Andreev bound states and current-phase relations in three-dimensional topological insulators

TL;DR

This paper theoretically investigates superconductor/topological insulator/superconductor junctions, revealing how Majorana states influence Andreev bound states and Josephson effects, and proposing ways to observe these phenomena experimentally.

Contribution

It demonstrates that 4pi periodic Andreev bound states can be observed in 3D topological insulators with magnetic layers, even at high electron densities.

Findings

Double periodicity of ABS due to Majorana states can persist at high densities.

Magnetization tuning controls the Josephson gap size.

4pi periodic ABS observable with magnetic layers in 3DTIs.

Abstract

To guide the search for the Majorana fermion, we theoretically study superconductor/topological/superconductor (S/TI/S) junctions in an experimentally relevant regime. We find that the striking features present in these systems, including the doubled periodicity of the Andreev bound states (ABSs) due to tunneling via Majorana states, can still be present at high electron densities. We show that via the inclusion of magnetic layers, this 4pi periodic ABS can still be observed in three-dimensional topological insulators, where finite angle incidence usually results in the opening of a gap at zero energy and hence results in a 2pi periodic ABS. Furthermore, we study the Josephson junction characteristics and find that the gap size can be controlled and decreased by tuning the magnetization direction and amplitude. These findings pave the way for designing experiments on S/3DTI/S junctions.