Collective and separate metal-insulator transitions in correlated vanadium dioxide

TL;DR

This study demonstrates reversible control over collective and separate metal-insulator transitions in VO2 systems through ionic manipulation, enabling dynamic tuning of electronic phases for advanced correlated electronic devices.

Contribution

It introduces a method to actively manipulate the collective and separate MIT in VO2 by ionic control, transforming the collective length scale into a design parameter.

Findings

Artificial oxygen deficiency extends the collective MIT length scale.

TiO2 interlayer induces a crossover to a two-step separate MIT.

Hydrogen incorporation enables reversible multi-state MIT control.

Abstract

Deciphering the complicated interplay between collective and separate behaviors lies at the heart of first-order metal-insulator transition (MIT) in correlated electron systems, enabling the rational design of exotic electronic states and functionalities. The critical balance between collective and separate behaviors defines a fundamental collective length scale, typically shorter than 5 nm, that governs emergent quantum orders, yet active control over this dichotomy remains elusive. Here, we realize on-demand manipulation of the collective and separate MIT within the correlated VO2 system in a reversible fashion. Artificially designing the oxygen deficiency in VO2/VO2-x homojunction fosters a collective MIT with an extended collective length scale, whereas the introduction of a TiO2 interlayer drives a crossover from this collective to a two-step separate MIT via decoupling of the electronic order parameter. Incorporating mobile hydrogens into the VO2/TiO2/VO2-x trilayer enables reversible control over electronic phase modulations, transitioning a two-step MIT towards either a one-step MIT or collective electron localization. This ionic control over the electronic band structure of VO2 flexibly triggers multi-state MIT, a process governed by hydrogen-related band filling. Our findings transform the collective length scale from a passive threshold into a dynamic design parameter, establishing a viable handle for engineering collective and separate MIT for adaptive correlated electronics.