A new optical microcavity achieves room-temperature quantum supersolidity

A new optical microcavity fabricated with a nematic liquid crystal and two layers of the organic polymer MeLPPP has achieved room-temperature supersolidity in a quantum fluid of light. The work demonstrates exciton-polariton condensation and reveals density stripes appearing randomly within the condensate, even when exposed to a “random disorder potential.” This resilience indicates superfluidity and a spontaneous breaking of translational invariance, while the random appearance of vortices confirms this behavior via the Kibble-Zurek mechanism. The researchers report this is a state of matter combining crystalline order with frictionless flow.

Room-Temperature Supersolidity via Exciton-Polariton Condensation

Unlike lead halide perovskites previously used for similar experiments, MeLPPP demonstrates high saturation density, quantum efficiency and photostability, enabling repeated single-shot measurements at a given sample location. Exciton-polariton condensation was demonstrated within the microcavity, specifically in the two distinct degenerate minima created by Rashba-Dresselhaus spin-orbit coupling. The resulting condensate exhibits a periodic density modulation, characteristic of crystals, alongside superfluid behavior.

Measurements of pulsed non-resonant excitation show the emission intensity, linewidth and energy of the V-polarized polariton mode varying with pumping density. The team used an average of 500 to 2500 pulses for multiple-shot experiments, but also obtained sufficient signal for single-shot measurements above the threshold, further validating the observed phenomena and confirming the spontaneous breaking of translational invariance.

Spin-Orbit Coupling Creates Degenerate Minima for BEC Formation

The creation of two degenerate energy minima, achieved through Rashba-Dresselhaus spin-orbit coupling (RDSOC), is fundamental to the observed room-temperature supersolidity within a newly fabricated optical microcavity. These minima, possessing opposite wavevectors, facilitate condensate formation and subsequent interference, directly manifesting as density stripes in real space; the period of these stripes is governed by the wavevector magnitude, k₀. The positions of these minima are determined by the detuning between horizontally and vertically polarized modes, a parameter precisely controlled by an applied voltage, as described by the effective Hamiltonian detailed in the work.

Beyond the static structure of the condensate, the research team also documented the spontaneous emergence of quantized vortices in approximately 10% of condensate realizations. These vortices, a hallmark of superfluidity, arise from the Kibble-Zurek mechanism, confirming the fluid-like nature of the condensate despite the presence of a random disorder potential.

Microcavity Design Enables Strong Exciton-Photon Coupling

The fabrication of optical microcavities incorporating a nematic liquid crystal and organic polymer layers enables strong coupling even with variations in exciton-photon detuning, a feature consistently observed across multiple samples. While an anticrossing wasn’t present in every instance due to broadening effects, all samples demonstrated strongly coupled exciton-photon states at negative exciton-photon detuning, confirming robust light-matter interaction. This consistency is notable given that the cumulative broadening from both environmental factors and temperature approached the magnitude of the Rabi splitting, a measure of coupling strength.

Single-shot experiments and simulations corroborate the presence of these vortices, visually manifesting as dislocations within the density stripes formed in real space. This resilience to disorder further supports the superfluid nature of the condensate, indicating immunity to imperfections within the microcavity structure.

Random Stripe Patterns Confirm Spontaneous Symmetry Breaking

Single-shot experiments reveal that the density stripes within the condensate are not fixed, but instead position themselves randomly with each new condensation process. This random placement demonstrates the spontaneous breaking of translational invariance, a key characteristic of the supersolid state achieved within the optical microcavity. The persistence of this symmetry breaking, even when a disorder potential is present in the sample, is a hallmark of superfluidity. The emergence of topological defects, specifically vortices, confirms superfluidity within the newly created room-temperature supersolid via the Kibble-Zurek mechanism, a process where rapid condensation spontaneously generates these structures.

MeLPPP Polymer Achieves Room-Temperature Condensation

This microcavity design hosts exciton resonances that are essential for achieving strong exciton-photon coupling, a phenomenon where light and matter interact strongly to create hybrid light-matter quasiparticles. The use of MeLPPP addresses limitations of lead halide perovskites, materials previously employed for this purpose but prone to instability under photo-excitation.

This condensation is assisted by a vibron resonance and occurs with an exciton-photon detuning of -190 meV, demonstrating precise control over the light-matter interaction. “The combination of strong exciton-photon coupling with mode tunability including the RDSOC regime has so far been achieved using lead halide perovskites as an active material,” the paper notes, highlighting the advantage of the new approach.

Disorder Immunity Demonstrates Robust Superfluidity

The ability of a condensate to maintain its structural order even when surrounded by imperfections confirms its superfluidity, a property rarely observed at room temperature. These vortices emerge randomly via the Kibble-Zurek mechanism, a theoretical process describing how topological defects form during symmetry breaking. The researchers from the University of Warsaw, Université Clermont Auvergne, Research Europe, Zurich, among other institutions, verified the strength of the coupling regime even above the condensation threshold, and confirmed these features are consistent across multiple samples.

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