Andreev spectroscopy of Majorana states in topological superconductors with multipocket Fermi surfaces

TL;DR

This paper investigates how multiband Fermi surface topology influences Majorana states in topological superconductors, using Andreev spectroscopy and quantum waveguide theory to relate Fermi surface changes to Majorana mode variations.

Contribution

It demonstrates that Fermi surface topology critically determines the number of Majorana states, with a theoretical framework linking band structure parameters to observable conductance signatures.

Findings

Number of Majorana modes varies with Fermi surface topology.

Andreev conductance reflects changes in Majorana states.

Quantum waveguide theory accurately predicts Majorana count.

Abstract

The topological properties of a multiband topological superconductor in two dimensions are studied, when the latter is obtained by introducing electron pairing in an otherwise topological insulator. The type of pairing, doping and Fermi surface topology play an essential role. Considering the Andreev reflection problem, we use a previously developed quantum waveguide theory for multiorbital systems and find that, when the Fermi surface has several pockets, this theory retrieves the correct number of Majorana fermion states as predicted by the topological index. By varying band structure parameters, the Fermi surface topology of the normal phase can be made to change, whereby the number of Majorana modes also varies. We calculate the effect of such transitions on the Andreev differential conductance.