Optimal condition to probe strong coupling of two-dimensional excitons and zero-dimensional cavity modes

TL;DR

This paper identifies the optimal spatial extent of 2D materials for maximizing strong exciton-cavity coupling, revealing counterintuitive effects and practical considerations for experimental setups.

Contribution

It introduces a calculation of radiation-matter coupling for 2D excitons and 0D cavities, showing an optimal monolayer size for strong coupling, challenging traditional models.

Findings

Optimal monolayer size maximizes coupling strength.

Near zero detuning suppresses transmission efficiency.

Counterintuitive relationship between monolayer size and oscillator strength.

Abstract

The light-matter interaction associated with a two-dimensional (2D) excitonic transition coupled to a zero-dimensional (0D) photonic cavity is fundamentally different from coupling localized excitations in quantum dots or color centers, which have negligible spatial extent compared to the cavity-confined mode profile. By calculating the radiation-matter coupling of the exciton transition of a surface deposited 2D material and a 0D photonic crystal nanobeam mode, we found that there is an optimal spatial extent of the monolayer material that maximizes such an interaction strength due to the competition between minimizing the excitonic envelope function area and maximizing the total integrated field. This is counter to the intuition from the Dicke model, where the oscillator strength is expected to monotonically grow with the number of oscillators, which correlates to the monolayer area assuming the excitonic wavefunction is delocalized over the entire quantum well. We also found that at near zero exciton-cavity detuning, the direct transmission efficiency of a waveguide-integrated cavity can be severely suppressed, which suggests performing experiments by using a side-coupled cavity to get better performances.