Correlation-driven insulator-metal transition in near-ideal vanadium dioxide films

TL;DR

This study reveals that in strained VO2 films, the insulator-metal transition is driven by electronic correlation softening within V-V dimers, occurring just below the transition temperature and preceding structural changes.

Contribution

It demonstrates that Coulomb correlation softening within V-V dimers drives the insulator-metal transition in strained VO2, highlighting an electronic precursor to structural transformation.

Findings

Electronic softening begins 7 K below transition temperature.

Transition involves collapse of insulating gap and symmetry change.

Electronic correlations are key to the insulator-metal transition.

Abstract

We use polarization- and temperature-dependent x-ray absorption spectroscopy, in combination with photoelectron microscopy, x-ray diffraction and electronic transport measurements, to study the driving force behind the insulator-metal transition in VO2. We show that both the collapse of the insulating gap and the concomitant change in crystal symmetry in homogeneously strained single-crystalline VO2 films are preceded by the purely-electronic softening of Coulomb correlations within V-V singlet dimers. This process starts 7 K (+/- 0.3 K) below the transition temperature, as conventionally defined by electronic transport and x-ray diffraction measurements, and sets the energy scale for driving the near-room-temperature insulator-metal transition in this technologically-promising material.