Majorana-Weyl crossings in topological multi-terminal junctions

TL;DR

This paper predicts a topologically protected crossing in the Andreev spectrum of a four-terminal topological superconductor junction, detectable via quantized transconductance, expanding understanding of topology in multi-terminal Josephson devices.

Contribution

It demonstrates the existence of a topologically protected crossing in the Andreev spectrum of multi-terminal junctions, a novel feature in topological superconducting systems.

Findings

Protected crossing in Andreev spectrum identified

Quantized transconductance as detection method proposed

Potential realizations with nanowires and quantum-spin Hall insulators discussed

Abstract

We analyze the Andreev spectrum in a four-terminal Josephson junction between one-dimensional topological superconductors in class D. We find that a topologically protected crossing in the space of three superconducting phase differences can occur between the two lowest Andreev bound states. This crossing can be detected through the transconductance quantization, in units of $2e^2/h$, between two voltage-biased terminals. Our prediction provides yet another example of topology in multi-terminal Josephson junctions. We discuss possible realizations of such junctions with semiconducting crossed nanowires and with quantum-spin Hall insulators.