共查询到20条相似文献,搜索用时 234 毫秒
1.
The phase transition “triangular lattice-vortex liquid” in layered high-T
c
superconductors in the presence of pinning centers is studied. A two-dimensional system of vortices simulating the superconducting
layers in a high-T
c
Shubnikov phase is calculated by the Monte Carlo method. It was found that in the presence of defects the melting of the
vortex lattice proceeds in two stages: First, the ideal triangular lattice transforms at low temperature (≃3 K)into islands
which are pinned to the pinning centers and rotate around them and then, at a higher temperature (≃8 K for T
c
584 K), the boundaries of the “islands” become smeared and the system transforms into a vortex liquid. As the pinning force
increases, the temperatures of both phase transitions shift: The temperature of the point “triangular lattice-rotating lattice”
decreases slightly (to ≃2 K)and the temperature of the phase transition “rotating lattice-vortex liquid” increases substantially
(≃70 K).
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 4, 269–274 (25 August 1997) 相似文献
2.
R. M. Arutyunyan V. L. Ginzburg G. F. Zharkov 《Journal of Experimental and Theoretical Physics》1997,84(6):1186-1196
The question of a surface barrier which determines the behavior of a vortex in a hollow superconducting cylinder of finite
thickness in an external magnetic field is discussed, taking into account magnetic flux quantization in the cavity. The behavior
of magnetic vortices in a hollow superconductor in the presence of a thermoelectric current is also considered. Pairs of magnetic
vortices with opposite magnetic field orientations (vortex-antivortex pairs) are generated by this current near T
c. The thermoelectric current drives the antivortex (the vortex with oppositely directed field) out of the cylinder, whereas
the vortex is ejected into the cavity and remains on the inside cylinder surface as a current. The number of magnetic flux
quanta trapped inside the cylinder increases by one. The relation of this mechanism to the “giant” thermoelectric effect in
hollow superconductors is discussed.
Zh. éksp. Teor. Fiz. 111, 2175–2193 (June 1997) 相似文献
3.
Excitation of plasma oscillations during the motion of Josephson vortices in layered superconductors
The electric and magnetic fields arising during uniform motion of a vortex lattice in a magnetic field oriented parallel to
the conducting layers are calculated in an exactly solvable model. For low temperatures and high velocities of the lattice,
features due to the excitation of plasma oscillations of the superconducting electrons appear in the current-voltage characteristic.
Peaks associated with plasmon excitation and the Cherenkov effect are present in the radiation spectrum.
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 12, 811–816 (25 December 1997) 相似文献
4.
V. N. Krivoruchko 《Journal of Experimental and Theoretical Physics》1997,84(2):300-308
The formation of the superconducting phase in short-period proximity-effect layered superlattices of the superconductor-band-antiferromagnetic-metal
(SC/AF) type is studied. The exact solution of the Usadel equations is used to discuss the possibility of formation in such
structures of a ground state in which the order parameters of the adjacent superconducting layers have opposite signs (the
“π-phase”). The dependence of the superconducting transition temperature and the upper critical field normal to the layers on
the lattice period, the intensity of magnetic interaction in the antiferromagnetic layer, and the state of the interface between
the layers is examined. It is found that there exists a nonlinear dependence of the conditions for the appearance of the superconducting
state in a layered SC/AF system on the system’s parameters. Finally, the conditions for the appearance of the superconducting
phase in proximity-effect superlattices consisting of a superconductor with nonmagnetic, ferromagnetic, and antiferromagnetic
metals are compared.
Zh. éksp. Teor. Fiz. 111, 547–561 (February 1997) 相似文献
5.
Yu. Kh. Vekilov I. A. Gordeev É. I. Isaev 《Journal of Experimental and Theoretical Physics》1999,89(5):995-999
The electronic spectrum and wave functions of a new quasicrystal structure—a two-dimensional Fibonacci lattice—are investigated
in the tight-binding approximation using the method of the level statistics. This is a self-similar structure consisting of
three elementary structural units. The “central” and “nodal” decoration of this structure are examined. It is shown that the
electronic energy spectrum of a two-dimensional Fibonacci lattice contains a singular part, but in contrast to a one-dimensional
Fibonacci lattice the spectrum does not contain a hierarchical gap structure. The measure of allowed states (Lebesgue measure)
of the spectrum is different from zero, and for “central” decoration it is close to 1. The character of the localization of
the wave functions is investigated, and it is found that the wave functions are “critical.”
Zh. éksp. Teor. Fiz. 116, 1834–1842 (November 1999) 相似文献
6.
An analysis is made of a two-electron system of two adjacent quantum dots (QD) with a two-dimensional parabolic lateral confining
potential, and of two coupled or double, spatially separated QDs (a “horizontal” and a “vertical” QD molecule), and of their
behavior in an external transverse magnetic field. The ground-state energies and energy spectra of the system have been determined
by various methods (Heitler-London, molecular-orbital, variational approach, and numerical diagonalization of Hamiltonian),
with inclusion of electron-electron interaction, and for a broad range of confining-potential steepness, QD-center spacing
(interlayer distance), and external magnetic field.
Fiz. Tverd. Tela (St. Petersburg) 40, 2127–2133 (November 1998) 相似文献
7.
A.A. Zvyagin D.M. Apal'kov 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):565-569
We present a Bethe Ansatz based investigation of a one-dimensional (1D) Heisenberg spin chain in a real 3D crystal lattice.
We have shown that due to an influence of the lattice distortion on a crystalline field of ligands of magnetic ions, a Heisenberg
antiferromagnetic spin chain is unstable under the appearance of a magnetic anisotropy of the “easy-plane” type. The effects of an external magnetic
field and nonzero temperature onto such a phase transition are studied.
Received: 19 January 1998 / Revised: 16 March 1998 / Accepted: 17 March 1998 相似文献
8.
M. V. Sadovskii 《JETP Letters》1999,69(6):483-489
Calculations of the optical conductivity are performed in a simple model of the electronic spectrum of a two-dimensional system
with “hot regions” on the Fermi surface. The model leads to a strong restructuring of the spectral density (pseudogap) in
these regions. It is shown that this model makes it possible to reproduce qualitatively the basic features of the optical
measurements in the pseudogap state of high-temperature superconducting cuprates.
Pis’ma Zh. éksp. Teor. Fiz. 69, No. 6, 447–452 (25 March 1999) 相似文献
9.
The shape of the EPR line in a thin (=λ/2, where λ is the London penetration depth of the magnetic field in the superconductor) paramagnetic film deposited on the surface of
an anisotropic superconductor is calculated in an oblique magnetic field with allowance for the inhomogeneity of the local
magnetic field of the Abrikosov vortex lattice. It is shown that, as the tilt angle of the external magnetic field is varied,
the shape of the EPR line changes noticeably. This fact can give additional information about the superconductor parameters
(the symmetry type of the vortex lattice and the anisotropy parameter of the superconductor).
Fiz. Tverd. Tela (St. Petersburg) 41, 386–388 (March 1999) 相似文献
10.
We developed a self-consistent method for the calculation of spatial current distributions in high-T c grain-boundary junctions. It is found that crystallographic anisotropy of high-T c superconducting electrodes results in the effects, which previously were not taken into account for interpretations of experimental data. Among them is a significant redistribution of electrical currents in superconducting electrodes in the vicinity of a grain boundary. In particular in the case of [100]-tilt bicrystal junctions, this current redistribution results in a substantial focusing to the top or bottom part of a thickness of the grain boundary, depending on “roof”- or “valley”-type of the grain boundary. This redistribution is accompanied by generation of vortex currents around the grain boundary, which leads to self-biasing of grain-boundary junctions by magnetic field nucleated by these vortex currents. It is shown that twinning or variation of geometrical shape of the high-T c electrode may also result in intensive redistribution of electrical currents and nucleation of local magnetic fields inside a high-T c superconducting electrodes. 相似文献
11.
A. I. Belousov S. A. Berzakov Yu. E. Lozovik 《Journal of Experimental and Theoretical Physics》1998,87(2):322-328
The phase diagram of a two-dimensional Josephson array of mesoscopic objects (superconducting granules, superfluid helium
in a porous medium, traps with Bose-condensed atoms, etc.) is examined. Quantum fluctuations in both the modulus and phase
of the superconducting order parameter are taken into account within a lattice boson Hubbard model. Modulating the average
occupation number n
0 of the sites in the system (the “number of Cooper pairs” per granule, the number of atoms in a trap, etc.) leads to changes
in the state of the array, and the character of these changes depends significantly on the region of the phase diagram being
examined. In the region where there are large quantum fluctuations in the phase of the superconducting order parameter, variation
of the chemical potential causes oscillations with alternating superconducting (superfluid) and normal states of the array.
On the other hand, in the region where the bosons interact weakly, the properties of the system depend monotonically on n
0. Lowering the temperature and increasing the particle interaction force lead to a reduction in the width of the region of
variation in n
0 within which the system properties depend weakly on the average occupation number. The phase diagram of the array is obtained
by mapping this quantum system onto a classical two-dimensional XY model with a renormalized Josephson coupling constant and is consistent with our quantum path-integral Monte Carlo calculations.
Zh. éksp. Teor. Fiz. 114, 591–604 (August 1998) 相似文献
12.
P. H. Chavanis 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,80(3):275-306
We study the thermodynamics of the Hamiltonian mean field
(HMF) model with an external potential playing the role of a
“magnetic field”. If we consider only fully stable states,
the caloric curve does not present any phase
transition. However, if we take into account metastable states (for
a restricted class of perturbations), we find a very rich
phenomenology. In particular, the caloric curve
displays a region of negative specific heat in the microcanonical
ensemble in which the temperature decreases as the energy
increases. This leads to ensembles inequivalence and to zeroth
order phase transitions similar to the “gravothermal catastrophe”
and to the “isothermal collapse” of self-gravitating systems. In
the present case, they correspond to the reorganization of the
system from an “anti-aligned” phase (magnetization pointing in
the direction opposite to the magnetic field) to an “aligned”
phase (magnetization pointing in the same direction as the magnetic
field). We also find that the magnetic susceptibility can be
negative in the microcanonical ensemble so that the magnetization
decreases as the magnetic field increases. The magnetic curves can
take various shapes depending on the values of energy or temperature. We
describe first order phase
transitions and hysteretic cycles involving positive or negative
susceptibilities. We also show that this model exhibits gaps in the
magnetization at fixed energy, resulting in ergodicity breaking. 相似文献
13.
E. D. Gutlyanskii 《JETP Letters》1998,67(3):239-245
A longitudinal ultrasonic wave should drag the vortex structure of superconductors at an acute angle with respect to the direction
of wave propagation. This motion engenders longitudinal and transverse electric fields in the superconductor and, moreover,
effects of the “optical rectification” type contribute to the observed longitudinal and transverse electric fields. The effect
should be observed in all type-II superconductors above the irreversibility line. Both fields have extrema with respect to
temperature and magnetic field. In contrast to the acoustoelectric effect in the normal state, the sign of the induced electric
field depends on the external magnetic field.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 3, 222–227 (10 February 1998) 相似文献
14.
Angular dependences of the magnetization hysteresis loops have been studied at T=77 K on YBCO single crystals exhibiting the peak effect. The peak effect is shown to be related to the pinning of longitudinal
vortices along the c axis at twin boundary-type ordered defects. The behavior of the peak effect at intermediate angles is explained by anisotropic
magnetic field penetration into quasi-two-dimensional superconductors. In thin crystals with a dilute ordered-defect structure
this can result in an enhanced peak effect due to formation of a vortex kink structure and to “internal” pinning of transverse
vortex segments at Cu-O sheets.
Fiz. Tverd. Tela (St. Petersburg) 39, 425–431 (March 1997) 相似文献
15.
M. V. Krasin’kova 《Technical Physics》1998,43(11):1347-1349
The question of the dimensionality of superconductivity is considered within the framework of a model of superconductivity
via asymmetric, delocalized “crystalline” π orbitals (analogous to the corresponding molecular orbitals) extending along chains of covalently bonded copper and oxygen
ions. It is shown that superconductivity is preceded by a separation of the bonds in the CuO2 layer into covalent and ionic bonds with ordering of the covalent bonds into chains. Such an ordering facilitates the formation
of a crystalline π orbital lowering the crystal energy by the resonance energy of the π bond and is therefore favored. The superconducting current is created by non-dissipative motion of π-electron pairs along the asymmetric, “crystalline” π orbitals extending along chains of covalently bonded copper and oxygen ions, in the presence of an ionic bond between neighboring
chains extending through the easily polarizable O2− ions. This ionic bond correlates the motion of the electron pairs along all the π orbitals and stabilizes the superconducting state. Only in this sense is the apparent “onedimensionality” of superconductivity
in cuprate superconductors to be understood.
Zh. Tekh. Fiz. 68, 82–84 (November 1998) 相似文献
16.
The results of an experimental investigation of the dependence of the dissipation in a vortex lattice on the magnetic field
strength and orientation of a Bi 2212 crystal at a temperature of ~15 K are presented. A sharp peak, whose width depends on
the orientation of the superconductor relative to the field, is observed in the dissipation. The results can be explained
qualitatively by the appearance of a geometrical barrier that leads to a substantial redistribution of the magnetic field
in the bulk of the sample.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 5, 331–335 (10 March 1996) 相似文献
17.
s. Roth 《Applied physics. B, Lasers and optics》1978,15(1):1-11
Experimental work on systems showing evidence of the coexistence of superconductivity and magnetic order is reviewed. The
presently known systems are shown to be “superconducting spin glasses” rather than “ferromagnetic superconductors”. In those
systems where the magnetic order is expected to be long-ranged (up to now) superconductivity vanishes as soon as the magnetic
order appears. But it is not excluded that magnetic order with a correlation length larger than the superconductive coherence
length can coexist with superconductivity. 相似文献
18.
Over the last ten years interest in the physics of de Sitter space—time has been growing very fast. Besides the supposed existence
of a “de Sitterian period” in inflation theories, the observational evidence of an acceleration of the universe expansion
(interpreted as a positive cosmological constant or a “dark energy” or some form of “quintessence”) has triggered a lot of
attention in the physics community. A specific de Sitterian field called “massless minimally coupled field” (mmc) plays a
fundamental role in inflation models and in the construction of the de Sitterian gravitational field. A covariant quantization
of the mmc field, à la Krein—Gupta—Bleuler was proposed in Class. Quantum. Grav. 17, 1415 (2000). In this talk, we will review this construction and explain the relevance of such a field in the construction
of a massless spin-2 field in de Sitter space—time. 相似文献
19.
The melting of two-dimensional microclusters of “particles” which repel one another according to a logarithmic law and are
confined by an external quadratic potential is investigated. The model describes Abrikosov vortices in a superconducting island
of vortices in a rotating superfluid liquid and electrons in a semiconductor nanostructure surrounded by a low-permittivity
medium. The structure of clusters and its dependence on temperature and melting are investigated. The melting of microclusters of vortices proceeds in two stages: 1. A transition from a frozen phase into a state corresponding to rotational reorientation of crystal shells relative to one another. 2. At a higher temperature, the radial order vanishes. This is connected with the fact that the
barrier for rotation of the shells is much lower than the barrier for radial breakup of the shells.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 3, 268–273 (10 February 1997) 相似文献
20.
A. É. Filippov 《Physics of the Solid State》1998,40(9):1546-1549
The molecular dynamics method is used to examine the ordering of interacting subsystems in a two-component, two-dimensional
Coulomb gas, consisting of equal amounts of positively and negatively charged particles, which simulates the behavior of a
system of interacting vortices. In particular, it is found that when the system temperature is lowered from the Kosterlitz-Thouless
transition point, additional ordering of the vortex chains may take place. It is noted that this process may stimulate the
development of vortex chains observed in real superfluid, magnetic, and superconducting systems. Possible applications of
the molecular dynamics method to phase separation and the ordering of adiabatically slowly moving subsystems in the collective
field of a fast subsystem are considered.
Fiz. Tverd. Tela (St. Petersburg) 40, 1701–1704 (September 1998) 相似文献