Optical Absorption by Indirect Excitons in a Transition Metal Dichalcogenide Double Layer

TL;DR

This paper models the optical properties of indirect excitons in TMDC double layers separated by h-BN, providing theoretical predictions for binding energies, transition energies, and absorption characteristics as a function of interlayer separation.

Contribution

It offers a comprehensive theoretical framework for calculating optical properties of indirect excitons in TMDC heterostructures using the Keldysh potential, including bounds based on material parameters.

Findings

Absorption coefficient varies with interlayer separation.

Binding energies depend on material parameters and separation.

Predictions are suitable for experimental verification via two-photon spectroscopy.

Abstract

We calculate the binding energy, transition energies, oscillator strength, and absorption coefficient of indirect excitons in transition metal dichalcogenide (TMDC) double layers separated by an integer number of hexagonal boron nitride (h-BN) monolayers. The absorption factor, a dimensionless quantity which gives the fraction of incoming photons absorbed by the indirect excitons in the double layer, is evaluated. The aforementioned optical quantities are obtained for transitions from the ground state to the first two excited states. All quantities are studied as a function of the interlayer separation, which may be experimentally controlled by varying the number of h-BN monolayers between the TMDC layers. Calculations are performed by using the exciton wave function and eigenenergies obtained for the Keldysh potential. For each material, we choose a combination of the exciton reduced mass and the dielectric screening length from the existing literature which give the largest and the smallest indirect exciton binding energy. These combinations of material parameters provide upper and lower bounds on all quantities presented. Our findings can be examined experimentally via two-photon spectroscopy.