817 research outputs found
Driven Disordered Polymorphic Solids: Phases and Phase Transitions, Dynamical Coexistence and Peak Effect Anomalies
We study a model for the depinning and driven steady state phases of a solid
tuned across a polymorphic phase transition between ground states of triangular
and square symmetry. These include pinned states which may have dominantly
triangular or square correlations, a plastically flowing liquid-like phase, a
moving phase with hexatic correlations, flowing triangular and square states
and a dynamic coexistence regime characterized by the complex interconversion
of locally square and triangular regions. We locate these phases in a dynamical
phase diagram. We demonstrate that the apparent power-law orientational
correlations we obtain in our moving hexatic phase arise from circularly
averaging an orientational correlation function with qualitatively different
behaviour in the longitudinal (drive) and transverse directions. The
intermediate coexistence regime exhibits several novel properties, including
substantial enhancement in the current noise, an unusual power-law spectrum of
current fluctuations and striking metastability effects. This noise arises from
the fluctuations of the interface separating locally square and triangular
ordered regions. We demonstrate the breakdown of effective ``shaking
temperature'' treatments in the coexistence regime by showing that such shaking
temperatures are non-monotonic functions of the drive in this regime. Finally
we discuss the relevance of these simulations to the anomalous behaviour seen
in the peak effect regime of vortex lines in the disordered mixed phase of
type-II superconductors. We propose that this anomalous behavior is directly
linked to the behavior exhibited in our simulations in the dynamical
coexistence regime, thus suggesting a possible solution to the problem of the
origin of peak effect anomalies.Comment: 22 pages, double column, higher quality figures available from
author
p-wave Holographic Superconductors from Born-Infeld Black Holes
We obtain (2+1) dimensional p-wave holographic superconductors from charged
Born-Infeld black holes in the presence of massive charged vector fields in a
bulk Einstein-Born-Infeld theory through the -
correspondence. Below a certain critical transition temperature the charged
black hole develops vector hair that corresponds to charged vector condensate
in the strongly coupled (2+1) dimensional boundary field theory that breaks
both the symmetry as well as the rotational invariance. The holographic
free energy is computed for the boundary field theory which shows that the
vector order parameter exhibits a rich phase structure involving zeroth order,
first order, second order and retrograde phase transitions for different values
of the backreaction and the Born-Infeld parameters. We numerically compute the
ac conductivity for the p-wave superconducting phase of the strongly coupled
(2+1) dimensional boundary field theory which also depends on the relative
values of the parameters in the theory.Comment: 26 pages, 18 figure
Thermodynamic Geometry and Phase Transitions of AdS Braneworld Black Holes
The thermodynamics and phase transitions of charged RN-AdS and rotating
Kerr-AdS black holes in a generalized Randall-Sundrum braneworld are
investigated in the framework of thermodynamic geometry. A detailed analysis of
the thermodynamics, stability and phase structures in the canonical and the
grand canonical ensembles for these AdS braneworld black holes are described.
The thermodynamic curvatures for both these AdS braneworld black holes are
computed and studied as a function of the thermodynamic variables. Through this
analysis we illustrate an interesting dependence of the phase structures on the
braneworld parameter for these black holes.Comment: 21 pages, 10 figures and Appendix adde
Hidden Isometry in a Chiral Gauged WZW Model
It is shown that the asymmetric chiral gauging of the WZW models give rise to
consistent string backgrounds. The target space structure of the model is analyzed and the
presence of a hidden isometry in this background is demonstrated. A nonlinear
coordinate transformation is obtained which transforms the asymmetric model to
the symmetric one, analyzed recently by two of the present authors.Comment: 11 pages, IP/BBSR/92-67, IISC/CTS/92-
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