Magnetoelectrics in Disordered Topological Insulator Josephson Junctions

TL;DR

This paper predicts a controllable $ $-junction state in disordered topological insulator Josephson junctions, driven by quasiparticle injection, revealing strong charge-spin coupling and potential for quantum device applications.

Contribution

It introduces a method to induce and control a $ $-phase shift in topological insulator Josephson junctions via quasiparticle injection, highlighting a novel way to manipulate superconducting phases.

Findings

Edelstein effect is significantly enhanced in topological insulator surface states.

A $ $-phase Josephson junction can be achieved by quasiparticle injection.

The $ $-shift is proportional to the applied voltage difference.

Abstract

We theoretically study the coupling of electric charge and spin polarization in an equilibrium and nonequilibrium electric transport across a two dimensional Josephson configuration comprised of disordered surface channels of a three dimensional topological insulator. In the equilibriun state of the system we predict the Edelstein effect, which is much more pronounced than its counterpart in conventional spin orbit coupled materials. Employing a quasiclassical Keldysh technique, we demonstrate that the ground state of system can be experimentally shifted into arbitrary macroscopic superconducting phase differences other than the standard `$0$' or `$\pi$', constituting a $\phi_0$-junction, solely by modulating a quasiparticle flow injection into the junction. We propose a feasible experiment where the quasiparticles are injected into the topological insulator surface by means of a normal electrode and voltage gradient so that oppositely oriented stationary spin densities can be developed along the interfaces and allow for directly making use of the spin-momentum locking nature of Dirac fermions in the surface channels. The $\phi_0$-state is proportional to the voltage difference applied between the injector electrode and superconducting terminals that calibrates the injection rate of particles and, therefore, the $\phi_0$ shift.