Observation of a supersolid phase in a spin-orbit coupled exciton-polariton Bose-Einstein condensate at room temperature

TL;DR

The work demonstrates room-temperature supersolidity in a spin-orbit–coupled exciton-polariton fluid by engineering a nematic liquid crystal–organic polymer microcavity that supports strong exciton–photon coupling with Rashba-Dresselhaus SOC. Condensation occurs into two degenerate RD-SOC minima at $\pm k_0$, producing spontaneously modulated density and polarization stripes whose positions vary between realizations, evidencing spontaneous translational symmetry breaking that remains robust against disorder. The Stripe phase exhibits superfluid characteristics, including random stripe positioning without backscattering and the observation of vortices via the Kibble-Zurek mechanism, supported by both experiment and Boltzmann-Gross-Pitaevskii simulations that reveal gapless bogolon modes. The combination of room-temperature operation, strong coupling with tunable SOC, and robust supersolid behavior opens avenues for exploring SOC-driven quantum fluids of light and topological photonics in non-Hermitian, real-world devices. Key quantitative findings include a Rabi splitting of $\Omega\approx93$ meV, two minima at $\pm k_0$, stripe spacing $\approx \pi/k_0$, and a stripe contrast that ranges with density and disorder, all captured by a Tavis-Cummings–type and spinor GP modeling framework.

Abstract

In Bose-Einstein condensates (BEC), spin-orbit coupling (SOC) produces supersolidity. It is a peculiar state of matter, which, in addition to the superfluid behaviour shows periodic density modulation typical for crystals. Here, we report the fabrication of a new type of optical microcavity allowing to achieve room-temperature supersolidity for a quantum fluid of light. The microcavity is filled with a nematic liquid crystal (LC) and two layers of the organic polymer MeLPPP hosting exciton resonances. We demonstrate exciton-polariton condensation in the two distinct degenerate minima of the dispersion created by the LC induced Rashba-Dresselhaus (RD) SOC. The condensate real-space distribution shows density stripes located randomly from one condensate realization to another despite the presence of a random disorder potential. This demonstrates the immunity of stripes against disorder (that is, superfluidity) and the spontaneous breaking of translational invariance. We also report the random appearance of vortices via the Kibble-Zurek mechanism, another smoking gun of superfluidity.

Figures (17)

• Figure 1: SOC condensate and microcavity scheme (a) SOC condensate forms with different elliptical polarizations and phases $\Phi_1$ and $\Phi_2$ in the two dispersion minima. Their interference results in the formation of density stripes in real space with position depending on $\Phi_1-\Phi_2$ (b) Microcavity scheme: thick LC layer sandwiched between two organic polymer layers (MeLPPP), two DBRs, and two ITO electrodes.
• Figure 1: Experimental setup scheme.
• Figure 2: Demonstration of strong coupling regime. (a,b,c) experimentally measured angle-resolved PL for different values of voltage, showing tunability of the H polarized modes and (a) reach of the RDSOC regime; red, green and yellow text labels the number and polarization of the mode(s); black solid lines show the fitting (a) by Hamiltonian \ref{['RDSOC']} and (b,c) by parabola; the excitonic resonance is centered at $E_X=2.715$ eV; (d) LPB mass as a function of LPB detuning: extracted from the experiment (blue dots) and numerical simulation (red dots); numerical model uses the mode photonic mass at each voltage (yellow dots);(e) Emission intensity (red dots), linewidth (blue squares), and (f) mode energy (green diamonds) as a function of the excitation density. An extra point from reflectivity (gray hexagon) added for comparison.
• Figure 2: MeLPPP absorption and complex refractive index. Left: Experimentally measured absorption of a single MeLPPP layer on the DBR (solid blue line); the fit of the main absorption peak by Gaussian function representing inhomogeneous broadening of excitons (dashed red line); Right: real (Re($n$), blue line) and imaginary (Im($n$), red line) parts of complex refractive index obtained by variable angle spectroscopic ellipsometry.
• Figure 3: Stripe phase in a polariton condensate. Photoluminescence measured at 0 V (first column), 7.6 V in the presence of RDSOC (second column). The first row (a,b) shows the $k_x$-dependent total emission with the double minima dispersion in (b). The second row (c,d) shows the real space total emission with stripes absent in (c) and present in (d). The third (e,f) rows show the real space distribution of the linear $S_1$ polarization degree. (g) Fourier transform of the experimental intensity from (c,d) with a marked stripes diffraction peak.