Majorana bound states in topological insulators without a vortex

TL;DR

This paper demonstrates that Majorana bound states can be realized in topological insulator wires without vortices, by using inhomogeneous chemical potential and magnetic fields, simplifying experimental setups.

Contribution

It introduces a new method to generate Majorana bound states in topological insulator wires without requiring superconducting vortices, broadening experimental feasibility.

Findings

Majorana bound states appear at wire ends under specific conditions.

Inhomogeneous chemical potential lifts subband degeneracy.

Magnetic fields induce topological phase transition at weak fields.

Abstract

We consider a three-dimensional topological insulator (TI) wire with a non-uniform chemical potential induced by gating across the cross-section. This inhomogeneity in chemical potential lifts the degeneracy between two one-dimensional surface state subbands. A magnetic field applied along the wire, due to orbital effects, breaks time-reversal symmetry and lifts the Kramers degeneracy at zero-momentum. If placed in proximity to an $s$-wave superconductor, the system can be brought into a topological phase at relatively weak magnetic fields. Majorana bound states (MBSs), localized at the ends of the TI wire, emerge and are present for an exceptionally large region of parameter space in realistic systems. Unlike in previous proposals, these MBSs occur without the requirement of a vortex in the superconducting pairing potential, which represents a significant simplification for experiments. Our results open a pathway to the realisation of MBSs in present day TI wire devices.