9,630 research outputs found
Vortex tilt modulus in Fulde-Ferrell-Larkin-Ovchinnikov state
Vortex tilt response in Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) vortex
lattice is theoretically examined as a probe reflecting the spatial structure
of this state. In the FFLO state with nodal planes perpendicular to the
magnetic field in a quasi 2D material under a parallel field, the tilt modulus
E_{2} {\it of the nodal planes} decreases as the paramagnetic effect is
effectively enhanced, and this reduction of E_{2} in turn reduces the vortex
tilt modulus. This reduction of vortex tilt modulus, more remarkable in more
anisotropic systems, accompanying the FFLO transition may be an origin of the
monotonous reduction of sound velocity detected upon cooling in a ultrasound
measurement for CeCoIn5.Comment: 14 pages, 5 figures. Accepted for publication in Phys. Rev.
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
Instability of a gapless color superconductor with respect to inhomogeneous fluctuations
We systematically apply density functional theory to determine the kind of
inhomogeneities that spontaneously develop in a homogeneous gapless phase of
neutral two-flavor superfluid quark matter. We consider inhomogeneities in the
quark and electron densities and in the phases and amplitude of the order
parameter. These inhomogeneities are expected to lead the gapless phase to a
BCS-normal coexisting phase, a Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) state
with phase oscillations alone, and a LOFF state with amplitude oscillations. We
find that which of them the homogeneous system tends towards depends
sensitively on the chemical potential separation between up and down quarks and
the gradient energies.Comment: 15 pages, 3 figures; corrected Eq. (36) and changed content
associated with d quark clustering instabilit
On the ground state of gapless two flavor color superconductors
This paper is devoted to the study of some aspects of the instability of two
flavor color superconductive quark matter. We find that, beside color
condensates, the Goldstone boson related to the breaking of suffers of
a velocity instability. We relate this wrong sign problem, which implies the
existence of a Goldstone current in the ground state or of gluonic
condensation, to the negative squared Meissner mass of the gluon in
the g2SC phase. Moreover we investigate the Meissner masses of the gluons and
the squared velocity of the Goldstone in the multiple plane wave LOFF states,
arguing that in such phases both the chromo-magnetic instability and the
velocity instability are most probably removed. We also do not expect Higgs
instability in such multiple plane wave LOFF. The true vacuum of gapless two
flavor superconductors is thus expected to be a multiple plane wave LOFF state.Comment: 16 pages, RevTe3X4 styl
Exciton Condensate Modulation in Electron-Hole Bilayers: A Real-Space Visualization
We study the texture of the exciton condensate at low temperatures in an
independently gated electron-hole bilayer system. A model Hamiltonian is solved
in real space within a mean-field approximation. It is found that, with
increased electron-hole density polarization, the system experiences phase
transformations from the zero center-of-mass momentum superfluid state, through
one- and two-dimensional exciton pair modulated states, into the normal state.
At weak density polarization, the modulating state resembles the
Larkin-Ovchinikov state in superconductors in the presence of an exchange field
in the weak-coupling BCS limit, and becomes stripe-like in the strong coupling
BEC limit. In the one-dimensional modulated phase, the density of states
exhibits low-energy intra-gap resonance quasiparticle states, which are
localized in the nodal region.Comment: 4+ pages, 6 eps figure
Characterizing the Larkin-Ovchinnikov-Fulde-Ferrel phase induced by the chromomagnetic instability
We discuss possible destinations from the chromomagnetic instability in color
superconductors with Fermi surface mismatch . In the two-flavor
superconducting (2SC) phase we calculate the effective potential for color
vector potentials which are interpreted as the net momenta of
pairing in the Larkin-Ovchinnikov-Fulde-Ferrel (LOFF) phase. When
where is the gap energy, the effective
potential suggests that the instability leads to a LOFF-like state which is
characterized by color-rotated phase oscillations with small . In the
vicinity of the magnitude of continuously
increases from zero as the effective potential has negative larger curvature at
vanishing that is the Meissner mass squared. In the gapless 2SC
(g2SC) phase, in contrast, the effective potential has a minimum at
even when the negative Meissner mass squared
is infinitesimally small. Our results imply that the chromomagnetic instability
found in the gapless phase drives the system toward the LOFF state with
.Comment: 6 pages, 3 figures; fatal typo about the conclusion corrected;
reference adde
The low temperature Fulde-Ferrell-Larkin-Ovchinnikov phases in 3 dimensions
We consider the nature of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phases
in three dimensions at low temperature. We introduce a new method to handle the
quasiclassical equations for superconductors with space dependent order
parameter, which makes use of a Fourier expansion. This allows us to show that,
at T=0, an order parameter given by the linear combination of three cosines
oscillating in orthogonal directions is preferred over the standard single
cosine solution. The transition from the normal state to this phase is first
order, and quite generally the transition below the tricritical point to the
FFLO phases is always first order.Comment: 4 pages, revtex, 1 figur
Larkin-Ovchinnikov-Fulde-Ferrell state in two-color quark matter
We explore the phase structure of two-color and two-flavor QCD in the space
of the quark chemical potential \mu_q and the isospin chemical potential \mu_I.
Using a mean-field model we calculate the chiral and diquark condensates,
\sigma and \Delta, self-consistently. In weak coupling and in the chiral limit,
we confirm the interval of the isospin chemical potential,
0.71\Delta_0<\mu_I<0.75\Delta_0, in which a single plane-wave
Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) phase is favored over isotropic
superfluidity and normal quark matter. The LOFF window becomes slightly wider
at high density. For stronger coupling with nonzero quark mass, which is
relevant to currently available numerical simulations in lattice two-color QCD,
the single plane-wave LOFF phase appears only at sufficiently high density. The
prediction obtained for the LOFF region could be tested with lattice since we
can prove that the present system is free from the fermion sign problem. We
draw the energy landscape on which local minima corresponding to the isotropic
superfluid phase and the LOFF phase and a local maximum corresponding to the
gapless phase are manifest. Our results clearly illustrate the path from the
the unstable gapless phase down to the LOFF phase.Comment: 10 pages, 8 figure
Superfluid and Pseudo-Goldstone Modes in Three Flavor Crystalline Color Superconductivity
We study the bosonic excitations in the favorite cubic three flavor
crystalline LOFF phases of QCD. We calculate in the Ginzburg-Landau
approximation the masses of the eight pseudo Nambu-Goldstone Bosons (NGB)
present in the low energy theory. We also compute the decay constants of the
massless NGB Goldstones associated to superfluidity as well as those of the
eight pseudo NGB. Differently from the corresponding situation in the
Color-Flavor-Locking phase, we find that meson condensation phases are not
expected in the present scenario.Comment: 10 pages, RevTeX4 class. Section IIIA enlarged, to appear on Phys.
Rev.
Decorrelating a compressible turbulent flow: an experiment
Floating particles that are initially distributed uniformly on the surface of
a turbulent fluid, subsequently coagulate, until finally a steady state is
reached. This being so, they manifestly form a compressible system. In this
experiment, the information dimension D_1, and the Lyapunov exponents of the
coagulated floaters, are measured. The trajectories and the velocity fields of
the particles are captured in a sequence of rapidly acquired images. Then the
velocity sequence is randomly shuffled in time to generate new trajectories.
This analysis mimics the Kraichnan ensemble and yields properties of a velocity
correlation function that is delta-correlated in time (but not in space). The
measurements are compared with theoretical expectations and with simulations of
Boffetta et al., that closely mimic the laboratory experiment reported here.Comment: 6 pages, 5 figure
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