10,205 research outputs found
Theory of the striped superconductor
We define a distinct phase of matter, a "pair density wave" (PDW), in which
the superconducting order parameter varies periodically as a function of
position such that when averaged over the center of mass position, all
components of vanish identically. Specifically, we study the simplest,
unidirectional PDW, the "striped superconductor," which we argue may be at the
heart of a number of spectacular experimental anomalies that have been observed
in the failed high temperature superconductor, La BaCuO. We
present a solvable microscopic model with strong electron-electron interactions
which supports a PDW groundstate. We also discuss, at the level of Landau
theory, the nature of the coupling between the PDW and other order parameters,
and the origins and some consequences of the unusual sensitivity of this state
to quenched disorder.Comment: 16 pages, 3 figures, 1 table; Journal ref. adde
Attractive Fermi gases with unequal spin populations in highly elongated traps
We investigate two-component attractive Fermi gases with imbalanced spin
populations in trapped one dimensional configurations. The ground state
properties are determined within local density approximation, starting from the
exact Bethe-ansatz equations for the homogeneous case. We predict that the
atoms are distributed according to a two-shell structure: a partially polarized
phase in the center of the trap and either a fully paired or a fully polarized
phase in the wings. The partially polarized core is expected to be a superfluid
of the FFLO type. The size of the cloud as well as the critical spin
polarization needed to suppress the fully paired shell, are calculated as a
function of the coupling strength.Comment: Final accepted versio
How many phases meet at the chiral critical point?
We explore the phase diagram of NJL-type models near the chiral critical
point allowing for phases with spatially inhomogeneous chiral condensates. In
the chiral limit it turns out that the region in the mean-field phase diagram
where those phases are energetically preferred very generically reaches out to
the chiral critical point. The preferred inhomogeneous ground state in this
vicinity possibly resembles a lattice of domain wall solitons. This raises the
question of their relevance for the phase diagram of QCD.Comment: 7 pages, 1 figure; v2: minor corrections, as published in PR
Recovering of superconductivity in exchange fields exceeding Pauli limiting field under spin-dependent quasiparticle distribution
We study theoretically the simultaneous influence of spin accumulation
potential and the Zeeman exchange field on singlet
superconductivity. It is shown that the pair-breaking effect of the Zeeman
field can be fully compensated by creation of the appropriate spin accumulation
potential in the superconductor. Moreover, superconductivity can be recovered
for exchange fields well exceeding the Pauli limiting field. It is proposed
that the effect can be experimentally realized on the basis of voltage biased
junction consisting of a thin superconducting film sandwiched between two half
metals.Comment: 4 pages, 1 figure, published versio
Pairing states of a polarized Fermi gas trapped in a one-dimensional optical lattice
We study the properties of a one-dimensional (1D) gas of fermions trapped in
a lattice by means of the density matrix renormalization group method, focusing
on the case of unequal spin populations, and strong attractive interaction. In
the low density regime, the system phase-separates into a well defined
superconducting core and a fully polarized metallic cloud surrounding it. We
argue that the superconducting phase corresponds to a 1D analogue of the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, with a quasi-condensate of
tightly bound bosonic pairs with a finite center-of-mass momentum that scales
linearly with the magnetization. In the large density limit, the system allows
for four phases: in the core, we either find a Fock state of localized pairs or
a metallic shell with free spin-down fermions moving in a fully filled
background of spin-up fermions. As the magnetization increases, the Fock state
disappears to give room for a metallic phase, with a partially polarized
superconducting FFLO shell and a fully polarized metallic cloud surrounding the
core.Comment: 4 pages, 5 fig
Localization and Interaction Effects in Strongly Underdoped La2-xSrxCuO4
The in-plane magnetoresistance (MR) in La2-xSrxCuO4 films with 0.03 < x <
0.05 has been studied in the temperature range 1.6 K to 100 K, and in magnetic
fields up to 14 T, parallel and perpendicular to the CuO2 planes. The behavior
of the MR is consistent with a predominant influence of interaction effects at
high temperatures, switching gradually to a regime dominated by spin scattering
at low T. Weak localization effects are absent. A positive orbital MR appears
close to the boundary between the antiferromagnetic and the spin-glass phase,
suggesting the onset of Maki-Thompson superconducting fluctuations deep inside
the insulating phase.Comment: 4 pages, 3 figures, to appear in Phys. Rev. Letter
Two-bands effect on the superconducting fluctuating diamagnetism in MgB₂
The field dependence of the magnetization above the transition temperature Tc
in MgB₂ is shown to evidence a diamagnetic contribution consistent with
superconducting fluctuations reflecting both the σ and π bands. In
particular, the upturn field Hup in the magnetization curve, related to the
incipient effect of the magnetic field in quenching the fluctuating pairs,
displays a double structure, in correspondence to two correlation lengths. The
experimental findings are satisfactorily described by the extension to the
diamagnetism of a recent theory for paraconductivity, in the framework of a
zero-dimensional model for the fluctuating superconducting droplets above Tc
Proximity Action theory of superconductive nanostructures
We review a novel approach to the superconductive proximity effect in
disordered normal-superconducting (N-S) structures. The method is based on the
multicharge Keldysh action and is suitable for the treatment of interaction and
fluctuation effects. As an application of the formalism, we study the subgap
conductance and noise in two-dimensional N-S systems in the presence of the
electron-electron interaction in the Cooper channel. It is shown that singular
nature of the interaction correction at large scales leads to a nonmonotonuos
temperature, voltage and magnetic field dependence of the Andreev conductance.Comment: RevTeX, 6 pages, 5 eps figures. This is a concise review of
cond-mat/0008463; to be published in the Proceedings of the conference
"Mesoscopic and strongly correlated electron systems" (Chernogolovka, Russia,
July 2000
Suppression or enhancement of the Fulde-Ferrell-Larkin-Ovchinnikov order in a one-dimensional optical lattice with particle correlated tunnelling
We study through controlled numerical simulation the ground state properties
of spin-polarized strongly interacting fermi gas in an anisotropic optical
lattice, which is described by an effective one-dimensional general Hubbard
model with particle correlated hopping rate. We show that the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) type of state, while enhanced by a
negative correlated hopping rate, can be completely suppressed by positive
particle correlated hopping, yielding to an unusual magnetic phase even for
particles with on-site attractive interaction We also find several different
phase separation patterns for these atoms in an inhomogeneous harmonic trap,
depending on the correlated hopping rate
- …