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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Cao G. X., Korshunov M. M., Gao Y. Z., Le Tacon M., Singh D. J., Lin C. T.
Заглавие : Anomalous in-plane electronic scattering in charge ordered Na 0.41CoO 2•0.6H 2O
Место публикации : Phys. Rev. Lett.: American Physical Society, 2012. - Vol. 108, Is. 23. - Ст.236401. - ISSN 0031-9007, DOI 10.1103/PhysRevLett.108.236401
Примечания : Cited References: 41. - We thank H. Habermeier, D. Mandrus, B. C. Sales, I. Eremin, I. I. Mazin, and P. J. Hirschfeld for useful discussions. G. Cao acknowledges support from NSFC (No. 10804068, 10774097). M. M. K. acknowledges support from RFBR (Grant No. 09-02-00127), Presisium of RAS program "Quantum physics of condensed matter" N5.7, Integration Grant of SBRAS-UrBRAS N40, and Russian FCP (GK 16.740.12.0731), and The Dynasty Foundation and ICFPM. Work at ORNL was supported by the Department of Energy, BES, Materials Science and Engineering Division.
Предметные рубрики: SUPERCONDUCTIVITY
TRIPLET
FLUCTUATIONS
IONS
Аннотация: We report electronic transport measurements on high quality floating zone grown NaxCoO2 and Na0.41CoO2·0.6H2O single crystals. We find an in-plane electronic scattering minimum near 11 K and a clear charge ordering at approximately 50 K. The electronic and magnetic properties in hydrated and nonhydrated Na0.41CoO2 samples are similar at higher temperature, but evolve in markedly different ways below ∼50 K, where a strong ferromagnetic tendency is observed in the hydrated sample. Model calculations show the relationship of this tendency to the structure of the Fermi surface. The results, particularly the clear differences between the hydrated and nonhydrated material show a substantially enhanced ferromagnetic tendency upon hydration. Implications for superconductivity are discussed.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Dzebisashvili D. M.
Заглавие : Electron spectrum and heat capacity of heavy fermions in the canted phase of antiferromagnetic intermetallides
Коллективы :
Место публикации : J. Exp. Theor. Phys. - 2010. - Vol. 110, Is. 2. - P.301-318. - ISSN 1063-7761, DOI 10.1134/S1063776110020147
Примечания : Cited References: 41. - This study was supported by the program "Quantum Physics of Condensed Media" of the Presidium of the Russian Academy of Sciences, interdisciplinary integration project no. 53 of the Siberian Branch of the Russian Academy of Sciences, and the Russian Foundation for Basic Research (project no. 07-02-00226).
Предметные рубрики: PERIODIC ANDERSON MODEL
PRESSURE-INDUCED SUPERCONDUCTIVITY
KONDO-LATTICE
FERROMAGNETISM
FLUCTUATIONS
COEXISTENCE
CERHIN5
SYSTEMS
DIAGRAM
CENISN
Ключевые слова (''Своб.индексиров.''): antiferromagnetic phase--antiferromagnetics--antiferromagnets--electron spectrum--electronic heat capacity--energy spectra--experimental data--external magnetic field--heat capacities--heavy fermion--low temperatures--magnetic sublattices--magnetic subsystems--sommerfeld constant--structural rearrangement--temperature dependence--antiferromagnetism--cerium--cerium compounds--fermions--magnetic fields--phase transitions--specific heat--spectroscopy--antiferromagnetic materials
Аннотация: The energy spectrum of heavy fermions in an external magnetic field is calculated for canted magnetic sublattices of antiferromagnetic intermetallides. This makes it possible to determine low-temperature features of electronic heat capacity of heavy-fermion antiferromagnets with the metal-type ground state taking into account the structural rearrangement of the magnetic subsystem. The calculated temperature dependences of the magnetization, heat capacity, and Sommerfeld constant in the vicinity of the point of transition to the antiferromagnetic phase correlate with experimental data obtained for heavy-fermion antiferromagnets PuGa3, Ce2Au2Cd, YbNiSi3, and PuPd5Al2.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Balaev D. A., Gokhfeld D. M., Dubrovskii A. A., Popkov S. I., Shaikhutdinov K. A., Petrov M. I.
Заглавие : Magnetoresistance hysteresis in granular HTSCs as a manifestation of the magnetic flux trapped by superconducting grains in YBCO+CuO composites
Разночтения заглавия :авие SCOPUS: Magnetoresistance hysteresis in granular HTSCs as a manifestation of the magnetic flux trapped by superconducting grains in YBCO + CuO composites
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2007. - Vol. 105, Is. 6. - P1174-1183. - ISSN 1063-7761, DOI 10.1134/S1063776107120084
Примечания : Cited References: 53
Предметные рубрики: HIGH-TEMPERATURE SUPERCONDUCTOR
CRITICAL-CURRENT-DENSITY
CURRENT-VOLTAGE CHARACTERISTICS
BA-CU-O
TRANSPORT-PROPERTIES
FIELD
YBA2CU3O7-DELTA
FLUCTUATIONS
FINGERPRINT
NETWORK
Ключевые слова (''Своб.индексиров.''): critical currents--hysteresis--hysteresis loops--josephson junction devices--magnetic flux--magnetoresistance--yttrium barium copper oxides--granular superconductors--hysterestic dependence--negative magnetoresistance--transport current--composite materials
Аннотация: Hysterestic behavior of the magnetoresistance of granular HTSCs and its interaction with the magnetic hysteresis are studied by measuring magnetoresistance R(H) and critical current I-c(H) of composites formed by HTSC Y0.75Lu0.25Ba2CU3O7 and CuO. A network of Josephson junctions is formed in such composites, in which the nonsuperconducting component plays the role of barriers between HTSC grains. Hysteretic dependences R(H) of magnetoresistance are studied in a wide range of transport current density j and are analyzed in the framework of the two-level model of a granular superconductor, in which dissipation takes place in the Josephson medium and the magnetic flux can be pinned both in grains and in the Josephson medium. The interrelation between the hysteresis of critical current I-c(H) and the evolution of the hysterestic dependence R(H) of the magnetoresistance upon transport current variation is demonstrated experimentally. The effect of the magnetic past history on the hysteretic behavior of R(H) and the emergence of a segment with a negative magnetoresistance are analyzed. It is shown for the first time that the R(H) dependences are characterized by a parameter that is independent of the transport current, viz., the width of the R(H) hysteresis loop.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bulgakov E. N., Rotter I., Sadreev A. F.
Заглавие : Correlated behavior of conductance and phase rigidity in the transition from the weak-coupling to the strong-coupling regime
Место публикации : Phys. Rev. B: AMER PHYSICAL SOC, 2007. - Vol. 76, Is. 21. - Ст.214302. - ISSN 1098-0121, DOI 10.1103/PhysRevB.76.214302
Примечания : Cited References: 42
Предметные рубрики: OPEN QUANTUM-SYSTEMS
NUCLEAR CROSS-SECTIONS
UNIFIED THEORY
FLUCTUATIONS
CONTINUUM
BILLIARD
STATES
Аннотация: We study the transmission through different small systems as a function of the coupling strength v to the two attached leads. The leads are identical with only one propagating mode xi(E)(C) in each of them. In addition to the conductance G, we calculate the phase rigidity rho of the scattering wave function Psi(E)(C) in the interior of the system. Most interesting results are obtained in the regime of strongly overlapping resonance states where the crossover from staying to traveling modes takes place. The crossover is characterized by collective effects. Here, the conductance is plateaulike enhanced in some energy regions of finite length while corridors with zero transmission (total reflection) appear in other energy regions. This transmission picture depends only weakly on the spectrum of the closed system. It is caused by the alignment of some resonance states of the system with the propagating modes xi(E)(C) in the leads. The alignment of resonance states takes place stepwise by resonance trapping, i.e., it is accompanied by the decoupling of other resonance states from the continuum of propagating modes. This process is quantitatively described by the phase rigidity rho of the scattering wave function. Averaged over energy in the considered energy window, G is correlated with 1-rho . In the regime of strong coupling, only two short-lived resonance states survive each aligned with one of the channel wave functions xi(E)(C). They may be identified with traveling modes through the system. The remaining M-2 trapped narrow resonance states are well separated from one another.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gekht R. S., Bondarenko I. N.
Заглавие : A quantum spin liquid in a two-layer triangular antiferromagnet
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2005. - Vol. 101, Is. 5. - P868-880. - ISSN 1063-7761, DOI 10.1134/1.2149066
Примечания : Cited References: 43
Предметные рубрики: ONE-DIMENSIONAL ANTIFERROMAGNETS
DIMER GROUND-STATE
MEAN-FIELD THEORY
HEISENBERG-ANTIFERROMAGNET
SYSTEM SRCU2(BO3)(2)
PHASE-TRANSITION
GAP
FLUCTUATIONS
EXCITATIONS
LATTICE
Ключевые слова (''Своб.индексиров.''): antiferromagnetic materials--magnetic fields--magnetization--phase diagrams--spectrum analysis--thermodynamics--analogous systems--square lattices--thermodynamic quantities--two-layer triangular antiferromagnets--quantum theory
Аннотация: The possibility of implementing a quantum-spin-liquid-type state in a two-layer triangular spin-1/2 antiferromagnet at T = 0 is investigated. The ratio of intra- to interlayer exchange constants (j) is found under which a transition from the classical state with 120 degrees triangular order to a quantum state with zero magnetization per site occurs; in this case, the spins of adjacent layers form singlets that are separated from triplet excitations by an energy gap. Compared with an analogous system with the square lattice, the range of j in which the classical ordered state is realized turns out to be an order of magnitude smaller due to the effects of frustration; in this case, the behavior of thermodynamic quantities is analogous, on the whole, to that in two-layer square lattices; a difference manifests itself in the behavior of the gap in the spectrum of quasiparticles in an external magnetic field h. For small fields h, a j-h phase diagram is constructed that determines the domains in which the 120 degrees and the singlet phases exist. It is established that, in the neighborhood of the second-order phase transition, the contribution, to the thermodynamic quantities, of longitudinal spin fluctuations, which are disregarded in the spin-wave description, is comparable to the contribution of transverse fluctuations. (c) 2005 Pleiades Publishing, Inc.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Sadreev A. F., Berggren K. F.
Заглавие : Current statistics for wave transmission through an open Sinai billiard: Effects of net currents
Место публикации : Phys. Rev. E: AMER PHYSICAL SOC, 2004. - Vol. 70, Is. 2. - Ст.26201. - ISSN 1539-3755, DOI 10.1103/PhysRevE.70.026201
Примечания : Cited References: 27
Предметные рубрики: EIGENVECTOR STATISTICS
OPEN SYSTEMS
EIGENFUNCTIONS
CHAOS
FLUCTUATIONS
CROSSOVER
ELECTRONS
INTENSITY
Ключевые слова (''Своб.индексиров.''): acoustic wave transmission--boundary conditions--computer simulation--continuum mechanics--current density--fermi level--mathematical transformations--microwaves--probability density function--quantum theory--random processes--reverberation--statistical methods--surface waves--waveguides--microwave cavities--poynting vector--sinai billiard--wave functions--cavity resonators
Аннотация: Transport through quantum and microwave cavities is studied by analytic and numerical techniques. In particular, we consider the statistics for a finite net probability current (Poynting vector) j flowing through an open ballistic Sinai billiard to which two opposite leads/wave guides are attached. We show that if the net probability current is small, the scattering wave function inside the billiard is well approximated by a Gaussian random complex field. In this case, the current statistics are universal and obey simple analytic forms. For larger net currents, these forms still apply over several orders of magnitudes. However, small characteristic deviations appear in the tail regions. Although the focus is on electron and microwave billiards, the analysis is relevant also to other classical wave cavities as, for example, open planar acoustic reverberation rooms, elastic membranes, and water surface waves in irregularly shaped vessels.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Nazmitdinov R. G., Pichugin K. N., Rotter I., Seba P.
Заглавие : Conductance of open quantum billiards and classical trajectories
Место публикации : Phys. Rev. B: AMERICAN PHYSICAL SOC, 2002. - Vol. 66, Is. 8. - Ст.85322. - ISSN 1098-0121, DOI 10.1103/PhysRevB.66.085322
Примечания : Cited References: 46
Предметные рубрики: BALLISTIC MICROSTRUCTURES
CHAOTIC SCATTERING
FLUCTUATIONS
DOTS
TRANSPORT
DYNAMICS
STATES
MAGNETOTRANSPORT
STATISTICS
RESONANCES
Аннотация: We analyze the transport phenomena of two-dimensional quantum billiards with convex boundary of different shape. The quantum mechanical analysis is performed by means of the poles of the S matrix while the classical analysis is based on the motion of a free particle inside the cavity along trajectories with a different number of bounces at the boundary. The value of the conductance depends on the manner in which the leads are attached to the cavity. The Fourier transform of the transmission amplitudes is compared with the length of the classical paths. There is good agreement between classical and quantum mechanical results when the conductance is achieved mainly by special short-lived states such as whispering gallery modes and bouncing ball modes. In these cases, also the localization of the wave functions agrees with the picture of the classical paths. The S matrix is calculated classically and compared with the transmission coefficients of the quantum mechanical calculations for five modes in each lead. The number of modes coupled to the special states is effectively reduced.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Alekseev K. N., Priimak D. S.
Заглавие : Squeezed states and quantum chaos
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 1998. - Vol. 86, Is. 1. - P61-70. - ISSN 1063-7761, DOI 10.1134/1.558469
Примечания : Cited References: 41
Предметные рубрики: PERIODICALLY KICKED PENDULUM
CLASSICAL CORRESPONDENCE
SYSTEMS
LIGHT
FLUCTUATIONS
OSCILLATOR
MECHANICS
MASER
Аннотация: We examine the dynamics of a wave packet that initially corresponds to a coherent state in the model of a quantum rotator excited by a periodic sequence of kicks. This model is the main model of quantum chaos and allows for a transition from regular behavior to chaotic in the classical limit. By doing a numerical experiment we study the generation of squeezed states in quasiclassical conditions and in a time interval when quantum-classical correspondence is well-defined. We find that the degree of squeezing depends on the degree of local instability in the system and increases with the Chirikov classical stochasticity parameter. We also discuss the dependence of the degree of squeezing on the initial width of the packet, the problem of stability and observability of squeezed states in the transition to quantum chaos, and the dynamics of disintegration of wave packets in quantum chaos. (C) 1998 American Institute of Physics.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Berman G. P., Bulgakov E. N., Campbell D. K., Gubernatis J. E., Sadreev A. F., Wang X. D.
Заглавие : Phase transition in the one-dimensional quantum discrete phi(4)-phi(2) model
Место публикации : Phys. Rev. B: AMERICAN PHYSICAL SOC, 1997. - Vol. 56, Is. 18. - P11518-11530. - ISSN 0163-1829, DOI 10.1103/PhysRevB.56.11518
Примечания : Cited References: 16
Предметные рубрики: FRENKEL-KONTOROVA MODEL
FIELD-THEORY
GROUND-STATE
FLUCTUATIONS
Аннотация: We consider the ground-state phase transition from broken to restored phases of the one-dimensional quantum discrete phi(4)-phi(2) model as a function of two parameters: the strength of the quantum fluctuations (measured by a dimensionless Planck constant (h) over bar), and the classical dimensionless coupling parameter gamma, which characterizes the strength of interaction of the neighboring atoms. We introduce several distinct variational methods based on self-consistent phonons and soliton wave functions, and compare their predictions for the phase diagram with the (numerically exact) results of previous quantum Monte Carlo simulations. Our calculations show that in the region of weak coupling (gamma 1), both the ''tunneling soliton'' and the ''two-level'' approaches provide good approximations to the true result. In the intermediate coupling region (gamma(c) gamma 1), the method of self-consistent phonons gives a satisfactory description of phase transition. We also compare and contrast our results with previously published approximate methods, and discuss problems for further investigation. [S0163-1829(97)06242-5].
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Korshunov M. M., Shneyder E. I.
Заглавие : Lifshits Quantum Phase Transitions and Rearrangement of the Fermi Surface upon a Change in the Hole Concentration in High-Temperature Superconductors
Коллективы : Presidium of the Russian Academy of Sciences [5.7]; Russian academy of Sciences; Russian Foundation for Basic Research [09-02-00127]
Разночтения заглавия :авие SCOPUS: Lifshits quantum phase transitions and rearrangement of the fermi surface upon a change in the hole concentration in high-temperature superconductors
Место публикации : J. Exp. Theor. Phys. - 2009. - Vol. 109, Is. 5. - Pю775-785. - ISSN 1063-7761, DOI 10.1134/S1063776109110077
Примечания : Cited References: 71. - The authors thank A. A. Kordyuk for discussion of the results and T. M. Ovchinnikova for technical assistance in data processing.This study was supported by the program "Quantum Physics of Condensed Media" of the Presidium of the Russian Academy of Sciences (project no. 5.7), integrated project no. 40 of the Siberian Branch-Ural Division of the Russian academy of Sciences, and the Russian Foundation for Basic Research (project no. 09-02-00127).
Предметные рубрики: T-J MODEL
CORRELATED ELECTRONS
COPPER OXIDES
SPECTRUM
PSEUDOGAP
METAL
FLUCTUATIONS
EXCITATIONS
INSULATOR
SYSTEMS
Ключевые слова (''Своб.индексиров.''): critical points--cuprates--electron heat--electron structures--experimental data--high-t--layered cuprates--low temperatures--normal phase--quantum oscillations--quantum phase transitions--sign reversal--strong correlation--copper compounds--electronic structure--equations of state--fermi surface--fermions--high temperature superconductors--hole concentration--superconductivity--surface structure--phase transitions
Аннотация: Changes in the electronic structure in the normal phase of high-T-c superconductors (HTSCs), viz., layered cuprates, are considered. The results of LDA + GTB calculations of the electron structure and the Fermi surface of La2-xSrxCuO4 one-layer cuprates with allowance for strong correlations are compared with ARPES and quantum oscillations data. Two critical points x(c1) and x(c2) are discovered at which the rearrangement of the Fermi surface takes place. In the vicinity of these points, changes in the thermodynamic properties at low temperatures are determined using the Lifshits ideology concerning 2.5-order quantum phase transitions. A singularity delta(C/T) proportional to (x-x(e))(1/2) in the electron heat capacity agrees well with the available experimental data in the vicinity of x(c1)approximate to 0.15. Sign reversal of the Hall constant upon doping is also considered qualitatively.
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