239 research outputs found
Vortex-glass phases in type-II superconductors
A review is given on the theory of vortex-glass phases in impure type-II
superconductors in an external field. We begin with a brief discussion of the
effects of thermal fluctuations on the spontaneously broken U(1) and
translation symmetries, on the global phase diagram and on the critical
behaviour. Introducing disorder we restrict ourselves to the experimentally
most relevant case of weak uncorrelated randomness which is known to destroy
the long-ranged translational order of the Abrikosov lattice in three
dimensions. Elucidating possible residual glassy ordered phases, we distinguish
betwee positional and phase-coherent vortex glasses. The discussion of elastic
vortex glasses, in two and three dimensions occupy the main part of our review.
In particular, in three dimensions there exists an elastic vortex-glass phase
which still shows quasi-long-range translational order: the `Bragg glass'. It
is shown that this phase is stable with respect to the formation of
dislocations for intermediate fields. Preliminary results suggest that the
Bragg-glass phase may not show phase-coherent vortex-glass order. The latter is
expected to occur in systems with weak disorder only in higher dimensions. We
further demonstrate that the linear resistivity vanishes in the vortex-glass
phase. The vortex-glass transition is studied in detail for a superconducting
film in a parallel field. Finally, we review some recent developments
concerning driven vortex-line lattices moving in a random environment.Comment: 133 pages Latex with figures. accepted for publication in Adv. Phy
Elastic theory of quantum Hall smectics: effects of disorder
We study the effect of disorder on quantum Hall smectics within the framework
of an elastic theory. Based on a renormalization group calculation, we derive
detailed results for the degrees of translational and orientational order of
the stripe pattern at zero temperature and carefully map out the disorder and
length-scale regimes in which the system effectively exhibits smectic, nematic,
or isotropic behavior. We show that disorder always leads to a finite density
of free dislocations and estimate the scale on which they begin to appear.Comment: 4 pages latex with 1 EPS figur
Renormalization group approach to layered superconductors
A renormalization group theory for a system consisting of coupled
superconducting layers as a model for typical high-temperature superconducters
is developed. In a first step the electromagnetic interaction over infinitely
many layers is taken into account, but the Josephson coupling is neglected. In
this case the corrections to two-dimensional behavior due to the presence of
the other layers are very small. Next, renormalization group equations for a
layered system with very strong Josephson coupling are derived, taking into
account only the smallest possible Josephson vortex loops. The applicability of
these two limiting cases to typical high-temperature superconductors is
discussed. Finally, it is argued that the original renormalization group
approach by Kosterlitz is not applicable to a layered system with intermediate
Josephson coupling.Comment: RevTeX, 15 pages, 4 figures can be obtained from the author by
conventional mail; accepted for publication in Phys. Rev.
XY models with disorder and symmetry-breaking fields in two dimensions
The combined effect of disorder and symmetry-breaking fields on the
two-dimensional XY model is examined. The study includes disorder in the
interaction among spins in the form of random phase shifts as well as disorder
in the local orientation of the field. The phase diagrams are determined and
the properties of the various phases and phase transitions are calculated. We
use a renormalization group approach in the Coulomb gas representation of the
model. Our results differ from those obtained for special cases in previous
works. In particular, we find a changed topology of the phase diagram that is
composed of phases with long-range order, quasi-long-range order, and
short-range order. The discrepancies can be ascribed to a breakdown of the
fugacity expansion in the Coulomb gas representation.
Implications for physical systems such as planar Josephson junctions and the
faceting of crystal surfaces are discussed.Comment: 17 pages Latex with 5 eps figures, change: acknowledgment extende
- …