Non-equilibrium phase precursors to the insulator-metal transition in V2O3

TL;DR

This study uncovers ultrafast structural precursors to the insulator-metal transition in V2O3, revealing a transient phase that precedes the full electronic transition, with nanoscale phonons influencing the dynamics.

Contribution

It demonstrates the existence of a non-equilibrium precursor phase in V2O3 and elucidates the role of nanoscale phonons and structural decoupling during the transition.

Findings

Ultrafast enhancement of structural order observed before electronic transition.

Decoupling of symmetry change and volume change in time domain.

Nanoscale phonons govern ultrafast precursor dynamics.

Abstract

The discovery of novel phases of matter is at the core of modern physics. In quantum materials, subtle variations in atomic-scale interactions can induce dramatic changes in macroscopic properties and drive phase transitions. Despite their importance, the mesoscale processes underpinning phase transitions often remain elusive because of the vast differences in timescales between atomic and electronic changes and thermodynamic transformations. Here, we photoinduce and directly observe with x-ray scattering an ultrafast enhancement of the structural long-range order in the archetypal Mott system V2O3. Despite the ultrafast change in crystal symmetry, the change of unit cell volume occurs an order of magnitude slower and coincides with the insulator-to-metal transition. The decoupling between the two structural responses in the time domain highlights the existence of a transient photoinduced precursor phase, which is distinct from the two structural phases present in equilibrium. X-ray nanoscopy reveals that acoustic phonons trapped in nanoscale blocks govern the dynamics of the ultrafast transition into the precursor phase, while nucleation and growth of metallic domains dictate the duration of the slower transition into the metallic phase. The enhancement of the long-range order before completion of the electronic transition demonstrates the critical role the non-equilibrium structural phases play during electronic phase transitions in correlated electrons systems.