共查询到20条相似文献,搜索用时 957 毫秒
1.
R. Gonczarek L. Jacak M. Krzyzosiak A. Gonczarek 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,49(2):171-186
Based upon the tight-binding formalism a model of a
high-Tc superconductor with isotropic and anisotropic
attractive interactions is considered analytically. Symmetry
facets of the group C4v are included within a method of
successive transformations of the reciprocal space. Complete sets
of basis functions of C4v irreducible representations are
given. Plausible spin-singlet and spin-triplet superconducting
states are classified with regard to the chosen basis functions. It
is displayed that pairing interaction coefficients and the
dispersion relation, which can be characterized by the parameter
η= 2t1/t0, have a diverse and mutually competing
influence on the value of the transition temperature. It is also
shown that
in the case of a nearly half-filled conduction band
and an anisotropic pairing interaction the spin-singlet
d-wave symmetry superconducting state is realized for
small values of the parameter η, whereas in the opposite
limit, for sufficiently large values, the spin-triplet
p-wave symmetry superconducting state has to be formed.
This result cannot be obtained within the Van Hove scenario or
BCS-type approaches, where the p-wave symmetry
superconducting state absolutely dominates. The specific heat jump
and the isotope shift as functions of the parameter η are
assessed and discussed for the d-wave symmetry singlet and
the p-wave symmetry triplet states. 相似文献
2.
C. Honerkamp M. Salmhofer T.M. Rice 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(1):127-134
We extend the analysis of the renormalization group flow in the two-dimensional Hubbard model close to half-filling using
the recently developed temperature flow formalism. We investigate the interplay of d-density wave and Fermi surface deformation tendencies with those towards d-wave pairing and antiferromagnetism. For a ratio of next nearest to nearest neighbor hoppings, t'/t = - 0.25, and band fillings where the Fermi surface is inside the Umklapp surface, only the d-pairing susceptibility diverges at low temperatures. When the Fermi surface intersects the Umklapp surface close to the saddle
points, d-wave pairing, d-density wave, antiferromagnetic and, to a weaker extent, d-wave Fermi surface deformation susceptibilities grow together when the interactions flow to strong coupling. We interpret
these findings as indications for a non-trivial strongly coupled phase with short-ranged superconducting and antiferromagnetic
correlations, in close analogy with the spin liquid ground state in the well-understood two-leg Hubbard ladder.
Received 23 January 2002 相似文献
3.
R. Jursa S. Wermbter G. Czycholl 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(3):387-391
We study the influence of the short-ranged Hubbard correlation U between the conduction electrons on the Cooper pair formation in normal (s-wave) superconductors. The Coulomb correlation is considered within the standard second order perturbation theory, which
becomes exact in the weak coupling limit but goes beyond the simple Hartree-Fock treatment by yielding a finite lifetime of
the quasiparticles at finite temperature. An attractive pairing interaction V, which may be mediated by the standard electron-phonon mechanism, is considered between nearest neighbor sites. A critical
value for the attractive interaction is required to obtain a superconducting state. For finite temperature a gapless superconductivity is obtained due to the finite lifetime of the quasiparticles, i.e. the Coulomb correlation has a pair-breaking influence. The energy gap and depend very sensitively on U, V and band filling n and develop a maximum away from half filling as function of n. The ratio varies with n, being higher than the BCS value near half filling and reaching the BCS value for lower n.
Received 17 February 1999 相似文献
4.
A.A. Aligia E. Gagliano L. Arrachea K. Hallberg 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):371-378
We consider a generalized Hubbard model with on-site and nearest-neighbour repulsions U and V respectively, and nearest-neighbour hopping for spin up (down) which depends on the total occupation nb of spin down (up) electrons on both sites involved. The hopping parameters are t
AA
, tAB and tBB for n
b
=0,1,2 respectively. We briefly summarize results which support that the model exhibits s-wave superconductivity for certain parameters and extend them by studying the Berry phases. Using a generalized Hartree-Fock(HF)
BCS decoupling of the two and three-body terms, we obtain that at half filling, for t
AB
<t
AA
=t
BB
and sufficiently small U and V the model leads to triplet p-wave superconductivity for a simple cubic lattice in any dimension. In one dimension, the resulting phase diagram is compared
with that obtained numerically using two quantized Berry phases (topological numbers) as order parameters. While this novel
method supports the previous results, there are quantitative differences.
Received: 2 February 1998 / Accepted: 17 March 1998 相似文献
5.
P. Paci C. Grimaldi L. Pietronero 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(2):235-243
The inclusion of nonadiabatic corrections to the electron-phonon interaction leads to a strong momentum dependence in the
generalized Eliashberg equations beyond Migdal's limit. For a s-wave symmetry of the order parameter, this induced momentum dependence leads to an enhancement of when small momentum transfer is dominant. Here we study how the d-wave symmetry affects the above behavior. We find that the nonadiabatic corrections depend only weakly on the symmetry of
the order parameter provided that only small momentum scatterings are allowed for the electron-phonon interaction. In this
situation, We show that also for a d-wave symmetry of the order parameter, the nonadiabatic corrections enhance . We also discuss the possible interplay and crossover between s- and d-wave depending on the material's parameters.
Received 12 May 2000 相似文献
6.
7.
V. V. Val’kov D. M. Dzebisashvili M. M. Korovushkin A. F. Barabanov 《Journal of Experimental and Theoretical Physics》2017,125(5):810-821
The effect of the Coulomb repulsion of holes on the Cooper instability in an ensemble of spin–polaron quasiparticles has been analyzed, taking into account the peculiarities of the crystallographic structure of the CuO2 plane, which are associated with the presence of two oxygen ions and one copper ion in the unit cell, as well as the strong spin–fermion coupling. The investigation of the possibility of implementation of superconducting phases with d-wave and s-wave of the order parameter symmetry has shown that in the entire doping region only the d-wave pairing satisfies the self-consistency equations, while there is no solution for the s-wave pairing. This result completely corresponds to the experimental data on cuprate HTSC. It has been demonstrated analytically that the intersite Coulomb interaction does not affect the superconducting d-wave pairing, because its Fourier transform V q does not appear in the kernel of the corresponding integral equation. 相似文献
8.
R. Zeyher A. Greco 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(4):473-485
The feasibility of a perturbation expansion for Green's functions of the t-J model directly in terms of X-operators is demonstrated using the Baym-Kadanoff functional method. As an application we derive explicit expressions for
the kernel of the linearized equation for the superconducting order parameter in leading order of a 1/N expansion. The linearized equation is solved numerically on a square lattice taking instantaneous and retarded contributions
into account. Classifying the order parameter according to irreducible representations of the point group C4v of the square lattice and according to even or odd parity in frequency we find that a reasonably strong instability occurs
only for even frequency pairing with d-wavelike symmetry. The corresponding transition temperature Tc is where t is the nearest-neighbor hopping integral. The underlying effective interaction consists of an attractive, instantaneous term
and a retarded term due to charge and spin fluctuations. The latter is weakly attractive at low frequencies below ,strongly repulsive up to and attractive towards even higher energies. Tc increases with decreasing doping until a d-wavelike bond-order wave instability is encountered near optimal doping at for J=0.3. Tc is essentially linear in J and rather insensitive to an additional second-nearest neighbor hopping integral t'. A rather striking property of Tc is that it is hardly affected by the soft mode associated with the bond-order wave instability or by the Van Hove singularity
in the case with second-nearest neighbor hopping. This unique feature reflects the fact that the solution of the gap equation
involves momenta far away from the Fermi surface (due to the instantaneous term) and many frequencies (due to the retarded
term) so that singular properties in momentum or frequency are averaged out very effectively.
Received: 16 June 1998 / Accepted: 14 July 1998 相似文献
9.
We present a theoretical study of superconductivity of polarons in the Hubbard-Holstein model. A residual kinematic interaction proportional to the square of the polaron hopping energy between polarons and phonons provides a pairing field for the polarons. We find that superconducting instability in the d-wave channel is possible with small transition temperatures which is maximum in the large to small polaron cross-over region. An s-wave instability is found to be not possible when the effective on-site interaction between polarons is repulsive.Received: 9 July 2004, Published online: 12 October 2004PACS:
63.20.Kr Phonon-electron and phonon-phonon interactions - 74.20.Mn Polarons and bipolarons - 74.20.Fg BCS theoy and its developmentR. Ramakumar: Present address (on leave from SINP): Department of Physics and Astrophysics, Delhi University, Delhi-110017, India 相似文献
10.
We investigate the pairing symmetry of layered BiS2 compomlds by assuming that electron-electron correlation is still important so that the pairing is rather short range. We lind that the extended .s-wave pairing symmetry always wins over d-wave when the pairing is confined between two short range sites up to next nearest neighbors. The pairing strength is peaked around the doping level :r = 0.5. which is consistent with experimental observation. The extended s-wave pairing symmetry is very robust against spin orbital coupling because it is mainly determined by the structure of Fermi surfaces, Moreover. the extended s-wave pafiring can be distinguished from conventional swave pairing by measuring and comparing superconducting gaps of different Fermi surfaces. 相似文献
11.
T. Maitra H. Beck A. Taraphder 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(4):527-533
The competition between antiferromagnetism and the d + id superconducting state is studied in a model with near and next near neighbour interactions in the absence of any on-site
repulsion. A mean field study shows that it is possible to have simultaneous occurrence of an antiferromagnetic and a singlet
d + id superconducting state in this model. In addition, such a coexistence generates a triplet d + id superconducting order parameter with centre of mass momentum Q = (π,π) dynamically having the same orbital symmetry as the singlet superconductor. Inclusion of next nearest neighbour hopping in the band stabilises
the dxy superconducting state away from half filling, the topology of the phase diagram, though, remains similar to the near neighbour
model. In view of the very recent observation of a broad region of coexistence of antiferromagnetic and unconventional superconducting
states in organic superconductors, the possibility of observation of the triplet state has been outlined.
Received 30 November 2000 and Received in final form 27 March 2001 相似文献
12.
13.
R. B. Laughlin 《哲学杂志》2013,93(9):1165-1171
A new superconducting Hamiltonian is introduced for which the exact ground state is the Anderson resonating valence bond. It differs from the t–J and Hubbard Hamiltonians in possessing a powerful attractive force. Its superconducting state is characterized by a full and intact d-wave tunnelling gap, quasiparticle photoemission intensities that are strongly suppressed, a suppressed superfluid density, and an incipient Mott–Hubbard gap. 相似文献
14.
We explore the correlation between the Hall coefficient, penetration depth, transition temperature, gap anisotropy and hole concentration in a tight binding model for layered high-temperature superconductors. By adopting the BCS strategy, nearest neighbor intralayer singlet and extendeds-wave pairing cut off at the hole Fermi energy, remarkable agreement with generic experimental facts is obtained. Thus, a cylindrical hole Fermi surface and intralayer extendeds-wave singlet pairing appear to be generic features of the cuprate semiconductors. For high doping levels, however, intralayerd-wave singlet pairing appears to be the stable phase. 相似文献
15.
The problem of Cooper instability is studied by implementing the Kohn-Luttinger mechanism in the framework of the Shubin-Vonsowsky model taking into account the intersite Coulomb interactions within the first and second coordination spheres. It is shown that the Kohn-Luttinger renormalization for the effective interaction in the second-order terms of perturbation theory, as well as the inclusion of intersite hoppings in the second and third coordination spheres, significantly affects the interplay between the superconducting phases with d xy -, p-, s-, and $d_{x^2 - y^2 }$ -wave symmetries of the order parameter. 相似文献
16.
A superconductor with 4-fermion attraction, considered by Maćkowiak and Tarasewicz is modified by adding to the Hamiltonian
a long-range magnetic interaction V between conduction fermions and localized distinguishable spin 1/2 magnetic impurities. V has the form of a reduced s-d interaction. An upper and lower bound to the system’s free energy density f(H, β) is derived and the two bounds are shown to coalesce in the thermodynamic limit. The resulting mean-field equations for the
gap Δ and a parameter y, characterizing the impurity subsystem are solved and the solution minimizing f is found for various values of magnetic coupling constant g and impurity concentration. The phase diagrams of the system are depicted with five distinct phases: the normal phase, unperturbed
superconducting phase, perturbed superconducting phase with nonzero gap in the excitation spectrum, perturbed gapless superconducting
phase and impurity phase with completely suppressed superconductivity. 相似文献
17.
A. A. Ovchinnikov M. Ya. Ovchinnikova E. A. Plekhanov 《Journal of Experimental and Theoretical Physics》1999,88(2):356-369
The phase diagram, nature of the normal state pseudogap, type of the Fermi surface, and behavior of the superconducting gap
in various cuprates are discussed in terms of a correlated state with valence bonds. The variational correlated state, which
is a band analogue of the Anderson (RVB) states, is constructed using local unitary transformations. Formation of valence
bonds causes attraction between holes in the d-channel and corresponding superconductivity compatible with antiferromagnetic spin order. Our calculations indicate that
there is a fairly wide range of doping with antiferromagnetic order in isolated CuO2 planes. The shape of the Fermi surface and phase transition curve are sensitive to the value and sign of the hopping interaction
t′ between diagonal neighboring sites. In underdoped samples, the dielectrization of various sections of the Fermi boundary,
depending on the sign of t′, gives rise to a pseudogap detected in photoemission spectra for various quasimomentum directions. In particular, in bismuth-and
yttrium-based ceramics (t′>0), the transition from the normal state of overdoped samples to the pseudogap state of underdoped samples corresponds to
the onset of dielectrization on the Brillouin zone boundary near k=(0,π) and transition from “large” to “small” Fermi surfaces. The hypothesis about s-wave superconductivity of La-and Nd-based ceramics has been revised: a situation is predicted when, notwithstanding the d-wave symmetry of the superconducting order parameter, the excitation energy on the Fermi surface does not vanish at all points
of the phase space owing to the dielectrization of the Fermi boundary at k
x=±
k
y. The model with orthorhombic distortions and two peaks on the curve of T
c versus doping is discussed in connection with experimental data for the yttrium-based ceramic.
Zh. éksp. Teor. Fiz. 115, 649–674 (February 1999) 相似文献
18.
Spontaneous internal field around the non-magnetic impurity in spin-triplet p-wave superconductivity
M. Takigawa M. Ichioka K. Kuroki Y. Tanaka 《Physica E: Low-dimensional Systems and Nanostructures》2005,29(3-4):619
The electronic structure around an impurity in spin triplet p-wave superconductors is investigated by the Bogoliubov–de Gennes theory on a tight-binding model. We calculate the spontaneous current and the local density of states around the impurity and discuss the difference between -wave and -wave superconducting states. 相似文献
19.
The superconducting order parameter and LDOS spectra near an impenetrable surface are studied on the basis of self-consistent
calculations for a two band superconductor with nodeless extended s-wave order parameter symmetry, as possibly realized in Fe-based high-temperature superconductors. It is found that for a
wide range of parameters the spatial behavior of the order parameter at a surface is not reduced to a trivial suppression.
If the interband scattering at a surface is of the order of the intraband one or dominates it, it can be energetically favorable
to change the symmetry of the superconducting state near the surface from s
± to conventional s-wave. The range of existing of this surface conventional superconductivity is very sensitive to the relative values of interband
and intraband pairing potentials. It is shown that the LDOS spectra near the surface can qualitatively differ upon calculating
with and without taking into account the self-consistency of the order parameter. 相似文献
20.
V. Hankevych F. Wegner 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(3):333-342
We present a stability analysis of the 2D t
-
t' Hubbard model on a square lattice for various values of the next-nearest-neighbor hopping t' and electron concentration. Using the free energy expression, derived by means of the flow equations method, we have performed
numerical calculation for the various representations under the point group C
4ν
in order to determine at which temperature symmetry broken phases become more favorable than the symmetric phase. A surprisingly
large number of phases has been observed. Some of them have an order parameter with many nodes in -space. Commonly discussed types of order found by us are antiferromagnetism, d
x2 - y2
-wave singlet superconductivity, d-wave Pomeranchuk instability and flux phase. A few instabilities newly observed are a triplet analog of the flux phase, a
particle-hole instability of p-type symmetry in the triplet channel which gives rise to a phase of magnetic currents, an s*-magnetic phase, a g-wave Pomeranchuk instability and the band splitting phase with p-wave character. Other weaker instabilities are found also. A comparison with experiments is made.
Received 25 July 2002 / Received in final form 28 November 2002 Published online 14 February 2003
RID="a"
ID="a"Current address: Département de physique and Centre de recherche sur les propriétés électroniques de matériaux avancés, Université de Sherbrooke,
Sherbrooke, Québec, Canada J1K 2R1 e-mail: vaha@physique.usherb.ca 相似文献