160 research outputs found
Thermodynamically stable noncomposite vortices in mesoscopic two-gap superconductors
In mesoscopic two-gap superconductors with sizes of the order of the
coherence length noncomposite vortices are found to be thermodynamically stable
in a large domain of the phase diagram. In these phases the vortex
cores of one condensate are spatially separated from the other condensate ones,
and their respective distributions can adopt distinct symmetries. The
appearance of these vortex phases is caused by a non-negligible effect of the
boundary of the sample on the superconducting order parameter and represents
therefore a genuine mesoscopic effect. For low values of interband Josephson
coupling vortex patterns with can arise in addition to the
phases with , where and are total vorticities in the two
condensates. The calculations show that noncomposite vortices could be observed
in thin mesoscopic samples of MgB.Comment: 5 pages, 3 figures, to be published in Europhysics Letter
Numerical bifurcation study of superconducting patterns on a square
This paper considers the extreme type-II Ginzburg-Landau equations that model
vortex patterns in superconductors. The nonlinear PDEs are solved using
Newton's method, and properties of the Jacobian operator are highlighted.
Specifically, it is illustrated how the operator can be regularized using an
appropriate phase condition. For a two-dimensional square sample, the numerical
results are based on a finite-difference discretization with link variables
that preserves the gauge invariance. For two exemplary sample sizes, a thorough
bifurcation analysis is performed using the strength of the applied magnetic
field as a bifurcation parameter and focusing on the symmetries of this system.
The analysis gives new insight in the transitions between stable and unstable
states, as well as the connections between stable solution branches.Comment: 31 page
Spin reversal in Fe8 under fast pulsed magnetic fields
We report measurements on magnetization reversal in the Fe8 molecular magnet using fast pulsed magnetic fields of 1.5 kT s−1 and in the temperature range of 0.6–4.1 K. We observe and analyze the temperature dependence of the reversal process, which involves in some cases several resonances. Our experiments allow observation of resonant quantum tunneling of magnetization up to a temperature of ~4 K. We also observe shifts in the maxima of the relaxation within each resonance field with temperature that suggest the emergence of a thermal instability—a combination of spin reversal and self-heating that may result in a magnetic deflagration process. The results are mainly understood in the framework of thermally-activated quantum tunneling transitions in combination with emergence of a thermal instability
Spin reversal in Fe8 under fast pulsed magnetic fields
We report measurements on magnetization reversal in the Fe8 molecular magnet using fast pulsed magnetic fields of 1.5 kT s−1 and in the temperature range of 0.6–4.1 K. We observe and analyze the temperature dependence of the reversal process, which involves in some cases several resonances. Our experiments allow observation of resonant quantum tunneling of magnetization up to a temperature of ~4 K. We also observe shifts in the maxima of the relaxation within each resonance field with temperature that suggest the emergence of a thermal instability—a combination of spin reversal and self-heating that may result in a magnetic deflagration process. The results are mainly understood in the framework of thermally-activated quantum tunneling transitions in combination with emergence of a thermal instability
Type-1.5 Superconductors
We demonstrate the existence of a novel superconducting state in high quality
two-component MgB2 single crystalline superconductors where a unique
combination of both type-1 (kappa_1 0.707)
superconductor conditions is realized for the two components of the order
parameter. This condition leads to a vortex-vortex interaction attractive at
long distances and repulsive at short distances, which stabilizes
unconventional stripe- and gossamer-like vortex patterns that we have
visualized in this type-1.5 superconductor using Bitter decoration and also
reproduced in numerical simulations.Comment: accepted in Phys. Rev. Let
Giant vortices, vortex rings and reentrant behavior in type-1.5 superconductors
We predict that in a bulk type-1.5 superconductor the competing magnetic
responses of the two components of the order parameter can result in a vortex
interaction that generates group-stabilized giant vortices and unusual vortex
rings in the absence of any extrinsic pinning or confinement mechanism. We also
find within the Ginzburg-Landau theory a rich phase diagram with successions of
behaviors like type-1 -> type-1.5 -> type-2 -> type-1.5 as temperature
decreases.Comment: 5 pages, 4 figure
Single-electron transport through the vortex core levels in clean superconductors
We develop a microscopic theory of single-electron transport in N-S-N hybrid
structures in the presence of applied magnetic field introducing vortex lines
in a superconductor layer. We show that vortex cores in a thick and clean
superconducting layer are similar to mesoscopic conducting channels where the
bound core states play the role of transverse modes. The transport through not
very thick layers is governed by another mechanism, namely by resonance
tunneling via vortex core levels. We apply our method to calculation of the
thermal conductance along the magnetic field.Comment: 4 pages, 1 figur
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Preface
Preface - The second International Conference on Mathematical Modeling in Physical Sciences (IC-MSQUARE) took place at Prague, Czech Republic, from Sunday 1 September to Thursday 5 September 2013
Antivortices due to competing orbital and paramagnetic pair-breaking effects
Thermodynamically stable vortex-antivortex structures in a
quasi-two-dimensional superconductor in a tilted magnetic field are predicted.
For this geometry, both orbital and spin pair-breaking effects exist, with
their relative strength depending on the tilt angle \Theta. The spectrum of
possible states contains as limits the ordinary vortex state (for large \Theta)
and the Fulde-Ferrell-Larkin-Ovchinnikov state (for \Theta=0). The
quasiclassical equations are solved near H_{c2} for arbitrary \Theta and it is
shown that stable states with coexisting vortices and antivortices exist in a
small interval close to \Theta=0. The results are compared with recent
predictions of antivortices in mesoscopic samples.Comment: 11 pages, 3 figure
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