Local density of states in metal - topological superconductor hybrid systems

TL;DR

This paper investigates the local density of states in semiconductor nanowires coupled to superconductors, revealing how Majorana states and Andreev-bound states behave under various coupling conditions and topological phases.

Contribution

It provides a detailed analysis of Majorana and Andreev states in multi-band nanowires, highlighting effects of interface transmission and topological phase transitions.

Findings

Zero-energy Majorana peaks broaden with increased coupling, eventually disappearing.

Majorana states can persist near topological transitions even with an even number of channels.

The topological nature can be distinguished by zero-energy crossings in Andreev spectra.

Abstract

We study by means of the recursive Green's function technique the local density-of-states of (finite and semi-infinite) multi-band spin-orbit coupled semiconducting nanowires in proximity to an s-wave superconductor and attached to normal-metal electrodes. When the nanowire is coupled to a normal electrode, the zero-energy peak, corresponding to the Majorana state in the topological phase, broadens with increasing transmission between the wire and the leads, eventually disappearing for ideal interfaces. Interestingly, for a finite transmission a peak is present also in the normal electrode, even though it has a smaller amplitude and broadens more rapidly with the strength of the coupling. Unpaired Majorana states can survive close to a topological phase transition even when the number of open channels (defined in the absence of superconductivity) is even. We finally study the Andreev-bound-state spectrum in superconductor-normal metal-superconductor junctions and find that in multi-band nanowires the distinction between topologically trivial and non-trivial systems based on the number of zero-energy crossings is preserved.