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

We propose a microscopic mechanism to resolve the long-standing puzzle of the insulator-to-metal transition in correlated electronic systems, most notably the large discrepancy between the experimental and predicted switching fields in 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 an 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 the existence of two-stage versus single-stage switching events which we associate with CDW and Mott resistive phase transitions, respectively. The behavior of electron and phonon temperatures, as well as the temperature dependence of the threshold fields, demonstrates how a crossover between the thermal and quantum switching scenarios emerges within a unified framework of the quantum avalanche.