Mott Transition in VO ₂ Revealed by Infrared Spectroscopy and Nano-Imaging

TLDR

Electrons in correlated insulators are prevented from conducting by Coulomb repulsion, and when an insulator‑to‑metal transition is induced by doping or heating, the resulting conducting state can differ radically from conventional metals. The study reports on the temperature‑induced metallic state of vanadium dioxide and establishes an experimental framework for probing nanoscale charge dynamics in other inhomogeneous correlated electron systems. Scanning near‑field infrared microscopy directly images nanoscale metallic puddles that appear at the onset of the insulator‑to‑metal transition. The combined infrared spectroscopy data reveal a Mott transition characterized by divergent quasiparticle mass within the metallic puddles.

Abstract

Electrons in correlated insulators are prevented from conducting by Coulomb repulsion between them. When an insulator-to-metal transition is induced in a correlated insulator by doping or heating, the resulting conducting state can be radically different from that characterized by free electrons in conventional metals. We report on the electronic properties of a prototypical correlated insulator vanadium dioxide in which the metallic state can be induced by increasing temperature. Scanning near-field infrared microscopy allows us to directly image nanoscale metallic puddles that appear at the onset of the insulator-to-metal transition. In combination with far-field infrared spectroscopy, the data reveal the Mott transition with divergent quasi-particle mass in the metallic puddles. The experimental approach used sets the stage for investigations of charge dynamics on the nanoscale in other inhomogeneous correlated electron systems.