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Seminarium Fizyki Ciała Stałego

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Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

prof. Bartłomiej Graczykowski (Faculty of Physics, Adam Mickiewicz University)

Phonons to Functionality: Mechanical, Thermal, and Light-Driven Responses of Nanomaterials

Dimensionality, interfaces, and structural disorder play a crucial rolein nanomaterials' mechanical and thermal properties. In this seminar, Iwill present our experimental studies of these effects, primarily usingBrillouin light scattering and Raman spectroscopy. I will first discuss the elastic anisotropy of van der Waals crystalsand size-dependent mechanical properties of suspended nanomembranes [1].Next, I will focus on phononic and colloidal crystals, showing howperiodicity, local resonances, and disorder affect GHz phononpropagation and acoustic band gaps [2]. I will then address thermal transport, highlighting two-laser Ramanthermometry to study thermal conductivity suppression in nanostructuredmembranes and thermal rectification in silicon-based devices [3,4].Finally, I will demonstrate how light can be converted into mechanicalmotion in polydopamine- and pDAP-based nanomembranes and microactuators[5]. These examples illustrate how nanoscale structure can be used tocontrol mechanical and thermal properties and enable newfunctionalities.

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

dr Helgi Sigurðsson (Institute of Experimental Physic, Faculty of Physics, University of Warsaw)

"Topological Jackiw-Rebbi states in photonic van der Waals heterostructures"

Topological photonic systems offer robust light confinementand controlled transport, with promising applications in nanophotonics,localization, and lasing. Meanwhile, van der Waals (vdW) materialsprovide unique optoelectronic properties and intrinsic adhesion todiverse substrates, enabling complex multilayer architectures. I willtalk about our recent work on one-dimensional topological photonicplatform based on stacked nanostructured and planar layers of quasi-bulkWS₂. By engineering two topologically distinct gratings, we realizeJackiw-Rebbi interface states operating in the near-infrared spectralregion around 750 nm. These states are characterized through far-fieldoptical measurements, exhibiting linewidths of approximately 10 meV,highly directional emission, and narrow angular bandwidth. Scanningnear-field optical microscopy further reveals strong spatial confinementof the Jackiw-Rebbi mode at the interface between the gratings. Todemonstrate the potential of these states for controlling lightemission, we incorporate monolayer WSe₂ into a five-layer vdW gratingheterostructure and couple its photoluminescence to the topologicalinterface state. This interaction produces directional enhancement ofexcitonic emission by up to 22-fold compared with an uncoupledmonolayer. Our results offer fresh perspectives on vdW-based topologicalphotonic heterostructures as a versatile platform for robust lightlocalization, directional emission, and enhanced light-matterinteractions.

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

dr hab. Jacek Szczytko, prof. uczelni (IFD UW)

When Light Becomes Supersolid - Supersolid Phase in a Spin-Orbit Coupled Exciton-Polariton Bose-Einstein Condensate

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.

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

prof. dr hab. Michał Boćkowski (Institute of High Pressure Physics “UNIPRESS”, Polish Academy of Sciences.)

" From High-Pressure Physics to Full-Stack GaN. Building a Technology from Crystal to Device"

From High-Pressure Physics to Full-Stack GaN Building a Technology from Crystal to Device Michal Bockowski and AI GaN-Unipress, Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw, Poland Gallium nitride has evolved from a fundamental materials-physics challenge into one of the key semiconductor platforms for power electronics, optoelectronics and emerging quantum technologies. This evolution requires much more than an efficient crystal-growth method. Device performance ultimately reflects the entire history of the material – from bulk crystallization through wafer preparation and epitaxy to processing and device fabrication. This evolution will be presented from the perspective of research carried out at the Institute of High Pressure Physics of the Polish Academy of Sciences, Unipress. The story begins with the thermodynamic constraints governing GaN stability and early high-pressure solution-growth experiments. It then turns to the implementation and further scaling of ammonothermal crystallization at Unipress, and to the challenges of producing large-area native GaN substrates with controlled defect, impurity and stress distributions. The central theme is the coupling between successive stages of the technology. Wafer preparation modifies the near-surface defect structure; polarity, miscut and surface condition affect epitaxial growth; substrate defects and impurities influence the electrical and optical performance of devices; and ion implantation combined with ultra-high-pressure annealing provides additional routes for selective doping and functionalization. Examples from power devices and optoelectronic structures illustrate how device performance can serve as a sensitive probe of the complete materials history. Finally, I will show how recent infrastructure and research programs at Unipress are integrating these capabilities into a full-stack GaN platform – connecting crystal growth, substrates, epitaxy, processing, metrology and devices, and creating a basis for pilot-line activities and future industrialization. The central message is simple: GaN is no longer merely a crystal-growth problem. Progress increasingly depends on controlling not only each stage from crystal to device, but also the interfaces between them.