Charge and Spin Transport in Superconducting Weak Links

TL;DR

This paper investigates charge and spin transport in superconducting weak links, revealing vortex behavior influenced by interface reflection and temperature, and explores spin polarization and current-phase relations in triplet superconductor junctions.

Contribution

It introduces new insights into vortex dynamics, spin polarization, and current-phase relations in various superconducting weak link configurations, including triplet and non-unitary superconductors.

Findings

Vortices are destroyed by interface reflection but restored by temperature increases.

Spin current polarization depends on the misorientation of gap vectors.

Distinct current-phase relations differentiate between superconductor pairing symmetries.

Abstract

The coherent mixing of the current states in the superconducting weak link subject to a Josephson phase difference $\phi$ and subject to an external transport current in the banks is one of the aims of this work. At $\phi=\pi $ the nonlocal mixing of current states produces two vortices close to the point-contact between superconducting bulks. The effect of point-contact reflection in an impenetrable interface and effect of temperature on the vortices have been studied. It is obtained that increasing the reflection of the point-contact destroys the vortices while increasing the temperature restore these vortices. The vortex state is a new version of the interference between the macroscopic states and quantum tunnelling. Also, the weak link between unitary triplet superconductors which have $f-$wave and $p+h-$wave pairing symmetry has been studied from the spin and charge current-phase relation point of view. The main result in the second part of this thesis, is the polarization of the spin transport when a junction between triplet superconductors is used. It is observed that the spin current is the result of the misorientation between the gap vectors of two supercondcutors. In addition, the weak link between two bipolar non-unitary triplet superconductors is studied mathematically. The current-phase relations obtained in third part of this thesis are totally different from the junctions between the unitary spin-triplet superconductors and between the spin-singlet superconductors. The current phase diagrams which have been obtained in this work can be used to distinguish the symmetry of the order parameter in the crystals.