Josephson junctions with spin-orbit and spin-flip interactions

TL;DR

This thesis investigates how spin-orbit coupling, spin-flip scattering, and junction geometry influence supercurrent behavior, 0-$ ext{pi}$ transitions, and critical current in ballistic S/2DEG/S Josephson junctions.

Contribution

It provides a detailed analysis of supercurrent-phase relations and critical current dependencies in Josephson junctions with spin-orbit and spin-flip interactions, including conditions for non-zero zero-phase current.

Findings

Supercurrent relation varies with junction length, spin-orbit coupling, and scattering strengths.

Conditions for 0-$ ext{pi}$ transition and second harmonic emergence are identified.

Critical current can be optimized by tuning spin interactions and geometries.

Abstract

In this thesis we study short Josephson junctions which include a region with Rashba spin-orbit coupling effect. Our junctions consists of two superconductors (S) and a 2-dimensional electron gas (2DEG) layer between them: S/2DEG/S junction. We also include two thin insulating interfaces between the superconductors and the 2DEG, which are capable of both normal and spin-flip scattering. The junctions we study are assumed to be in the ballistic limit and so, we do not consider the effects of impurities. The basic equations we use for our model are the Bogoliubov-de Gennes equations. We give particular emphasis in the relation between the supercurrent of the junction as a function of difference of the phase parameters of the two superconductors. We study thoroughly how this relation differs to the change of the junction's length, the spin-orbit coupling constant, the normal scattering strength and the spin-flip scattering strength and direction. We are also interested in the 0-$\pi$ transition and the second harmonic appearance, as well as the symmetries which occur in the current-phase relation, for different geometries of the two spin-flip interfaces. In addition, we show how the Critical current of our junction is affected to the change of the above parameters and under which conditions it is optimized. Finally, we study the supercurrent flowing at zero phase difference (ZPC) of the two superconductors. We emphasize the conditions under which it is non-zero and also examine the cases it becomes maximized.