Nonequilibrium Quantum Dynamics and Relaxation Phenomena in Many Body Systems, December 16 – 19, 2018, Krvavec, Slovenia

Nonequilibrium Quantum dynamics is becoming one of the most advanced contemporary research areas in solid state physics, ultracold atoms, nano physics and quantum devices. Understanding of such dynamics in real world systems presents a challenge to experimentalists and theory alike. The time-evolution of many-body quantum systems can be viewed as the time-evolution of quantum information, opening the way to new experimental ideas. At the same time, new and sometimes unexpected experimental discoveries provide stimulus for theory. This workshop continues a tradition with the 7th in the series of focused worskops on nonequilibrium quantum phenomena which by all accounts have been extremely stimulating. This workshop intends to bring together scientists working in the field of:

  • Nonequilibrium quantum dynamics and relaxation phenomena in closed quantum systems
  • Nonequilibrium quantum dynamics in CDW’s, superconductors and frustrated magnetic systems
  • Nonequilibrium quantum dynamics of ultracold atoms in optical lattices

http://f7-4.ijs.si/

Splay Nematic Phase

Researchers from the Department for Complex Matter Jožef Stefan Institute Alenka Mertelj, Nerea Sebastián, Luka Cmok in Martin Čopič have in collaboration with researchers from University of York, UK, studied a recently designed nematic phase, which appears in materials made of polar wedge-shaped molecules. They discovered that average molecular orientation in the new phase organizes in a manner that resembles a modulated array of Japanese fans. The modulated structure is biaxial and antiferroelectric. The described phase is a major step forward towards the realization of an often-speculated polar nematic phase, which could lead to materials with optical and electrical behaviors desired for a wide range of applications. The study was published in the paper Splay Nematic Phase in Physical Review X.

Raziskovalci Odseka za kompleksne snovi Instituta “Jožef Stefan” Alenka Mertelj, Nerea Sebastián, Luka Cmok in  Martin Čopič so skupaj s kolegi iz Univerze v Yorku, Velika Britanija, preučili novo nematično fazo, ki se pojavi v snoveh, zgrajenih iz močno polarnih molekul klinaste oblike. Ugotovili so, da ima povprečna ureditev molekul  v novi fazi modulirano pahljačasto strukturo, kar povzroči, da je faza dvoosna in antiferoelektrična. Fazo so poimenovali pahljačasta nematična faza. Opisana faza predstavlja pomemben korak k uresničitvi polarne nematične faze, ki lahko vodi do materialov z optičnimi in električnimi lastnostmi, želenimi za raznovrstne aplikacije. Rezultati raziskave z naslovom Splay Nematic Phase so bili objavljeni v reviji Physical Review X.

Aleksander Yu. Kuntsevich, 22.11.2018 at 11:00, F7 Seminar room

SrₓBi₂Se₃-nematicity, superconductivity, crystals and thin films

Aleksander Yu. Kuntsevich, P. N. Lebedev Physicsl Institute, Moscow, Russia

Abstract:

3D topological insulator Bi₂Se₃ attracts much attention as a platform for future low consumption spintronics and quantum computations. Recently, nematic (and possibly topological) superconductivity was discovered in AₓBi₂Se₃, where A = Cu, Sr, Nb. In my talk I will discuss phenomenology of the nematicity, observed in SrₓBi₂Se₃ single crystals in both superconducting and normal states. I will also review our efforts on molecular beam epitaxy growth of both parent compound Bi₂Se₃ and Sr-doped Bi₂Se₃ thin films. The latter appear to be non-superconducting because Sr atoms in the films get different positions than in the crystals. Our results call for novel growth approaches for design of superconducting SrₓBi₂Se₃ thin films.

Poster [PDF]

Andrej Kranjec, 13.11.2018 at 14:30, F7 Seminar room

Vertex directed analysis of the hidden state relaxation in 1T-TaS2

Andrej KranjecDepartment for Complex Matter, JSI

Abstract:

I will be presenting a brief summary of our latest results obtained by applying a global interdomain shifts recognition algorithm on a high quality STM sequence of the relaxation of the H-state in 1T-TaS2. We show how the results of the algorithm provide a basis for the study of dislocations by determining trivial and non-trivial vertices where domain walls meet by constructing Burgers circuits and vectors around selected vertices. The analysis shows that some of the relaxation dynamics could be consistent within the scope of dislocation theory.

Poster [PDF]

Prof. Dr. Michele Fabrizio, 4.10.2018 at 13:00, Physics seminar room

Transient cooling of quasiparticles in K3C60  by mid-infrared laser pulses 

 Prof. Dr. Michele Fabrizio, International School for Advanced Studies SISSA, Trieste, Italy

Abstract:

We propose an explanation of the transient superconducting-like optical behavior observed at temperatures as high as ten times Tc in K3C60 irradiated by mid-infrared laser pulses.  In our theory the phenomenon is due to the laser pulse effectively cooling down low energy quasiparticles much below the external temperature. The mechanism is quite general and relies on the existence of  localised excitations, in K3C60 these are spin-triplet excitons,  that act as entropy sink when the laser is on, while, when the laser is off, they release back the stolen entropy very gradually.

Poster [PDF]

Mimoza Naseska, 19.9.2018 at 13:00, F7 Seminar room

Spin density wave dynamics in iron based pnictides 

Mimoza Naseska, Department of Complex Matter, JSI

Abstract:

We present ultrafast optical time-resolved spectroscopy measurements of the ultrafast system trajectory through the spin density wave (SDW) phase transition in SrFe2As2 and EuFe2As2. Using the standard pump-probe technique we determined the threshold fluence for the nonthermal destruction of the SDW order (Fth ≈ 0.2 mJ/cm2) at two different pump-photon energies (1.55 eV and 3.1 eV). The SDW destruction timescale obtained from the multipulse measurements is ~ 150 fs. We found that the destruction pulse penetration depth in the mJ/cm2  excitation-fluences range significantly exceeds the equilibrium optical penetration depth suggesting the absorption saturation. The recovery dynamics of the SDW order was simulated using an extended three temperature model (3TM). The analysis suggests that the optical-phonons energy-relaxation surprisingly plays an important role in the recovery of almost exclusively electronically driven SDW order.

Poster [PDF]

Maria D’Antuono, 18.7.2018 at 13:00 in F7 Seminar room

Magnetotransport properties of 2DEG formed in LAO/ETO/STO heterostructures studied using the electric field effect

Maria D’Antuono, University of Naples Federico II, Naples, Italy

Abstract:

In 2004 Ohtomo and Hwang reported the formation of a high mobility 2-dimensional electron gas (2DEG) at the interface between two wide bandgap insulators oxides, namely LaAlO3 (LAO) and SrTiO3 (STO). In this work, we show that the 2DEG created at the LAO/STO interface becomes both electric-field-tunable spin polarized and superconducting by introducing a few atomic layers of EuTiO3 (ETO) which is an antiferromagnetic (AF) insulator iso-structural to STO . Among the most interesting characteristics of this 2DEG are the remarkably large Rashba-spin-orbit interactions and unconventional superconductivity and magnetism, possibly related to the presence of strong correlations in quantum-confined 3d-bands. The occurrence of magnetic interactions, superconductivity and spin-orbit interactions in the same 2DEG system makes the LAO/ETO/STO an intriguing platform for the emergence of novel quantum phases in low-dimensional devices. The main goal of this work was to investigate the electrical transport of the LAO/ETO/STO interface and to shed more light on the complex nature of this system and its phase diagram. In particular, we focused on the interplay between Rashba-spin-orbit interactions and ferromagnetism. In fact, the LAO/ETO/STO 2DEG is one of the few systems where such interplay can be studied and it is therefore of great interest for future spintronic applications.

Poster [PDF]

Vitomir Sever, 6.7.2018 at 13:00 in F7 Seminar room

Study of the efficiency of the solar updraft tower as a function of its height
Vitomir Sever, Material Science and Engineering Department at Institute National des Sciences  Appliquées (INSA), Lyon

Abstract:

With the constant increase in pollution, the need to find new systems that provide clean energy becomes more and more important. One of these solutions could be the solar updraft tower. This tower allows us to create electrical energy from the solar energy. Air is heated by solar radiation under a circular transparent roof open at the periphery. In the middle of this collector is a vertical tower with air inlets at its base. As hot air is lighter than cold air it rises up the tower. Suction from the tower then draws in more hot air from the collector, and cold air comes in from the outer perimeter. Therefore, turbines at the base of the tower generates electricity.

The goal of this project was to find out how the height of the tower influences its efficiency. Using a very simple theoretical model and making measurements on a real model, it can be seen that the height varies with the air velocity in power of 1/2, and with the recoverable power in power of 5/2. This model remains correct for heights lower than 1m which is very limiting. Finally, many improvements remain to be made, such as the theoretical model, geometry,  materials and precision.

Poster [PDF]

Dr. Satoshi Tsuchiya, 22.6.2018 at 13:00 in F7 Seminar room

Spectrally resolved and three pulse pump-probe spectroscopy in strongly correlated organic conductors
Dr. Satoshi Tsuchiya, Complex Matter Department, Jozef Stefan Institute, Slovenia; Department of Applied Physics, Hokkaido University, Japan

Abstract:

The series of k-(BEDT-TTF)2X (X: anion molecules) has attracted much interest in fundamental physics related with strong electron correlation and application of devices because of a rich variety of electronic phases under equilibrium such as the Mott insulator and superconductor, as well as nonequilibrium related with photoinduced phase transition. In my long-term stay in JSI, spectrally-resolved pump probe spectroscopy was carried out to investigate superconducting phase in this system. On the other hand, three-pulse pump probe spectroscopy was applied for photoinduced phase separation. In the seminar, I will show the obtained results briefly and discuss in detail.

Poster [PDF]

Koichi Nakagawa, 1.6.2018 at 13:30 in the Physics Seminar room

Polarized pump-probe measurements in organic superconductors near Mott boundary
Koichi Nakagawa, Department of Applied Physics, Hokkaido University, Sapporo, Japan

Abstract:

A series of κ-type organic superconductors offers an ideal electronic system to investigate crucial electronic properties such as pseudogap and fluctuating superconductivity, for understanding mechanism of unconventional superconductivity since chemical substitution in insulating/conducting molecules can lead to change of effective electron correlation, contributed by its flexible nature. Recently, behavior of the superconducting electronic state near the Mott boundary has attracted much attention since the Nernst effect measurements, which can detect finite superconducting quantum vortices even above Tc, reported the huge onset temperature divergently up to ~5 Tc with reaching the boundary.   However, the consensus about the fluctuating state has yet to be reached due to the inconsistencies from the other experimental methods. Thus, spectroscopic methods, which can characterize the superconducting gap formation, have been required. In the presentation, I would like to talk about the results of the polarized pump-probe spectroscopic measurements, which are sensitive to the gap formation near EF, for κ-type organics, in which the electron correlation is finely tunable around the Mott boundary by a ratio of deuterated conducting molecules.

Poster [PDF]

Asst. Prof. Dr. Hiroyoshi Nobukane, 1.6.2018 at 13:00 in the Physics Seminar room

High-Tc superconductivity in ruthenates
Asst. Prof. Dr. Hiroyoshi Nobukane, Department of Physics, Hokkaido University, Sapporo, Japan

Abstract:

Layered perovskite materials can control quantum states from superconductivity to a Mott insulator by tuning physical and chemical pressure. By reducing the thickness of a layered crystal to nanometer range, a nanofilm due to a negative pressure effect leads to novel quantum states that have not been found yet in bulk crystals. We will discuss the emergence of high-Tc superconductivity near 100 K in Ca2RuO4 nanofilms. A thin film of Ca2RuO4 exhibits supercurrent and typical Berezinskii-Kosterlitz-Thouless transition behavior. We also found that the tuned  film thickness and the induced bias current cause a superconductor-insulator transition. Our results demonstrate the presence of two-dimensional superconductivity from a high temperature. The fabrication of nanofilms made of layered material enables us to discuss rich superconducting phenomena in ruthenates.

Poster [PDF]

Jaka Vodeb, 25.5.2018 at 13:00 in F7 Seminar room

Charged lattice gas of polarons in 1T-TaS2
Jaka Vodeb, Department for Complex Matter, Jozef Stefan Institute, Ljubljana, Slovenia

Abstract:

Motivation for this work comes from the discovery of a new metastable amorphous (A) state in 1T-TaS2 (TAS)1. The A state represents a disordered polaron pattern, which exhibits metallic behavior. We employed a classical charged lattice gas of polarons with screened Coulomb interaction and a fixed polaron concentration as a model for the A state. The idea has been used successfully in the work of Brazovskii2 who first proposed the model and used it to model the commensurate state. Karpov et al.3 also used it to model the hidden state, observed in TAS4. Our work has shown that the A state can be successfully modeled using classical charged polarons. Further investigation of the model has shown that there exists an infinite number of crystalline phases within the model as a function of polaron concentration. There also exist other amorphous phases which lie in between the crystalline phases. They exhibit glassy behavior and in contrast to the current paradigm of glass formation5 appear to be the ground state of the system.

Poster [PDF]

Michele Diego, 17.5.2018 at 11:00 in F7 Seminar room

Out of equilibrium electronic properties of ZrTe5
Michele Diego, Department of Complex Matter, JSI

Abstract:

Transition metal pentatelluride, ZrTe5, displays a set of unique and exotic transport properties, which make this material an ideal candidate for magnetic and thermoelectric devices. In particular, the best known anomaly is its resistivity trend, which shows a metallic behavior or a semiconductor behavior,  respectively, for temperatures below or above a critical temperature. Several theoretical models have been proposed to interpret this anomaly, based on charge density wave or polaron formation, but with no direct experimental verification. In this work we report on the temperature dependence of the ZrTe5 valence band, studied at equilibrium and out of equilibrium, by means of time and angle resolved photoemission spectroscopy. Our results unveil the dependence of the band structure across the Fermi level on the sample temperature. By performing temperature dependent experiments, we are able to observe an energy shift of the ZrTe5 valence band. The same effect is observed both by varying the equilibrium sample temperature and by optically exciting the system out-of equilibrium.
Finally, by following the out-of-equilibrium time evolution of the valance band, we report the relaxation times of its position, width and intensity.

Poster [PDF]

Matjaž Ličen, 20.4.2018 at 13:00 in F7 Seminar room

Photoregulating the self-assembly of lipophilic guanosine derivaters at the air-water interface
Odsek za kompleksne snovi, IJS

Abstract:

Basic blocks of DNA are very interesting constituents for designing supramolecular single-layer and multilayer surface  architectures. Our recent studies of self-assembly of nucleoside derivatives in monolayer films at the air-water interface (Langmuir films) reveal that guanosine derivatives exhibit very different behaviour from analogous derivatives containing other nucleobases [1]. We also demonstrated that the number of lipophilic chains attached to the sugar hydroxyl groups and the type/concentration of ions present in the water subphase strongly affected molecular organization of guanosine derivatives in Langmuir monolayers as well as in Langmuir-Blodgett (LB) films deposited on various solid substrates [2,3,4]. Modifications of these parameters hence provide a possibility of tuning intermolecular organization in thin film configurations.  An appealing strategy for control and manipulation of intermolecular organization is to use optical irradiation. To test the applicability of this method in case of guanosine derivatives we investigated Langmuir films of azo-functionalised guanosine molecules in which the isomerization can be switched from trans to cis and vice versa by irradiation with UV and visible light. Photoinduced modifications within Langmuir films were studied by film balance experiments and by Brewster angle microscopy (BAM). We were able to reversibly induce changes in the surface pressure of the film by alternatingly irradiating with UV and blue light, indicating a light-induced change in the film structure. The measurements for several different films mixed from a photoactive guanosine derivative and other non-photoactive nucleosides were compared to a simplified model of the film. The results from the model are in good agreement with the measurements for all films, except for the film formed by mixing guanosine and cytidine molecules, which hints at specific bonding between these two molecules.

[1] L. Coga, T. Ilc, M. Devetak, S. Masiero, L. Gramigna, G. P. Spada, and I. Drevensek Olenik, Colloid. Surface B103, 45 – 51 (2013).
[2] M. Devetak, S. Masiero, S. Pieraccini, G. P. Spada, M. Copic, and I. Drevensek Olenik, Appl. Surf. Sci. 256,2038  2043 (2010)
[3] L. Coga, S. Masiero, and I. Drevensek Olenik, Colloid. Surface B 121, 114 – 121 (2014)
[4] L. Coga, S. Masiero, and I. Drevensek Olenik, Langmuir 31, 4837 – 4843 (2015)

Splay nematic phase

BioMedical Optics

Microfluidics

Picnic 2018

New Year’s dinner 2017

Hidden quantum resistance of a superconductor nanowire, Science Advances

Superconductors are known for zero electrical resistance, which is one of the consequences of superconductivity as a macroscopic quantum phenomenon.
However, in an unusual experiment on extremely narrow superconducting nanowires performed by Ivan Madan and Jože Buh under the leadership of Dragan Mihailovic, the superconductor is switched by ultrashort laser pulses to a hidden metastable resistive quantum state with the introduction of quantum phase slip centers. While the work demonstrates a new fundamental quantum phenomenon of nonequilibrium superconducting states related to quantum chaos, it is also of interest for designing new single photon detectors for use in quantum encrypted communications.
The nanowires were synthesised by Aleš Mrzel, while the theory calculations were performed by Viktor Kabanov and his student Vladimir Baranov, so everything from nanomaterial synthesis, nanocircuit technology to electrical and optical measurements, including theory is proprietary knowledge developed at the Jozef Stefan Institute and the CENN Nanocenter. The work was published on March 30 in Science Advances.

____________________________

Skrita kvantna upornost superprevodne nanožice

Superprevodniki so znani po tem, da nimajo električnega upora, kar je ena izmed posledic makroskopske kvantne narave tega pojava. Vendar pa se izkaže, da v to ne velja vedno. V eksperimentu, ki sta ga izvedla Ivan Madan in Jože Buh pod vodstvom Dragana Mihailovića s kratkimi laserskimi sunki so raziskovalci pokazali, da je možno superprevodne nanožice z majhnimi premeri spraviti v metastabilno kvantno stanje v katerih je upor končen. Poleg tega, da delo odkriva nov temeljni kvantni pojav neravnovesnih superprevodnih stanj povezan s kvantnim kaosom, je odkritje zanimivo tudi iz vidika razvoja novih detektorjev posameznih fotonov v kvantnih šifriranih komunikacijah. Nanožice je sintentiziral Aleš Mrzel, teoretične izračune pa opravil Viktor Kabanov s svojim študentom Vladimirom Baranovim. Celotno delo, ki vključuje sintezo nanožic po novi poti, priprave vezij nanometrskih dimenzij, električnih in optičnih meritev ter teoretičnimi izračuni, je rezultat lastnega znanja z Inštituta »Jožef Stefan« in CO Nanocentra. Delo je objavljeno 30. marca v ugledni reviji Science Advances.

Anisotropic magnetic nanoparticles: A review of their properties, synthesis and potential applications

A review article Anisotropic magnetic nanoparticles: A review of their properties, synthesis and potential applications has been published in the journal Materials Science (impact factor 31.140), after an invitation from the Editor, by Prof. Dr. Darja Lisjak (Department for Materials Synthesis) and Dr. Alenka Mertelj (Department of Complex Matter). The research on magnetic nanoparticles has been increasing in the last two decades or so due to their interesting properties and a wide range of applications in techniques, ecology and bio-medicine. The authors focused on the anisotropic magnetic nanoparticles that, in addition to their nano dimensions, show scientifically relevant and applicable properties due to their anisotropic shapes. Progress of Materials Science, Vol. 95, June 2018, 286-328

Dr. Andrey Leontyev, 12.4.2018 at 13:00 in F7 Seminar room

Nonresonant multi-pulse selective spectroscopy of interaction-induced responses in liquids using optical Kerr effect

Kazan E.K. Zavoisky Physical-Technical Institute, Kazan, Russia

Abstract:

An ultrafast selective spectroscopic measurements of vibrational-rotational dynamics of molecules in liquids were implemented using optical Kerr effect (OKE) detection under multi-pulse nonresonant xcitation. Introducing additional excitation pulses and creating either constructive or destructive interference of corresponding wave packets allows one to isolate the responses of certain molecular motions (orientational,inter-orintramolecular)in OKE signal. As a result,the  parameters of molecular rotations and coherent vibrations could be evaluated with significantly greater precision compared to conventional single pulse excitation scenario.

Matej Prijatelj, 23.3.2018 at 13:00 in F7 Seminar room

Expansion of transition metal dichalcogenides

Hella Saturnus Slovenija d.o.o., HSS – Ljubljana

Abstract:

Layered two-dimensional materials have unique physical and chemical properties due to their highly anisotropic nature.
A few of the layered crystals can be further expanded to low density / high specific surface area materials by introducing molecules to the inter planar spaces. These can be rapidly transformed to gas which inflates the layers and transforms the compact crystals to low density foam like structures. The most notable examples of expanded layered crystals are expanded vermiculite and expanded graphite. Both have numerous uses both in science and industry.
Transition metal dichalcogenides (TMDs) form layered crystals of stoichiometry MX2 (M=transition metal, X=S, Se, or Te). The best known compound, MoS2, is an earth abundant mineral and has been used for decades as a solid lubricant and as a catalyst for petroleum desulphurization.
In this seminar I will present our results in preparation and expansion of air stable expandable MoS2 and expanded TiS2 and TaS2. The quality of the expanded crystals has been shown by various analytical techniques not to differ from the parent compounds and our findings show that expandable MoS2 can be considered an analogue to expandable graphite.

Prof. dr. Roman Sobolewski, 16.3.2018 at 13:00 in the Physics Seminar room

Nanostructured superconducting single-photon detectors as photon energy, number, and polarization resolving devices

Departments of Electrical and Computer Engineering and Physics and Astronomy, and the Materials Science Program and Laboratory for Laser Energetics, University of Rochester, Rochester, NY

Abstract:

We present an overview of the physics of operation of superconducting single-photon detectors (SSPDs) and their implementation as the photon-energy, photon-number, and polarization resolving devices. The detection mechanism of SSPDs is based on photon-induced hotspot formation and, subsequent, generation of a voltage transient across a nanostructured superconducting NbN meander (~4-nm-thick and ~100-nm-wide stripe). The NbN SSPD operates in the 4.2-2 K temperature range. The best devices exhibit quantum efficiency of up to near 100% (when encapsulated in a cavity) in the near-infrared (1550 nm) wavelength range, dark count rates <1 Hz, and the noise-equivalent power (NEP) of ~510-21 W/Hz.1/2 For our photon-energy resolution studies, we have adopted a statistical method based on a well-documented fact that quantum efficiency (QE) of SSPDs very strongly (quasi-exponentially) depends on the photon wavelength and the normalized current bias. Thus, by measuring the SSPD QE at different bias levels, we were able to resolve the wavelength of the incident photons with a 50-nm resolution. In another approach, we have implemented a low-noise, cryogenic high-electron-mobility transistor (HEMT) as a very high impedance element to separate the 50-Ω output transmission line from the SSPD. This arrangement allowed us to achieve some amplitude resolution of the recorded output transients and, subsequently, photons with different energies could be distinguished by comparing the output transient amplitude distributions. Next, by designing SSPDs with different physical geometries, we could unambiguously demonstrate their sensitivity to photon polarization. At the end of our presentation, we will present new directions of the SSPD research, focusing on superconductor/ferromagnetic nanostripes.

Yelyzaveta Chernolevska, 14.3.2018 at 13:00, Seminar room F7

Cluster structure of monohydric alcohol

Yelyzaveta Chernolevska, Faculty of Physics of Taras Scevchenko, National University of Kyiv, Ukraine

Kolokvij Oddelka za fiziko, FMF, 12.3.2018 at 16:15

Artificial Life at Low Reynolds Number
dr. Mojca Vilfan , Jozef Stefan Institute, Department for complex matter

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Best poster Award LEES at 2018 for Mimoza Naseska

Young researcher Mimoza Naseska was awarded Best Poster Award at the 2018 Low Energy Electrodynamics of Solids (LEES) conference, June 24-29, 2018, Portonovo, Ancona, Italy for poster “Optical quench and recovery of SDW state SeFe2As2 and EuFe2As2”.

Best Poster Award at QCM 2018 for Mimoza Naseska

Young researcher Mimoza Naseska was awarded Best Poster Award at the International Workshop Quantum Complex Matter (QCM 2018) and Frontiers Condensed Matter Physics (FCMP),  June 11-15, 2018, Rome, Italy for poster “Optical quench and recovery of SDW state SeFe2As2 and EuFe2As2”.