# Evidence for topological contribution to spin shift current in antiferromagnetic Ti[image]C[image]

## TL;DR

This paper shows that a topological effect contributes to a type of photocurrent in a magnetic material, even when symmetry is broken.

## Contribution

The study provides first-principles evidence of a reverting Thouless pump in a centrosymmetric antiferromagnetic material.

## Key findings

- Antiferromagnetic Ti4C3 shows a giant spin-resolved shift current despite broken inversion symmetry.
- The material hosts mid-gap edge states and is classified as a fragile topological insulator.
- Perturbations destroy quantization of the topological invariant but do not eliminate the photocurrent.

## Abstract

The shift current is a non-linear photocurrent generally associated with the underlying quantum geometry. However, a topological origin for the shift photocurrent in non-centrosymmetric systems has recently been proposed. The corresponding topological classification goes beyond the ten-fold paradigm and is associated with the presence of a reverting Thouless pump (RTP). In this work we perform a first-principles computational analysis of antiferromagnetic monolayer within the family of MXenes, Ti\documentclass[12pt]{minimal}
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\begin{document}$$_{3}$$\end{document}. This material is centrosymmetric, however, magnetic ordering violates inversion symmetry. We demonstrate evidence of an RTP in each spin-sector which has been perturbed, destroying quantization of the invariant. Nevertheless, a giant spin-resolved shift current persists. We further investigate the mid-gap edge states and classification of the system as a fragile topological insulator to which trivial bands have been coupled.