Materials and Cavity Design Principles for Exciton-Polariton Condensates

Abstract

Exciton-polariton condensation offers a promising path to low-threshold coherent light sources, impacting fields from communications to healthcare. These hybrid quasiparticles, arising from strong exciton-photon coupling, combine the low effective mass from their photonic component and the strong nonlinear interactions from excitons. While polariton condensation has been achieved in a range of inorganic and organic materials, many systems still face significant challenges despite fulfilling the main properties requirements. In this perspective, we examine condensation mechanisms across different materials and highlight that universal guidelines do not exist; instead, we believe that exciton-polariton condensation is governed by the intrinsic properties of the active material. We propose using 2D perovskites as versatile platforms to investigate how specific structural and electronic characteristics influence the nonlinear processes driving exciton-polariton condensation. By exploiting the versatility of 2D perovskites, we can systematically explore and establish universal principles guiding the realization of polariton condensation in various material systems.

Keywords: 2D perovskites; exciton-polariton condensation; semiconductors.

Figure 1

Engineering of exciton-polariton condensation. (a) Microcavity schematic in the strong light matter coupling regime, where γ_ex is the exciton recombination rate and γ_ph is the optical mode leakage rate. (b) N emitters interact strongly with photons to yield hybrid LP, UP and N – 1 dark states. (c) Characteristic angle dependent energy dispersion in the strong coupling regime displaying two emergent energy states: the lower and upper polariton (LP and UP), where δ is the detuning. The most common materials systems studied are inorganic (d), organic (e), and halide perovskites (f).

Figure 2

Threshold fluence for a nonresonant pump into the exciton reservoir estimated using a kinetic model described by eq 1 (and the associated coupled equation for the exciton population), plotted as a function of the polariton lifetime and the transfer rate from the reservoir to the lower polariton state.

Figure 3

Schematic representation of (a) radiative pumping, (b) polariton-polariton scattering and vibronically assisted relaxation processes that populate the k = 0 state in the lower polariton dispersion and subsequently initiating the condensation process. Below each schematic are the reported examples of condensation in material systems, where such relaxation processes have been invoked. Refer to refs (,−, and 56).

Figure 4

Polariton condensation roadblocks in halide perovskites as a function of structural dimensionality. (a) 2D n = 1 halide perovskites, (b) mixed dimensional materials where more than one (n > 1) inorganic slabs are separated by bulky cations, and (c) traditional 3D perovskites with no bulky cations involved. The proposed processes for polariton formation are depicted below the structures.

Figure 5

Structural handles to modify optoelectronic properties in halide perovskites. (a) A-site cation interactions with the lead halide octahedra enables control over their distortions. (b) Chemical manipulation enables bandgap, bond length, and octahedral tilt control. (c) A-site cation chemistries enable their rigidity in between the lead halide sheets. (d) Materials processing can be used to control preferred crystallographic orientation.