Evidence for topological origin of large spin-shift current in antiferromagnetic Ti$_{4}$C$_{3}$

TL;DR

This study reveals a giant spin-resolved shift current in antiferromagnetic Ti$_{4}$C$_{3}$ MXene, linked to a topological origin involving a reverting Thouless pump, despite the material's centrosymmetry and broken inversion symmetry.

Contribution

It provides evidence of a topological origin for the large spin-shift current in an antiferromagnetic MXene, introducing a new perspective on topological classification beyond the ten-fold way.

Findings

Presence of a reverting Thouless pump in each spin sector.

Persistence of a giant spin-resolved shift current despite perturbations.

Identification of the system as a fragile topological insulator.

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 examine an antiferromagnetic monolayer within the family of MXenes, Ti$_{4}$C$_{3}$. 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.