News

Journal Physical Review Letters published a paper “Dynamics and Topology of Symmetry Breaking with Skyrmions”, by Jaka Pišljar, Andriy Nych, Uliana Ognysta, Andrej Petelin, Samo Kralj and Igor Muševič, from J. Stefan Institute and Institute of Physics, Kyiv. The authors showed how the formation of the half-skyrmions-vortices from the high temperature isotropic phase dramatically changes as the chiral liquid crystal sample is confined to thickness below 100 nm. They observed unusally slow fluctuations, which represent spontanoeus formation and decay of individual half-skyrmions, also shown in the accompanying figure. The rate of such dynamics is 4 orders of magnitude slower of what was expected and is explained by the mechanism of thermal hopping between states, which become energetically accessible due to the strong confinement effects. This phenomenon is interesting from the topological point of view as well, as the experiments reveal the mechanisms of  topological charge conservation at the phase transition. The paper was also highlighted in the journal Physics.

Aljaž Kavčič and doc. dr. Matjaž Humar from the Laboratory for biological and soft photonics, Department of Condensed Matter Physics, along with dr. Nerea Sebastian from the Department of Complex Matter at the “Jožef Stefan” Institute, in collaboration with colleagues from the “Max-Planck Institute for the Science of Light”, have published an article in Nature titled Tuneable entangled photon pair generation in a liquid crystal. In their work, they, for the first time, demonstrate the generation of entangled photons in liquid crystals and, with this, in any organic material. In addition to the fact that the efficiency of entangled photon generation in liquid crystals is comparable to the best existing sources, their main advantage lies in the tunability of the state of photon pairs. This tunability can be achieved by applying an electric field or by arranging the liquid crystal molecules into the appropriate configuration. The ability to tune the quantum state indicates significant practical potential for numerous quantum technologies. A summary of the research can also be viewed in a short video.

Iztok Urbančič and Boštjan Kokot (Laboratory of Biophysics, Condensed Matter Physics Department, F5) have, together with colleagues from the Institute for Applied Optics and Biophysics (Jena, Germany), published a paper titled Effects and avoidance of photoconversion-induced artefacts in confocal and STED microscopy in Nature Methods. Authors have shown that high laser powers in fluorescence microscopy should be used with care; besides the well-known photobleaching, the dye’s emission spectrum can shift towards lower wavelengths (“photoblueing”). The fluorescence signal is consequently detected in another spectral channel attributed to another dye, possibly leading to erroneous experimental conclusions. The characterization of this phenomenon was made possible by a unique combination of a STED microscope equipped with a spectral detector, implemented at JSI.

https://www.nature.com/articles/s41592-024-02297-4

Assist. Prof. Žiga Kos, PhD published a paper with colleques from Ulsan National Institute of Science and Technology titled Symmetrically pulsating bubbles swim in an anisotropic fluid by nematodynamics in Nature Communications. Swimming at low Reynolds numbers typically requires breaking of the time-reversal symmetry and centrosymmetry of the swimming strokes. The authors show that symmetrically pulsating bubbles can swim in anisotropic fluids, where the required symmetries are broken by the fluid’s internal structure, suggesting a new possible mechanism of micropropulsion.

Franci Bajd, PhD, Mikac Urška, PhD, Assist. Prof. Aleš Mohorič, PhD and Prof. Igor Serša, PhD from the Department of Solid State Physics F5 have published an article titled The Effect of Polymer–Solvent Interaction on the Swelling of Polymer Matrix Tablets: A Magnetic Resonance Microscopy Study Complemented by Bond Fluctuation Model Simulations in the journal Polymers.

Understanding the tablet hydration process is important for the development of drug delivery systems that exhibit high drug loading capacity and controlled release potential. In this study, MRI was used to experimentally analyze the water hydration process of xanthan-based tablets and to characterize their swelling process with erosion, swelling, and penetration fronts. These results are complemented by numerical simulations of the polymer-matrix hydration process by the Bond Fluctuation Model, in which the polymer tablet matrix is modeled as an assembly of interacting chains with embedded drug particles, while its hydration process is mediated by interaction with solvent particles.