Excitonic gap formation in neutral bilayer structures

TL;DR

This paper investigates excitonic gap formation in neutral bilayer structures using a Hubbard model, revealing the coexistence of Frenkel and Wannier-Mott excitons, and analyzing effects of Coulomb interactions, hopping asymmetry, and temperature.

Contribution

It introduces a detailed analysis of excitonic pairing mechanisms in bilayer systems, highlighting the roles of Coulomb interactions and hopping asymmetry without external fields.

Findings

Presence of both Frenkel and Wannier-Mott excitons in the system.

Distinct chemical potential behavior at low temperatures for Frenkel pairing.

Influence of inter-plane hopping and temperature on excitonic gap formation.

Abstract

We consider the pairing between conduction band electrons, and the valence band holes in the neutral bilayer-type structures. By employing the bilayer Hubbard model, we show the possibility of the inter-plane exciton formation in the system without applied external field. The in-plane and inter-plane Coulomb interaction effects on the pairing mechanism are considered, and the role of the in-plane particle hopping asymmetry on the gap behavior is analyzed in the paper. We show that both Frenkel-type pairing channel and Wannier-Mott-type excitonic pairings are present in the considered system. We analyze also the structure of the chemical potential in the bilayer system. The temperature effects, and the tunable inter-plane electron hopping effects are discussed. For the Frenkel channel, we have shown a particular behavior of the chemical potential at the very low temperatures, which is related to the degenerated Frenkel-gap.