Excitonic resonances in the 2D extended Falicov-Kimball model

TL;DR

This study uses a renormalization method to explore excitonic insulator phases and bound states in a 2D Falicov-Kimball model, revealing conditions for exciton formation and stability at high temperatures.

Contribution

It demonstrates the existence of excitonic insulator phases and bound states in a 2D lattice model with local Coulomb attraction using a projector-based renormalization approach.

Findings

Confirmed the existence of excitonic insulator phase.

Identified excitonic resonances in the band gap.

Analyzed temperature effects on exciton stability.

Abstract

Using the projector-based renormalization method we investigate the formation of the excitonic insulator phase in the two-dimensional (2D) spinless Falicov-Kimball model with dispersive $f$ electrons and address the existence of excitonic bound states at high temperatures on the semiconductor side of the semimetal-semiconductor transition. To this end we calculate the imaginary part of the dynamical electron-hole pair susceptibility and analyze the wave-vector and energy dependence of excitonic resonances emerging in the band gap. We thereby confirm the existence of the exciton insulator and its exciton environment within a generic two-band lattice model with local Coulomb attraction.