Instability of insulators near quantum phase transitions

TL;DR

This paper investigates the instability of insulating phases near quantum critical points, revealing that large current discontinuities vanish at the transition, indicating a fundamental and general instability in insulators approaching quantum phase transitions.

Contribution

It demonstrates that the onset voltage for current discontinuities vanishes near the quantum critical point, highlighting a universal instability in insulators close to such transitions.

Findings

Onset voltage for discontinuities vanishes near critical point

Insulating phase becomes unstable under any applied voltage near transition

Discontinuous departure from equilibrium observed in the system

Abstract

Thin films of Amorphous indium oxide undergo a magnetic field driven superconducting to insulator quantum phase transition. In the insulating phase, the current-voltage characteristics show large current discontinuities due to overheating of electrons. We show that the onset voltage for the discontinuities vanishes as we approach the quantum critical point. As a result the insulating phase becomes unstable with respect to any applied voltage making it, at least experimentally, immeasurable. We emphasize that unlike previous reports of the absence of linear response near quantum phase transitions, in our system, the departure from equilibrium is discontinuous. Because the conditions for these discontinuities are satisfied in most insulators at low temperatures, and due to the decay of all characteristic energy scales near quantum phase transitions, we believe that this instability is general and should occur in various systems while approaching their quantum critical point. Accounting for this instability is crucial for determining the critical behavior of systems near the transition.