Phonon-driven multipolar dynamics in a spin-orbit coupled Mott insulator

TL;DR

This paper explores how resonant phonon excitation influences multipolar order and dynamics in spin-orbit coupled Mott insulators, revealing mechanisms for ultrafast control and probing of hidden multipolar phases.

Contribution

It introduces a theoretical framework combining Monte Carlo and molecular dynamics to study phonon-driven multipolar dynamics in Mott insulators with complex order.

Findings

Resonant ${ m E}_g$ phonon excitation induces multipolar precession.

Coherent two-phonon Floquet drive can switch octupolar order.

Phonon-driven dynamics enable probing hidden multipolar orders.

Abstract

Motivated by advances in pump-probe experiments and light-driven phenomena, we theoretically study the impact of pumped and driven phonons in Mott insulators which host multipole moments, thus going beyond conventional dipolar magnetism. As a case study, we examine pseudospin-1/2 Mott insulators hosting quadrupolar and octupolar moments, and investigate the effect of resonantly exciting ${\cal E}_g$ phonon modes which couple linearly to the quadrupoles. We show that this leads to multipolar precession, with the back action resulting in chiral phonon dynamics below the octupolar phase transition. We further explore the impact of a coherent two-phonon Floquet drive, showing that it can be used to `train' octupolar order or even switch its sign on ultrafast timescales. Our results are obtained combining a generalized Monte Carlo code incorporating phonons with molecular dynamics simulations which numerically integrate the coupled spin-phonon equations of motion. Our work shows how phonon-driven dynamics can be used to probe and control hidden orders in solids.