Does VO$_2$ Host a Transient Monoclinic Metallic Phase?

TL;DR

This study reexamines the ultrafast insulator-metal transition in VO$_2$, demonstrating that heat, rather than a nonthermal Mott-Hubbard transition, drives the phase change when properly accounted for, aligning with thermodynamic expectations.

Contribution

The paper clarifies that heat plays a crucial role in the ultrafast phase transition of VO$_2$, challenging previous claims of a nonthermal Mott-Hubbard transition.

Findings

Heat is essential in the ultrafast phase transition of VO$_2$.

No evidence of a hidden nonthermal Mott-Hubbard phase was found.

The transition threshold matches the thermodynamic insulator-metal transition.

Abstract

Ultrafast phase transitions induced by femtosecond light pulses present a new opportunity for manipulating the properties of materials. Understanding how these transient states are different from, or similar to, their thermal counterparts is key to determining how materials can exhibit properties that are not found in equilibrium. In this paper, we reexamine the case of the light-induced insulator-metal phase transition in the prototypical, strongly correlated material VO$_2$, for which a nonthermal Mott-Hubbard transition has been claimed. Here, we show that heat, even on the ultrafast timescale, plays a key role in the phase transition. When heating is properly accounted for, we find a single phase-transition threshold corresponding to the thermodynamic structural insulator-metal phase transition, and we find no evidence of a hidden transient Mott-Hubbard nonthermal phase. The interplay between the initial thermal state and the ultrafast transition may have implications for other transient states of matter.