25 research outputs found

### Giant oscillations of energy levels in mesoscopic superconductors

The interplay of geometrical and Andreev quantization in mesoscopic
superconductors leads to giant mesoscopic oscillations of energy levels as
functions of the Fermi momentum and/or sample size. Quantization rules are
formulated for closed quasiparticle trajectories in the presence of normal
scattering at the sample boundaries. Two generic examples of mesoscopic systems
are studied: (i) one dimensional Andreev states in a quantum box, (ii) a single
vortex in a mesoscopic cylinder.Comment: 4 pages, 3 figure

### Andreev transport in two-dimensional normal-superconducting systems in strong magnetic fields

The conductance in two-dimensional (2D) normal-superconducting (NS) systems
is analyzed in the limit of strong magnetic fields when the transport is
mediated by the electron-hole states bound to the sample edges and NS
interface, i.e., in the Integer Quantum Hall Effect regime.The Andreev-type
process of the conversion of the quasiparticle current into the superflow is
shown to be strongly affected by the mixing of the edge states localized at the
NS and insulating boundaries. The magnetoconductance in 2D NS structures is
calculated for both quadratic and Dirac-like normal state spectra. Assuming a
random scattering of the edge modes we analyze both the average value and
fluctuations of conductance for an arbitrary number of conducting channels.Comment: 5 pages, 1 figur

### Electron-phonon heat transfer in giant vortex states

We examine energy relaxation of nonequilibrium quasiparticles (QPs) in different vortex configurations in "dirty" s-wave superconductors (SCs). The heat flow from the electronic subsystem to phonons in a mesoscopic SC disk with a radius of the order of several coherence lengths is calculated both in the Meissner and in the giant vortex states using the Usadel approach. The recombination process is shown to be strongly affected by interplay of the subgap states, located in the vortex core and in the region at the sample edge where the spectral gap Eg is reduced by the Meissner currents. In order to uncover the physical origin of the results, we develop a semiquantitative analytical approximation based on the combination of homogeneous solutions of Usadel equations in Meissner and vortex states of a mesoscopic SC disk and analytically calculate the corresponding spatially resolved electron-phonon heat rates. Our approach provides important information about nonequilibrium QPs cooling by the magnetic field-induced traps in various mesoscopic SC devices

### Magnetization reversal of ferromagnetic nanodisc placed above a superconductor

Using numerical simulation we have studied a magnetization distribution and a
process of magnetization reversal in nanoscale magnets placed above a
superconductor plane. In order to consider an influence of superconductor on
magnetization distribution in the nanomagnet we have used London approximation.
We have found that for usual values of London penetration depth the ground
state magnetization is mostly unchanged. But at the same time the fields of
vortex nucleation and annihilation change significantly: the interval where
vortex is stable enlarges on 100-200 Oe for the particle above the
superconductor. Such fields are experimentally observable so there is a
possibility of some practical applications of this effect.Comment: 8 pages, 9 figure

### Hybridization and interference effects for localized superconducting states in strong magnetic field

Within the Ginzburg-Landau model we study the critical field and temperature
enhancement for crossing superconducting channels formed either along the
sample edges or domain walls in thin-film magnetically coupled superconducting
- ferromagnetic bilayers. The corresponding Cooper pair wave function can be
viewed as a hybridization of two order parameter (OP) modes propagating along
the boundaries and/or domain walls. Different momenta of hybridized OP modes
result in the formation of vortex chains outgoing from the crossing point of
these channels. Near this crossing point the wave functions of the modes merge
giving rise to the increase in the critical temperature for a localized
superconducting state. The origin of this critical temperature enhancement
caused by the wave function squeezing is illustrated for a limiting case of
approaching parallel boundaries and/or domain walls. Using both the variational
method and numerical simulations we have studied the critical temperature
dependence and OP structure vs the applied magnetic field and the angle between
the crossing channels.Comment: 12 pages, 13 figure

### Ionization-induced leaking-mode channeling of intense short laser pulses in gases

We demonstrate that short laser pulse self-guiding
over distances of many Rayleigh lengths can be achieved
in the absence of any focusing nonlinearity as a result
of trapping of a leaking wave in a plasma channel produced
by field-induced ionization in the saturation regime. A
detailed computational study of the new self-guiding effect
in both cases of comparatively long laser pulses, when
the traditional approximation of the slowly varying complex
amplitude is valid, and of high intense ultrashort laser
pulses comprising only few field cycles have been performed

### Vortex Core States in Superconducting Graphene

The distinctive features of the electronic structure of vortex states in
superconducting graphene are studied within the Bogolubov-de Gennes theory
applied to excitations near the Dirac point. We suggest a scenario describing
the subgap spectrum transformation which occurs with a change in the doping
level. For an arbitrary vorticity and doping level we investigate the problem
of existence of zero energy modes. The crossover to a Caroli - de Gennes -
Matricon type of spectrum is studied.Comment: 4 pages, 2 figure

### Interacting circular nanomagnets

Regular 2D rectangular lattices of permalloy nanoparticles (40 nm in
diameter) were prepared by the method of the electron lithography. The
magnetization curves were studied by Hall magnetometry with the compensation
technique for different external field orientations at 4.2K and 77K. The shape
of hysteresis curves indicates that there is magnetostatic interaction between
the particles. The main peculiarity is the existence of remanent magnetization
perpendicular to easy plain. By numerical simulation it is shown, that the
character of the magnetization reversal is a result of the interplay of the
interparticle interaction and the magnetization distribution within the
particles (vortex or uniform).Comment: 16 pages, 8 figure