Robust and fragile Majorana bound states in proximitized topological insulator nanoribbons

TL;DR

This paper models topological insulator nanoribbons with induced superconductivity, revealing conditions for robust Majorana bound states and their experimental signatures, highlighting their potential for topological quantum computing.

Contribution

It provides a detailed modeling of TI nanoribbons with superconductivity, analyzing phase diagrams, disorder effects, and tunneling spectroscopy to identify conditions for stable Majorana states.

Findings

Majorana bound states depend on chemical potential and magnetic flux.

Robust MBSs occur when the Fermi level is near the Dirac point.

Tunneling spectroscopy can detect topological phases and MBSs.

Abstract

Topological insulator (TI) nanoribbons with proximity-induced superconductivity are a promising platform for Majorana bound states (MBSs). In this work, we consider a detailed modeling approach for a TI nanoribbon in contact with a superconductor via its top surface, which induces a superconducting gap in its surface-state spectrum. The system displays a rich phase diagram with different numbers of end-localized MBSs as a function of chemical potential and magnetic flux piercing the cross section of the ribbon. These MBSs can be robust or fragile upon consideration of electrostatic disorder. We simulate a tunneling spectroscopy setup to probe the different topological phases of top-proximitized TI nanoribbons. Our simulation results indicate that a top-proximitized TI nanoribbon is ideally suited for realizing fully gapped topological superconductivity, in particular when the Fermi level is pinned near the Dirac point. In this regime, the setup yields a single pair of MBSs, well separated at opposite ends of the proximitized ribbon, which gives rise to a robust quantized zero-bias conductance peak.