Excitonic Instability and Origin of the Mid-Gap States

TL;DR

This paper models how doping in semiconductors can induce an excitonic insulator phase and generate mid-gap states due to strong exciton-electron interactions, expanding understanding of electronic phase transitions.

Contribution

It provides a self-consistent two-band model for excitonic transitions in doped 2D semiconductors, highlighting the role of interactions in stabilizing new electronic states.

Findings

Doping can induce excitonic phases in initially stable semiconductors.

Strong exciton-electron interactions lead to mid-gap states.

The model predicts excitonic transitions in 2D systems.

Abstract

In the framework of the two-band model of a doped semiconductor the self-consistent equations describing the transition into the excitonic insulator state are obtained for the 2D case. It is found that due to the exciton-electron interactions the excitonic phase may arise with doping in a semiconductor stable initially with respect to excitonic transition in the absence of doping. The effects of the strong interactions between electron (hole) Fermi-liquid (FL) and excitonic subsystems can lead to the appearance of the states lying in the middle of the insulating gap.