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

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.

Strong photoluminescence enhancement in indirect bandgap MoSe$_2$ nanophotonic resonator

“…Another way to solve this problem is to use the Purcell effect to brighten multilayered TMDCs. 31,32 This approach was successfully used to brighten Si in optical cavities. [33][34][35][36] Although due to strong free charge carriers absorption in Si, the effect was not game-changing.…”

Gate tunable light-matter interaction in natural biaxial hyperbolic van der Waals heterostructures

“…Extensive research on van der Waals (vdW) crystals [2,4,5], supporting PhPs and PPs, have demonstrated inherent hyperbolic anisotropy and their applications in various nanophotonic devices such as infrared optical components [6][7][8], thermal emitters [9], enhanced spontaneous emission rate (SER) [10], and others [11]. In particular, anisotropic spontaneous emission rate [12,13], associated with Purcell effect [14], has great relevance for applications to light sources [10,15], quantum interference [13,16], Kerr nonlinearity enhancement [17], selective coupling to dark and bright excitons and others [18,19]. However, tunability and anisotropy of PhPs over large operational bandwidth in conventional vdW materials [2] are major limitations for enhanced anisotropic SER applications.…”