Wydział Fizyki UW > Badania > Seminaria i konwersatoria > Seminarium Fizyki Materii Skondensowanej

Seminarium Fizyki Materii Skondensowanej

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Zapraszamy do sali 0.03a, ul. Pasteura 5 o godzinie 12:15

prof. Jacek Gapiński (UAM Poznań)

Local order in Yukawa colloidal suspensions – Rogers-Young numerical calculations and SAXS experiment

A short summary of my last seminar at the same place (November 2013) willserve as an introduction to our experimental and numerical study oncolloidal systems of strongly interacting Yukawa particles. The formerresults were related mainly to dynamic properties of such systems focusedon the hydrodynamic function in conditions close to crystallization. Inthis report I would like to focus on static properties of highly orderedYukawa colloids represented by silica particles in DMF with smalladditions of LiCl as added salt, studied experimentally by means of smallangle x-ray scattering (SAXS) and analyzed using numerical calculationsbased on Ornstein-Zernicke scheme with Rogers-Young closure relation. Theexperimental results served as an inspiration for thorough numericalRogers-Young calculations of local structure in strongly interactingYukawa particles systems studied from the point of view of anexperimentalist. Such parameters as volume fraction, effective charge andadded salt concentration were chosen for calculating the phase diagrams ofYukawa systems. The applicability of Rogers-Young scheme was shown on thebasis of master plots created in a 2D space with two parameters being thereduced screening length λ and reduced temperature , which coincide withthe plots obtained from computer simulations of such systems. Moreover,structural parameters of colloidal systems close to freezing conditionshave been shown to resemble those characteristic for crystalline colloidalstructures, fcc or bcc, depending on the value of λ. Finally, it will beshown that Rogers-Young calculations suggest that the local structure ofYukawa colloids is preserved even after severe dilution of the system.

Zapraszamy do sali 0.03a, ul. Pasteura 5 o godzinie 12:15

prof. Andrzej M. Oleś (Jagiellonian University Kraków; Max Planck Stuttgart)

Frustration and Entanglement in Spin-Orbital Models: Spin-Orbital Order in Systems with Orbital Dilution

Entanglement in the theory of condensed matter occurs for spin-orbital superexchange [1]. Inter alia, it leads to a cute and surprising rigorous topological order in the SU(2)⊗XY spin-orbital ring [2]. In doped Mott insulators spin-orbital order ia locally or even globally changed when a host with 4d4 ions and S = 1 spins is doped by 3d3 magnetic impurities with S = 3/2 spins (orbital dilution [3]). Frustration of spin- orbital interactions and the role of quantum fluctuations will be discussed.[1] Andrzej M. Oleś, J. Phys.: Condensed Matter 24, 313201 (2012). [2] W. Brzezicki, J. Dziarmaga, and A.M. Oleś, Phys. Rev. Lett. 112,117204 (2014). [3] W. Brzezicki, A.M. Oleś, and M. Cuoco, Phys. Rev. X 5, 011037 (2015).

Zapraszamy do sali 0.03a, ul. Pasteura 5 o godzinie 12:15

Nevill Gonzalez-Szwacki (IFT UW)

Borophene, a 2D boron crystal: structure, properties, and computational hints towards an experimental realization on a large scale

Computational studies suggested that an extended one-atom thick boroncrystal is stable. Very recently a fragment of such 2D crystal has been obtained experimentally. Borophene is also a parent structure of one‐dimensional nanotubes and zero‐dimensional nanocages. The structure and properties of these materials will be presented.

Zapraszamy do sali 0.03a, ul. Pasteura 5 o godzinie 12:15

Krzysztof Pomorski (IFT UW)

Justification of the canonical quantization of the Josephson effect

Quantum devices based on Josephson effect in superconductors are usually described by a Hamiltonian obtained by commonly used canonical quantization. However, this recipe has not been yet rigorously justified. We show that this approach is indeed correct in certain range of parameters. We find the condition of the validity of such quantization and the lowest corrections to the Josephson energy.

Zapraszamy do sali 0.03a, ul. Pasteura 5 o godzinie 12:15

Paweł Jakubczyk (IFT UW)

Quantum interfacial phase transitions in two dimensions: a path to non-universal critical singularities

I will present the renormalization-group theory of interface unbinding(wetting) transitions in two spatial dimensions, occurring in the limit of vanishing temperature.

Zapraszamy do sali 0.03a, ul. Pasteura 5 o godzinie 12:15

prof. Józef Spałek (Uniwersytet Jagielloński, Kraków)

Teoria nadprzewodnictwa wysokotemperaturowego: wyjście poza teorię zrenomalizowanego pola średniego i porównanie z eksperymentem

Zapraszamy do sali 0.03a, ul. Pasteura 5 o godzinie 12:15

Krzysztof Wohlfeld (IFT UW)

Spin-orbital separation in the quasi-1D copper oxides

In contrast to collective spin excitations, the collective orbitalexcitations (orbitons) are hard to detect. However, recent advancements inresonant inelastic x-ray scattering have allowed for a rather unambiguousdetection of orbitons in the quasi-1D copper oxides [1, 2]. A closerinvestigation of the observed 1D orbiton dispersion suggested that thisdispersion could not be understood using a simple linear orbital wavepicture. Instead, it occurred that the orbiton in these materialsinteracts with the spin degrees of freedom [3, 4]. Nevertheless, due tothe quasi-1D character of these copper oxides, there is an effectivedecoupling of the orbiton from the spin excitation -- the so-calledspin-orbital separation [1-4].During the seminar I will explain in detail the idea of spin-orbitalseparation. I will show how the orbital excitation in the quasi-1Dcuprates, which actually can be understood as carrying both spin andorbital quantum numbers, can 'separate' into an independent orbiton andspinon excitation.References:[1] J. Schlappa et al.; Nature 485, 82 (2012).[2] V. Bisogni et al.; Phys. Rev. Lett in press (2015) and arxiv:1310.8346.[3] K. Wohlfeld et al.; Phys. Rev. Lett. 107, 147201 (2011).[4] K. Wohlfeld et al.; Phys. Rev. B 88, 195138 (2013).

Zapraszamy do sali 0.03a, ul. Pasteura 5 o godzinie 12:15

prof. Jerzy Górecki (ICHF PAN)

Chemical computing with reaction-diffusion media

The activity of nerve systems and brains in living organisms is based onan excitable chemical dynamics. My seminar will be concerned withinformation processing with Belousov-Zhabotinsky (BZ) reaction proceedingin a non-homogeneous medium. The time evolution of excitations in suchmedium seems qualitatively similar to propagation of nerve signals. I willdiscuss different methods of information coding in BZ medium. Chemicalrealizations of the basic logic gates for different strategies ofinformation coding will be presented. This demonstrates that the chemicalcomputing with reaction-diffusion medium is universal. In thereaction-diffusion computing the structure of medium is as important as thedynamics of chemical reactions involved. Some structures interesting forinformation processing operations can be automatically generated inmicrofluidic reactors. Concluding the seminar I will discuss classifiersconstructed with a chemical medium and present a strategy of their trainingto achieve the required functionality.

Zapraszamy do sali 0.03a, ul. Pasteura 5 o godzinie 12:15

dr Jarek Duda (Jagiellonian University, Purdue University)

Maximal Entropy Random Walk jako kwantowe poprawki dla modeli dyfuzyjnych

Standardowy wybór błądzenia losowego okazuje się być w wieluprzypadkach rozbieżny z eksperymentem, poprawnie opisywanym przezmechanikę kwantową. Przykładowo pozwoliłby on swobodnie poruszać sięelektronom po zdefektowanej sieci półprzewodnika, podczas gdy wiemy żenie jest on przewodnikiem - te elektrony powinny być uwięzione(lokalizacja Andersona). Maximal Entropy Random Walk (MERW) pozwalazrozumieć i naprawić tą rozbieżność poprzez wybór błądzenia zgodny zpodstawową dla fizyki statystycznej: zasadą maksymalizacji niewiedzy.MERW prowadzi do stacjonarnej gęstości prawdopodobieństwa dokładniejak przewidywana przez mechanikę kwantową, na przykład z elektronamipółprzewodnika uwięzionymi w studniach entropijnych. Opowiem pokrótce teżo innych zastosowaniach MERW: do maksymalizacji pojemności kanałuinformacyjnego przy zadanych więzach, oraz do analizy złożonych grafów, np.jako alternatywa dla PageRank lub do wyszukiwania wyróżniających sięobszarów obrazka.

Zapraszamy do sali 0.03a, ul. Pasteura 5 o godzinie 12:15

prof. Kalliopi Trohidou (Institute of Nanoscience and Nanotechology NCSR “Demokritos”, Athens, Greece)

Multiscale Modelling of the exchange bias behaviour of magnetic nanoparticles with core/shell (surface) morphology and their assemblies

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