Optical Non-linearities in Plasmon-Exciton Core-Shell Particles: the Role of Heat

TL;DR

This study demonstrates that heat generated inside plasmon-exciton core-shell nanoparticles is the primary cause of their non-linear transient optical features, confirmed through experiments and analytical simulations.

Contribution

It provides the first conclusive evidence linking heat to non-linear optical behavior in plasmon-exciton systems, supported by precise simulations matching experimental data.

Findings

Heat is the main source of non-linear features in transient spectra.

Simulations accurately reproduce experimental results using temperature rise assumptions.

Heating effects are consistent across various excitation powers.

Abstract

Strong coupling between plasmons and excitons gives rise to new hybrid polariton states with various fields of potential applications. Despite a plethora of research on plasmon--exciton systems, their transient behaviour is not yet fully understood. Besides Rabi oscillations in the first femtoseconds after an optical excitation, coupled systems show interesting non-linear features on the picosecond time scale. Here, we conclusively show that the source of these features is heat that is generated inside the particles. Until now, this hypothesis was only based on phenomenological arguments. We investigate the role of heat by recording transient spectra of plasmon--exciton core--shell nanoparticles with excitation off the polariton resonance. We present analytical simulations that precisely recreate the measurements solely by assuming an initial temperature rise of the electron gas inside the particles. The simulations combine established strategies for describing uncoupled plasmonic particles with a recently published model for static spectra. The simulations are consistent for various excitation powers confirming that indeed heating of the particles is the root of the changes in the transient signals.