Andrej Vilfan from the Department of Condensed Matter Physics F5 and colleagues from Germany and Great Britain have published an article in the journal Physical Review Letters with the title Lorentz Reciprocal Theorem in Fluids with Odd Viscosity. Fluids with odd viscosity break the time reversal symmetry and consequently the Lorentz reciprocal theorem does not hold. Here we report a way of restoring its validity and demostrate how it can be applied to predict the motion of active particles in such a fluid.
Article in ACS Omega
September 25, 2023
Denis Arčon and Matej Pregelj from the Department of Condensed Matter Physics F5, in collaboration with colleagues from the University of Nova Gorica and researchers from Bulgaria, published the article The Role of Lattice Defects on the Optical Properties of TiO2 Nanotube Arrays for Synergistic Water Splitting. The article reports a one-step chemical method that enables the reduction of an array of titanium dioxide nanotubes with point defects. In-depth chemical analysis is supported by electron paramagnetic resonance measurements, which confirm the presence of oxygen vacancies. The prepared samples show an enhanced photocurrent for water splitting due to pronounced light absorption in the visible region, enhanced electrical conductivity, and improved charge transportation.
Article in Ceramics International
September 25, 2023
Matej Pregelj from the Department of Condensed Matter Physics F-5, in collaboration with colleagues from the Department of Thin Films and Surfaces and other researchers from Slovenia and Serbia, published the article Perpendicular magnetic anisotropy at room-temperature in sputtered a-Si/Ni/a-Si layered structure with thick Ni (nickel) layers. In the article, they presented a detailed study of nanometer Si/Ni/Si layers, where perpendicular magnetic anisotropy was observed. It is one of the first observations of this property in Si/Ni/Si layers and thus opens up possibilities for the use of such layers in memory units, sensors, logic chips, etc.
Article in Journal of Physics: Energy
September 25, 2023
Dr. Dejvid Črešnar, Nikita Derets, Dr. Andraž Rešetič, Dr. Marta Lavrič, Prof. Dr. Boštjan Zalar, prof. Dr. Samo Kralj, Prof. Dr. Zdravko Kutnjak, Assist. Prof. Dr. Brigita Rožič from the Department of Condensed Matter Physics F5, former colleague of the Department of Condensed Matter Physics F-5 Dr. Maja Trček, and colleagues Assist. Prof. Dr. Gregor Skačej, Faculty of Mathematics and Physics, University of Ljubljana, and Prof. Dr. Valentina Domenici, Department of Chemistry and Industrial Chemistry, University of Pisa, Italy, have, on the invitation (to Rožič) of Editors Prof. Dr. N. Mathur and Prof. Dr. X. Moya from the University of Cambridge, published an article entitled Caloric effects in liquid crystal-based soft materialsin a special issue of the Journal of Physics: Energy (IF=7.5) dedicated to caloric materials. In the mentioned article, the authors presented their latest research results of very large caloric responses observed in soft materials such as liquid crystals (TK) and liquid crystal elastomers (TKE). Through direct measurements, they showed that the size of the electrocaloric phenomenon in TK could exceed 8.3 K at a relatively small change in the electric field of 30 kV/cm and the existence of a record high elastocaloric responsivity of 24.2K/MPa in TKE.
They study numerically the reconfiguration process of colliding |m|=1/2 strength disclinations in a nematic liquid crystal (NLC). A Landau-de Gennes approach in terms of a tensor nematic order parameters is used. Initially, different pairs of parallel wedge disclinations were formed connecting opposite substrates confining the NLC in a plane-parallel cell. The collisions are triggered by the relative rotation of the azimuthal angle of the substrates that strongly pin the defect end points. They illustrate qualitatively different rewiring processes.
Article in Front. Soft. Matter
June 11, 2023
Amid Ranjkesh, Samo Kralj in Aleksander Zidanšek from the Department of Condensed Matter Physics F5 and colleagues from Faculty of Natural Sciences and Mathematics, University of Maribor and Jožef Stefan International Postgraduate School have published a paper in Front. Soft. Matter with the tittle Phase behavior of nematic-nanoparticle mixtures.
We study the effects of nanoparticles (NPs) on thermotropic nematic liquid crystals (LCs) in relatively dilute NP–LC mixtures. We are interested in the fundamental generic mechanisms that quantitatively and qualitatively affect the phase behavior of LCs. A simple molecular field analysis shows that a phase transition will likely occur upon entry into the ordered phase. Moreover, the interaction between nematogenic NPs and LCs could force a sergeant–soldier-like behavior, in which only the phase behavior of one component is affected despite the symmetric appearance of the coupling term. When NPs are anisotropic, their influence on LC phase behavior can be qualitatively different depending on the anchoring, even in the absence of the disorder. We illustrate numerically that a random-field-type disorder might impose either short-range, quasi-long-range, or even long-range order, which might survive.
Article in ACS Photonics
June 9, 2023
Abdur Rehman Anwar, Maruša Mur, and Matjaž Humar from the Department of Condensed Matter Physics F5 have published a review paper in ACS Photonics entitled Microcavity- and Microlaser-Based Optical Barcoding: A Review of Encoding Techniques and Applications. In the paper they review the potential of microcavity- and microlaser-based barcodes for a broad range of applications such as cell tracking, anticounterfeiting, and product labeling. In microcavity-based barcodes the information is encoded in various ways in the properties of the emitted light, most frequently in the spectrum. Spectra of microcavity- and microlaser-based barcodes contain very narrow spectral lines and depend on properties of the microcavity, such as size, shape, and gain material, therefore enabling generation of millions of unique barcodes. Microcavity- and microlaser-based barcoding is a very powerful tool which holds great promise. By developing new kinds of microcavities as well as optical systems for their detection, they could become both a tool in research as well as useful for labeling products in everyday life.
Article inJournal of Physics: Conference Series
June 7, 2023
Tina Arh, Matjaž Gomilšek, Andrej Zorko, and colleagues from Switzerland have published a paper in the Journal of Physics: Conference Series with the title An experimental procedure to determine quantitative muon Knight shifts about muon spectroscopy experiments. In the paper, they presented a method for more accurate determination of internal fields in a studied sample via simultaneous measurements of the response of a sample and a reference silver plate.
M. Ravnik and colleagues from the USA and Poland published an article in the journal Physical Review Letters entitled Nematronics: Reciprocal Coupling between Ionic Currents and Nematic Dynamics. It is an interdisciplinary model prediction of the potential existence of coupling between ion currents and nematic dynamics. The prediction comes from an interdisciplinary theoretical connection between the fields of spintronics and complex soft matter.
Article in Physical Review Letters
March 31, 2023
Active nematic fluids are non-equilibrium systems characterized by a chaotic dynamic state known as active turbulence, which in three-dimensional active nematics is realized as a dynamic network of defect lines. Nika Kralj, Miha Ravnik and Žiga Kos showed how active turbulence dynamically reacts to changes in material properties and external parameters, which leads to coarsening and refinement of defect line density. In the limit of passive nematic liquids, such a phenomenon describes the last stage of the Kibble-Zurek mechanism and appears in many physical systems, from cosmic strings to superfluid helium and liquid crystals. The authors show how such a process takes place in active matter, which leads to interesting parallels with cosmic string coarsening models.
In the published paper, the researchers synthesized MoS2 with different isotopes of sulphur, revealing the influence of phonons on the optoelectronic properties of MoS2. By varying the isotopic composition, the optoelectronic properties of the material can be adjusted for various applications, and at the same time provides a unique platform for understanding the fundamentals of optical processes in 2D systems.
An overview of the lipid vesicle adsorption and rupture under different experimental conditions is given. The current understanding of the mechanisms relies on surface sensitive techniques, such as quartz crystal microbalance with dissipation monitoring and atomic force microscopy. We provide various examples how the vesicle adsorption and rupture are influenced by varying the lipid size and charge, the type of buffer and the adhesion strength of solid substrate.
We have studied phase transitions in a series of mixtures of liquid crystals RM734 and DIO exhibiting new types of ferroelectric nematic phases. RM734 exhibits a nematic (N) and a ferroelectric nematic (NF) phase, whereas DIO has an intermediate phase (Nx) between N and NF. By means of high-resolution calorimetry, we have derived the precise phase diagram as a function of mixture composition, i.e., as a function of variable ferroelectric coupling. The phase diagram is consistent with ideal mixture behavior, provided that the total enthalpy values are used in the analysis. The critical behavior of Nx-NF phase transition exhibited by the mixtures shows a systematic trend of the critical exponent values from α = 0.88 ± 0.10 for DIO towards α = 0.50 ± 0.05 (tricritical) when increasing the concentration of RM734.
Strong enhancement of the electric breakdown strength in properly matched polymer blends
February 14, 2023
One of the major challenges in developing materials for energy storage systems is realizing high energy density while maintaining low dielectric losses. The composite approach, where conductive particles are dispersed in the dielectric matrix, effectively increases the dielectric permittivity but also boosts the losses. An alternative approach is an operation under high electric fields, i.e. increasing the electric breakdown strength (Eb) without increasing the dielectric permittivity.
Phenyl groups are fundamental chain components of many high-temperature polymers and, depending on the polymer's molecular structure, delocalized electrons in these groups may exhibit a partially positive or negative charge. We prepared blends of polyetherimide (PEI) and polyimide (PI) by the solution casting method and performed their extensive dielectric characterization. We demonstrated a significant enhancement of Eb in blends due to strong electrostatic interactions between different polymer chains; PEI namely contains three negatively charged phenyls, while PI has two strong positively charged phenyl groups. Electrostatic interactions (i) strongly reduce the number of space charges and (ii) lead to much higher chain packing density in blends. Since the breakdown is initiated by charges that are accelerated by an applied electric field in weak points, i.e. voids in the system, both features contribute to the enhancement of Eb. The blending of appropriately matched polymers thus turned out as an outstanding strategy for improving the dielectric properties of polymer systems.
Assistant Professor Anton Gradišek and Professor Tomaž Apih, together with colleagues from Lisbon, Portugal, published a study Observing short-range orientational order in small-molecule liquidsin the journal Scientific Reports. The authors address a phenomenon that has been known for decades in the scientific community, but never systematically addressed. In the isotropic phase of liquid crystals, far from the clearing point, we can still observe short-lived clusters with local ordering. The same phenomenon was observed also in liquids that do not even form a liquid crystalline phase. The analysis was conducted with the use of NMR relaxometry and X-ray diffraction. The findings are important in view of understanding the crystallization process.
Article in Particle & Particle Systems Characterization
Neuromorphic computing seeks functional materials capable of emulating brain-like dynamics to solve complex computational problems. Interestingly, the transport properties of memristive materials show feature that is closely oriented toward the behavior of artificial neurons. However, artificial neurons are rather rigid mathematical concepts than realistic projections of complex neuronal dynamics.
Neuroscience suggests that highly efficient information representation on the level of individual neurons relies on dynamical features such as excitatory and inhibitory contributions, irregularity of firing patterns, and temporal correlations. Here, a conductive atomic force microscopy approach is applied to probe the memristive dynamics of nanoscale assemblies of AgPt-nanoparticles at the stability border of the conducting state, where physical forces causing the formation and decay of filamentary structures appear to be balanced. This unveils a dynamic regime, where the memristive response is governed by irregular firing patterns. The significance of such a dynamical regime is motivated by close similarities to excitation and inhibition-governed behavior in biological neuronal systems, which is crucial to tune biological neuronal systems into a state most suitable for information representation and computation.
Article in Journal of Apicultural Research
January 24, 2023
Assis. prof. Anton Gradišek and colleagues published a paper Bumble bee nest thermoregulation: a field study in Journal of Apicultural Research. They studied six bumblebee colonies of different species using a home-made setup. The study focused on the nest thermoregulation, which is important in order for the larvae to develop properly. They identified some thermoregulation strategies that have not previously been reported in bumblebees.
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