arXiv subjects

M. B. Sobnack

Publications and source records attributed to M. B. Sobnack.

3 recordsLinked to original sources

arXiv2017

Phase Slip Avalanches in Small Superconductors

We study the effect of phase slips in a quasi 1d superconducting channel along which a current flows and report a new phenomenon where an avalanche of phase slips occurs. This limits the critical current in thin films and wires and drives the system to a topological phase transition at a temperature lower than the bulk critical temperature. We describe the mechanism of such a catastrophic phase slip avalanche and, following Kosterlitz and Thouless, we use group renormalization techniques to derive an exact analytical expression for the critical current as a function of film width and temperature. Our results are in very good agreement with, and reproduce, the available experimental data on superconducting MgB$_2$ thin films. The phenomenon we describe is very general and can be used in the construction of new devices where the superconducting state can coexist with the normal state.

cond-mat.supr-con↗

arXiv2010

Stability Studies of Vortex State in Superconducting Disks

We are going to analyze the nucleation of vortices in a thin mesoscopic superconducting disk. The Gibbs free energy from London model is formulated. This energy function, with an arbitrary configuration of vortices, is assoicated with the disk's size, applied magnetic field and finite temperature. Then, the optimal solution is obtained by differentiating with respect position r, for fixed applied field and temperature. We also investigate the stability of the different vortex states inside the disk and compare our results with those of other theoretical studies and with available experimental observations. Our results agree with experiments. Besides, we formulate the Gibbs free energy by Ginzburg-Landau (GL) model. Theoretically, the free energy by GL model takes the superconducting density into account but not in London model. Our simulations from both theories show the same quantum states of vortex. We find that the Gibbs free energy by GL model is smaller than by London model.

cond-mat.supr-con↗

arXiv2000

Suppression of Superconductivity in Mesoscopic Superconductors

We propose a new boundary-driven phase transition associated with vortex nucleation in mesoscopic superconductors (of size of the order of, or larger than, the penetration depth). We derive the rescaling equations and we show that boundary effects associated with vortex nucleation lowers the conventional transition temperature in mesoscopic superconductors by an amount which is a function of the size of the superconductor. This result explains recent experiments in small superconductors where it was found that the transition temperature depends on the size of the system and is lower than the critical Berezinskĭ-Kosterlitz-Thouless temperature.

cond-mat.supr-con↗