Monoclinic and Correlated Metal Phase in VO_2 as Evidence of the Mott Transition: Coherent Phonon Analysis

TL;DR

This study uses femtosecond pump-probe measurements to identify a monoclinic correlated metal phase in VO_2, providing evidence for a Mott transition distinct from structural changes.

Contribution

It reveals a photo-induced Mott transition in VO_2 characterized by a distinct intermediate phase, supported by coherent phonon analysis.

Findings

Identification of a monoclinic correlated metal phase between MIT and SPT.

Evidence of Mott transition driven by photo-assisted hole excitation.

Sequential phase transitions involving non-equilibrium states.

Abstract

In femtosecond pump-probe measurements, the appearance of coherent phonon oscillations at 4.5 THz and 6.0 THz indicating the rutile metal phase of VO_2 does not occur simultaneously with the first-order metal-insulator transition (MIT) near 68^oC. The monoclinic and correlated metal(MCM) phase between the MIT and the structural phase transition (SPT) is generated by a photo-assisted hole excitation which is evidence of the Mott transition. The SPT between the MCM phase and the rutile metal phase occurs due to subsequent Joule heating. The MCM phase can be regarded as an intermediate non-equilibrium state.