3,260 research outputs found
Motion and homogenization of vortices in anisotropic Type II superconductors
The motion of vortices in an anisotropic superconductor is considered. For a system of well-separated vortices, each vortex is found to obey a law of motion analogous to the local induction approximation, in which velocity of the vortex depends upon the local curvature and orientation. A system of closely packed vortices is then considered, and a mean field model is formulated in which the individual vortex lines are replaced by a vortex density
Analysis of the measurements of anisotropic a.c. vortex resistivity in tilted magnetic fields
Measurements of the high-frequency complex resistivity in superconductors are
a tool often used to obtain the vortex parameters, such as the vortex
viscosity, the pinning constant and the depinning frequency. In anisotropic
superconductors, the extraction of these quantities from the measurements faces
new difficulties due to the tensor nature of the electromagnetic problem. The
problem is specifically intricate when the magnetic field is tilted with
respect to the crystallographic axes. Partial solutions exist in the
free-flux-flow (no pinning) and Campbell (pinning dominated) regimes. In this
paper we develop a full tensor model for the vortex motion complex resistivity,
including flux-flow, pinning, and creep. We give explicit expressions for the
tensors involved. We obtain that, despite the complexity of the physics, some
parameters remain scalar in nature. We show that under specific circumstances
the directly measured quantities do not reflect the true vortex parameters, and
we give procedures to derive the true vortex parameters from measurements taken
with arbitrary field orientations. Finally, we discuss the applicability of the
angular scaling properties to the measured and transformed vortex parameters
and we exploit these properties as a tool to unveil the existence of
directional pinning.Comment: 21 pages, 3 figures. arXiv admin note: text overlap with
arXiv:1402.316
Observation of two species of vortices in the anisotropic spin-triplet superconductor
Magnetic flux structures in single crystals of the layered spin triplet
superconductor SrRuO are studied by scanning micro SQUID Force
microscopy. Vortex chains appear as the applied field is tilted along the
in-plane direction of the superconductor. The vortex chains align along the
direction of the in-plane component of the applied magnetic field. The
decoration of in-plane vortices by crossing Abrikosov vortices is observed: two
vortex orientations are apparent simultaneously, one along the layers and the
other perpendicular to the layers. The crossing vortices appear preferentially
on the in-plane vortices
Vortex Pinball Under Crossed AC Drives in Superconductors with Periodic Pinning Arrays
Vortices driven with both a transverse and a longitudinal AC drive which are
out of phase are shown to exhibit a novel commensuration-incommensuration
effect when interacting with periodic substrates. For different AC driving
parameters, the motion of the vortices forms commensurate orbits with the
periodicity of the pinning array. When the commensurate orbits are present,
there is a finite DC critical depinning threshold, while for the incommensurate
phases the vortices are delocalized and the DC depinning threshold is absent.Comment: 4 pages, 4 postscript figure
Signatures of unconventional pairing in near-vortex electronic structure of LiFeAs
A major question in Fe-based superconductors remains the structure of the
pairing, in particular whether it is of unconventional nature. The electronic
structure near vortices can serve as a platform for phase-sensitive
measurements to answer this question. By solving Bogoliubov-de Gennes equations
for LiFeAs, we calculate the energy-dependent local electronic structure near a
vortex for different nodeless gap-structure possibilities. At low energies, the
local density of states (LDOS) around a vortex is determined by the
normal-state electronic structure. However, at energies closer to the gap
value, the LDOS can distinguish an anisotropic from a conventional isotropic
s-wave gap. We show within our self-consistent calculation that in addition,
the local gap profile differs between a conventional and an unconventional
pairing. We explain this through admixing of a secondary order parameter within
Ginzburg-Landau theory. In-field scanning tunneling spectroscopy near vortices
can therefore be used as a real-space probe of the gap structure
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