Non-equilibrium magnetic interactions in strongly correlated systems

TL;DR

This paper develops a low-energy theoretical framework for understanding non-equilibrium magnetic interactions in strongly correlated multi-band systems, incorporating novel twist exchange interactions induced by external electric fields.

Contribution

It introduces a new theoretical approach to describe dynamical magnetic interactions, including a novel twist exchange mechanism, in non-equilibrium multi-band Hubbard models.

Findings

Derived expressions for dynamical exchange parameters using non-equilibrium Green functions.

Identified and characterized a new 'twist exchange' interaction resembling Dzyaloshinskii-Moriya coupling.

Provided a method to compute time-dependent magnetic interaction parameters.

Abstract

We formulate a low-energy theory for the magnetic interactions between electrons in the multi-band Hubbard model under non-equilibrium conditions determined by an external time-dependent electric field which simulates laser-induced spin dynamics. We derive expressions for dynamical exchange parameters in terms of non-equilibrium electronic Green functions and self-energies, which can be computed, e.g., with the methods of time-dependent dynamical mean-field theory. Moreover, we find that a correct description of the system requires, in addition to exchange, a new kind of magnetic interaction, that we name "twist exchange", which formally resembles Dzyaloshinskii-Moriya coupling, but is not due to spin-orbit, and is actually due to an effective three-spin interaction. Our theory allows the evaluation of the related time-dependent parameters as well.