Engineering Purcell factor anisotropy for dark and bright excitons in two dimensional semiconductors

TL;DR

This paper proposes a method to enhance the interaction of dark excitons in 2D semiconductors with cavity modes by engineering Purcell factor anisotropy, enabling better optical access at room temperature.

Contribution

It introduces a novel approach to selectively couple out-of-plane exciton dipoles to cavity modes using tapered silica micro-disks, improving dark exciton accessibility.

Findings

Numerical simulations show effective selective coupling of out-of-plane dipoles.

Tapered micro-disk design enhances Purcell factor anisotropy.

Method applicable to various transition metal dichalcogenides.

Abstract

Tightly bound dark excitons in atomically thin semiconductors can be used for various optoelectronic applications including light storage and quantum communication. Their optical accessibility is however limited due to their out-of-plane transition dipole moment. We thus propose to strengthen the coupling of dark excitons in two dimensional materials with out-of-plane resonant modes of a cavity at room temperature, by engineering the anisotropy in the Purcell factor. A silica micro-disk characterised by high confinement of light in small modal volume, high Q-factor and free spectral range is used to couple to the excitons in monolayer transition metal dichalcogenides. We show numerically that the tapering of sidewalls of the micro-disk is an extremely versatile route for achieving the selective coupling of whispering gallery modes to light emitted from out-of-plane dipoles to the detriment of that from in-plane ones for four representative monolayer transition metal dichalcogenides.