Interlayer excitons in transition metal dichalcogenide heterostructures

TL;DR

This paper develops a comprehensive theoretical model for interlayer excitons in transition metal dichalcogenide heterostructures, analyzing how dielectric environments influence exciton binding energies and optical properties.

Contribution

It introduces a four-band Hamiltonian for interlayer excitons and accounts for complex dielectric and polarization effects, advancing understanding of excitonic behavior in TMD heterostructures.

Findings

Exciton binding energy strongly depends on the dielectric constant of the barrier.

Polarization effects can increase binding energy under certain substrate conditions.

Interlayer exciton peak shifts linearly with perpendicular electric field.

Abstract

Starting from the single-particle Dirac Hamiltonian for charge carriers in monolayer transition metal dichalcogenides (TMDs), we construct a four-band Hamiltonian describing interlayer excitons consisting of an electron in one TMD layer and a hole in the other TMD layer. An expression for the electron-hole interaction potential is derived, taking into account the effect of the dielectric environment above, below, and between the two TMD layers as well as polarization effects in the transition metal layer and in the chalcogen layers of the TMD layers. We calculate the interlayer exciton binding energy and average in-plane interparticle distance for different TMD heterostructures. The effect of different dielectric environments on the exciton binding energy is investigated and a remarkable dependence on the dielectric constant of the barrier between the two layers is found, resulting from competing effects as a function of the in-plane and out-of-plane dielectric constants of the barrier. The polarization effects in the chalcogen layers, which in general reduce the exciton binding energy, can lead to an increase in binding energy in the presence of strong substrate effects by screening the substrate. The excitonic absorbance spectrum is calculated and we show that the interlayer exciton peak depends linearly on a perpendicular electric field, which agrees with recent experimental results.