Photoinduced phase transitions in narrow-gap Mott insulators: the case of VO$_2$

TL;DR

This paper investigates the ultrafast photoinduced phase transitions in VO$_2$, revealing rapid relaxation to a pseudothermal state and the potential formation of a metastable metallic phase, providing insights into nonequilibrium dynamics in correlated materials.

Contribution

It combines quantum Boltzmann and Hartree-Fock methods to analyze nonequilibrium electron dynamics and predicts a metastable metallic phase in VO$_2$ not accessible in equilibrium.

Findings

Rapid femtosecond relaxation to pseudothermal state

Identification of a metastable M$_1$ metallic phase

Consistency with recent experimental observations

Abstract

We study the nonequilibrium dynamics of photoexcited electrons in the narrow-gap Mott insulator VO$_2$. The initial stages of relaxation are treated using a quantum Boltzmann equation methodology, which reveals a rapid ($\sim$ femtosecond time scale) relaxation to a pseudothermal state characterized by a few parameters that vary slowly in time. The long-time limit is then studied by a Hartree-Fock methodology, which reveals the possibility of nonequilibrium excitation to a new metastable $M_1$ metal phase that is qualitatively consistent with a recent experiment. The general physical picture of photoexcitation driving a correlated electron system to a new state that is not accessible in equilibrium may be applicable in similar materials.