15 research outputs found
Soft vortex matter in a type-I/type-II superconducting bilayer
Magnetic flux patterns are known to strongly differ in the intermediate state
of type-I and type-II superconductors. Using a type-I/type-II bilayer we
demonstrate hybridization of these flux phases into a plethora of unique new
ones. Owing to a complicated multi-body interaction between individual
fluxoids, many different intriguing patterns are possible under applied
magnetic field, such as few-vortex clusters, vortex chains, mazes or
labyrinthal structures resembling the phenomena readily encountered in soft
matter physics. However, in our system the patterns are tunable by sample
parameters, magnetic field, current and temperature, which reveals transitions
from short-range clustering to long-range ordered phases such as parallel
chains, gels, glasses and crystalline vortex lattices, or phases where lamellar
type-I flux domains in one layer serve as a bedding potential for type-II
vortices in the other - configurations clearly beyond the soft-matter analogy
Conditions for non-monotonic vortex interaction in two-band superconductors
We describe a semi-analytic approach to the two-band Ginzburg-Landau theory,
which predicts the behavior of vortices in two-band superconductors. We show
that the character of the short-range vortex-vortex interaction is determined
by the sign of the normal domain - superconductor interface energy, in analogy
with the conventional differentiation between type-I and type-II
superconductors. However, we also show that the long-range interaction is
determined by a modified Ginzburg-Landau parameter , different from
the standard of a bulk superconductor. This opens the possibility for
non-monotonic vortex-vortex interaction, which is temperature-dependent, and
can be further tuned by alterations of the material on the microscopic scale
Different length-scales for order parameters in two-gap superconductors: the extended Ginzburg-Landau theory
Using the Ginzburg-Landau theory extended to the next-to-leading order we
determine numerically the healing lengths of the two order parameters at the
two-gap superconductor/normal metal interface. We demonstrate on several
examples that those can be significantly different even in the strict domain of
applicability of the Ginzburg-Landau theory. This justifies the use of this
theory to describe relevant physics of two-gap superconductors, distinguishing
them from their single-gap counterparts. The calculational degree of complexity
increases only slightly with respect to the conventional Ginzburg-Landau
expansion, thus the extended Ginzburg-Landau model remains numerically far less
demanding compared to the full microscopic approaches.Comment: 5 pages, 4 figure
Two-band superconductors: Hidden criticality deep in the superconducting state
We show that two-band superconductors harbor hidden criticality deep in the
superconducting state, stemming from the critical temperature of the weaker
band taken as an independent system. For sufficiently small interband coupling
the coherence length of the weaker band exhibits a remarkable
deviation from the conventional monotonic increase with temperature, namely, a
pronounced peak close to the hidden critical point. The magnitude of the peak
scales proportionally to \gamma^(-\mu), with the Landau critical exponent \mu =
1/3, the same as found for the mean-field critical behavior with respect to the
source field in ferromagnets and ferroelectrics. Here reported hidden
criticality of multi-band superconductors can be experimentally observed by,
e.g., imaging of the variations of the vortex core in a broader temperature
range. Similar effects are expected for the superconducting multilayers.Comment: 6 pages, 2 figures, Supplementary material included. Accepted for
publication in PR
Critical and non-critical coherence lengths in a two-band superconductor
We study the peculiarities of coherency in a two-gap superconductor. The both
intraband couplings, inducing superconductivity in the independent bands, and
interband pair-transfer interaction have been taken into account. On the basis
of the Ginzburg-Landau equations derived from the Bogoliubov-de Gennes
equations and the relevant self-consistency conditions for a two-gap system, we
find critical and non-critical coherence lengths in the spatial behaviour of
the fluctuations of order parameters. The character of the temperature
dependencies of these length scales is determined by the relative contributions
from intra- and interband interaction channels.Comment: Accepted for publication in Journal of Superconductivity and Novel
Magnetis