Seminarium Fizyki Ciała Stałego

In solid-state systems broken inversion symmetry gives rise to Dresselhaus and Bychkov-Rashba spin-orbit couplings (SOC), which are crucial for spintronics, topological insulators, and superconductors. Unlike SOC in solid-state materials, which is challenging to manipulate, birefringent optical cavities offer substantial tunability of photonic modes. The properties of polarized electromagnetic waves propagating through one- or two-dimensional structures can be effectively described using a two-mode Hamiltonian, which represents a massive particle with spin 1/2 using Pauli matrices.We have developed a method to electrically control the SOC of light using specially designed photonic structures – birefringent microcavities. These consist of a 2-3 μm thin liquid crystal (LC) layer enclosed between two parallel distributed Bragg reflectors deposited on transparent electrodes. We report the fabrication of an optical microcavity filled with a nematic LC sandwiched between two layers of the organic polymer MeLPPP. The structure demonstrates the formation of cavity exciton-polaritons in the presence of Rashba-Dresselhaus spin-orbit coupling (RDSOC), which is tuned by external voltage controlling the LC birefringence. We demonstrate room-temperature exciton-polariton condensation with the condensate polarization tunable by voltage and polarization of the pumping laser. In the RDSOC regime, condensation occurs in the two distinct degenerate minima of the dispersion, as well as in the negative mass states separating them, which is a signature of the interaction between polaritons and the non-resonantly created excitonic reservoir. The condensate real space distribution shows both polarization and density stripes, characteristic for supersolid phase, which stem from the interference between the condensate components characterized by different wavevectors and polarizations. Supersolidity is a peculiar state of matter, which, in addition to the superfluid behaviour of weakly interacting Bose condensates, shows a periodic modulation of its density typical for crystals and called stripe phase.The possibilities offered by this platform open wide perspectives for detailed future studies of the static and dynamical behavior of supersolids and of quantum fluids in presence of SOC and topologically non-trivial bands. “Observation of a supersolid phase in a spin-orbit coupled exciton-polariton Bose-Einstein condensate” Marcin Muszyński, Pavel Kokhanchik, Rafał Mirek, Darius Urbonas, Pietro Tassan, Piotr Kapuściński, Przemysław Oliwa, Ioannis Georgakilas, Thilo Stöferle, Rainer F. Mahrt, Michael Forster, Ullrich Scherf, Dmitriy Dovzhenko, Rafał Mazur, Przemysław Morawiak, Wiktor Piecek, Przemysław Kula, Barbara Piętka, Dmitry Solnyshkov, Guillaume Malpuech, Jacek Szczytko; Science Advances (2026) in press.