1,637 research outputs found
Phase diagram of asymmetric Fermi gas across Feshbach resonance
We study the phase diagram of the dilute two-component Fermi gas at zero
temperature as a function of the polarization and coupling strength. We map out
the detailed phase separations between superfluid and normal states near the
Feshbach resonance. We show that there are three different coexistence of
superfluid and normal phases corresponding to phase separated states between:
(I) the partially polarized superfluid and the fully polarized normal phases,
(II) the unpolarized superfluid and the fully polarized normal phases and (III)
the unpolarized superfluid and the partially polarized normal phases from
strong-coupling BEC side to weak-coupling BCS side. For pairing between two
species, we found this phase separation regime gets wider and moves toward the
BEC side for the majority species are heavier but shifts to BCS side and
becomes narrow if they are lighter.Comment: 4 pages, 3 figures. Submitted to LT25 on June 200
Phase diagram of a dilute fermion gas with density imbalance
We map out the phase diagram of a dilute two-component atomic fermion gas
with unequal populations and masses under a Feshbach resonance. As in the case
of equal masses, no uniform phase is stable for an intermediate coupling
regime. For majority component heavier, the unstable region moves towards the
BEC side. When the coupling strength is increased from the normal phase, there
is an increased parameter space where the transition is into the FFLO state.
The converse is true if the majority is light.Comment: Proceeding for MS-HTSC VIII meeting, July 9-14 2006, Dresden; To
appear in Physica
Theory for Superconducting Properties of the Cuprates: Doping Dependence of the Electronic Excitations and Shadow States
The superconducting phase of the 2D one-band Hubbard model is studied within
the FLEX approximation and by using an Eliashberg theory. We investigate the
doping dependence of , of the gap function and
of the effective pairing interaction. Thus we find that becomes maximal
for doping. In {\it overdoped} systems decreases due to the
weakening of the antiferromagnetic correlations, while in the {\it underdoped}
systems due to the decreasing quasi particle lifetimes. Furthermore, we find
{\it shadow states} below which affect the electronic excitation spectrum
and lead to fine structure in photoemission experiments.Comment: 10 pages (REVTeX) with 5 figures (Postscript
Superconducting instability in the Holstein-Hubbard model: A numerical renormalization group study
We have studied the d-wave pairing-instability in the two-dimensional
Holstein-Hubbard model at the level of a full fluctuation exchange
approximation which treats both Coulomb and electron-phonon (EP) interaction
diagrammatically on an equal footing. A generalized numerical renormalization
group technique has been developed to solve the resulting self-consistent field
equations. The -wave superconducting phase diagram shows an optimal T_c at
electron concentration ~ 0.9 for the purely electronic Hubbard system. The
EP interaction suppresses the d-wave T_c which drops to zero when the
phonon-mediated on-site attraction becomes comparable to the on-site
Coulomb repulsion . The isotope exponent is negative in this model
and small compared to the classical BCS value or compared
to typical observed values in non-optimally doped cuprate superconductors.Comment: 4 pages RevTeX + 3 PS figures include
Low-Frequency Electromagnetic Backscattering from Tunnels
Low-frequency electromagnetic scattering from one or more tunnels in a lossy dielectric half-space is considered. The tunnel radii are assumed small compared to the wavelength of the electromagnetic field in the surrounding medium; a tunnel can thus be modeled as a thin scatterer, described by an equivalent impedance per unit length. We examine the normalized backscattering width for cases in which the air-ground interface is either smooth or rough
The Isotope Effect in d-Wave Superconductors
Based on recently proposed anti-ferromagnetic spin fluctuation exchange
models for -superconductors, we show that coupling to harmonic
phonons {\it{cannot}} account for the observed isotope effect in the cuprate
high- materials, whereas coupling to strongly anharmonic multiple-well
lattice tunneling modes {\it{can}}. Our results thus point towards a strongly
enhanced {\it{effective}} electron-phonon coupling and a possible break-down of
Migdal-Eliashberg theory in the cuprates.Comment: 12 pages + 2 figures, Postscript files, all uuencoded Phys. Rev.
Lett. (1995, to be published
Resonant pairing between Fermions with unequal masses
We study the pairing between Fermions of different masses, especially at the
unitary limit. At equal populations, the thermodynamic properties are identical
with the equal mass case provided an appropriate rescaling is made. At unequal
populations, for sufficiently light majority species, the system does not phase
separate. For sufficiently heavy majority species, the phase separated normal
phase have a density larger than that of the superfluid. For atoms in harmonic
traps, the density profiles for unequal mass Fermions can be drastically
different from their equal-mass counterparts.Comment: 10 pages, 4 figure
Superfluid stability in BEC-BCS crossover
We consider a dilute atomic gas of two species of fermions with unequal
concentrations under a Feshbach resonance. We find that the system can have
distinct properties due to the unbound fermions. The uniform state is stable
only when either (a) beyond a critical coupling strength, where it is a gapless
superfluid, or (b) when the coupling strength is sufficiently weak, where it is
a normal Fermi gas mixture. Phase transition(s) must therefore occur when the
resonance is crossed.Comment: 4 pages, 4 figure
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