Tunable hybridization of Majorana bound states at the quantum spin Hall edge

TL;DR

This paper explores how the interplay of magnetic and superconducting regions at the edge of a topological insulator can be tuned to control the formation and hybridization of Majorana and Andreev bound states, with implications for quantum information.

Contribution

It introduces a method to manipulate Majorana and Andreev bound states via magnetization direction and superconducting phase, revealing their local and nonlocal pairing properties.

Findings

Hybridization of bound states can be controlled by magnetization and phase differences.

Pairing symmetry reveals the nature of the bound states.

Local density of states correlates with nonlocal pairing amplitudes.

Abstract

Confinement at the helical edge of a topological insulator is possible in the presence of proximity-induced magnetic (F) or superconducting (S) order. The interplay of both phenomena leads to the formation of localized Majorana bound states (MBS) or likewise (under certain resonance conditions) the formation of ordinary Andreev bound states (ABS). We investigate the properties of bound states in junctions composed of alternating regions of F or S barriers. Interestingly, the direction of magnetization in F regions and the relative superconducting phase between S regions can be exploited to hybridize MBS or ABS at will. We show that the local properties of MBS translate into a particular nonlocal superconducting pairing amplitude. Remarkably, the symmetry of the pairing amplitude contains information about the nature of the bound state that it stems from. Hence, this symmetry can in principle be used to distinguish MBS from ABS, owing to the strong connection between local density of states and nonlocal pairing in our setup.