Room-Temperature Polariton Lasing from CdSe Core-Only Nanoplatelets

Abstract

This paper reports how CdSe core-only nanoplatelets (NPLs) coupled with plasmonic Al nanoparticle lattices can exhibit exciton-polariton lasing. By improving a procedure to synthesize monodisperse 4-monolayer CdSe NPLs, we could resolve polariton decay dynamics and pathways. Experiment and theory confirmed that the system is in the strong coupling regime based on anticrossings in the dispersion diagrams and magnitude of the Rabi-splitting values. Notably, polariton lasing is observed only for cavity lattice periodicities that exhibit specific dispersive characteristics that enable polariton accumulation. The threshold of polariton lasing is 25-fold lower than the reported photon lasing values from CdSe NPLs in similar cavity designs. This open-cavity platform offers a simple approach to control exciton polaritons anticipated to benefit quantum information processing, optoelectronics, and chemical reactions.

Electrochemical Control of Strong Coupling of CdSe Exciton-Polaritons in Plasmonic Cavities

“…k || = ± 2.3 μm –1 and 2.42 eV. The LP band occurs below the HH in energy and is overlaid with a cyan dashed line based on a fit from the coupled oscillator model. , Below ∼2.3 eV, the LP retains a significant SLR character, matching the transmission from the uncoupled lattice. However, at energies close to the HH, the bands begin to bend outward, resulting in flat bands at large k || reminiscent of the HH band.…”

“…The Ag/AgNO 3 reference electrode and Pt wire counter electrode complete the cell and were mounted offset so as not to obstruct the transmission of light through the cell under an applied potential. This architecture allows the electrochemical cell to be mounted into a Fourier transform microscope between a condenser and objective lens , so that changes to polaritons as a result of bias can be quantified in real time (Figure b).…”

“…Four-monolayer, oleate-capped CdSe NPLs (Figure c) were synthesized using our improved procedure and cast into an 110 nm thick film. There are two excitonic transitions in CdSe NPLs: (1) the heavy hole (HH) valence band to the conduction band at 2.42 eV (∼512 nm) and (2) the light hole (LH) valence band to the conduction band at 2.58 eV (∼480 nm) .…”

“…Exciton-polaritons are hybrid light–matter quasiparticles that form under strong coupling, which occurs when the coupling between an optical cavity and an exciton exceeds the losses of either. , Exciton-polaritons are important in diverse fields, ranging from quantum computing to sensing to low-threshold lasing . Recently, these quasiparticles have gained attention to control the product distribution of chemical reactions by altering potential energy surfaces .…”

“…Typically, the higher energy eigenmode is referred to as the upper polariton (UP) while the lower energy mode is defined as the lower polariton (LP). Since CdSe NPLs support two excitonic absorptions, depending on the operational frequency of the cavity, a middle polariton (MP) mode can also be present Scheme summarizes how an applied bias can inhibit HH and LH excitonic transitions by populating the NPL conduction band with electrons.…”