News

As the beginning of the COVID-19 pandemic caused a general lack of medical protective equipment, the researchers from “Jožef Stefan” Institute, including associates of our department, decided to look into the option of using ionizing radiation to sterilize used masks and allow their reuse. The results showed that facepiece respirators type FFP2 and FFP3 can be sterilized by Gamma irradiation and electron beam irradiation. This method of sterilization preserves the mechanical and chemical characteristics of masks and does not harm the efficiency of aerosol particle filtration. While 20 kGy radiation does cause the loss of the polypropylene membrane filters static charge, re-application of the charge brings the filtration efficiency back to the previous level. Masks can be sterilized up to two times using this method. The research was carried out by Luka Pirker, Anja Pogačnik Krajnc, Anton Gradišek, Andreja Jelen, Maja Remškar, Igor B. Mekjavić, Janez Kovač, Miran Mozetič, Luka Snoj, Jan Malec and Vladimir Radulović, and the results were published in the Journal of Membrane Science in the article entitled Sterilization of polypropylene membranes of facepiece respirators by ionizing radiation.

Abdou Hassanien from the F5 Department of Jozef Stefan Institute has published, in collaboration with Biao Zhou and Akiko Kobayashi from Nihon University, Tokyo, Japan, an article in the Journal of Advanced Electronic Materials titled Spontaneous Antiferromagnetic Ordering in a Single Layer of (BETS)2GaCl4 Organic Superconductor. The fabrication of such well-defined and atomically clean interfaces between materials of different orders are of fundamental interest to engineer novel functionalities and to study emergent phenomena in condensed matter physics. The paper illustrates the interplay between electronic orders of hybrid mix of nested antiferromagnetic molecular chains and superconducting molecular stripes at the single layer limit. Results of low temperature scanning tunneling microscopy and spectroscopy have shown that low level vibronic and magnetic excitations that dominate the higher temperature phase are absent below Tc which point to their cooperative existence and possible renormalization to mediate superconductivity in such d-wave superconductors.

1. Tilen Knaflič, Quantum magnetism in ????????‐electron molecular systems: doctoral dissertation, Ljubljana, 2020 (mentor Denis Arčon).

2. Jože Luzar, Design and properties of lime‐cement structural injection grouts for strengthening of heritage buildings: doctoral dissertation, Ljubljana, 2020 (mentor Janez Dolinšek).

3. Luka Pirker, Electrical, optical and structural properties of low‐ dimensional materials based on tungsten: doctoral dissertation, Ljubljana, 2020 (mentor Maja Remškar).

4. Anja Pusovnik, Flow of light in metamaterials based on nematic fluids: doctoral dissertation, Ljubljana, 2020 (mentor Miha Ravnik).

5. Mitja Zidar, Analysis and prediction of aggregation and degradation in protein‐based biopharmaceuticals: doctoral dissertation, Ljubljana, 2020 (mentor Miha Ravnik).

Guilhem Poy from Faculty of Mathematics and Physics at University of Ljubljana and Slobodan Žumer from Jozef Stefan Institute in collaboration with the group of Ivan Smalyukh from University of Colorado in Boulder in Physical Review X published the paper that Control of Light by Topological Solitons in Soft Chiral Birefringent Media, was highlighted in APS Physics Focus by the editorial article “Liquid-Crystal Vortices Focus Light”. Topological solitons appearing in different areas of physics are fascinating localized perturbations of ordering fields enjoying topological protection. The authors demonstrate refraction, reflection, and lensing of weak laser beams by various topological solitons in frustrated chiral nematics and show how interactions of light with such topological solitons are well described using a generalized Snell’s law and ray-tracing models. These may lead to new means for controlling flow of light for use in optics and photonics.

Slobodan Žumer from Jozef Stefan Institute and Guilhem Poy from Faculty of mathematics and Physics at University of Ljubljana in collaboration with Andrew Hess and Ivan Smalyukh from University of Colorado in Boulder published the paper Chirality-enhanced periodic self-focusing of light in birefringent soft media in Physical Review Letters. It presents numerical, experimental and theoretical evidence of chirality enhanced nonlinear optical response of frustrated chiral nematics. In achiral nematics, the reorientation of molecules around laser beams with appropriate power is responsible for the generation of spatial optical solitons called “nematicons”. In unwounded chiral nematics, the frustration caused by a confinement incompatible with their lowest-energy states allows a relatively weak light to locally destabilize the initially uniform orientational fields and thus boost their nonlinear optical responses. Our research findings are expected to allow new self-focusing based applications.