38 research outputs found
The role of domain walls on the vortex creep dynamics in unconventional superconducors
We investigate the influence of domain walls on the vortex dynamics in
superconductors with multi-component order parameters. We show that, due to
their complex structure domain walls can carry vortices with fractional flux
quanta. The decay of conventional vortices into fractional ones on domain walls
is examined. This decay presents an extraordinarily strong pinning mechanism
for vortices and turns domain walls occupied with pinned fractional vortices
into efficient barriers for the vortex motion. Therefore, domain walls can act
as fences for the flux flow, preventing the decay of the remnant magnetic flux
enclosed by them. Furthermore, the consequences of this property of domain
walls on the vortex dynamics are discussed in connection with observed noise in
the hysteresis cycle, using the Bean model of the critical vortex state. Based
on this picture experimental data in the unconventional superconductors
UPt, UThBe and SrRuO are interpreted.Comment: 18 pages, 9 figures, to appear in Progress of Theoretical Physic
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
Ising superconductivity and magnetism in NbSe
Recent studies on superconductivity in NbSe have demonstrated a large
anisotropy in the superconducting critical field when the material is reduced
to a single monolayer. Motivated by this recent discovery, we use density
functional theory (DFT) calculations to quantitatively address the
superconducting properties of bulk and monolayer NbSe. We demonstrate that
NbSe is close to a ferromagnetic instability, and analyze our results in
the context of experimental measurements of the spin susceptibility in
NbSe. We show how this magnetic instability, which is pronounced in a
single monolayer, can enable sizeable singlet-triplet mixing of the
superconducting order parameter, contrary to contemporary considerations of the
pairing symmetry in monolayer NbSe, and discuss approaches as to how this
degree of mixing can be addressed quantitatively within our DFT framework. Our
calculations also enable a quantitative description of the large anisotropy of
the superconducting critical field, using DFT calculations of monolayer
NbSe in the normal stateComment: 13 pages, 6 figure