Nanoscale-femtosecond dielectric response of Mott insulators captured by two-colour near-field ultrafast electron microscopy

TL;DR

This study employs two-colour near-field ultrafast electron microscopy to observe the nanoscale dielectric response of a VO2 nanowire during an insulator-to-metal transition, revealing ultrafast electronic dynamics without lattice perturbation.

Contribution

It introduces a novel method combining femtosecond electron pulses and near-field microscopy to capture ultrafast electronic changes in nanostructured Mott insulators.

Findings

Ultrafast photo-doping induces metallic state in VO2 nanowire within 150 fs.

The electronic transition occurs without immediate lattice disturbance.

The method offers high spatial and temporal resolution for nanoscale material dynamics.

Abstract

Characterizing and controlling the out-of-equilibrium state of nanostructured Mott insulators hold great promises for emerging quantum technologies while providing an exciting playground for investigating fundamental physics of strongly-correlated systems. Here, we use two-colour near-field ultrafast electron microscopy to photo-induce the insulator-to-metal transition in a single VO2 nanowire and probe the ensuing electronic dynamics with combined nanometer-femtosecond resolution. We take advantage of a femtosecond temporal gating of the electron pulse mediated by an infrared laser pulse, and exploit the sensitivity of inelastic electron-light scattering to changes in the material dielectric function. By spatially mapping the near-field dynamics of an individual nanowire of VO2, we observe that ultrafast photo-doping drives the system into a metallic state on a time scale of about 150 fs without yet perturbing the crystalline lattice. Due to the high versatility and sensitivity of the electron probe, our method would allow capturing the electronic dynamics of a wide range of nanoscale materials with ultimate spatio-temporal resolution.