Topological exciton insulator phase in two-dimensional semiconductor systems*

Exciton insulator was firstly proposed by Prof. Mott in 1961.This concept has been widely studied theoretically and confirmed experimentally in recent years. Here, We demonstrate theoretically the existence of topological exciton insulating phases in two-dimensional (2D) semiconductor systems. We consider two kinds of systems: InAs/GaSb quantum wells [1] and 2D Van der Waals heterostructures[2]. In InAs/GaSb quantum wells, i.e., a 2D topological insulator, we demonstrate theoretically that the ground state of the system is a topological exciton insulator when the Coulomb interaction between electrons and holes is included. For a 2D VdH system, we find that a perpendicular electric field can decrease the bandgap, which even becomes smaller than the exciton binding energy, leading to the formation of exciton insulator phase. Due to large exciton binding energy, the exciton insulator phase in the 2D VdH system could be observed at room temperature.
[1] L.-J. Du, X.-W. Li, W.-K. Lou, G. Sullivan, Kai Chang*, J. Kono,* and Rui Rui Du*, Nature Commun. 8, 1971 (2017) .
[2] W. Lou, W. Yang, Kai Chang, (in preparation)