Ultrafast Dynamics of Nonequilibrium Organic Exciton–Polariton Condensates

Abstract

Exciton–polariton condensation in organic materials, arising from the coupling of Frenkel excitons to the electromagnetic field in cavities, is a phenomenon resulting in low-threshold coherent light emission among other fascinating properties. The exact mechanisms leading to the thermalization of organic exciton–polaritons toward condensation are not yet understood, partly due to the complexity of organic molecules and partly to the canonical microcavities used in condensation studies, which limit broadband studies. Here, we exploit an entirely different cavity design, i.e., an array of plasmonic nanoparticles strongly coupled to organic molecules, to successfully measure the broadband ultrafast dynamics of the strongly coupled system. Sharp features emerge in the transient spectrum originating from the formation of a condensate with a well-defined molecular vibrational composition. These measurements represent the first direct experimental evidence that molecular vibrations drive condensation in organic systems and provide a benchmark for modeling the dynamics of organic-based exciton–polariton condensates.

Untargeted effects in organic exciton–polariton transient spectroscopy: A cautionary tale

“…63 Similar effects can be obtained within organic films, as reported for instance from a PMMA waveguide mode not coupled to any electronic excitations. 80 We further highlight the pronounced growth kinetics observed in the PIA at 775 nm. These may potentially be related to the coherent phonon oscillations within the Ag mirror, 63 but we additionally note that photoexcitation has been reported to create localized strain in thin films, resulting in propagating strain waves that manifest as time-domain oscillations in the transmission signal.…”

Tunable exciton-polaritons emerging from WS2 monolayer excitons in a photonic lattice at room temperature

“…Exciton-polaritons in optical lattices have matured to a very promising and versatile platform in applied information technology [1][2][3][4] . Their bosonic character enables ultra-fast condensation processes [5][6][7][8] , which are already exploited in classical emulation applications 1,2 , and can be also harnessed in ultra-fast quantum annealing architectures 9 . Their intrinsically strong nonlinearity has very recently opened the new area of genuine quantum polaritonics 10,11 .…”

Sub-picosecond thermalization dynamics in condensation of strongly coupled lattice plasmons

“…In photon condensates 19,20 , the thermal bath is easily controlled 21,22 . Recently periodic two-dimensional (2D) arrays of metal nanoparticles, so-called plasmonic lattices or crystals 23 , have emerged as a multifaceted platform for room temperature lasing and condensation at weak [24][25][26][27][28] and strong coupling [29][30][31] regimes.…”

“…2e) than observed for the same molecular concentration in our previous work 28 (0.08 eV/ps), further confirming that the larger number of photons and stimulated processes are contributing to the speedup. A discrete step of simultaneous creation of a low energy polariton and a vibrational quantum is often quoted as the route for organic semiconductor polariton condensation 14,29,31,57,58 . The microscopic foundation of this phenomenon is the same as that of photon condensation, but the parameter regimes differ.…”