У оквиру семинара Лабораторије за фотоакустику Центра за фотонику Института за физику у Београду, у четвртак, 24. октобра 2019. у 11 часова у сали „Звонко Марић“, проф. Јацек Закшевски (Институт за физику, Универзитет Никола Коперник, Торуњ, Пољска) одржаће предавање:

Photothermal Spectroscopy of Bulk Crystals and Heterostructures

САЖЕТАК:

The presentation shows the latest results obtained in the Applied
Physics Group in Torun (Poland) by piezoelectric photothermal
spectroscopy. Thermal and optical parameters of CdZnSe mixed crystals
and AlGaAs/GaAs heterostructures were characterized by this method.

The investigated bulk crystals were grown by the high-pressure Bridgman
method under argon overpressure. The crystals were cut into 1-1.2 mm
thick plates and mechanically grounded, polished and chemically etched.
The influence of zinc content and preparation method on the amplitude
and phase spectra is observed.
Mechanical, chemical and thermal treatment of the surface can create the
damaged subsurface layer which introduces additional defects states in
the material. The increase of the zinc content can also be associated
with the creation of volume defects in the material. Several features
of the crystals were revealed from the spectra, with the increase of
zinc content: a shift of the energy gap, broadening of the absorption
band, increase of the surface absorption.
For semiconductors, there are three main sources of photothermal signal:
thermal, plasma waves (associated with diffusion and recombination of
carriers). In the photoacoustic investigation of transport in
semiconductors one can also take into account immediate thermalization
of carriers and nonradiative surface recombination. Their influence on
the character of amplitude and phase spectra is showed and discussed.

Piezoelectric photothermal spectroscopy was also used to characterize
AlGaAs/GaAs heterostructures. The two-layer model proposed by Fernelius
and the interference model of Malinski were chosen to analyze the phase
and amplitude of PPS spectra. For each type of experimental setup
configuration, the theoretical models were fitted to experimental data
in order to obtain the thermal and optical parameters of the
investigated material.

У оквиру семинара Лабораторије за спектроскопију плазме и ласере, у среду, 23. октобра 2019. у 12 часова у читаоници библиотеке „Др Драган Поповић“, Марко Цвејић (Weissman Institute of Physical Sciences, Israel) одржаће предавање:

Challenges in the investigation of compression of magnetized plasma

САЖЕТАК:

The seminar will refer to a compression of magnetic flux that is
initially embedded in a plasma that undergoes an implosion. The plasma
is produced in a Z-pinch configuration in which a gas puff load is
ionized and implodes under the J×B forces resulting from a 1-μs long,
300 kA, current pulse.
The subject of compression of magnetic flux and magnetized plasma is a
fundamental problem manifested in a variety of conducting fluid
phenomena in laboratory plasmas and astrophysics. Recently, this subject
has gained particular interest due to the advances in producing plasmas
of high temperature and density for fusion purposes, based on the
approach of magnetized plasma compression.
We report the first-time development and employment of spectroscopic
methods, based on the Zeeman effect and polarization techniques, to
measure both the compressed (axial) and the compressing (azimuthal)
magnetic fields throughout the implosion and stagnation processes. Time
and space resolved spectroscopic measurements showed that the
application of a relatively weak axial magnetic field (Bz0) has a
dramatic effect on the implosion dynamics affecting significantly the
current distribution in the plasma [1]. It was found that in the
presence of Bz a large part of the current does not flow in the
imploding plasma, rather it flows through a slow-imploding low-density
plasma (LDP) residing at large radii. Furthermore, it is observed that
the fraction of total current that flows in the LDP increases with Bz0.
We suggest an explanation of the phenomena, based on the development of
a force-free current configuration.
Previously unpredicted observations in high-power magnetized-plasma
experiments, including recent unexplained structures observed in the
Magnetized Liner Inertial Fusion experiment, may be connected to the
present discovery.
[1] Mikitchuk, D., Cvejić, M., Doron, R., Kroupp, E., Stollberg, C.,
Maron, Y., Velikovich, A. L., Ouart, N. D., Giuliani, J. L., Mehlhorn,
T. A., Yu, E. P., and Fruchtman, A. “Effects of a preembedded axial
magnetic field on the current distribution in a Z-pinch implosion”,
Phys. Rev. Lett. 122, 045001 (2019).

У оквиру семинара Лабораторије за квантну и атомску оптику у уторак, 22. октобра 2019. у 13 часова у читаоници библиотеке „Др Драган Поповић“, Марија Ћурчић ће одржати предавање:

Примена квантних и нелинеарних феномена у пари калијума за контролу особина ласерског зрачења

У уводном делу Душан Арсеновић ће говорити о садржају истраживања по темама: квантни и нелинеарни процеси и феномени у парама алкалних метала, плазмонски материјали и увезана стања, нумерика и закони одржања, солитони, дисперзионе релације у Дираковој тачки.

САЖЕТАК:

Алкални метали, као активне средине, показали су се као погодни медијуми за генерисање квантних и нелинеарних ефеката. У лабораторији за Нелинеарну и квантну оптику се бавимо студијом кохерентних ефеката у пари калијума, и на који начин их можемо искористити за добијање нових, некласичних стања светлости. У фокусу нашег истраживања је ефекат четвороталасног мешања таласа у двострукој
ламбда конфигурацији, и његова примена за добијање амплитудски стиснуте светлости. С друге стране, проширујемо наше истраживање и на студију електромагнетски индуковане транспаренције, на степеничастој атомској шеми, са високо побуђеним Ридерговим стањима, у жељи да одговоримо на питање – могу ли се и на овај начин генерисати стиснута стања светлости?

У оквиру семинара Центра за изучавање комплексних система Института за физику, у четвртак, 24. октобра 2019. у 14 часова у читаоници библиотеке „Др Драган Поповић“, др Игор Станковић (Лаборатирија за примену рачунара у науци, Центар за изучавање комплексних система, Институт за физику у Београду) одржаће предавање:

How can simple models help us understand experiments?

САЖЕТАК:

Physical models are simplified versions of real systems that allow us to understand and sometimes predict their behaviour. While designing a model we evaluate different mechanisms present in the system and pare it down to a few essential. If designed well, a model gives a better understanding of the measured quantities and fully reveals the interplay of mechanisms behind. In this talk, we will review challenges and modelling work performed for reproducing AFM experiment [1,2], understanding the relationship between the molecular shape of ionic liquids and their behaviour [3], and exploring the phase diagram of the magnetic cubes [4].

[1] B. Vasic, A. Matkovic, R. Gajic, IS, Wear Properties of Graphene Edges Probed by Atomic Force Microscopy Based Lateral Manipulation, Carbon 107, 723 (2016).
[2] B. Vasic, IS, A. Matkovic, M. Kratzer, C. Ganser, R. Gajic, C. Teichert, Molecules on Rails: Friction Anisotropy and Preferential Sliding Directions of Organic Nanocrystallites on Two-dimensional Materials, Nanoscale 10, 18835 (2018).
[3] M. Dasic, IS, K. Gkagkas, Molecular Dynamics Investigation of the Influence of the Shape of Cation on the Structure and Lubrication Properties of Ionic Liquids, Phys. Chem. Chem. Phys. 21, 4375 (2019).
[4] L. Balcells, IS, Z. Konstantinovic, A. Alagh, V. Fuentes, L. Lopez-Mir, J. Oro, N. Mestres, C. Garcia, A. Pomar, B. Martínez, Spontaneous In-flight Assembly of Magnetic Nanoparticles into Macroscopic Chains, Nanoscale 11, 14194-14202 (2019).

У Београду се 15. и 16. октобра одржава седма конференција Теорија информација и комплексни системи (TINKOS) у организацији Математичког института Српске академије наука и уметности и Института за физику у Београду.

Овај интердисциплинарни догађај окупља истраживаче који се баве теоријом информација и комплексним системима, а основна тематска поља су комплексност, ентропија, нелинеарна динамика, комплексне мреже и машинско учење.

Теме конференције се односе подједнако на теорију и праксу, а један од главних циљева је окупљање истраживача и развијање мреже за дељење знања и идеја.

Конференција се одржава у просторијама МИ САНУ.

Више информација и програм скупа можете пронаћи на следећој страници.

У оквиру традиционалног колоквијума Института за физику у Београду, у уторак, 15. октобра 2019. у 12 часова у сали „Звонко Марић“ предавање под насловом:

A new era in superconductivity: Dawn of the nickel age?

одржаће Проф. др Филип Хансман (Max Planck Institute for Chemical Physics of Solids, Dresden, Germany)

САЖЕТАК:

The idea to find cuprate-analogue high-Tc superconductors is as old as the cuprate high-Tc phenomenon itself. This materials hunt has been revitalized in the past decade due to technological advances in heterostructure synthesis. Especially nickelates have always been high on the candidates list and are in a continuous focus of experimental and theoretical researchers alike. In August this year, finally, superconductivity was observed for the first time in a nickelate structure when Sr-doped NdNiO2 was found to be superconducting at 10 K. In this colloquium talk we will give a „theory-biased“ overview about past and present efforts put into nickelate-based superstructures, as well as preliminary insights about the new superconductors from a low energy effective model perspective.

Фотографија (едитована): ResearchGate.net/Philipp_Hansmann

Поводом сећања на оснивача и дугогодишњег руководица семинара из историје науке и епистемологије, др Петра Грујића, у читаоници библиотеке „Др Драган Поповић“ у уторак, 15. октобра 2019. у 13:30 др Мирослав Ивановић (Инситут за криминолошка и социолошка истраживања, Београд) одржаће предавање:

Историја, друштво и култура – о радовима Петра Грујића

Предавање је посвећено истраживачком раду др Петра Грујића у неколико области из домена друштвених наука.

У оквиру семинара Центра за изучавање комплексних система Института за физику, у среду, 16. октобра 2019. у 14 часова у читаоници библиотеке „Др Драган Поповић“, др Сандра Ступар (ETH, Zurich, Switzerland) одржаће предавање:

Time and clocks in quantum theory

САЖЕТАК:

Time in classical theory is absolute and global, and usually taken as a time parameter. On the other hand, in quantum mechanics there is no time operator, and quantum time as such does not exist, hence the classical time parameter is used in quantum evolution equations. But where does this notion of classical time physically arise from? And would it be possible to introduce very precise and well-synchronised quantum clocks in a similar way as classical clocks are used? In this talk we will start from the assumption that the only observable time is the one given by clocks, and hence to learn more about quantum time we need to build good quantum clocks and try to synchronize them. We will define clocks as quantum systems that need to provide a time reference, such as a sequence of ticks. Further, we will attempt to find limits on their synchronization, since it is well known that quantum systems interact with their environment thereby getting disturbed. What we will find out is that the performance of the quantum clocks we define depends crucially on their dimension (number of the distinguishable states available), and that the quantum clocks of a certain dimension could possibly perform better than the classical ones with the same state space size. The limitations to synchronizing local quantum clocks suggest that global time in quantum mechanics might not be a physically grounded notion. We will also further briefly discuss what limitations would be imposed on the evolution of our Universe, if it itself was/contained a quantum clock providing ticks that we observe as time.