Simulations of plasmon-mediated superradiance for molecules in STM-based nanocavity

Scanning tunnelling microscopy (STM) can be considered as a kind of nanocavity due to its structure of a metallic tip and substrate, where the interaction between molecular clusters and plasmons can be controlled by moving the tip, thus changing the level of radiation. In this article, we apply the semi-classical method by combining macroscopic quantum electrodynamics theory with open quantum systems theory, to calculate the transient radiation of molecules arranged horizontally and vertically in the nanocavity. Our calculations show that the free-space field-mediated coherent coupling in the former case is about two orders of magnitude larger than the dissipative coupling. In contrast, in the latter case, the coherent coupling is cancelled by the contribution of the scattering field mediated by plasmons, and the dissipative coupling and molecular excitation are dramatically enhanced by the plasmons, which enables the possibility of generating fast superradiant pulses. We clarify the configuration required to reach the plasmon-mediated superradiant pulses with the STM-based nanocavity, to guide further experiments in this direction.