Bose-Einstein condensation of polaritons at room temperature in a GaAs/AlGaAs structure

TL;DR

The paper demonstrates room-temperature Bose-Einstein condensation of polaritons in a GaAs/AlGaAs microcavity. A simple three-level model for heavy-hole and light-hole excitons coupled to cavity photons predicts a well-defined lower polariton with substantial light–matter interaction, enabling condensation at room temperature. Through angle-resolved spectroscopy and BE-distribution fits, the authors observe a sharp linewidth narrowing to $\sim 0.24\ \text{meV}$, a strong nonlinear intensity increase, and coherence, with an effective polariton temperature around $T \sim 220\ \text{K}$ and a threshold density near $n_c \sim 1.6\ \mu\mathrm{m}^{-2}$ (measured around $n \approx 3\ \mu\mathrm{m}^{-2}$ at threshold). These results, in a well-studied III-V platform, indicate potential for room-temperature nonlinear optical devices and transistor-like operation based on polariton condensation; they also highlight the role of exciton–photon interactions in achieving and stabilizing room-temperature BEC. $N(E) = \frac{1}{e^{(E - E(0) - \mu)/k_B T} - 1}$ encapsulates the BE distribution used to characterize thermalization, and the reported linewidths and blue shifts reflect strong polariton interactions and coherence buildup.

Abstract

We report the canonical properties of Bose-Einstein condensation of polaritons, seen previously in many low-temperature experiments, at room temperature in a GaAs/AlGaAs structure. These effects include a nonlinear energy shift of the polaritons, showing that they are not non-interacting photons, and dramatic line narrowing due to coherence, giving coherent emission with spectral width of 0.24 meV at room temperature with no external stabilization. This opens up the possibility of room temperature nonlinear optical devices based on polariton condensation.

Figures (8)

• Figure 1: Ultralow linewidth.(a) The intensity at $k=0$ at $P/P_{th} = 0.8$ (blue) and $P/P_{th} = 1.34$. The linewidth is extracted by fitting a Lorenzian, giving a linewidth of $2.5 \;\mathrm{meV}$ for the blue curve and $0.24 \;\mathrm{meV}$ for the red curve. (b) the polariton energy dispersion corresponding to blue curve in (a). (b) the polariton energy dispersion corresponding to red curve in (a).
• Figure 2: Blue shift and linewidth narrowing. (a) Full width at half max at $k=0$ and the intensity as a function of the pump power. (b) the blue shift at $k=0$ as a function of the pump power.
• Figure 3: Coherence of polaritons. Real-space interference of the polaritons, recorded by superposing the spatial image of the emission with its mirror-image. (a) $P/P_{th} = 0.17$ and (b) $P/P_{th} = 1.22$
• Figure 4: Thermalization of polaritons. (a) Occupation number of the polaritons as a function of energy. The solid lines are best fits to the equilibrium Bose-Einstein distribution. (b) the effective temperature and (b) the reduced chemical potential of the polaritons obtained from the fits to the Bose-Einstein distribution. The vertical dashed line in (b-c) denotes the critical density, defined as the total density of the polaritons at $P/P_{th} = 1$.
• Figure S1: Method of extracting the occupation. (a) A typical energy dispersion of the thermalized polaritons. (b) A vertical slice in (a) at $k_{y} = 0$ showing the CCD counts. The red line is a fit to a Lorentzian function predicting an energy $1.5066$ meV for the polaritons at $k_{y} = 0$. The occupation number for this energy is proportional to the integral of the $I(E)$ curve.