Universal excitonic superexchange in spin-orbit-coupled Mott insulators

Department of Physics and HKU-UCAS Joint Institute for Theoretical and Computational Physics at Hong Kong, The University of Hong Kong - Hong Kong, China and The University of Hong Kong Shenzhen Institute of Research and Innovation - Shenzhen 518057, China

^(a) gangchen@hku.hk (corresponding author)

Received: 29 May 2022
Accepted: 2 August 2022

Abstract

We point out the universal presence of the excitonic superexchange in spin-orbit-coupled Mott insulators. It is observed that the restriction to the lowest spin-orbit-entangled “J” states may sometimes be insufficient to characterize the microscopic physics, and the virtual excitonic processes via the upper “J” states provide an important correction to the superexchange. We illustrate this excitonic superexchange from a two-dimensional 5d iridate Sr₂IrO₄ and explain its physical consequences such as the orbital-like coupling to the external magnetic flux and the nonlinear magnetic susceptibility. The universal presence of the excitonic superexchange in other spin-orbit-coupled Mott insulators such as 3d Co-based Kitaev magnets and even f electron rare-earth magnets is further discussed.