72 research outputs found
Domain walls and their experimental signatures in s+is superconductors
Arguments were recently advanced that hole-doped BaKFeAs
exhibits state at certain doping. Spontaneous breaking of time reversal
symmetry in state, dictates that it possess domain wall excitations.
Here, we discuss what are the experimentally detectable signatures of domain
walls in state. We find that in this state the domain walls can have
dipole-like magnetic signature (in contrast to the uniform magnetic signature
of domain walls superconductors). We propose experiments where
quench-induced domain walls can be stabilized by geometric barriers and be
observed via their magnetic signature or their influence on the magnetization
process, thereby providing an experimental tool to confirm state.Comment: Replaced with a version in print in Physical Review Letters; Minor
changes; 8 pages, 9 figure
Topological defects in mixtures of superconducting condensates with different charges
We investigate the topological defects in phenomenological models describing
mixtures of charged condensates with commensurate electric charges. Such
situations are expected to appear for example in liquid metallic deuterium.
This is modeled by a multicomponent Ginzburg-Landau theory where the
condensates are coupled to the same gauge field by different coupling constants
whose ratio is a rational number. We also briefly discuss the case where
electric charges are incommensurate. Flux quantization and finiteness of the
energy per unit length dictate that the different condensates have different
winding and thus different number of (fractional) vortices. Competing
attractive and repulsive interactions lead to molecule-like bound state between
fractional vortices. Such bound states have finite energy and carry integer
flux quanta. These can be characterized by topological
invariant that motivates their denomination as skyrmions.Comment: Replaced with a version in print in Phys. Rev. B; Improved and
extended as compared to the first version; 14 pages, 8 figure
Skyrmionic state and stable half-quantum vortices in chiral p-wave superconductors
Observability of half-quantum vortices and skyrmions in p-wave
superconductors is an outstanding open question. Under the most common
conditions, fractional flux vortices are not thermodynamically stable in bulk
samples. Here we show that in chiral p-wave superconductors, there is a regime
where, in contrast lattices of integer flux vortices are not thermodynamically
stable. Instead skyrmions made of spatially separated half-quantum vortices are
the topological defects produced by an applied external field.Comment: Replaced with a version in print in Physical Review B, Rapid
Communications; References added; 8 pages, 9 figure
Microscopic prediction of skyrmion lattice state in clean interface superconductors
When an in-plane field is applied to a clean interface superconductor, a
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-like phase is stabilized. This phase
has a symmetry and, in principle, this
symmetry allows for flux carrying topological excitations different from
Abrikosov vortices (which are the simplest defects associated with maps). However, in practice, largely due to electromagnetic and other
intercomponent interactions, such topological excitations are very rare in
superconducting systems. Here we demonstrate that a realistic microscopic
theory for interface superconductors, such as SrTiO/LaAlO, predicts an
unconventional magnetic response where the flux-carrying objects are skyrmions,
characterized by homotopy invariants of maps. Additionally, we
show that this microscopic theory predicts that stable fractional vortices form
near the boundary of these superconductors. It also predicts the appearance of
type-1.5 superconductivity for some range of parameters. Central to these
results is the assumption that the Rashba spin orbit coupling is much larger
than the superconducting gap.Comment: Replaced with a version in print in Phys. Rev. B; Improved and
extended as compared to the first version; 10 pages, 6 figure
Properties of dirty two-bands superconductors with repulsive interband interaction: normal modes, length scales, vortices and magnetic response
Disorder in two-band superconductors with repulsive interband interaction
induces a frustrated competition between the phase-locking preferences of the
various potential and kinetic terms. This frustrated interaction can result in
the formation of an superconducting state, that breaks the time-reversal
symmetry. In this paper we study the normal modes and their associated
coherence lengths in such materials. We especially focus on the consequences of
the soft modes stemming from the frustration and time-reversal-symmetry
breakdown. We find that two-bands superconductors with such impurity-induced
frustrated interactions display a rich spectrum of physical properties that are
absent in their clean counterparts. It features a mixing of Leggett's and
Anderson-Higgs modes, and a soft mode with diverging coherence length at the
impurity-induced second order phase transition from states to
the state. Such a soft mode generically results in long-range attractive
intervortex forces that can trigger the formation of vortex clusters. We find
that, if such clusters are formed, their size and internal flux density have a
characteristic temperature dependence that could be probed in
muon-spin-rotation experiments. We also comment on the appearance of
spontaneous magnetic fields due to spatially varying impurities.Comment: Added discussion of spontaneous magnetic fields due to spatially
varying impurities; Replaced with a version in print in Phys. Rev. B; 17
pages, 8 figure
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