Tunneling Breakdown of a Strongly Correlated Insulating State in VO$_2$ Induced by Intense Multi-Terahertz Excitation

TL;DR

This study demonstrates that intense multi-terahertz fields can induce a non-thermal insulator-to-metal transition in VO$_2$ through a tunneling process analogous to the Schwinger effect, revealing a new ultrafast control mechanism for correlated materials.

Contribution

It provides direct experimental evidence of THz field-induced tunneling causing a metastable metallic state in VO$_2$, linking condensed matter phenomena with quantum electrodynamics concepts.

Findings

Non-thermal switching governed by THz field amplitude.

No excitonic self-trapping signatures below threshold.

Good agreement with pair production formula using electronic correlation length.

Abstract

We directly trace the near- and mid-infrared transmission change of a VO$_2$ thin film during an ultrafast insulator-to-metal transition triggered by high-field multi-terahertz transients. Non-thermal switching into a metastable metallic state is governed solely by the amplitude of the applied terahertz field. In contrast to resonant excitation below the threshold fluence, no signatures of excitonic self-trapping are observed. Our findings are consistent with the generation of spatially separated charge pairs and a cooperative transition into a delocalized metallic state by THz field-induced tunneling. The tunneling process is a condensed-matter analogue of the Schwinger effect in nonlinear quantum electrodynamics. We find good agreement with the pair production formula by replacing the Compton wavelength with an electronic correlation length of 2.1 $\AA$.