Optical control of competing exchange interactions and coherent spin-charge coupling in two-orbital Mott insulators

TL;DR

This paper investigates how ultrafast electric fields can control exchange interactions and induce spin-charge coupling in two-orbital Mott insulators, revealing tunable exchange parameters and a novel coherent transfer mechanism.

Contribution

It introduces a generalized time-dependent approach to derive an effective Hamiltonian for two-orbital systems under periodic driving, uncovering new regimes of exchange interaction control and spin-charge coupling.

Findings

Electric fields can modify bilinear and biquadratic exchange interactions.

Enhanced, reduced, or sign-changing exchange interactions depend on driving frequency.

A novel spin-charge coupling enables coherent transfer between spin and charge states.

Abstract

In order to have a better understanding of ultrafast electrical control of exchange interactions in multi-orbital systems, we study a two-orbital Hubbard model at half filling under the action of a time-periodic electric field. Using suitable projection operators and a generalized time-dependent canonical transformation, we derive an effective Hamiltonian which describes two different regimes. First, for a wide range of non-resonant frequencies, we find a change of the bilinear Heisenberg exchange $J_{\textrm{ex}}$ that is analogous to the single-orbital case. Moreover we demonstrate that also the additional biquadratic exchange interaction $B_{\textrm{ex}}$ can be enhanced, reduced and even change sign depending on the electric field. Second, for special driving frequencies, we demonstrate a novel spin-charge coupling phenomenon enabling coherent transfer between spin and charge degrees of freedom of doubly ionized states. These results are confirmed by an exact time-evolution of the full two-orbital Mott-Hubbard Hamiltonian.