Researchers observed a supersolid state of matter at room temperature by combining an organic semiconductor with a liquid-crystal microcavity. Published in Science Advances, the findings bring experiments out of traditional cryogenic systems and into photonic systems operating under ambient conditions.
For more than half a century, supersolidity remained a theoretical prediction. Physicists in the 1960s theorized that a superfluid could simultaneously develop a periodic crystal-like structure, retaining frictionless flow while exhibiting spatial order. Supersolidity was experimentally observed in 2017 in ultracold atomic Bose-Einstein condensates.
Instead of relying on ultracold atoms, a research group called TopoLight investigated exciton polaritons. These are hybrid quasiparticles created through the intense interaction of light and matter inside an optical microcavity.
The research team included scientists from the Faculty of Physics University of Warsaw, the Military University of Technology in Poland, IBM Research Zurich, and the French National Centre for Scientific Research (CNRS).
Building a Room-Temperature Supersolid
The optical microcavity was filled with a specially designed liquid crystal and coated with an organic semiconductor. This combination enabled strong light-matter coupling at room temperature.
Our liquid-crystal microcavities can operate even at temperatures approaching 60°C,
said Professor Wiktor Piecek from the Military University of Technology, whose group developed the liquid-crystal structures.
The transition into the supersolid phase appeared as regularly spaced bright fringes in the light emitted from the sample. This signaled that the condensate had spontaneously formed a periodic density modulation.
With every laser pulse exciting the sample, the fringes appeared at a different position. This demonstrated that the system independently selected one of many equivalent configurations.
This is a textbook example of spontaneous symmetry breaking,
explained Professor Guillaume Malpuech from Institut Pascal (CNRS). Theory predicted that the supersolid could choose among several equivalent states, and that is exactly what we observed.
At the same time, the condensate exhibited a persistent spin helix, creating two distinct forms of order simultaneously: one in polarization and another in light intensity.
Overcoming Experimental Hurdles in the Laboratory
We had to plan the entire sequence of experiments in advance,
recalled Marcin Muszyński. Repeating a measurement meant fabricating an entirely new sample.
IBM Research Zurich served as the site for the main measurements. Thin films of the organic semiconductor were applied to photonic structures built at the Military University of Technology.
We have studied the organic semiconductor MeLPPP (methyl-substituted ladder-type poly(paraphenylene) for many years and previously observed Bose-Einstein condensation in this material,
said Thilo Stöferle from IBM Research. This was the first time we combined it with a liquid-crystal microcavity.
Until now, most studies of exotic quantum phases required expensive cryogenic systems operating near absolute zero. The recent findings show that comparable quantum behaviors can be investigated using photonic systems. These systems run at room temperature.