Electrical Breakdown of Excitonic Insulator

Yuelin Shao, Xi Dai

Published 2023-02-15Version 1

The intrinsic electrical breakdown of normal insulators is usually attributed to inter-band Zener tunneling. This occurs when the gate voltage reaches the same level as the bandgap. As a result, the Zener critical field is inversely proportional to the size of the system. However, when the electrical field is strong enough to disrupt excitons, an excitonic insulator will also break down, as its insulation is due to the pairing of free electrons and holes. Unlike the Zener mechanism, the pair-breaking critical field has little dependence on system size and has a finite value in the thermodynamic limit. To understand the relationship between these two mechanisms, a Hartree Fock calculation that takes into account polarization was performed on a 2D bilayer model. Phase diagrams were generated as a function of electrical field, system size, and exciton density. The results showed that, at the large scale (low exciton density) limit, the breakdown is dominated by Zener tunneling and transitions smoothly to the pair-breaking case as the system size decreases (exciton density increases). This provides a straightforward way to distinguish excitonic insulators from normal insulators.