6,808 research outputs found
Relaxation of superflow in a network: an application to the dislocation model of supersolidity of helium crystals
We have considered the dislocation network model for the supersolid state in
He-4 crystals. In difference with uniform 2D and 3D systems, the temperature of
superfluid transition T_c in the network is much smaller than the degeneracy
temperature T_d. It is shown that a crossover into a quasi superfluid state
occurs in the temperature interval between T_c and T_d. Below the crossover
temperature the time of decay of the flow increases exponentially under
decrease of the temperature. The crossover has a continuous character and the
crossover temperature does not depend on the density of dislocations.Comment: Corrected typo
Quenched Dislocation Enhanced Supersolid Ordering
I show using Landau theory that quenched dislocations can facilitate the
supersolid (SS) to normal solid (NS) transition, making it possible for the
transition to occur even if it does not in a dislocation-free crystal. I make
detailed predictions for the dependence of the SS to NS transition temperature
T_c(L), superfluid density %\rho_S(T, L), and specific heat C(T,L) on
temperature T and dislocation spacing L, all of which can be tested against
experiments. The results should also be applicable to an enormous variety of
other systems, including, e.g., ferromagnets.Comment: 5 pages, 2 figure
Entropy in quantum chromodynamics
We review the role of zero-temperature entropy in several closely-related
contexts in QCD. The first is entropy associated with disordered condensates,
including . The second is vacuum entropy arising from QCD
solitons such as center vortices, yielding confinement and chiral symmetry
breaking. The third is entanglement entropy, which is entropy associated with a
pure state, such as the QCD vacuum, when the state is partially unobserved and
unknown. Typically, entanglement entropy of an unobserved three-volume scales
not with the volume but with the area of its bounding surface. The fourth
manifestation of entropy in QCD is the configurational entropy of
light-particle world-lines and flux tubes; we argue that this entropy is
critical for understanding how confinement produces chiral symmetry breakdown,
as manifested by a dynamically-massive quark, a massless pion, and a condensate.Comment: 22 pages, 2 figures. Preprint version of invited review for Modern
Physics Letters
Non-dissipative drag of superflow in a two-component Bose gas
A microscopic theory of a non-dissipative drag in a two-component superfluid
Bose gas is developed. The expression for the drag current in the system with
the components of different atomic masses, densities and scattering lengths is
derived. It is shown that the drag current is proportional to the square root
of the gas parameter. The temperature dependence of the drag current is studied
and it is shown that at temperature of order or smaller than the interaction
energy the temperature reduction of the drag current is rather small. A
possible way of measuring the drag factor is proposed. A toroidal system with
the drag component confined in two half-ring wells separated by two Josephson
barriers is considered. Under certain condition such a system can be treated as
a Bose-Einstein counterpart of the Josephson charge qubit in an external
magnetic field. It is shown that the measurement of the difference of number of
atoms in two wells under a controlled evolution of the state of the qubit
allows to determine the drag factor.Comment: 13 pages, 3 figures. This preprint is extended and substantially
revised variant of related preprint cond-mat/040456
Dislocation-induced superfluidity in a model supersolid
Motivated by recent experiments on the supersolid behavior of He, we
study the effect of an edge dislocation in promoting superfluidity in a Bose
crystal. Using Landau theory, we couple the elastic strain field of the
dislocation to the superfluid density, and use a linear analysis to show that
superfluidity nucleates on the dislocation before occurring in the bulk of the
solid. Moving beyond the linear analysis, we develop a systematic perturbation
theory in the weakly nonlinear regime, and use this method to integrate out
transverse degrees of freedom and derive a one-dimensional Landau equation for
the superfluid order parameter. We then extend our analysis to a network of
dislocation lines, and derive an XY model for the dislocation network by
integrating over fluctuations in the order parameter. Our results show that the
ordering temperature for the network has a sensitive dependence on the
dislocation density, consistent with numerous experiments that find a clear
connection between the sample quality and the supersolid response.Comment: 10 pages, 6 figure
Superfluidity of electron-hole pairs in randomly inhomogeneous bilayer systems
In bilayer systems electron-hole (e-h) pairs with spatially separated
components (i.e., with electrons in one layer and holes in the other) can be
condensed to a superfluid state when the temperature is lowered. This article
deals with the influence of randomly distributed inhomogeneities on the
superfluid properties of such bilayer systems in a strong perpendicular
magnetic field. Ionized impurities and roughenings of the conducting layers are
shown to decrease the superfluid current density of the e-h pairs. When the
interlayer distance is smaller than or close to the magnetic length, the
fluctuations of the interlayer distance considerably reduce the superfluid
transition temperature.Comment: 13 pages, 3 figure
Drag of superfluid current in bilayer Bose systems
An effect of nondissipative drag of a superfluid flow in a system of two Bose
gases confined in two parallel quasi two-dimensional traps is studied. Using an
approach based on introduction of density and phase operators we compute the
drag current at zero and finite temperatures for arbitrary ratio of densities
of the particles in the adjacent layers. We demonstrate that in a system of two
ring-shape traps the "drag force" influences on the drag trap in the same way
as an external magnetic flux influences on a superconducting ring. It allows to
use the drag effect to control persistent current states in superfluids and
opens a possibility for implementing a Bose analog of the superconducting
Josephson flux qubit.Comment: 12 pages, 2 figures, new section is added, refs are adde
- …