Softening of the insulating phase near Tc for the photo-induced insulator-to-metal phase transition in vanadium dioxide

TL;DR

This study investigates how the insulator-to-metal transition in vanadium dioxide becomes easier near the critical temperature due to phase coexistence, using optical-pump terahertz-probe spectroscopy and a dynamic effective medium model.

Contribution

It provides new insights into the softening of the insulating phase near Tc and models the transition dynamics with a Bruggeman effective medium approach.

Findings

Reduced fluence needed for transition near Tc

Phase coexistence facilitates homogeneous metallic phase growth

Effective medium model describes initial condition sensitivity

Abstract

We use optical-pump terahertz-probe spectroscopy to investigate the near-threshold behavior of the photoinduced insulator-to-metal (IM) transition in vanadium dioxide thin films. Upon approaching Tc a reduction in the fluence required to drive the IM transition is observed, consistent with a softening of the insulating state due to an increasing metallic volume fraction (below the percolation limit). This phase coexistence facilitates the growth of a homogeneous metallic conducting phase following superheating via photoexcitation. A simple dynamic model using Bruggeman effective medium theory describes the observed initial condition sensitivity.