Probing quantum geometry through optical conductivity and magnetic circular dichroism

TL;DR

This paper demonstrates how optical conductivity and magnetic circular dichroism measurements can effectively probe the quantum geometry and topology of antiferromagnetic topological insulator MnBi₂Te₄ thin films, revealing enhanced dichroism and quantum weight.

Contribution

It introduces a first-principles approach to connect optical responses with ground-state quantum geometry and topology in MnBi₂Te₄ thin films, highlighting the potential of optical methods for such investigations.

Findings

Enhanced magnetic circular dichroism in MnBi₂Te₄ thin films.

Quantum weight exceeds the Chern number lower bound.

Optical methods effectively probe quantum geometry and topology.

Abstract

Probing ground-state quantum geometry and topology through optical response is not only of fundamental interest, but it can also offer several practical advantages. Here, using first-principles calculations on antiferromagnetic topological insulator MnBi$_2$Te$_4$ thin films, we demonstrate how the generalized optical weight arising from the absorptive part of the optical conductivity can be used to probe the ground state quantum geometry and topology. We show that three septuple layers MnBi$_2$Te$_4$ exhibit an enhanced almost perfect magnetic circular dichroism for a narrow photon energy window in the infrared region. We calculate the quantum weight in a few septuple layers MnBi$_2$Te$_4$ and show that it far exceeds the lower bound provided by the Chern number. Our results suggest that the well-known optical methods are powerful tools for probing the ground state quantum geometry and topology.