Influence of disorder on antidot vortex Majorana states in 3D topological insulators

TL;DR

This study numerically explores how disorder, chemical potential, and antidot size influence Majorana vortex states in topological insulator/superconductor heterostructures, revealing non-monotonic spectral gap behavior and tunability via gate voltage.

Contribution

It introduces a large-scale numerical model to analyze disorder effects on Majorana vortex states in 3D topological insulators, providing insights into device design for quantum computing.

Findings

Spectral gap shows non-monotonic dependence on disorder strength.

Gate voltage can tune the vortex subgap spectrum.

Disorder and antidot size critically affect Majorana mode stability.

Abstract

Topological insulator/superconductor two-dimensional heterostructures are promising candidates for realizing topological superconductivity and Majorana modes. In these systems, a vortex pinned by a pre-fabricated antidot in the superconductor can host Majorana zero-energy modes (MZMs), which are exotic quasiparticles that may enable quantum information processing. However, a major challenge is to design devices that can manipulate the information encoded in these MZMs. One of the key factors is to create small and clean antidots, so the MZMs, localized in the vortex core, have a large gap to other excitations. If the antidot is too large or too disordered, the level spacing for the subgap vortex states may become smaller than temperature. In this paper, we numerically investigate the effects of disorder, chemical potential, and antidot size on the subgap vortex spectrum, using a two-dimensional effective model of the topological insulator surface. Our model allows us to simulate large system sizes with vortices up to 1.8 $\mu$m in diameter (with a 6 nm lattice constant). We also compare our disorder model with the transport data from existing experiments. We find that the spectral gap can exhibit a non-monotonic behavior as a function of disorder strength, and that it can be tuned by applying a gate voltage.