394 research outputs found
Magnetic skyrmion lattices in heavy fermion superconductor UPt3
Topological analysis of nearly SO(3)_{spin} symmetric Ginzburg--Landau
theory, proposed for UPt by Machida et al, shows that there exists a new
class of solutions carrying two units of magnetic flux: the magnetic skyrmion.
These solutions do not have singular core like Abrikosov vortices and at low
magnetic fields they become lighter for strongly type II superconductors.
Magnetic skyrmions repel each other as at distances much larger then the
magnetic penetration depth , forming a relatively robust triangular
lattice. The magnetic induction near is found to increase as
. This behavior agrees well with experiments.Comment: 4 pages, 2 figures, 2 column format; v2:misprint in the title is
correcte
Superconductor-Ferromagnet Bi-Layers: a Comparison of s-Wave and d-Wave Order Parameters
We study superconductor-ferromagnet bi-layers, not only for s-wave but also
for d-wave superconductors. We observe oscillations of the critical temperature
when varying the thickness of the ferromagnetic layer for both s-wave and
d-wave superconductors. However, for a rotated d-wave order parameter the
critical temperature differs considerably from that for the unrotated case. In
addition we calculate the density of states for different thicknesses of the
ferromagnetic layer; the results reflect the oscillatory behaviour of the
superconducting correlations.Comment: 11 pages, 5 figures, accepted for publication in J. Phys.: Condens.
Matte
Magnetic skyrmions and their lattices in triplet superconductors
Complete topological classification of solutions in SO(3) symmetric
Ginzburg-Landau free energy has been performed and a new class of solutions in
weak external magnetic field carrying two units of magnetic flux has been
identified. These solutions, magnetic skyrmions, do not have singular core like
Abrikosov vortices and at low magnetic field become lighter for strongly type
II superconductors. As a consequence, the lower critical magnetic field Hc1 is
reduced by a factor of log(kappa). Magnetic skyrmions repel each other as 1/r
at distances much larger then magnetic penetration depth forming relatively
robust triangular lattice. Magnetic induction near Hc1 increases gradually as
(H-Hc1)^2. This agrees very well with experiments on heavy fermion
superconductor UPt3. Newly discovered Ru based compounds Sr2RuO4 and
Sr2YRu(1-x)Cu(x)O6 are other possible candidates to possess skyrmion lattices.
Deviations from exact SO(3) symmetry are also studied.Comment: 23 pages, 10 eps figure
Vortex Core Structure and Dynamics in Layered Superconductors
We investigate the equilibrium and nonequilibrium properties of the core
region of vortices in layered superconductors. We discuss the electronic
structure of singly and doubly quantized vortices for both s-wave and d-wave
pairing symmetry. We consider the intermediate clean regime, where the
vortex-core bound states are broadened into resonances with a width comparable
to or larger than the quantized energy level spacing, and calculate the
response of a vortex core to an {\em a.c.} electromagnetic field for vortices
that are pinned to a metallic defect. We concentrate on the case where the
vortex motion is nonstationary and can be treated by linear response theory.
The response of the order parameter, impurity self energy, induced fields and
currents are obtained by a self-consistent calculation of the distribution
functions and the excitation spectrum. We then obtain the dynamical
conductivity, spatially resolved in the region of the core, for external
frequencies in the range, 0.1\Delta < \hbar\omega \lsim 3\Delta. We also
calculate the dynamically induced charge distribution in the vicinity of the
core. This charge density is related to the nonequilibrium response of the
bound states and collective mode, and dominates the electromagnetic response of
the vortex core.Comment: Presented at the 2000 Workshop on ``Microscopic Structure and
Dynamics of Vortices in Unconventional Superconductors and Superfluids'',
held at the Max Planck Institute for the Physics of Complex Systems in
Dresden, Germany (28 pages with 15 figures). Alternate version with higher
resolution figures:
http://snowmass.phys.nwu.edu/~sauls/Eprints/Dresden2000.htm
Symmetries of Pairing Correlations in Superconductor-Ferromagnet Nanostructures
Using selection rules imposed by the Pauli principle, we classify pairing
correlations according to their symmetry properties with respect to spin,
momentum, and energy. We observe that inhomogeneity always leads to mixing of
even- and odd-energy pairing components. We investigate the superconducting
pairing correlations present near interfaces between superconductors and
ferromagnets, with focus on clean systems consisting of singlet superconductors
and either weak or half-metallic ferromagnets. Spin-active scattering in the
interface region induces all of the possible symmetry components. In
particular, the long-range equal-spin pairing correlations have odd-frequency
s-wave and even-frequency p-wave components of comparable magnitudes. We also
analyze the Josephson current through a half-metal. We find analytic
expressions and an interesting universality in the temperature dependence of
the critical current in the tunneling limit.Comment: 20 pages, 5 figures, added citations, corrected typo
- …