1,189 research outputs found
Superconductivity from a long-range interaction: a crossover between the electron gas and the lattice model
We explore how the superconductivity arising from the on-site
electron-electron repulsion will change when the repulsion is changed to a
long-ranged, 1/r-like one by introducing an extended Hubbard model with the
repulsion extending to distant (12th) neighbors. With a simplified
fluctuation-exchange approximation, we have found for the square lattice that
(i) as the band filling becomes dilute enough, the charge susceptibility
becomes comparable with the spin susceptibility, where p and then s pairings
become dominant, in agreement with the result for the electron gas by Takada,
while (ii) the d-wave, which reflects the lattice structure, dominates well
away from the half filling. All these can be understood in terms of the spin
and charge structures along with the shape and size of the Fermi surface.Comment: 5 pages, 6 figure
Electronic structure and spontaneous internal field around non-magnetic impurities in spin-triplet chiral p-wave superconductors
The electronic structure around an impurity in spin triplet p-wave
superconductors is studied by the Bogoliubov-de Gennes theory on a
tight-binding model, where we have chosen -wave
or -wave states which are
considered to be candidates for the pairing state in SrRuO.
We calculate the spontaneous current and the local density of states around
the impurity and discuss the difference between the two types of pairing.
We propose that it is possible to discriminate the two pairing states by
studying the spatial dependence of the magnetic field around a pair of
impurities.Comment: 4 pages, 4 figure
A unified origin for the 3D magnetism and superconductivity in NaCoO
We analyze the origin of the three dimensional (3D) magnetism observed in
nonhydrated Na-rich NaCoO within an itinerant spin picture using a 3D
Hubbard model. The origin is identified as the 3D nesting between the inner and
outer portions of the Fermi surface, which arise due to the local minimum
structure of the band at the -A line. The calculated spin wave
dispersion strikingly resembles the neutron scattering result. We argue that
this 3D magnetism and the spin fluctuations responsible for superconductivity
in the hydrated systems share essentially the same origin.Comment: 5pages, 6figure
Viscoelasticity of two-layer-vesicles in solution
The dynamic shape relaxation of the two-layer-vesicle is calculated. In
additional to the undulation relaxation where the two bilayers move in the same
direction, the squeezing mode appears when the gap between the two bilayers is
small. At large gap, the inner vesicle relaxes much faster, whereas the slow
mode is mainly due to the outer layer relaxation. We have calculated the
viscoelasticity of the dilute two-layer-vesicle suspension. It is found that
for small gap, the applied shear drives the undulation mode strongly while the
slow squeezing mode is not much excited. In this limit the complex viscosity is
dominated by the fast mode contribution. On the other hand, the slow mode is
strongly driven by shear for larger gap. We have determined the crossover gap
which depends on the interaction between the two bilayers. For a series of
samples where the gap is changed systematically, it is possible to observe the
two amplitude switchings
Quantum Monte Carlo study of the pairing symmetry competition in the Hubbard model
To shed light into the pairing mechanism of possible spin-triplet
superconductors (TMTSF)X and SrRuO, we study the competition among
various spin singlet and triplet pairing channels in the Hubbard model by
calculating the pairing interaction vertex using the ground state quantum Monte
Carlo technique. We model (TMTSF)X by a quarter-filled quasi-one
dimensional (quasi-1D) Hubbard model,and the band of SrRuO by
a two dimensional (2D) Hubbard model with a band filling of . For the
quasi-1D system, we find that triplet -wave pairing not only dominates over
triplet p-wave in agreement with the spin fluctuation theory, but also looks
unexpectedly competitive against d-wave. For the 2D system, although the
results suggest presence of attractive interaction in the triplet pairing
channels, the d-wave pairing interaction is found to be larger than those of
the triplet channels
A crib-shaped triplet pairing gap function for an orthogonal pair of quasi-one dimensional Fermi surfaces in SrRuO
The competition between spin-triplet and singlet pairings is studied
theoretically for the tight-binding - bands in SrRuO,
which arise from two sets of quasi-one dimensional Fermi surfaces. Using
multiband FLEX approximation, where we incorporate an anisotropy in the spin
fluctuations as suggested from experiments, we show that (i) the triplet can
dominate over the singlet (which turns out to be extended s), and (ii) the
triplet gap function optimized in the Eliashberg equation has an unusual, very
non-sinusoidal form, whose time-reversal-broken combination exhibits a
crib-shaped amplitude with dips.Comment: 5 pages, RevTeX, to appear in Phys.Rev.B (Rapid Communications
Spectral function of the spiral spin state in the trestle and ladder Hubbard model
Eder and Ohta have found a violation of the Luttinger rule in the spectral
function for the t-t'-J model, which was interpreted as a possible breakdown of
the Tomonaga-Luttinger(TL) description in models where electrons can pass each
other. Here we have computed the spin correlation along with the spectral
function for the one-dimensional t-t' Hubbard model and two-leg Hubbard ladder.
By varying the Hubbard U we have identified that such a phenomenon is in fact a
spinless-fermion-like behavior of holes moving in a spiral spin configuration
that has a spin correlation length of the system size.Comment: 3 pages, RevTex, 8 figures in Postscript, to be published in Phys.
Rev. B (rapid communication
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