Correlated Insulator Collapse due to Quantum Avalanche via In-Gap Ladder States

TL;DR

This paper introduces a microscopic quantum avalanche mechanism involving in-gap ladder states that explains the insulator-to-metal transition in correlated materials under electric fields, highlighting the role of multi-phonon processes.

Contribution

It presents a novel quantum avalanche model with in-gap ladder states to explain insulator collapse in correlated systems under electric fields.

Findings

Electron avalanche can occur at arbitrarily small electric fields.

In-gap ladder states are created by multi-phonon emission.

Phonon spectrum influences the transition mechanism (single or two-stage).

Abstract

We propose a microscopic mechanism to resolve the long-standing puzzle of the insulator-to-metal transition in correlated electronic systems, most notably charge-density-wave (CDW) materials and Mott insulators, driven far-from-equilibrium by a DC electric field. By introducing a generic model of electrons coupled to an inelastic medium of phonons, we demonstrate that an electron avalanche can occur in the bulk limit of such insulators at arbitrarily small electric field. The quantum avalanche arises by the generation of a ladder of in-gap states, created by a multi-phonon emission process. Hot-phonons in the avalanche trigger a premature and partial collapse of the correlated gap. The details of the phonon spectrum dictate two-stage versus single-stage mechanisms which we associate with CDW and Mott resistive transitions, respectively. The electron and phonon temperatures, as well as the temperature dependence of the threshold fields, point to the quantum nature of this nonequilibrium phase transition.