Chiral excitonic systems in twisted bilayers from F\"{o}rster coupling and unconventional excitonic Hall effects

TL;DR

This paper develops a theoretical framework for chiral excitonic systems in twisted bilayer semiconductors, revealing unconventional Hall effects driven by quantum geometric properties of hybridized exciton states.

Contribution

It introduces a general effective exciton Hamiltonian incorporating F"{o}rster coupling and demonstrates novel Hall effects in twisted bilayer systems.

Findings

Chiral excitonic systems can exhibit unconventional Hall effects.

Quantum geometric properties influence exciton transport.

Layer hybridization leads to unique counterflow phenomena.

Abstract

In twisted bilayer semiconductors with arbitrary twisting angles, a chiral excitonic system can arise from the interlayer electron-hole Coulomb exchange interaction (F\"{o}rster coupling) that hybridizes the anisotropic intralayer excitons from individual layers. We present a general framework for the effective exciton Hamiltonian taking into account the electron-hole Coulomb exchange, using twisted homobilayer systems composed of transition metal dichalcogenides or black phosphorus as examples. We demonstrate that such chiral excitonic systems can feature unconventional Hall (Nernst) effects arising from quantum geometric properties characteristic of the layer hybridized wavefunctions under the chiral symmetry, for example, the time-reversal even layer Hall counter flow and the crossed nonlinear dynamical Hall effect, when mechanical and statistical force (temperature or density gradient) drives the exciton flow.