Spin-orbit coupling and electronic charge effects in Mott insulators

TL;DR

This paper derives effective charge and current operators in Mott insulators with spin-orbit coupling, revealing new electronic mechanisms for multiferroicity driven by geometric frustration and magnetic orderings.

Contribution

It introduces a theoretical framework for understanding electronic contributions to multiferroic behavior in strongly correlated systems with spin-orbit effects.

Findings

Spin-orbit coupling modifies charge density operators.

Electronic mechanisms for multiferroicity are demonstrated.

Geometric frustration enhances spin-charge coupling effects.

Abstract

We derive the effective charge- and current-density operators for the strong-coupling limit of a single-band Mott insulator in the presence of spin-orbit coupling and show that the spin-orbit contribution to the effective charge density leads to novel mechanisms for multiferroic behavior. In some sense, these mechanisms are the electronic counterpart of the ionic-based mechanisms, which have been proposed for explaining the electric polarization induced by spiral spin orderings. The new electronic mechanisms are illustrated by considering cycloidal and proper screw magnetic orderings on sawtooth and kagome lattices. As for the isotropic case, geometric frustration is crucial for achieving this purely electronic coupling between spin and charge degrees of freedom.