# Chirality blockade of Andreev reflection in a magnetic Weyl semimetal

## TL;DR

This paper investigates how the intrinsic chirality of Weyl fermions in a magnetic Weyl semimetal can block Andreev reflection at a superconductor interface, and how a Zeeman field can restore it.

## Contribution

It introduces the concept of chirality blockade in Weyl semimetals and demonstrates how a Zeeman field can enable Andreev reflection by switching chirality.

## Key findings

- Chirality blockade suppresses Andreev reflection in magnetic Weyl semimetals.
- A Zeeman field can activate Andreev reflection by providing chirality switching.
- Superconducting proximity effect is hindered without external magnetic influence.

## Abstract

A Weyl semimetal with broken time-reversal symmetry has a minimum of two species of Weyl fermions, distinguished by their opposite chirality, in a pair of Weyl cones at opposite momenta $\pm K$ that are displaced in the direction of the magnetization. Andreev reflection at the interface between a Weyl semimetal in the normal state (N) and a superconductor (S) that pairs $\pm K$ must involve a switch of chirality, otherwise it is blocked. We show that this "chirality blockade" suppresses the superconducting proximity effect when the magnetization lies in the plane of the NS interface. A Zeeman field at the interface can provide the necessary chirality switch and activate Andreev reflection.