Observability of surface Andreev bound states in a topological insulator in proximity to an s-wave superconductor

TL;DR

This paper investigates the superconducting pairing symmetries in topological insulators coupled with s-wave superconductors, highlighting the role of odd-frequency pairing in the emergence of Majorana zero-energy modes and their experimental signatures.

Contribution

It establishes a theoretical link between odd-frequency pairing and Majorana modes in 3D topological insulators, guiding experimental detection via tunneling conductance.

Findings

Odd-frequency pairing correlates with Majorana zero modes.

Tunneling conductance shapes reveal pairing symmetry regimes.

Ferromagnetic insulators are necessary to localize Majorana modes.

Abstract

To guide experimental work on the search for Majorana zero-energy modes, we calculate the superconducting pairing symmetry of a three-dimensional topological insulator in combination with an s-wave superconductor. In analogy to the case of nanowires with strong spin-orbit coupling we show how the pairing symmetry changes across different topological regimes. We demonstrate that a dominant p-wave pairing relation is not sufficient to realize a Majorana zero-energy mode useful for quantum computation. Our main result of this paper is the relation between odd-frequency pairing and Majorana zero energy modes by using Green functions techniques in three-dimensional topological insulators in the so-called Majorana regime. We discuss thereafter how the pairing relations in the different regimes can be observed in the shape of the tunneling conductance of an s-wave proximized three-dimensional topological insulator. We will discuss the necessity to incorporate a ferromagnetic insulator to localize the zero-energy bound state to the interface as a Majorana mode.