebras of continuous functions on quantum weighted projective lines are described and their K-groups computed.

  3. Thinking Critically about Critical Thinking

    ERIC Educational Resources Information Center

    Mulnix, Jennifer Wilson

    2012-01-01

    As a philosophy professor, one of my central goals is to teach students to think critically. However, one difficulty with determining whether critical thinking can be taught, or even measured, is that there is widespread disagreement over what critical thinking actually is. Here, I reflect on several conceptions of critical thinking, subjecting…

  4. Critical assumptions: thinking critically about critical thinking.

    PubMed

    Riddell, Thelma

    2007-03-01

    The concept of critical thinking has been featured in nursing literature for the past 20 years. It has been described but not defined by both the American Association of Colleges of Nursing and the National League for Nursing, although their corresponding accreditation bodies require that critical thinking be included in nursing curricula. In addition, there is no reliable or valid measurement tool for critical thinking ability in nursing. As a result, there is a lack of research support for the assumptions that critical thinking can be learned and that critical thinking ability improves clinical competence. Brookfield suggested that commitments should be made only after a period of critically reflective analysis, during which the congruence between perceptions and reality are examined. In an evidence-based practice profession, we, as nurse educators, need to ask ourselves how we can defend our assumptions that critical thinking can be learned and that critical thinking improves the quality of nursing practice, especially when there is virtually no consensus on a definition.

  5. Linear response at criticality

    NASA Astrophysics Data System (ADS)

    Svenkeson, Adam; Bologna, Mauro; Grigolini, Paolo

    2012-10-01

    We study a set of cooperatively interacting units at criticality, and we prove with analytical and numerical arguments that they generate the same renewal non-Poisson intermittency as that produced by blinking quantum dots, thereby giving a stronger support to the results of earlier investigation. By analyzing how this out-of-equilibrium system responds to harmonic perturbations, we find that the response can be described only using a new form of linear response theory that accounts for aging and the nonergodic behavior of the underlying process. We connect the undamped response of the system at criticality to the decaying response predicted by the recently established nonergodic fluctuation-dissipation theorem for dichotomous processes using information about the second moment of the fluctuations. We demonstrate that over a wide range of perturbation frequencies the response of the cooperative system is greatest when at criticality.

  6. Horizon as critical phenomenon

    NASA Astrophysics Data System (ADS)

    Lee, Sung-Sik

    2016-09-01

    We show that renormalization group flow can be viewed as a gradual wave function collapse, where a quantum state associated with the action of field theory evolves toward a final state that describes an IR fixed point. The process of collapse is described by the radial evolution in the dual holographic theory. If the theory is in the same phase as the assumed IR fixed point, the initial state is smoothly projected to the final state. If in a different phase, the initial state undergoes a phase transition which in turn gives rise to a horizon in the bulk geometry. We demonstrate the connection between critical behavior and horizon in an example, by deriving the bulk metrics that emerge in various phases of the U( N ) vector model in the large N limit based on the holographic dual constructed from quantum renormalization group. The gapped phase exhibits a geometry that smoothly ends at a finite proper distance in the radial direction. The geometric distance in the radial direction measures a complexity: the depth of renormalization group transformation that is needed to project the generally entangled UV state to a direct product state in the IR. For gapless states, entanglement persistently spreads out to larger length scales, and the initial state can not be projected to the direct product state. The obstruction to smooth projection at charge neutral point manifests itself as the long throat in the anti-de Sitter space. The Poincare horizon at infinity marks the critical point which exhibits a divergent length scale in the spread of entanglement. For the gapless states with non-zero chemical potential, the bulk space becomes the Lifshitz geometry with the dynamical critical exponent two. The identification of horizon as critical point may provide an explanation for the universality of horizon. We also discuss the structure of the bulk tensor network that emerges from the quantum renormalization group.

  7. Quantum Darwinism

    SciTech Connect

    Zurek, Wojciech H

    2008-01-01

    Quantum Darwinism - proliferation, in the environment, of multiple records of selected states of the system (its information-theoretic progeny) - explains how quantum fragility of individual state can lead to classical robustness of their multitude.

  8. Quantum memristors

    DOE PAGESBeta

    Pfeiffer, P.; Egusquiza, I. L.; Di Ventra, M.; Sanz, M.; Solano, E.

    2016-07-06

    Technology based on memristors, resistors with memory whose resistance depends on the history of the crossing charges, has lately enhanced the classical paradigm of computation with neuromorphic architectures. However, in contrast to the known quantized models of passive circuit elements, such as inductors, capacitors or resistors, the design and realization of a quantum memristor is still missing. Here, we introduce the concept of a quantum memristor as a quantum dissipative device, whose decoherence mechanism is controlled by a continuous-measurement feedback scheme, which accounts for the memory. Indeed, we provide numerical simulations showing that memory effects actually persist in the quantummore » regime. Our quantization method, specifically designed for superconducting circuits, may be extended to other quantum platforms, allowing for memristor-type constructions in different quantum technologies. As a result, the proposed quantum memristor is then a building block for neuromorphic quantum computation and quantum simulations of non-Markovian systems.« less

  9. Critical Care

    MedlinePlus

    Critical care helps people with life-threatening injuries and illnesses. It might treat problems such as complications from surgery, ... attention by a team of specially-trained health care providers. Critical care usually takes place in an ...

  10. Spin dynamics near a putative antiferromagnetic quantum critical point in Cu-substituted BaFe2As2 and its relation to high-temperature superconductivity

    SciTech Connect

    Kim, M. G.; Wang, M.; Tucker, G. S.; Valdivia, P. N.; Abernathy, D. L.; Chi, Songxue; Christianson, A. D.; Aczel, A. A.; Hong, T.; Heitmann, T. W.; Ran, S.; Canfield, P. C.; Bourret-Courchesne, E. D.; Kreyssig, A.; Lee, D. H.; Goldman, A. I.; McQueeney, R. J.; Birgeneau, R. J.

    2015-12-02

    We present the results of elastic and inelastic neutron scattering measurements on nonsuperconducting Ba(Fe0.957Cu0.043)2As2, a composition close to a quantum critical point between antiferromagnetic (AFM) ordered and paramagnetic phases. By comparing these results with the spin fluctuations in the low-Cu composition as well as the parent compound BaFe2As2 and superconducting Ba(Fe1–xNix)2As2 compounds, we demonstrate that paramagnon-like spin fluctuations are evident in the antiferromagnetically ordered state of Ba(Fe0.957Cu0.043)2As2, which is distinct from the AFM-like spin fluctuations in the superconducting compounds. Our observations suggest that Cu substitution decouples the interaction between quasiparticles and the spin fluctuations. In addition, we show that the spin-spin correlation length ξ(T) increases rapidly as the temperature is lowered and find ω/T scaling behavior, the hallmark of quantum criticality, at an antiferromagnetic quantum critical point.

  11. Archetypal Criticism.

    ERIC Educational Resources Information Center

    Chesebro, James W.; And Others

    1990-01-01

    Argues that archetypal criticism is a useful way of examining universal, historical, and cross-cultural symbols in classrooms. Identifies essential features of an archetype; outlines operational and critical procedures; illustrates archetypal criticism as applied to the cross as a symbol; and provides a synoptic placement for archetypal criticism…

  12. Kondo Effect at a Quantum Critical Point

    NASA Astrophysics Data System (ADS)

    Ramazashvili, Revaz; Coleman, Piers

    1998-03-01

    The Kondo effect in a metal on the verge of a zero-temperature magnetic instability provides a fascinating example of interference between local and long-range correlations. (A. I. Larkin and V. I. Mel'nikov, Sov. Phys. JETP 34, 656 (1972)) (P. Coleman and A. M. Tsvelik, cond-mat/9707003) (A. Sengupta, cond-mat/9707316) We discuss possible consequences of this interference, including the breakdown of the Fermi liquid state.

  13. Quantum critical behavior of semisimple gauge theories

    NASA Astrophysics Data System (ADS)

    Esbensen, Jacob Kamuk; Ryttov, Thomas A.; Sannino, Francesco

    2016-02-01

    We study the perturbative phase diagram of semisimple fermionic gauge theories resembling the Standard Model. We investigate an S U (N ) gauge theory with M Dirac flavors where we gauge first an S U (M )L and then an S U (2 )L⊂S U (M )L of the original global symmetry S U (M )L×S U (M )R×U (1 ) of the theory. To avoid gauge anomalies we add leptonlike particles. At the two-loop level an intriguing phase diagram appears. We uncover phases in which one, two or three fixed points exist and discuss the associated flows of the coupling constants. We discover a phase featuring complete asymptotic freedom and simultaneously an interacting infrared fixed point in both couplings. The analysis further reveals special renormalization group trajectories along which one coupling displays asymptotic freedom and the other asymptotic safety, while both flowing in the infrared to an interacting fixed point. These are safety free trajectories. We briefly sketch out possible phenomenological implications, among which an independent way to generate near-conformal dynamics à la walking is investigated.

  14. Coherence susceptibility as a probe of quantum phase transitions

    NASA Astrophysics Data System (ADS)

    Chen, Jin-Jun; Cui, Jian; Zhang, Yu-Ran; Fan, Heng

    2016-08-01

    We introduce a coherence susceptibility method, based on the fact that it signals quantum fluctuations, for identifying quantum phase transitions, which are induced by quantum fluctuations. This method requires no prior knowledge of order parameter, and there is no need for careful considerations concerning the choice of a bipartition of the system. It can identify different types of quantum phase transition points exactly. At finite temperatures, where quantum criticality is influenced by thermal fluctuations, our method can pinpoint the temperature frame of quantum criticality, which perfectly coincides with recent experiments.

  15. Quantum frames

    NASA Astrophysics Data System (ADS)

    Brown, Matthew J.

    2014-02-01

    The framework of quantum frames can help unravel some of the interpretive difficulties i the foundation of quantum mechanics. In this paper, I begin by tracing the origins of this concept in Bohr's discussion of quantum theory and his theory of complementarity. Engaging with various interpreters and followers of Bohr, I argue that the correct account of quantum frames must be extended beyond literal space-time reference frames to frames defined by relations between a quantum system and the exosystem or external physical frame, of which measurement contexts are a particularly important example. This approach provides superior solutions to key EPR-type measurement and locality paradoxes.

  16. Quantum cheques

    NASA Astrophysics Data System (ADS)

    Moulick, Subhayan Roy; Panigrahi, Prasanta K.

    2016-06-01

    We propose the idea of a quantum cheque scheme, a cryptographic protocol in which any legitimate client of a trusted bank can issue a cheque, that cannot be counterfeited or altered in anyway, and can be verified by a bank or any of its branches. We formally define a quantum cheque and present the first unconditionally secure quantum cheque scheme and show it to be secure against any no-signalling adversary. The proposed quantum cheque scheme can been perceived as the quantum analog of Electronic Data Interchange, as an alternate for current e-Payment Gateways.

  17. Quantum Darwinism

    NASA Astrophysics Data System (ADS)

    Zurek, Wojciech Hubert

    2009-03-01

    Quantum Darwinism describes the proliferation, in the environment, of multiple records of selected states of a quantum system. It explains how the quantum fragility of a state of a single quantum system can lead to the classical robustness of states in their correlated multitude; shows how effective `wave-packet collapse' arises as a result of the proliferation throughout the environment of imprints of the state of the system; and provides a framework for the derivation of Born's rule, which relates the probabilities of detecting states to their amplitudes. Taken together, these three advances mark considerable progress towards settling the quantum measurement problem.

  18. Critical Thinking vs. Critical Consciousness

    ERIC Educational Resources Information Center

    Doughty, Howard A.

    2006-01-01

    This article explores four kinds of critical thinking. The first is found in Socratic dialogues, which employ critical thinking mainly to reveal logical fallacies in common opinions, thus cleansing superior minds of error and leaving philosophers free to contemplate universal verities. The second is critical interpretation (hermeneutics) which…

  19. Critically Thinking about Critical Thinking

    ERIC Educational Resources Information Center

    Weissberg, Robert

    2013-01-01

    In this article, the author states that "critical thinking" has mesmerized academics across the political spectrum and that even high school students are now being called upon to "think critically." He furthers adds that it is no exaggeration to say that "critical thinking" has quickly evolved into a scholarly…

  20. How Critical Is Critical Thinking?

    ERIC Educational Resources Information Center

    Shaw, Ryan D.

    2014-01-01

    Recent educational discourse is full of references to the value of critical thinking as a 21st-century skill. In music education, critical thinking has been discussed in relation to problem solving and music listening, and some researchers suggest that training in critical thinking can improve students' responses to music. But what exactly is…

  1. Quantum Cryptography

    NASA Astrophysics Data System (ADS)

    Fehr, Serge

    2010-05-01

    Quantum cryptography makes use of the quantum-mechanical behavior of nature for the design and analysis of cryptographic schemes. Optimally (but not always), quantum cryptography allows for the design of cryptographic schemes whose security is guaranteed solely by the laws of nature. This is in sharp contrast to standard cryptographic schemes, which can be broken in principle, i.e., when given sufficient computing power. From a theory point of view, quantum cryptography offers a beautiful interplay between the mathematics of adversarial behavior and quantum information theory. In this review article, we discuss the traditional application of quantum cryptography, quantum key distribution (QKD), from a modern perspective, and we discuss some recent developments in the context of quantum two-party cooperation (2PC). QKD allows two distant parties to communicate in a provably-secure way in the presence of an outside eavesdropper, whereas 2PC is concerned with protecting information against possibly malicious insiders. We show the basic idea of constructing quantum cryptographic schemes, but we also show some connections to quantum information theory as needed for the rigorous security analyses, and we discuss some of the relevant quantum-information-theoretic results.

  2. Quantum Optics

    NASA Astrophysics Data System (ADS)

    Orvil Scully, Marlan; Zubairy, Muhammad Suhail

    1997-09-01

    Quantum optics has witnessed significant theoretical and experimental developments in recent years. This book provides an in-depth and wide-ranging introduction to the subject, emphasizing throughout the basic principles and their applications. The book begins by developing the basic tools of quantum optics, and goes on to show the application of these tools in a variety of quantum optical systems, including lasing without inversion, squeezed states, and atom optics. The final four chapters discuss quantum optical tests of the foundations of quantum mechanics, and particular aspects of measurement theory. Assuming only a background of standard quantum mechanics and electromagnetic theory, and containing many problems and references, this book will be invaluable to graduate students of quantum optics, as well as to researchers in this field.

  3. Magnetoresistance from quantum interference effects in ferromagnets

    PubMed

    Manyala; Sidis; DiTusa; Aeppli; Young; Fisk

    2000-04-01

    The desire to maximize the sensitivity of read/write heads (and thus the information density) of magnetic storage devices has stimulated interest in the discovery and design of new magnetic materials exhibiting magnetoresistance. Recent discoveries include the 'colossal' magnetoresistance in the manganites and the enhanced magnetoresistance in low-carrier-density ferromagnets. An important feature of these systems is that the electrons involved in electrical conduction are different from those responsible for the magnetism. The latter are localized and act as scattering sites for the mobile electrons, and it is the field tuning of the scattering strength that ultimately gives rise to the observed magnetoresistance. Here we argue that magnetoresistance can arise by a different mechanism in certain ferromagnets--quantum interference effects rather than simple scattering. The ferromagnets in question are disordered, low-carrier-density magnets where the same electrons are responsible for both the magnetic properties and electrical conduction. The resulting magnetoresistance is positive (that is, the resistance increases in response to an applied magnetic field) and only weakly temperature-dependent below the Curie point.

  4. Quantum emitters dynamically coupled to a quantum field

    NASA Astrophysics Data System (ADS)

    Acevedo, O. L.; Quiroga, L.; Rodríguez, F. J.; Johnson, N. F.

    2013-12-01

    We study theoretically the dynamical response of a set of solid-state quantum emitters arbitrarily coupled to a single-mode microcavity system. Ramping the matter-field coupling strength in round trips, we quantify the hysteresis or irreversible quantum dynamics. The matter-field system is modeled as a finite-size Dicke model which has previously been used to describe equilibrium (including quantum phase transition) properties of systems such as quantum dots in a microcavity. Here we extend this model to address non-equilibrium situations. Analyzing the system's quantum fidelity, we find that the near-adiabatic regime exhibits the richest phenomena, with a strong asymmetry in the internal collective dynamics depending on which phase is chosen as the starting point. We also explore signatures of the crossing of the critical points on the radiation subsystem by monitoring its Wigner function; then, the subsystem can exhibit the emergence of non-classicality and complexity.

  5. Quantum emitters dynamically coupled to a quantum field

    SciTech Connect

    Acevedo, O. L.; Quiroga, L.; Rodríguez, F. J.; Johnson, N. F.

    2013-12-04

    We study theoretically the dynamical response of a set of solid-state quantum emitters arbitrarily coupled to a single-mode microcavity system. Ramping the matter-field coupling strength in round trips, we quantify the hysteresis or irreversible quantum dynamics. The matter-field system is modeled as a finite-size Dicke model which has previously been used to describe equilibrium (including quantum phase transition) properties of systems such as quantum dots in a microcavity. Here we extend this model to address non-equilibrium situations. Analyzing the system’s quantum fidelity, we find that the near-adiabatic regime exhibits the richest phenomena, with a strong asymmetry in the internal collective dynamics depending on which phase is chosen as the starting point. We also explore signatures of the crossing of the critical points on the radiation subsystem by monitoring its Wigner function; then, the subsystem can exhibit the emergence of non-classicality and complexity.

  6. Quantum Feedback Amplification

    NASA Astrophysics Data System (ADS)

    Yamamoto, Naoki

    2016-04-01

    Quantum amplification is essential for various quantum technologies such as communication and weak-signal detection. However, its practical use is still limited due to inevitable device fragility that brings about distortion in the output signal or state. This paper presents a general theory that solves this critical issue. The key idea is simple and easy to implement: just a passive feedback of the amplifier's auxiliary mode, which is usually thrown away. In fact, this scheme makes the controlled amplifier significantly robust, and furthermore it realizes the minimum-noise amplification even under realistic imperfections. Hence, the presented theory enables the quantum amplification to be implemented at a practical level. Also, a nondegenerate parametric amplifier subjected to a special detuning is proposed to show that, additionally, it has a broadband nature.

  7. Consistent quantum measurements

    NASA Astrophysics Data System (ADS)

    Griffiths, Robert B.

    2015-11-01

    In response to recent criticisms by Okon and Sudarsky, various aspects of the consistent histories (CH) resolution of the quantum measurement problem(s) are discussed using a simple Stern-Gerlach device, and compared with the alternative approaches to the measurement problem provided by spontaneous localization (GRW), Bohmian mechanics, many worlds, and standard (textbook) quantum mechanics. Among these CH is unique in solving the second measurement problem: inferring from the measurement outcome a property of the measured system at a time before the measurement took place, as is done routinely by experimental physicists. The main respect in which CH differs from other quantum interpretations is in allowing multiple stochastic descriptions of a given measurement situation, from which one (or more) can be selected on the basis of its utility. This requires abandoning a principle (termed unicity), central to classical physics, that at any instant of time there is only a single correct description of the world.

  8. Criticality Model

    SciTech Connect

    A. Alsaed

    2004-09-14

    The ''Disposal Criticality Analysis Methodology Topical Report'' (YMP 2003) presents the methodology for evaluating potential criticality situations in the monitored geologic repository. As stated in the referenced Topical Report, the detailed methodology for performing the disposal criticality analyses will be documented in model reports. Many of the models developed in support of the Topical Report differ from the definition of models as given in the Office of Civilian Radioactive Waste Management procedure AP-SIII.10Q, ''Models'', in that they are procedural, rather than mathematical. These model reports document the detailed methodology necessary to implement the approach presented in the Disposal Criticality Analysis Methodology Topical Report and provide calculations utilizing the methodology. Thus, the governing procedure for this type of report is AP-3.12Q, ''Design Calculations and Analyses''. The ''Criticality Model'' is of this latter type, providing a process evaluating the criticality potential of in-package and external configurations. The purpose of this analysis is to layout the process for calculating the criticality potential for various in-package and external configurations and to calculate lower-bound tolerance limit (LBTL) values and determine range of applicability (ROA) parameters. The LBTL calculations and the ROA determinations are performed using selected benchmark experiments that are applicable to various waste forms and various in-package and external configurations. The waste forms considered in this calculation are pressurized water reactor (PWR), boiling water reactor (BWR), Fast Flux Test Facility (FFTF), Training Research Isotope General Atomic (TRIGA), Enrico Fermi, Shippingport pressurized water reactor, Shippingport light water breeder reactor (LWBR), N-Reactor, Melt and Dilute, and Fort Saint Vrain Reactor spent nuclear fuel (SNF). The scope of this analysis is to document the criticality computational method. The criticality

  9. Quantum entanglement, quantum communication and the limits of quantum computing

    NASA Astrophysics Data System (ADS)

    Ambainis, Andris

    Quantum entanglement is a term describing the quantum correlations between different parts of a quantum system. Quantum information theory has developed sophisticated techniques to quantify and study quantum entanglement. In this thesis, we show how to apply those techniques to problems in quantum algorithms, complexity theory, communication and cryptography. The main results are: (1) quantum communication protocols that are exponentially more efficient that conventional (classical) communication protocols, (2) unconditionally secure quantum protocols for cryptographic problems, (3) a new "quantum adversary" method for proving lower bounds on quantum algorithms, (4) a study of "one clean qubit computation", a model related to the experimental implementation of quantum computers using NMR (nucleo-magnetic resonance) technology.

  10. Quantum volume

    NASA Astrophysics Data System (ADS)

    Ryabov, V. A.

    2015-08-01

    Quantum systems in a mechanical embedding, the breathing mode of a small particles, optomechanical system, etc. are far not the full list of examples in which the volume exhibits quantum behavior. Traditional consideration suggests strain in small systems as a result of a collective movement of particles, rather than the dynamics of the volume as an independent variable. The aim of this work is to show that some problem here might be essentially simplified by introducing periodic boundary conditions. At this case, the volume is considered as the independent dynamical variable driven by the internal pressure. For this purpose, the concept of quantum volume based on Schrödinger’s equation in 𝕋3 manifold is proposed. It is used to explore several 1D model systems: An ensemble of free particles under external pressure, quantum manometer and a quantum breathing mode. In particular, the influence of the pressure of free particle on quantum oscillator is determined. It is shown also that correction to the spectrum of the breathing mode due to internal degrees of freedom is determined by the off-diagonal matrix elements of the quantum stress. The new treatment not using the “force” theorem is proposed for the quantum stress tensor. In the general case of flexible quantum 3D dynamics, quantum deformations of different type might be introduced similarly to monopole mode.

  11. Experimental teleportation of a quantum controlled-NOT gate.

    PubMed

    Huang, Yun-Feng; Ren, Xi-Feng; Zhang, Yong-Sheng; Duan, Lu-Ming; Guo, Guang-Can

    2004-12-10

    Teleportation of quantum gates is a critical step for the implementation of quantum networking and teleportation-based models of quantum computation. We report an experimental demonstration of teleportation of the prototypical quantum controlled-NOT (CNOT) gate. Assisted with linear optical manipulations, photon entanglement produced from parametric down-conversion, and postselection from the coincidence measurements, we teleport the quantum CNOT gate from acting on local qubits to acting on remote qubits. The quality of the quantum gate teleportation is characterized through the method of quantum process tomography, with an average fidelity of 0.84 demonstrated for the teleported gate. PMID:15697787

  12. Experimental teleportation of a quantum controlled-NOT gate.

    PubMed

    Huang, Yun-Feng; Ren, Xi-Feng; Zhang, Yong-Sheng; Duan, Lu-Ming; Guo, Guang-Can

    2004-12-10

    Teleportation of quantum gates is a critical step for the implementation of quantum networking and teleportation-based models of quantum computation. We report an experimental demonstration of teleportation of the prototypical quantum controlled-NOT (CNOT) gate. Assisted with linear optical manipulations, photon entanglement produced from parametric down-conversion, and postselection from the coincidence measurements, we teleport the quantum CNOT gate from acting on local qubits to acting on remote qubits. The quality of the quantum gate teleportation is characterized through the method of quantum process tomography, with an average fidelity of 0.84 demonstrated for the teleported gate.

  13. Quantum phase transition of the transverse-field quantum Ising model on scale-free networks.

    PubMed

    Yi, Hangmo

    2015-01-01

    I investigate the quantum phase transition of the transverse-field quantum Ising model in which nearest neighbors are defined according to the connectivity of scale-free networks. Using a continuous-time quantum Monte Carlo simulation method and the finite-size scaling analysis, I identify the quantum critical point and study its scaling characteristics. For the degree exponent λ=6, I obtain results that are consistent with the mean-field theory. For λ=4.5 and 4, however, the results suggest that the quantum critical point belongs to a non-mean-field universality class. Further simulations indicate that the quantum critical point remains mean-field-like if λ>5, but it continuously deviates from the mean-field theory as λ becomes smaller.

  14. Secret Sharing of a Quantum State.

    PubMed

    Lu, He; Zhang, Zhen; Chen, Luo-Kan; Li, Zheng-Da; Liu, Chang; Li, Li; Liu, Nai-Le; Ma, Xiongfeng; Chen, Yu-Ao; Pan, Jian-Wei

    2016-07-15

    Secret sharing of a quantum state, or quantum secret sharing, in which a dealer wants to share a certain amount of quantum information with a few players, has wide applications in quantum information. The critical criterion in a threshold secret sharing scheme is confidentiality: with less than the designated number of players, no information can be recovered. Furthermore, in a quantum scenario, one additional critical criterion exists: the capability of sharing entangled and unknown quantum information. Here, by employing a six-photon entangled state, we demonstrate a quantum threshold scheme, where the shared quantum secrecy can be efficiently reconstructed with a state fidelity as high as 93%. By observing that any one or two parties cannot recover the secrecy, we show that our scheme meets the confidentiality criterion. Meanwhile, we also demonstrate that entangled quantum information can be shared and recovered via our setting, which shows that our implemented scheme is fully quantum. Moreover, our experimental setup can be treated as a decoding circuit of the five-qubit quantum error-correcting code with two erasure errors. PMID:27472103

  15. Secret Sharing of a Quantum State

    NASA Astrophysics Data System (ADS)

    Lu, He; Zhang, Zhen; Chen, Luo-Kan; Li, Zheng-Da; Liu, Chang; Li, Li; Liu, Nai-Le; Ma, Xiongfeng; Chen, Yu-Ao; Pan, Jian-Wei

    2016-07-01

    Secret sharing of a quantum state, or quantum secret sharing, in which a dealer wants to share a certain amount of quantum information with a few players, has wide applications in quantum information. The critical criterion in a threshold secret sharing scheme is confidentiality: with less than the designated number of players, no information can be recovered. Furthermore, in a quantum scenario, one additional critical criterion exists: the capability of sharing entangled and unknown quantum information. Here, by employing a six-photon entangled state, we demonstrate a quantum threshold scheme, where the shared quantum secrecy can be efficiently reconstructed with a state fidelity as high as 93%. By observing that any one or two parties cannot recover the secrecy, we show that our scheme meets the confidentiality criterion. Meanwhile, we also demonstrate that entangled quantum information can be shared and recovered via our setting, which shows that our implemented scheme is fully quantum. Moreover, our experimental setup can be treated as a decoding circuit of the five-qubit quantum error-correcting code with two erasure errors.

  16. Secret Sharing of a Quantum State.

    PubMed

    Lu, He; Zhang, Zhen; Chen, Luo-Kan; Li, Zheng-Da; Liu, Chang; Li, Li; Liu, Nai-Le; Ma, Xiongfeng; Chen, Yu-Ao; Pan, Jian-Wei

    2016-07-15

    Secret sharing of a quantum state, or quantum secret sharing, in which a dealer wants to share a certain amount of quantum information with a few players, has wide applications in quantum information. The critical criterion in a threshold secret sharing scheme is confidentiality: with less than the designated number of players, no information can be recovered. Furthermore, in a quantum scenario, one additional critical criterion exists: the capability of sharing entangled and unknown quantum information. Here, by employing a six-photon entangled state, we demonstrate a quantum threshold scheme, where the shared quantum secrecy can be efficiently reconstructed with a state fidelity as high as 93%. By observing that any one or two parties cannot recover the secrecy, we show that our scheme meets the confidentiality criterion. Meanwhile, we also demonstrate that entangled quantum information can be shared and recovered via our setting, which shows that our implemented scheme is fully quantum. Moreover, our experimental setup can be treated as a decoding circuit of the five-qubit quantum error-correcting code with two erasure errors.

  17. Quantum Games under Decoherence

    NASA Astrophysics Data System (ADS)

    Huang, Zhiming; Qiu, Daowen

    2016-02-01

    Quantum systems are easily influenced by ambient environments. Decoherence is generated by system interaction with external environment. In this paper, we analyse the effects of decoherence on quantum games with Eisert-Wilkens-Lewenstein (EWL) (Eisert et al., Phys. Rev. Lett. 83(15), 3077 1999) and Marinatto-Weber (MW) (Marinatto and Weber, Phys. Lett. A 272, 291 2000) schemes. Firstly, referring to the analytical approach that was introduced by Eisert et al. (Phys. Rev. Lett. 83(15), 3077 1999), we analyse the effects of decoherence on quantum Chicken game by considering different traditional noisy channels. We investigate the Nash equilibria and changes of payoff in specific two-parameter strategy set for maximally entangled initial states. We find that the Nash equilibria are different in different noisy channels. Since Unruh effect produces a decoherence-like effect and can be perceived as a quantum noise channel (Omkar et al., arXiv: 1408.1477v1), with the same two parameter strategy set, we investigate the influences of decoherence generated by the Unruh effect on three-player quantum Prisoners' Dilemma, the non-zero sum symmetric multiplayer quantum game both for unentangled and entangled initial states. We discuss the effect of the acceleration of noninertial frames on the the game's properties such as payoffs, symmetry, Nash equilibrium, Pareto optimal, dominant strategy, etc. Finally, we study the decoherent influences of correlated noise and Unruh effect on quantum Stackelberg duopoly for entangled and unentangled initial states with the depolarizing channel. Our investigations show that under the influence of correlated depolarizing channel and acceleration in noninertial frame, some critical points exist for an unentangled initial state at which firms get equal payoffs and the game becomes a follower advantage game. It is shown that the game is always a leader advantage game for a maximally entangled initial state and there appear some points at which

  18. Quantum flywheel

    NASA Astrophysics Data System (ADS)

    Levy, Amikam; Diósi, Lajos; Kosloff, Ronnie

    2016-05-01

    In this work we present the concept of a quantum flywheel coupled to a quantum heat engine. The flywheel stores useful work in its energy levels, while additional power is extracted continuously from the device. Generally, the energy exchange between a quantum engine and a quantized work repository is accompanied by heat, which degrades the charging efficiency. Specifically when the quantum harmonic oscillator acts as a work repository, quantum and thermal fluctuations dominate the dynamics. Quantum monitoring and feedback control are applied to the flywheel in order to reach steady state and regulate its operation. To maximize the charging efficiency one needs a balance between the information gained by measuring the system and the information fed back to the system. The dynamics of the flywheel are described by a stochastic master equation that accounts for the engine, the external driving, the measurement, and the feedback operations.

  19. Critical Muralism

    ERIC Educational Resources Information Center

    Rosette, Arturo

    2009-01-01

    This study focuses on the development and practices of Critical Muralists--community-educator-artist-leader-activists--and situates these specifically in relation to the Mexican mural tradition of los Tres Grandes and in relation to the history of public art more generally. The study examines how Critical Muralists address artistic and…

  20. Quantum seismography

    NASA Astrophysics Data System (ADS)

    Lanzagorta, Marco; Jitrik, Oliverio; Uhlmann, Jeffrey; Venegas, Salvador

    2016-05-01

    A major scientific thrust from recent years has been to try to harness quantum phenomena to increase the performance of a wide variety of information processing devices. In particular, quantum radar has emerged as an intriguing theoretical concept that could revolutionize electromagnetic standoff sensing. In this paper we will discuss how the techniques developed for quantum radar could also be used towards the design of novel seismographs able to detect small ground vibrations., We use a hypothetical earthquake warning system in order to compare quantum seismography with traditional seismographic techniques.

  1. Quantum Dots

    NASA Astrophysics Data System (ADS)

    Tartakovskii, Alexander

    2012-07-01

    Part I. Nanostructure Design and Structural Properties of Epitaxially Grown Quantum Dots and Nanowires: 1. Growth of III/V semiconductor quantum dots C. Schneider, S. Hofling and A. Forchel; 2. Single semiconductor quantum dots in nanowires: growth, optics, and devices M. E. Reimer, N. Akopian, M. Barkelid, G. Bulgarini, R. Heeres, M. Hocevar, B. J. Witek, E. Bakkers and V. Zwiller; 3. Atomic scale analysis of self-assembled quantum dots by cross-sectional scanning tunneling microscopy and atom probe tomography J. G. Keizer and P. M. Koenraad; Part II. Manipulation of Individual Quantum States in Quantum Dots Using Optical Techniques: 4. Studies of the hole spin in self-assembled quantum dots using optical techniques B. D. Gerardot and R. J. Warburton; 5. Resonance fluorescence from a single quantum dot A. N. Vamivakas, C. Matthiesen, Y. Zhao, C.-Y. Lu and M. Atature; 6. Coherent control of quantum dot excitons using ultra-fast optical techniques A. J. Ramsay and A. M. Fox; 7. Optical probing of holes in quantum dot molecules: structure, symmetry, and spin M. F. Doty and J. I. Climente; Part III. Optical Properties of Quantum Dots in Photonic Cavities and Plasmon-Coupled Dots: 8. Deterministic light-matter coupling using single quantum dots P. Senellart; 9. Quantum dots in photonic crystal cavities A. Faraon, D. Englund, I. Fushman, A. Majumdar and J. Vukovic; 10. Photon statistics in quantum dot micropillar emission M. Asmann and M. Bayer; 11. Nanoplasmonics with colloidal quantum dots V. Temnov and U. Woggon; Part IV. Quantum Dot Nano-Laboratory: Magnetic Ions and Nuclear Spins in a Dot: 12. Dynamics and optical control of an individual Mn spin in a quantum dot L. Besombes, C. Le Gall, H. Boukari and H. Mariette; 13. Optical spectroscopy of InAs/GaAs quantum dots doped with a single Mn atom O. Krebs and A. Lemaitre; 14. Nuclear spin effects in quantum dot optics B. Urbaszek, B. Eble, T. Amand and X. Marie; Part V. Electron Transport in Quantum Dots Fabricated by

  2. Microstrip Superconducting Quantum Interference Devices for Quantum Information Science

    NASA Astrophysics Data System (ADS)

    De Feo, Michael P.

    Quantum-limited amplification in the microwave frequency range is of both practical and fundamental importance. The weak signals corresponding to single microwave photons require substantial amplification to resolve. When probing quantum excitations of the electromagnetic field, the substantial noise produced by standard amplifiers dominates the signal, therefore, several averages must be accumulated to achieve even a modest signal-to-noise ratio. Even worse, the back-action on the system due to amplifier noise can hasten the decay of the quantum state. In recent years, low-noise microwave-frequency amplification has been advancing rapidly and one field that would benefit greatly from this is circuit quantum electrodynamics (cQED). The development of circuit quantum electrodynamics—which implements techniques of quantum optics at microwave frequencies—has led to revolutionary progress in the field of quantum information science. cQED employs quantum bits (qubits) and superconducting microwave resonators in place of the atoms and cavities used in quantum optics permitting preparation and control of low energy photon states in macroscopic superconducting circuits at millikelvin temperatures. We have developed a microstrip superconducting quantum interference device (SQUID) amplifier (MSA) to provide the first stage of amplification for these systems. Employing sub-micron Josephson tunnel junctions for enhanced gain, these MSAs operate at microwave frequencies and are optimized to perform with near quantum-limited noise characteristics. Our MSA is utilized as the first stage of amplification to probe the dynamics of a SQUID oscillator. The SQUID oscillator is a flux-tunable microwave resonator formed by a capacitively shunted dc SQUID. Josephson plasma oscillations are induced by pulsed microwave excitations at the resonant frequency of the oscillator. Once pulsed, decaying plasma oscillations are observed in the time domain. By measuring with pulse amplitudes

  3. Dissipative quantum computing with open quantum walks

    SciTech Connect

    Sinayskiy, Ilya; Petruccione, Francesco

    2014-12-04

    An open quantum walk approach to the implementation of a dissipative quantum computing scheme is presented. The formalism is demonstrated for the example of an open quantum walk implementation of a 3 qubit quantum circuit consisting of 10 gates.

  4. Critics and Criticism of Education

    ERIC Educational Resources Information Center

    Ornstein, Allan C.

    1977-01-01

    Radical educational critics, such as Edgar Friedenberg, Paul Goodman, A. S. Neill, John Holt, Jonathan Kozol, Herbert Kohl, James Herndon, and Ivan Illich, have few constructive goals, no strategy for broad change, and a disdain for modernization and compromise. Additionally, these critics, says the author, fail to consider social factors related…

  5. Quantum communication and information processing

    NASA Astrophysics Data System (ADS)

    Beals, Travis Roland

    Quantum computers enable dramatically more efficient algorithms for solving certain classes of computational problems, but, in doing so, they create new problems. In particular, Shor's Algorithm allows for efficient cryptanalysis of many public-key cryptosystems. As public key cryptography is a critical component of present-day electronic commerce, it is crucial that a working, secure replacement be found. Quantum key distribution (QKD), first developed by C.H. Bennett and G. Brassard, offers a partial solution, but many challenges remain, both in terms of hardware limitations and in designing cryptographic protocols for a viable large-scale quantum communication infrastructure. In Part I, I investigate optical lattice-based approaches to quantum information processing. I look at details of a proposal for an optical lattice-based quantum computer, which could potentially be used for both quantum communications and for more sophisticated quantum information processing. In Part III, I propose a method for converting and storing photonic quantum bits in the internal state of periodically-spaced neutral atoms by generating and manipulating a photonic band gap and associated defect states. In Part II, I present a cryptographic protocol which allows for the extension of present-day QKD networks over much longer distances without the development of new hardware. I also present a second, related protocol which effectively solves the authentication problem faced by a large QKD network, thus making QKD a viable, information-theoretic secure replacement for public key cryptosystems.

  6. Quantum metrology

    NASA Technical Reports Server (NTRS)

    Lee, H.; Kok, P.; Dowling, J. P.

    2002-01-01

    This paper addresses the formal equivalence between the Mach-Zehnder interferometer, the Ramsey spectroscope, and a specific quantum logical gate. Based on this equivalence we introduce the quantum Rosetta Stone, and we describe a projective measurement scheme for generating the desired correlations between the interferometric input states in order to achieve Heisenberg-limited sensitivity.

  7. Quantum microbiology.

    PubMed

    Trevors, J T; Masson, L

    2011-01-01

    During his famous 1943 lecture series at Trinity College Dublin, the reknown physicist Erwin Schrodinger discussed the failure and challenges of interpreting life by classical physics alone and that a new approach, rooted in Quantum principles, must be involved. Quantum events are simply a level of organization below the molecular level. This includes the atomic and subatomic makeup of matter in microbial metabolism and structures, as well as the organic, genetic information code of DNA and RNA. Quantum events at this time do not elucidate, for example, how specific genetic instructions were first encoded in an organic genetic code in microbial cells capable of growth and division, and its subsequent evolution over 3.6 to 4 billion years. However, due to recent technological advances, biologists and physicists are starting to demonstrate linkages between various quantum principles like quantum tunneling, entanglement and coherence in biological processes illustrating that nature has exerted some level quantum control to optimize various processes in living organisms. In this article we explore the role of quantum events in microbial processes and endeavor to show that after nearly 67 years, Schrödinger was prophetic and visionary in his view of quantum theory and its connection with some of the fundamental mechanisms of life. PMID:21368338

  8. Contextuality supplies the 'magic' for quantum computation.

    PubMed

    Howard, Mark; Wallman, Joel; Veitch, Victor; Emerson, Joseph

    2014-06-19

    Quantum computers promise dramatic advantages over their classical counterparts, but the source of the power in quantum computing has remained elusive. Here we prove a remarkable equivalence between the onset of contextuality and the possibility of universal quantum computation via 'magic state' distillation, which is the leading model for experimentally realizing a fault-tolerant quantum computer. This is a conceptually satisfying link, because contextuality, which precludes a simple 'hidden variable' model of quantum mechanics, provides one of the fundamental characterizations of uniquely quantum phenomena. Furthermore, this connection suggests a unifying paradigm for the resources of quantum information: the non-locality of quantum theory is a particular kind of contextuality, and non-locality is already known to be a critical resource for achieving advantages with quantum communication. In addition to clarifying these fundamental issues, this work advances the resource framework for quantum computation, which has a number of practical applications, such as characterizing the efficiency and trade-offs between distinct theoretical and experimental schemes for achieving robust quantum computation, and putting bounds on the overhead cost for the classical simulation of quantum algorithms. PMID:24919152

  9. Contextuality supplies the 'magic' for quantum computation.

    PubMed

    Howard, Mark; Wallman, Joel; Veitch, Victor; Emerson, Joseph

    2014-06-19

    Quantum computers promise dramatic advantages over their classical counterparts, but the source of the power in quantum computing has remained elusive. Here we prove a remarkable equivalence between the onset of contextuality and the possibility of universal quantum computation via 'magic state' distillation, which is the leading model for experimentally realizing a fault-tolerant quantum computer. This is a conceptually satisfying link, because contextuality, which precludes a simple 'hidden variable' model of quantum mechanics, provides one of the fundamental characterizations of uniquely quantum phenomena. Furthermore, this connection suggests a unifying paradigm for the resources of quantum information: the non-locality of quantum theory is a particular kind of contextuality, and non-locality is already known to be a critical resource for achieving advantages with quantum communication. In addition to clarifying these fundamental issues, this work advances the resource framework for quantum computation, which has a number of practical applications, such as characterizing the efficiency and trade-offs between distinct theoretical and experimental schemes for achieving robust quantum computation, and putting bounds on the overhead cost for the classical simulation of quantum algorithms.

  10. Contextuality supplies the `magic' for quantum computation

    NASA Astrophysics Data System (ADS)

    Howard, Mark; Wallman, Joel; Veitch, Victor; Emerson, Joseph

    2014-06-01

    Quantum computers promise dramatic advantages over their classical counterparts, but the source of the power in quantum computing has remained elusive. Here we prove a remarkable equivalence between the onset of contextuality and the possibility of universal quantum computation via `magic state' distillation, which is the leading model for experimentally realizing a fault-tolerant quantum computer. This is a conceptually satisfying link, because contextuality, which precludes a simple `hidden variable' model of quantum mechanics, provides one of the fundamental characterizations of uniquely quantum phenomena. Furthermore, this connection suggests a unifying paradigm for the resources of quantum information: the non-locality of quantum theory is a particular kind of contextuality, and non-locality is already known to be a critical resource for achieving advantages with quantum communication. In addition to clarifying these fundamental issues, this work advances the resource framework for quantum computation, which has a number of practical applications, such as characterizing the efficiency and trade-offs between distinct theoretical and experimental schemes for achieving robust quantum computation, and putting bounds on the overhead cost for the classical simulation of quantum algorithms.

  11. Quantum picturalism

    NASA Astrophysics Data System (ADS)

    Coecke, Bob

    2010-01-01

    Why did it take us 50 years since the birth of the quantum mechanical formalism to discover that unknown quantum states cannot be cloned? Yet, the proof of the 'no-cloning theorem' is easy, and its consequences and potential for applications are immense. Similarly, why did it take us 60 years to discover the conceptually intriguing and easily derivable physical phenomenon of 'quantum teleportation'? We claim that the quantum mechanical formalism doesn't support our intuition, nor does it elucidate the key concepts that govern the behaviour of the entities that are subject to the laws of quantum physics. The arrays of complex numbers are kin to the arrays of 0s and 1s of the early days of computer programming practice. Using a technical term from computer science, the quantum mechanical formalism is 'low-level'. In this review we present steps towards a diagrammatic 'high-level' alternative for the Hilbert space formalism, one which appeals to our intuition. The diagrammatic language as it currently stands allows for intuitive reasoning about interacting quantum systems, and trivialises many otherwise involved and tedious computations. It clearly exposes limitations such as the no-cloning theorem, and phenomena such as quantum teleportation. As a logic, it supports 'automation': it enables a (classical) computer to reason about interacting quantum systems, prove theorems, and design protocols. It allows for a wider variety of underlying theories, and can be easily modified, having the potential to provide the required step-stone towards a deeper conceptual understanding of quantum theory, as well as its unification with other physical theories. Specific applications discussed here are purely diagrammatic proofs of several quantum computational schemes, as well as an analysis of the structural origin of quantum non-locality. The underlying mathematical foundation of this high-level diagrammatic formalism relies on so-called monoidal categories, a product of a fairly

  12. Enhancing robustness of multiparty quantum correlations using weak measurement

    SciTech Connect

    Singh, Uttam; Mishra, Utkarsh; Dhar, Himadri Shekhar

    2014-11-15

    Multipartite quantum correlations are important resources for the development of quantum information and computation protocols. However, the resourcefulness of multipartite quantum correlations in practical settings is limited by its fragility under decoherence due to environmental interactions. Though there exist protocols to protect bipartite entanglement under decoherence, the implementation of such protocols for multipartite quantum correlations has not been sufficiently explored. Here, we study the effect of local amplitude damping channel on the generalized Greenberger–Horne–Zeilinger state, and use a protocol of optimal reversal quantum weak measurement to protect the multipartite quantum correlations. We observe that the weak measurement reversal protocol enhances the robustness of multipartite quantum correlations. Further it increases the critical damping value that corresponds to entanglement sudden death. To emphasize the efficacy of the technique in protection of multipartite quantum correlation, we investigate two proximately related quantum communication tasks, namely, quantum teleportation in a one sender, many receivers setting and multiparty quantum information splitting, through a local amplitude damping channel. We observe an increase in the average fidelity of both the quantum communication tasks under the weak measurement reversal protocol. The method may prove beneficial, for combating external interactions, in other quantum information tasks using multipartite resources. - Highlights: • Extension of weak measurement reversal scheme to protect multiparty quantum correlations. • Protection of multiparty quantum correlation under local amplitude damping noise. • Enhanced fidelity of quantum teleportation in one sender and many receivers setting. • Enhanced fidelity of quantum information splitting protocol.

  13. The quantum Zeno paradox: A matter of information

    NASA Astrophysics Data System (ADS)

    Toschek, Peter E.

    2013-04-01

    The origin of the quantum Zeno paradox is critically re-evaluated. It is demonstrated, that the observation of expectation values, in particular of reduced decay constants, cannot qualify as the proof of a quantum Zeno effect. Rather, the detection of the transition times of individual quantum objects provides necessary and sufficient evidence.

  14. Realizing Controllable Quantum States

    NASA Astrophysics Data System (ADS)

    Takayanagi, Hideaki; Nitta, Junsaku

    1. Entanglement in solid states. Orbital entanglement and violation of bell inequalities in mesoscopic conductors / M. Büttiker, P. Samuelsson and E. V. Sukhoruk. Teleportation of electron spins with normal and superconducting dots / O. Sauret, D. Feinberg and T. Martin. Entangled state analysis for one-dimensional quantum spin system: singularity at critical point / A. Kawaguchi and K. Shimizu. Detecting crossed Andreev reflection by cross-current correlations / G. Bignon et al. Current correlations and transmission probabilities for a Y-shaped diffusive conductor / S. K. Yip -- 2. Mesoscopic electronics. Quantum bistability, structural transformation, and spontaneous persistent currents in mesoscopic Aharonov-Bohm loops / I. O. Kulik. Many-body effects on tunneling of electrons in magnetic-field-induced quasi one-dimensional systems in quantum wells / T. Kubo and Y. Tokura. Electron transport in 2DEG narrow channel under gradient magnetic field / M. Hara et al. Transport properties of a quantum wire with a side-coupled quantum dot / M. Yamaguchi et al. Photoconductivity- and magneto-transport studies of single InAs quantum wires / A. Wirthmann et al. Thermoelectric transports in charge-density-wave systems / H. Yoshimoto and S. Kurihara -- 3. Mesoscopic superconductivity. Parity-restricted persistent currents in SNS nanorings / A. D. Zaikin and S. V. Sharov. Large energy dependence of current noise in superconductingh/normal metal junctions / F. Pistolesi and M. Houzet. Generation of photon number states and their superpositions using a superconducting qubit in a microcavity / Yu-Xi Liu, L. F. Wei and F. Nori. Andreev interferometry for pumped currents / F. Taddei, M. Governale and R. Fazio. Suppression of Cooper-pair breaking against high magnetic fields in carbon nanotubes / J. Haruyama et al. Impact of the transport supercurrent on the Josephson effect / S. N. Shevchenko. Josephson current through spin-polarized Luttinger liquid / N. Yokoshi and S. Kurihara

  15. Quantum Chaos

    NASA Astrophysics Data System (ADS)

    Casati, Giulio; Chirikov, Boris

    2006-11-01

    Preface; Acknowledgments; Introduction: 1. The legacy of chaos in quantum mechanics G. Casati and B. V. Chirikov; Part I. Classical Chaos and Quantum Localization: 2. Stochastic behaviour of a quantum pendulum under a periodic perturbation G. Casati, B. V. Chirikov, F. M. Izrailev and J. Ford; 3. Quantum dynamics of a nonintegrable system D. R. Grempel, R. E. Prange and S. E. Fishman; 4. Excitation of molecular rotation by periodic microwave pulses. A testing ground for Anderson localization R. Blümel, S. Fishman and U. Smilansky; 5. Localization of diffusive excitation in multi-level systems D. K. Shepelyansky; 6. Classical and quantum chaos for a kicked top F. Haake, M. Kus and R. Scharf; 7. Self-similarity in quantum dynamics L. E. Reichl and L. Haoming; 8. Time irreversibility of classically chaotic quantum dynamics K. Ikeda; 9. Effect of noise on time-dependent quantum chaos E. Ott, T. M. Antonsen Jr and J. D. Hanson; 10. Dynamical localization, dissipation and noise R. F. Graham; 11. Maximum entropy models and quantum transmission in disordered systems J.-L. Pichard and M. Sanquer; 12. Solid state 'atoms' in intense oscillating fields M. S. Sherwin; Part II. Atoms in Strong Fields: 13. Localization of classically chaotic diffusion for hydrogen atoms in microwave fields J. E. Bayfield, G. Casati, I. Guarneri and D. W. Sokol; 14. Inhibition of quantum transport due to 'scars' of unstable periodic orbits R. V. Jensen, M. M. Sanders, M. Saraceno and B. Sundaram; 15. Rubidium Rydberg atoms in strong fields G. Benson, G. Raithel and H. Walther; 16. Diamagnetic Rydberg atom: confrontation of calculated and observed spectra C.-H. Iu, G. R. Welch, M. M. Kash, D. Kleppner, D. Delande and J. C. Gay; 17. Semiclassical approximation for the quantum states of a hydrogen atom in a magnetic field near the ionization limit M. Y. Kuchiev and O. P. Sushkov; 18. The semiclassical helium atom D. Wintgen, K. Richter and G. Tanner; 19. Stretched helium: a model for quantum chaos

  16. Quantum Chaos

    NASA Astrophysics Data System (ADS)

    Casati, Giulio; Chirikov, Boris

    1995-04-01

    Preface; Acknowledgments; Introduction: 1. The legacy of chaos in quantum mechanics G. Casati and B. V. Chirikov; Part I. Classical Chaos and Quantum Localization: 2. Stochastic behaviour of a quantum pendulum under a periodic perturbation G. Casati, B. V. Chirikov, F. M. Izrailev and J. Ford; 3. Quantum dynamics of a nonintegrable system D. R. Grempel, R. E. Prange and S. E. Fishman; 4. Excitation of molecular rotation by periodic microwave pulses. A testing ground for Anderson localization R. Blümel, S. Fishman and U. Smilansky; 5. Localization of diffusive excitation in multi-level systems D. K. Shepelyansky; 6. Classical and quantum chaos for a kicked top F. Haake, M. Kus and R. Scharf; 7. Self-similarity in quantum dynamics L. E. Reichl and L. Haoming; 8. Time irreversibility of classically chaotic quantum dynamics K. Ikeda; 9. Effect of noise on time-dependent quantum chaos E. Ott, T. M. Antonsen Jr and J. D. Hanson; 10. Dynamical localization, dissipation and noise R. F. Graham; 11. Maximum entropy models and quantum transmission in disordered systems J.-L. Pichard and M. Sanquer; 12. Solid state 'atoms' in intense oscillating fields M. S. Sherwin; Part II. Atoms in Strong Fields: 13. Localization of classically chaotic diffusion for hydrogen atoms in microwave fields J. E. Bayfield, G. Casati, I. Guarneri and D. W. Sokol; 14. Inhibition of quantum transport due to 'scars' of unstable periodic orbits R. V. Jensen, M. M. Sanders, M. Saraceno and B. Sundaram; 15. Rubidium Rydberg atoms in strong fields G. Benson, G. Raithel and H. Walther; 16. Diamagnetic Rydberg atom: confrontation of calculated and observed spectra C.-H. Iu, G. R. Welch, M. M. Kash, D. Kleppner, D. Delande and J. C. Gay; 17. Semiclassical approximation for the quantum states of a hydrogen atom in a magnetic field near the ionization limit M. Y. Kuchiev and O. P. Sushkov; 18. The semiclassical helium atom D. Wintgen, K. Richter and G. Tanner; 19. Stretched helium: a model for quantum chaos

  17. Quantum strategies of quantum measurements

    NASA Astrophysics Data System (ADS)

    Li, Chuan-Feng; Zhang, Yong-Sheng; Huang, Yun-Feng; Guo, Guang-Can

    2001-03-01

    In the classical Monty Hall problem, one player can always win with probability 2/3. We generalize the problem to the quantum domain and show that a fair two-party zero-sum game can be carried out if the other player is permitted to adopt quantum measurement strategy.

  18. Electric-field-tuned color in photonic crystal elastomers

    NASA Astrophysics Data System (ADS)

    Zhao, Qibin; Haines, Andrew; Snoswell, David; Keplinger, Christoph; Kaltseis, Rainer; Bauer, Siegfried; Graz, Ingrid; Denk, Richard; Spahn, Peter; Hellmann, Goetz; Baumberg, Jeremy J.

    2012-03-01

    Electrically tuned photonic crystals are produced by applying fields across shear-assembled elastomeric polymer opal thin films. At increasing voltages, the polymer opal films stretch biaxially under Maxwell stress, deforming the nanostructure and producing marked color changes. This quadratic electro-optic tuning of the photonic bandgap is repeatable over many cycles, switches within 100 ms, and bridges the gap between electro-active materials and photonic crystals.

  19. Quantum physics without quantum philosophy

    NASA Astrophysics Data System (ADS)

    Dürr, Detlef; Goldstein, Sheldon; Zanghì, Nino

    Quantum philosophy, a peculiar twentieth-century malady, is responsible for most of the conceptual muddle plaguing the foundations of quantum physics. When this philosophy is eschewed, one naturally arrives at Bohmian mechanics, which is what emerges from Schrödinger's equation for a nonrelativistic system of particles when we merely insist that 'particles' means particles. While distinctly non-Newtonian, Bohmian mechanics is a fully deterministic theory of particles in motion, a motion choreographed by the wave function. The quantum formalism emerges when measurement situations are analyzed according to this theory. When the quantum formalism is regarded as arising in this way, the paradoxes and perplexities so often associated with quantum theory simply evaporate.

  20. Quantum Computation Using Optically Coupled Quantum Dot Arrays

    NASA Technical Reports Server (NTRS)

    Pradhan, Prabhakar; Anantram, M. P.; Wang, K. L.; Roychowhury, V. P.; Saini, Subhash (Technical Monitor)

    1998-01-01

    A solid state model for quantum computation has potential advantages in terms of the ease of fabrication, characterization, and integration. The fundamental requirements for a quantum computer involve the realization of basic processing units (qubits), and a scheme for controlled switching and coupling among the qubits, which enables one to perform controlled operations on qubits. We propose a model for quantum computation based on optically coupled quantum dot arrays, which is computationally similar to the atomic model proposed by Cirac and Zoller. In this model, individual qubits are comprised of two coupled quantum dots, and an array of these basic units is placed in an optical cavity. Switching among the states of the individual units is done by controlled laser pulses via near field interaction using the NSOM technology. Controlled rotations involving two or more qubits are performed via common cavity mode photon. We have calculated critical times, including the spontaneous emission and switching times, and show that they are comparable to the best times projected for other proposed models of quantum computation. We have also shown the feasibility of accessing individual quantum dots using the NSOM technology by calculating the photon density at the tip, and estimating the power necessary to perform the basic controlled operations. We are currently in the process of estimating the decoherence times for this system; however, we have formulated initial arguments which seem to indicate that the decoherence times will be comparable, if not longer, than many other proposed models.

  1. Quantum computing with defects.

    PubMed

    Weber, J R; Koehl, W F; Varley, J B; Janotti, A; Buckley, B B; Van de Walle, C G; Awschalom, D D

    2010-05-11

    Identifying and designing physical systems for use as qubits, the basic units of quantum information, are critical steps in the development of a quantum computer. Among the possibilities in the solid state, a defect in diamond known as the nitrogen-vacancy (NV(-1)) center stands out for its robustness--its quantum state can be initialized, manipulated, and measured with high fidelity at room temperature. Here we describe how to systematically identify other deep center defects with similar quantum-mechanical properties. We present a list of physical criteria that these centers and their hosts should meet and explain how these requirements can be used in conjunction with electronic structure theory to intelligently sort through candidate defect systems. To illustrate these points in detail, we compare electronic structure calculations of the NV(-1) center in diamond with those of several deep centers in 4H silicon carbide (SiC). We then discuss the proposed criteria for similar defects in other tetrahedrally coordinated semiconductors.

  2. Quantum computing with defects

    PubMed Central

    Weber, J. R.; Koehl, W. F.; Varley, J. B.; Janotti, A.; Buckley, B. B.; Van de Walle, C. G.; Awschalom, D. D.

    2010-01-01

    Identifying and designing physical systems for use as qubits, the basic units of quantum information, are critical steps in the development of a quantum computer. Among the possibilities in the solid state, a defect in diamond known as the nitrogen-vacancy (NV-1) center stands out for its robustness—its quantum state can be initialized, manipulated, and measured with high fidelity at room temperature. Here we describe how to systematically identify other deep center defects with similar quantum-mechanical properties. We present a list of physical criteria that these centers and their hosts should meet and explain how these requirements can be used in conjunction with electronic structure theory to intelligently sort through candidate defect systems. To illustrate these points in detail, we compare electronic structure calculations of the NV-1 center in diamond with those of several deep centers in 4H silicon carbide (SiC). We then discuss the proposed criteria for similar defects in other tetrahedrally coordinated semiconductors. PMID:20404195

  3. Simulation of n-qubit quantum systems. III. Quantum operations

    NASA Astrophysics Data System (ADS)

    Radtke, T.; Fritzsche, S.

    2007-05-01

    During the last decade, several quantum information protocols, such as quantum key distribution, teleportation or quantum computation, have attracted a lot of interest. Despite the recent success and research efforts in quantum information processing, however, we are just at the beginning of understanding the role of entanglement and the behavior of quantum systems in noisy environments, i.e. for nonideal implementations. Therefore, in order to facilitate the investigation of entanglement and decoherence in n-qubit quantum registers, here we present a revised version of the FEYNMAN program for working with quantum operations and their associated (Jamiołkowski) dual states. Based on the implementation of several popular decoherence models, we provide tools especially for the quantitative analysis of quantum operations. Apart from the implementation of different noise models, the current program extension may help investigate the fragility of many quantum states, one of the main obstacles in realizing quantum information protocols today. Program summaryTitle of program: Feynman Catalogue identifier: ADWE_v3_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADWE_v3_0 Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Licensing provisions: None Operating systems: Any system that supports MAPLE; tested under Microsoft Windows XP, SuSe Linux 10 Program language used:MAPLE 10 Typical time and memory requirements: Most commands that act upon quantum registers with five or less qubits take ⩽10 seconds of processor time (on a Pentium 4 processor with ⩾2 GHz or equivalent) and 5-20 MB of memory. Especially when working with symbolic expressions, however, the memory and time requirements critically depend on the number of qubits in the quantum registers, owing to the exponential dimension growth of the associated Hilbert space. For example, complex (symbolic) noise models (with several Kraus operators) for multi-qubit systems

  4. Quantum Dots for Molecular Pathology

    PubMed Central

    True, Lawrence D.; Gao, Xiaohu

    2007-01-01

    Assessing malignant tumors for expression of multiple biomarkers provides data that are critical for patient management. Quantum dot-conjugated probes to specific biomarkers are powerful tools that can be applied in a multiplex manner to single tissue sections of biopsies to measure expression levels of multiple biomarkers. PMID:17251330

  5. Staying Critical

    ERIC Educational Resources Information Center

    Carr, Wilfred; Kemmis, Stephen

    2005-01-01

    In this article, the two authors of "Becoming Critical: education, knowledge and action research" look back at the book's history since its publication 20 years ago. We describe how the book was originally written, and the diverse responses and reactions that it has produced. We identify some of the book's inadequacies and limitations, and…

  6. PT quantum mechanics - Recent results

    NASA Astrophysics Data System (ADS)

    Bender, Carl M.

    2012-09-01

    Most quantum physicists believe that a quantum-mechanical Hamiltonian must be Dirac Hermitian (invariant under matrix transposition and complex conjugation) to be sure that the energy eigenvalues are real and that time evolution is unitary. However, the non-Dirac-hermitian Hamiltonian H = p2+ix3 has a real positive discrete spectrum and generates unitary time evolution and defines a fully consistent and physical quantum theory. Evidently, Dirac Hermiticity is too restrictive. While H = p2+ix3 is not Dirac Hermitian, it is PT symmetric (invariant under combined space reflection P and time reversal T). Another PT-symmetric Hamiltonian whose energy levels are real, positive and discrete is H = p2-x4, which contains an upside-down potential. The quantum mechanics defined by a PT-symmetric Hamiltonian is a complex generalization of ordinary quantum mechanics. When quantum mechanics and quantum field theory are extended into the complex domain, new kinds of theories having strange and remarkable properties emerge. In the past two years some of these properties have been verified in laboratory experiments. Here, we first discuss PT-symmetric Hamiltonians at a simple intuitive level and explain why the energy levels of such Hamiltonians may be real, positive, and discrete. Second, we describe a recent experiment in which the PT phase transition was observed. Third, we briefly mention that PT-symmetric theories can be useful at a fundamental level. While the double-scaling limit of an O(N)-symmetric gφ4 quantum field theory appears to be inconsistent because the critical value of g is negative, this limit is in fact not inconsistent because the critical theory is PT symmetric.

  7. Quantum Baseball.

    ERIC Educational Resources Information Center

    Peterson, Ivars

    1989-01-01

    An analogy from the game of baseball can be used to examine the philosophy involved in statistics surrounding quantum mechanical events. The "Strong Baseball Principle" is proposed and discussed. (CW)

  8. Low dimensional quantum paramagnets

    NASA Astrophysics Data System (ADS)

    Hong, Tao

    A quantum paramagnet is a material with interacting spins that possesses a paramagnetic ground state and an energy gap to all excitations. This dissertation focuses on studying the magnetic excitation spectrum and the quantum critical phenomena of such low dimensional quantum paramagnet systems. Inelastic neutron scattering (INS) measurements of Cu(Quinoxaline)Br 2 was performed on a partially deuterated powder sample. Magnetic neutron scattering was identified above an energy gap of 1.9 meV. Consideration of the sharp spectral max imum and wave vector dependence of the scattering and polymeric structure further identifies the material as a two-legged spin-1/2 ladder. The continuous uniform transformation theory provides an excellent account of the data with leg exchange J‖ =2.0 meV and the rung exchange J⊥ =3.3 meV. INS study of (2,3 - dimethylpyridinium)2CuBr4 (DIMPY) in both powder and single crystalline form are presented to understand the origin of the spin gap and what is the right spin Hamiltonian. Magnetic excitations are found above a 0.3 meV energy gap. The excitation only disperses along the a-direction with a bandwidth that exceeds 1.7 meV. The conclusion to be a S=1/2 two-legged spin ladder is supported by the material structure and INS measurement. External magnetic field drives the system into a critical region and induced low energy excitation continuum above critical field was studied. Piperazinium Hexachlorodicuprate (PHCC) is a two-dimensional antiferromagnet. We studied the behavior in the vicinity of the quantum critical point (QCP) where the spin gap is closed by an applied magnetic field by INS. The energy and damping of the low energy excitations were measured in the vicinity of the QCP where both quantities become strongly temperature dependent, which can be successfully described by a selfconsistent Hartree-Fock theory of strongly interacting bosons developed by Sachdev and Dunkel. A preliminary study of hydrostatic pressure effects

  9. Quantum Locality?

    NASA Astrophysics Data System (ADS)

    Stapp, Henry P.

    2012-05-01

    Robert Griffiths has recently addressed, within the framework of a `consistent quantum theory' that he has developed, the issue of whether, as is often claimed, quantum mechanics entails a need for faster-than-light transfers of information over long distances. He argues that the putative proofs of this property that involve hidden variables include in their premises some essentially classical-physics-type assumptions that are not entailed by the precepts of quantum mechanics. Thus whatever is proved is not a feature of quantum mechanics, but is a property of a theory that tries to combine quantum theory with quasi-classical features that go beyond what is entailed by quantum theory itself. One cannot logically prove properties of a system by establishing, instead, properties of a system modified by adding properties alien to the original system. Hence Griffiths' rejection of hidden-variable-based proofs is logically warranted. Griffiths mentions the existence of a certain alternative proof that does not involve hidden variables, and that uses only macroscopically described observable properties. He notes that he had examined in his book proofs of this general kind, and concluded that they provide no evidence for nonlocal influences. But he did not examine the particular proof that he cites. An examination of that particular proof by the method specified by his `consistent quantum theory' shows that the cited proof is valid within that restrictive version of quantum theory. An added section responds to Griffiths' reply, which cites general possibilities of ambiguities that might make what is to be proved ill-defined, and hence render the pertinent `consistent framework' ill defined. But the vagaries that he cites do not upset the proof in question, which, both by its physical formulation and by explicit identification, specify the framework to be used. Griffiths confirms the validity of the proof insofar as that pertinent framework is used. The section also shows

  10. Quantum correlations and distinguishability of quantum states

    SciTech Connect

    Spehner, Dominique

    2014-07-15

    A survey of various concepts in quantum information is given, with a main emphasis on the distinguishability of quantum states and quantum correlations. Covered topics include generalized and least square measurements, state discrimination, quantum relative entropies, the Bures distance on the set of quantum states, the quantum Fisher information, the quantum Chernoff bound, bipartite entanglement, the quantum discord, and geometrical measures of quantum correlations. The article is intended both for physicists interested not only by collections of results but also by the mathematical methods justifying them, and for mathematicians looking for an up-to-date introductory course on these subjects, which are mainly developed in the physics literature.

  11. Logarithmic correlations in quantum Hall plateau transitions

    NASA Astrophysics Data System (ADS)

    Vasseur, Romain

    2015-07-01

    The critical behavior of quantum Hall transitions in two-dimensional disordered electronic systems can be described by a class of complicated, nonunitary conformal field theories with logarithmic correlations. The nature and the physical origin of these logarithmic correlation functions remain, however, mysterious. Using the replica trick and the underlying symmetries of these quantum critical points, we show here how to construct nonperturbatively disorder-averaged observables in terms of Green's functions that scale logarithmically at criticality. In the case of the spin quantum Hall transition, which may occur in disordered superconductors with spin-rotation symmetry and broken time reversal invariance, we argue that our results are compatible with an alternative approach based on supersymmetry. The generalization to the integer quantum Hall plateau transition is also discussed.

  12. Critical Information at Critical Moments

    ERIC Educational Resources Information Center

    Fierman, Ben; Thrower, Raymond H., Jr.

    2011-01-01

    On a daily basis, administrators are reminded of the potential, perhaps the likelihood, of violence or natural crises on their campuses. Comprehensive studies have been conducted and point to recommendations and best practices for planning, preparing, responding to, and recovering from critical incidents. The International Association of Campus…

  13. Quantum Mechanics

    NASA Astrophysics Data System (ADS)

    Mandl, F.

    1992-07-01

    The Manchester Physics Series General Editors: D. J. Sandiford; F. Mandl; A. C. Phillips Department of Physics and Astronomy, University of Manchester Properties of Matter B. H. Flowers and E. Mendoza Optics Second Edition F. G. Smith and J. H. Thomson Statistical Physics Second Edition F. Mandl Electromagnetism Second Edition I. S. Grant and W. R. Phillips Statistics R. J. Barlow Solid State Physics Second Edition J. R. Hook and H. E. Hall Quantum Mechanics F. Mandl Particle Physics Second Edition B. R. Martin and G. Shaw The Physics of Stars Second Edition A. C. Phillips Computing for Scientists R. J. Barlow and A. R. Barnett Quantum Mechanics aims to teach those parts of the subject which every physicist should know. The object is to display the inherent structure of quantum mechanics, concentrating on general principles and on methods of wide applicability without taking them to their full generality. This book will equip students to follow quantum-mechanical arguments in books and scientific papers, and to cope with simple cases. To bring the subject to life, the theory is applied to the all-important field of atomic physics. No prior knowledge of quantum mechanics is assumed. However, it would help most readers to have met some elementary wave mechanics before. Primarily written for students, it should also be of interest to experimental research workers who require a good grasp of quantum mechanics without the full formalism needed by the professional theorist. Quantum Mechanics features: A flow diagram allowing topics to be studied in different orders or omitted altogether. Optional "starred" and highlighted sections containing more advanced and specialized material for the more ambitious reader. Sets of problems at the end of each chapter to help student understanding. Hints and solutions to the problems are given at the end of the book.

  14. Introduction to Quantum Simulation

    NASA Technical Reports Server (NTRS)

    Williams, Colin P.

    2005-01-01

    This viewgraph presentation addresses the problem of efficiently simulating the evolution of a quantum system. The contents include: 1) Quantum Simulation; 2) Extracting Answers from Quantum Simulations; 3) Quantum Fourier Transform; 4) Eigenvalue Estimation; 5) Fermionic Simulations.

  15. Quantum Physics for Beginners.

    ERIC Educational Resources Information Center

    Strand, J.

    1981-01-01

    Suggests a new approach for teaching secondary school quantum physics. Reviews traditional approaches and presents some characteristics of the three-part "Quantum Physics for Beginners" project, including: quantum physics, quantum mechanics, and a short historical survey. (SK)

  16. Measurement and Information Extraction in Complex Dynamics Quantum Computation

    NASA Astrophysics Data System (ADS)

    Casati, Giulio; Montangero, Simone

    Quantum Information processing has several di.erent applications: some of them can be performed controlling only few qubits simultaneously (e.g. quantum teleportation or quantum cryptography) [1]. Usually, the transmission of large amount of information is performed repeating several times the scheme implemented for few qubits. However, to exploit the advantages of quantum computation, the simultaneous control of many qubits is unavoidable [2]. This situation increases the experimental di.culties of quantum computing: maintaining quantum coherence in a large quantum system is a di.cult task. Indeed a quantum computer is a many-body complex system and decoherence, due to the interaction with the external world, will eventually corrupt any quantum computation. Moreover, internal static imperfections can lead to quantum chaos in the quantum register thus destroying computer operability [3]. Indeed, as it has been shown in [4], a critical imperfection strength exists above which the quantum register thermalizes and quantum computation becomes impossible. We showed such e.ects on a quantum computer performing an e.cient algorithm to simulate complex quantum dynamics [5,6].

  17. Quantum oblivion: A master key for many quantum riddles

    NASA Astrophysics Data System (ADS)

    Elitzur, Avshalom C.; Cohen, Eliahu

    2014-02-01

    A simple quantum interaction is analyzed, where the paths of two superposed particles asymmetrically cross, while a detector set to detect an interaction between them remains silent. Despite this negative result, the particles' states leave no doubt that a peculiar interaction has occurred: One particle's momentum is changed while the other's remains unaffected, in apparent violation of momentum conservation. Revisiting the foundations of the standard quantum measurement process offers the resolution. Prior to the macroscopic recording of no interaction, a brief critical interval (CI) prevails, during which the particles and the detector's pointer form a subtle entanglement which immediately dissolves. It is this self-cancellation, henceforth "quantum oblivion (QO)," that lies at the basis of some well-known intriguing quantum effects. Such is interaction-free measurement (IFM)1 and its more paradoxical variants like Hardy's Paradox2 and the quantum liar paradox.3 Even the Aharonov-Bohm (AB) effect4 and weak measurement (WM)5 turn out to belong to this group. We next study interventions within the CI that produce some other peculiar effects. Finally, we discuss some of the conceptual issues involved. Under a greater time-resolution of the CI, some non-local phenomena turn out to be local. Momentum is conserved due to the quantum uncertainties inflicted by the particle-pointer interaction, which sets the experiment's final boundary condition.

  18. Quantum Physics

    NASA Astrophysics Data System (ADS)

    Le Bellac, Michel

    2006-03-01

    Quantum physics allows us to understand the nature of the physical phenomena which govern the behavior of solids, semi-conductors, lasers, atoms, nuclei, subnuclear particles and light. In Quantum Physics, Le Bellac provides a thoroughly modern approach to this fundamental theory. Throughout the book, Le Bellac teaches the fundamentals of quantum physics using an original approach which relies primarily on an algebraic treatment and on the systematic use of symmetry principles. In addition to the standard topics such as one-dimensional potentials, angular momentum and scattering theory, the reader is introduced to more recent developments at an early stage. These include a detailed account of entangled states and their applications, the optical Bloch equations, the theory of laser cooling and of magneto-optical traps, vacuum Rabi oscillations, and an introduction to open quantum systems. This is a textbook for a modern course on quantum physics, written for advanced undergraduate and graduate students. Completely original and contemporary approach, using algebra and symmetry principles Introduces recent developments at an early stage, including many topics that cannot be found in standard textbooks. Contains 130 physically relevant exercises

  19. Speakable and Unspeakable in Quantum Mechanics

    NASA Astrophysics Data System (ADS)

    Bell, J. S.; Aspect, Introduction by Alain

    2004-06-01

    List of papers on quantum philosophy by J. S. Bell; Preface; Acknowledgements; Introduction by Alain Aspect; 1. On the problem of hidden variables in quantum mechanics; 2. On the Einstein-Rosen-Podolsky paradox; 3. The moral aspects of quantum mechanics; 4. Introduction to the hidden-variable question; 5. Subject and object; 6. On wave packet reduction in the Coleman-Hepp model; 7. The theory of local beables; 8. Locality in quantum mechanics: reply to critics; 9. How to teach special relativity; 10. Einstein-Podolsky-Rosen experiments; 11. The measurement theory of Everett and de Broglie's pilot wave; 12. Free variables and local causality; 13. Atomic-cascade photons and quantum-mechanical nonlocality; 14. de Broglie-Bohm delayed choice double-slit experiments and density matrix; 15. Quantum mechanics for cosmologists; 16. Bertlmann's socks and the nature of reality; 17. On the impossible pilot wave; 18. Speakable and unspeakable in quantum mechanics; 19. Beables for quantum field theory; 20. Six possible worlds of quantum mechanics; 21. EPR correlations and EPR distributions; 22. Are there quantum jumps?; 23. Against 'measurement'; 24. La Nouvelle cuisine.

  20. Quantum walk computation

    SciTech Connect

    Kendon, Viv

    2014-12-04

    Quantum versions of random walks have diverse applications that are motivating experimental implementations as well as theoretical studies. Recent results showing quantum walks are “universal for quantum computation” relate to algorithms, to be run on quantum computers. We consider whether an experimental implementation of a quantum walk could provide useful computation before we have a universal quantum computer.

  1. Scaling of entanglement close to a quantum phase transition.

    PubMed

    Osterloh, A; Amico, Luigi; Falci, G; Fazio, Rosario

    2002-04-11

    Classical phase transitions occur when a physical system reaches a state below a critical temperature characterized by macroscopic order. Quantum phase transitions occur at absolute zero; they are induced by the change of an external parameter or coupling constant, and are driven by quantum fluctuations. Examples include transitions in quantum Hall systems, localization in Si-MOSFETs (metal oxide silicon field-effect transistors; ref. 4) and the superconductor-insulator transition in two-dimensional systems. Both classical and quantum critical points are governed by a diverging correlation length, although quantum systems possess additional correlations that do not have a classical counterpart. This phenomenon, known as entanglement, is the resource that enables quantum computation and communication. The role of entanglement at a phase transition is not captured by statistical mechanics-a complete classification of the critical many-body state requires the introduction of concepts from quantum information theory. Here we connect the theory of critical phenomena with quantum information by exploring the entangling resources of a system close to its quantum critical point. We demonstrate, for a class of one-dimensional magnetic systems, that entanglement shows scaling behaviour in the vicinity of the transition point.

  2. Quantum Uniqueness

    NASA Astrophysics Data System (ADS)

    Sych, Denis; Leuchs, Gerd

    2015-12-01

    Classical physics allows for the existence of pairs of absolutely identical systems. Pairwise application of identical measurements to each of those systems always leads to exactly alike results irrespectively of the choice of measurements. Here we ask a question how the picture looks like in the quantum domain. Surprisingly, we get a counterintuitive outcome. Pairwise application of identical (but a priori unknown) measurements cannot always lead to exactly alike results. We interpret this as quantum uniqueness—a feature that has no classical analog.

  3. Quantum Foam

    SciTech Connect

    Lincoln, Don

    2014-10-24

    The laws of quantum mechanics and relativity are quite perplexing however it is when the two theories are merged that things get really confusing. This combined theory predicts that empty space isn’t empty at all – it’s a seething and bubbling cauldron of matter and antimatter particles springing into existence before disappearing back into nothingness. Scientists call this complicated state of affairs “quantum foam.” In this video, Fermilab’s Dr. Don Lincoln discusses this mind-bending idea and sketches some of the experiments that have convinced scientists that this crazy prediction is actually true.

  4. Critical gravity in four dimensions.

    PubMed

    Lü, H; Pope, C N

    2011-05-01

    We study four-dimensional gravity theories that are rendered renormalizable by the inclusion of curvature-squared terms to the usual Einstein action with a cosmological constant. By choosing the parameters appropriately, the massive scalar mode can be eliminated and the massive spin-2 mode can become massless. This "critical" theory may be viewed as a four-dimensional analogue of chiral topologically massive gravity, or of critical "new massive gravity" with a cosmological constant, in three dimensions. We find that the on-shell energy for the remaining massless gravitons vanishes. There are also logarithmic spin-2 modes, which have positive energy. The mass and entropy of standard Schwarzschild-type black holes vanish. The critical theory might provide a consistent toy model for quantum gravity in four dimensions. PMID:21635082

  5. Critical Gravity in Four Dimensions

    SciTech Connect

    Lue, H.; Pope, C. N.

    2011-05-06

    We study four-dimensional gravity theories that are rendered renormalizable by the inclusion of curvature-squared terms to the usual Einstein action with a cosmological constant. By choosing the parameters appropriately, the massive scalar mode can be eliminated and the massive spin-2 mode can become massless. This ''critical'' theory may be viewed as a four-dimensional analogue of chiral topologically massive gravity, or of critical 'new massive gravity' with a cosmological constant, in three dimensions. We find that the on-shell energy for the remaining massless gravitons vanishes. There are also logarithmic spin-2 modes, which have positive energy. The mass and entropy of standard Schwarzschild-type black holes vanish. The critical theory might provide a consistent toy model for quantum gravity in four dimensions.

  6. Critical gravity in four dimensions.

    PubMed

    Lü, H; Pope, C N

    2011-05-01

    We study four-dimensional gravity theories that are rendered renormalizable by the inclusion of curvature-squared terms to the usual Einstein action with a cosmological constant. By choosing the parameters appropriately, the massive scalar mode can be eliminated and the massive spin-2 mode can become massless. This "critical" theory may be viewed as a four-dimensional analogue of chiral topologically massive gravity, or of critical "new massive gravity" with a cosmological constant, in three dimensions. We find that the on-shell energy for the remaining massless gravitons vanishes. There are also logarithmic spin-2 modes, which have positive energy. The mass and entropy of standard Schwarzschild-type black holes vanish. The critical theory might provide a consistent toy model for quantum gravity in four dimensions.

  7. Quantum control limited by quantum decoherence

    SciTech Connect

    Xue, Fei; Sun, C. P.; Yu, S. X.

    2006-01-15

    We describe quantum controllability under the influences of the quantum decoherence induced by the quantum control itself. It is shown that, when the controller is considered as a quantum system, it will entangle with its controlled system and then cause quantum decoherence in the controlled system. In competition with this induced decoherence, the controllability will be limited by some uncertainty relation in a well-armed quantum control process. In association with the phase uncertainty and the standard quantum limit, a general model is studied to demonstrate the possibility of realizing a decoherence-free quantum control with a finite energy within a finite time. It is also shown that if the operations of quantum control are to be determined by the initial state of the controller, then due to the decoherence which results from the quantum control itself, there exists a low bound for quantum controllability.

  8. Quantum depinning transition of quantum Hall stripes.

    PubMed

    Li, M-R; Fertig, H A; Côté, R; Yi, Hangmo

    2004-05-01

    We examine the effect of disorder on the electromagnetic response of quantum Hall stripes using an effective elastic theory to describe their low-energy dynamics, and replicas and the Gaussian variational method to handle disorder effects. Within our model we demonstrate the existence of a depinning transition at a critical partial Landau level filling factor Deltanu(c). For DeltanuDeltanu(c). For Deltanu> or =Deltanu(c), we find a partial RSB solution in which there is free sliding only along the stripe direction. The transition is analogous to the Kosterlitz-Thouless phase transition.

  9. Quantum entanglement and quantum phase transitions in frustrated Majumdar-Ghosh model

    NASA Astrophysics Data System (ADS)

    Liu, Guang-Hua; Wang, Chun-Hai; Deng, Xiao-Yan

    2011-01-01

    By using the density matrix renormalization group technique, the quantum phase transitions in the frustrated Majumdar-Ghosh model are investigated. The behaviors of the conventional order parameter and the quantum entanglement entropy are analyzed in detail. The order parameter is found to peak at J2∼0.58, but not at the Majumdar-Ghosh point ( J2=0.5). Although, the quantum entanglements calculated with different subsystems display dissimilarly, the extremes of their first derivatives approach to the same critical point. By finite size scaling, this quantum critical point JC2 converges to around 0.301 in the thermodynamic limit, which is consistent with those predicted previously by some authors (Tonegawa and Harada, 1987 [6]; Kuboki and Fukuyama, 1987 [7]; Chitra et al., 1995 [9]). Across the JC2, the system undergoes a quantum phase transition from a gapless spin-fluid phase to a gapped dimerized phase.

  10. Quantum information-geometry of dissipative quantum phase transitions.

    PubMed

    Banchi, Leonardo; Giorda, Paolo; Zanardi, Paolo

    2014-02-01

    A general framework for analyzing the recently discovered phase transitions in the steady state of dissipation-driven open quantum systems is still lacking. To fill this gap, we extend the so-called fidelity approach to quantum phase transitions to open systems whose steady state is a Gaussian fermionic state. We endow the manifold of correlation matrices of steady states with a metric tensor g measuring the distinguishability distance between solutions corresponding to a different set of control parameters. The phase diagram can then be mapped out in terms of the scaling behavior of g and connections with the Liouvillean gap and the model correlation functions unveiled. We argue that the fidelity approach, thanks to its differential-geometric and information-theoretic nature, provides insights into dissipative quantum critical phenomena as well as a general and powerful strategy to explore them. PMID:25353417

  11. Quantum information-geometry of dissipative quantum phase transitions.

    PubMed

    Banchi, Leonardo; Giorda, Paolo; Zanardi, Paolo

    2014-02-01

    A general framework for analyzing the recently discovered phase transitions in the steady state of dissipation-driven open quantum systems is still lacking. To fill this gap, we extend the so-called fidelity approach to quantum phase transitions to open systems whose steady state is a Gaussian fermionic state. We endow the manifold of correlation matrices of steady states with a metric tensor g measuring the distinguishability distance between solutions corresponding to a different set of control parameters. The phase diagram can then be mapped out in terms of the scaling behavior of g and connections with the Liouvillean gap and the model correlation functions unveiled. We argue that the fidelity approach, thanks to its differential-geometric and information-theoretic nature, provides insights into dissipative quantum critical phenomena as well as a general and powerful strategy to explore them.

  12. Quantum dice

    SciTech Connect

    Sassoli de Bianchi, Massimiliano

    2013-09-15

    In a letter to Born, Einstein wrote [42]: “Quantum mechanics is certainly imposing. But an inner voice tells me that it is not yet the real thing. The theory says a lot, but does not really bring us any closer to the secret of the ‘old one.’ I, at any rate, am convinced that He does not throw dice.” In this paper we take seriously Einstein’s famous metaphor, and show that we can gain considerable insight into quantum mechanics by doing something as simple as rolling dice. More precisely, we show how to perform measurements on a single die, to create typical quantum interference effects, and how to connect (entangle) two identical dice, to maximally violate Bell’s inequality. -- Highlights: •Rolling a die is a quantum process admitting a Hilbert space representation. •Rolling experiments with a single die can produce interference effects. •Two connected dice can violate Bell’s inequality. •Correlations need to be created by the measurement, to violate Bell’s inequality.

  13. Quantum wormholes

    SciTech Connect

    Visser, M. )

    1991-01-15

    This paper presents an application of quantum-mechanical principles to a microscopic variant of the traversable wormholes recently introduced by Morris and Thorne. The analysis, based on the surgical grafting of two Reissner-Nordstroem spacetimes, proceeds by using a minisuperspace model to approximate the geometry of these wormholes. The thin shell'' formalism is applied to this minisuperspace model to extract the effective Lagrangian appropriate to this one-degree-of-freedom system. This effective Lagrangian is then quantized and the wave function for the wormhole is explicitly exhibited. A slightly more general class of wormholes---corresponding to the addition of some dust'' to the wormhole throat---is analyzed by recourse to WKB techniques. In all cases discussed in this paper, the expectation value of the wormhole radius is calculated to be of the order of the Planck length. Accordingly, though these quantum wormholes are of considerable theoretical interest they do not appear to be useful as a means for interstellar travel. The results of this paper may also have a bearing on the question of topological fluctuations in quantum gravity. These calculations serve to suggest that topology-changing effects might in fact be {ital suppressed} by quantum-gravity effects.

  14. Quantum abacus

    NASA Astrophysics Data System (ADS)

    Cheon, Taksu; Tsutsui, Izumi; Fülöp, Tamás

    2004-09-01

    We show that the point interactions on a line can be utilized to provide U(2) family of qubit operations for quantum information processing. Qubits are realized as states localized in either side of the point interaction which represents a controllable gate. The qubit manipulation proceeds in a manner analogous to the operation of an abacus.

  15. Quantum Gravity

    NASA Astrophysics Data System (ADS)

    Goradia, Shantilal

    2009-11-01

    The continuing search for quantum gravity and never ending attempts to unify gravity with other forces of nature represent tremendous waste of public and private funds directing students' energy towards non-creative manipulative work instead of learning from the scientific creativity in Einstein's 1919 paper that unifies gravity with nuclear force. It reflects Einstein's 1919 jump beyond his own 1915 theory of gravity, including that of Newton as implicitly demanded by Newton in 1686. Einstein corrected and retracted his 1917 introduction of cosmological constant in 1919. Dislike of the fact that Einstein did not use quantum mechanics to prove his point has no real value now, because we will use key ingredients (Planck scale and probabilistic aspect) of quantum mechanics and show that they reach the same conclusion. Newton explained the solar system known after Kepler. Likewise, our quantum mechanical approach explains the strong coupling as well the solar system and shows new horizons, otherwise unexplained. Explanation of unexplained observations need no prediction per Hawking, and obviously otherwise.

  16. Quantum Interferometry

    NASA Technical Reports Server (NTRS)

    Dowling, Jonathan P.

    2000-01-01

    Recently, several researchers, including yours truly, have been able to demonstrate theoretically that quantum photon entanglement has the potential to also revolutionize the entire field of optical interferometry, by providing many orders of magnitude improvement in interferometer sensitivity. The quantum entangled photon interferometer approach is very general and applies to many types of interferometers. In particular, without nonlocal entanglement, a generic classical interferometer has a statistical-sampling shot-noise limited sensitivity that scales like 1/Sqrt[N], where N is the number of particles (photons, electrons, atoms, neutrons) passing through the interferometer per unit time. However, if carefully prepared quantum correlations are engineered between the particles, then the interferometer sensitivity improves by a factor of Sqrt[N] (square root of N) to scale like 1/N, which is the limit imposed by the Heisenberg Uncertainty Principle. For optical (laser) interferometers operating at milliwatts of optical power, this quantum sensitivity boost corresponds to an eight-order-of-magnitude improvement of signal to noise. Applications are to tests of General Relativity such as ground and orbiting optical interferometers for gravity wave detection, Laser Interferometer Gravity Observatory (LIGO) and the European Laser Interferometer Space Antenna (LISA), respectively.

  17. Quantum transformations

    SciTech Connect

    Faraggi, A.E.; Matone, M.

    1998-01-09

    We show that the quantum Hamilton-Jacobi equation can be written in the classical form with the spatial derivative {partial_derivative}{sub q} replaced by {partial_derivative}{sub q} with dq = dq/{radical}1{minus}{beta}{sup 2}(q), where {beta}{sup 2}(q) is strictly related to the quantum potential. This can be seen as the opposite of the problem of finding the wave function representation of classical mechanics as formulated by Schiller and Rosen. The structure of the above {open_quotes}quantum transformation{close_quotes}, related to the recently formulated equivalence principle, indicates that the potential deforms space geometry. In particular, a result by Flanders implies that both W(q) = V(q) {minus} E and the quantum potential Q are proportional to the curvatures {kappa}{sub W} and {kappa}{sub Q} which arise as natural invariants in an equivalence problem for curves in the projective line. In this formulation the Schroedinger equation takes the geometrical form ({partial_derivative}{sub q}{sup 2} + {kappa}{sub W}){psi} = 0.

  18. Distribution of critical temperature at Anderson localization

    NASA Astrophysics Data System (ADS)

    Gammag, Rayda; Kim, Ki-Seok

    2016-05-01

    Based on a local mean-field theory approach at Anderson localization, we find a distribution function of critical temperature from that of disorder. An essential point of this local mean-field theory approach is that the information of the wave-function multifractality is introduced. The distribution function of the Kondo temperature (TK) shows a power-law tail in the limit of TK→0 regardless of the Kondo coupling constant. We also find that the distribution function of the ferromagnetic transition temperature (Tc) gives a power-law behavior in the limit of Tc→0 when an interaction parameter for ferromagnetic instability lies below a critical value. However, the Tc distribution function stops the power-law increasing behavior in the Tc→0 limit and vanishes beyond the critical interaction parameter inside the ferromagnetic phase. These results imply that the typical Kondo temperature given by a geometric average always vanishes due to finite density of the distribution function in the TK→0 limit while the typical ferromagnetic transition temperature shows a phase transition at the critical interaction parameter. We propose that the typical transition temperature serves a criterion for quantum Griffiths phenomena vs smeared transitions: Quantum Griffiths phenomena occur above the typical value of the critical temperature while smeared phase transitions result at low temperatures below the typical transition temperature. We speculate that the ferromagnetic transition at Anderson localization shows the evolution from quantum Griffiths phenomena to smeared transitions around the critical interaction parameter at low temperatures.

  19. Quantum roulette: an extended quantum strategy

    NASA Astrophysics Data System (ADS)

    Wang, Xiang-Bin; Kwek, L. C.; Oh, C. H.

    2000-12-01

    In a recent paper, Meyer demonstrated that with a quantum computer, an analogous zero-sum classically strategic game played with quantum strategy essentially become a bias game under a mixture of quantum and classical strategy. To illustrate his point, Meyer used a quantum coin tossing event. In this Letter, we generalize Meyer's argument to an N-state game.

  20. Quantum state and quantum entanglement protection using quantum measurements

    NASA Astrophysics Data System (ADS)

    Wang, Shuchao; Li, Ying; Wang, Xiangbin; Kwek, Leong Chuan; Yu, Zongwen; Zou, Wenjie

    2015-03-01

    The time evolution of some quantum states can be slowed down or even stopped under frequent measurements. This is the usual quantum Zeno effect. Here we report an operator quantum Zeno effect, in which the evolution of some physical observables is slowed down through measurements even though thequantum state changes randomly with time. Based on the operator quantum Zeno effect, we show how we can protect quantum information from decoherence with two-qubit measurements, realizable with noisy two-qubit interactions. Besides, we report the quantum entanglement protection using weak measurement and measurement reversal scheme. Exposed in the nonzero temperature environment, a quantum system can both lose and gain excitations by interacting with the environment. In this work, we show how to optimally protect quantum states and quantum entanglement in such a situation based on measurement reversal from weak measurement. In particular, we present explicit formulas of protection. We find that this scheme can circumvent the entanglement sudden death in certain conditions.