У оквиру семинара Центра за физику чврстог стања и нових материјала у среду, 7. новембра 2018. године у 14:30 часова, у читаоници „Др Драган Поповић“, проф. др Војислав Крстић (Department of Physics, Friedrich-Alexander-Universität, Erlangen, Germany) одржаће предавање:

Local Electronic Confinement in Graphene: From Raman Response of Covalent Derivatives to Optics with Electrons

САЖЕТАК:

Local electronic confinement is a key-ingredient for the successful control of electronic and optoelectronic properties of any material. In graphene however, due to its specific hexagonal lattice structure (two triangular sublattices) and the circumstance to be made of carbon atoms, electronic confinement can have many different flavours than just the localisation of electrons. Here we address two manifestations of electronic confinement, one mainly chemistry driven, the other driven by physical interactions:
Covalent functionalization of graphene is a continuously progressing field of research. However, in virtually all optical responses, an unresolved enhancement in peak intensity with increase of sp3 carbon content is observed. To elucidate this general phenomenon we present a phenomenological model [1] which takes into account the circumstance that upon covalent functionalization confined π-conjugated domains (photoluminescent) surrounded by sp3 carbon regions in graphene monolayers are formed.[2,3] Our model, underpinned by combined Raman measurements and an in-situ dry electrostatic doping technique, incorporates the modulation of the Raman intensities through the photoluminescence active domains, and correlates the individual D- and G-mode intensities to the degree of functionalization. Through this, evaluations of Raman spectra using our model circumvent the ambiguities and information loss encountered when using the ratio of D- and G-mode intensities. Physical confinement involves the use of potential barriers and wells in contrast to altering chemical bonds. However, the use of electrostatic potentials for confinement of the relativistic electrons in graphene is not efficient due to the Klein paradox. Nevertheless, the introduction of local electrostatic potentials is theoretically predicted to have a confining action in form of a caustic motion of electrons within the potential [4]. We will show that this effectively results in a guiding of electrons through scattering, which is the electronic analogue of the well-known Mie scattering [5].

РЕФЕРЕНЦЕ:

1. P. Vecera, S. Eigler, M. Koleśnik-Gray, V. Krstić, A. Vierck, J. Maultzsch, R. A. Schäfer, F. Hauke, A. Hirsch, Scientific Reports 7, 45165, DOI: 10.1038/srep45165 (2017)
2. J. Robertson, E.P. O’Reilly, Phys. Rev. B 35, 2946-2957 (1987).
3. F. Demichelis, S. Schreiter, A. Tagliaferro, Phys. Rev. B 51, 2143-2147 (1995).
4. R.L. Heinisch, F.X. Bronold, H. Fehske, Phys. Rev. B 87, 155409 (2013).
5. J.M. Caridad, S. Connaughton, C. Ott, H.B. Weber, V. Krstić, Nature Communications 7, 12894, DOI: 10.1038/NCOMMS12894 (2016)

У оквиру СЦЛ семинара Центра за физику комплексних система, у четвртак, 8. новембра 2018. године у 14 часова, у читаоници Института за физику „Др Драган Поповић“, Dr. Andreas Oestlin (Institute of physics, University of Augsburg, Germany), одржаће предавање:

Disorder and Correlation for Realistic Materials: a LDA+DMFT and CPA Approach

САЖЕТАК:

We introduce a computational scheme for calculating the electronic structure of random alloys that includes electronic correlations within the framework of the combined density functional and dynamical mean-field theory. By making use of the particularly simple parameterization of the electron Green’s function within the linearized muffin-tin orbitals method, it is possible to greatly simplify the embedding of the self-energy. This in turn facilitates the implementation of the coherent potential approximation, which is used to model the substitutional disorder. The computational technique is tested on the Cu-Pd binary alloy system, and for disordered Mn-Ni interchange in the half-metallic NiMnSb.

У оквиру СЦЛ семинара Центра за физику комплексних система, у уторак 6. новембра 2018. године у 14 часова, у читаоници Института за физику „Др Драган Поповић“, Dr. Wilhelm Appelt (Institute of physics, University of Augsburg, Germany), одржаће предавање:

„Predicting the conductance of strongly correlated molecules: the Kondo effect in PTM/Au junctions“

САЖЕТАК:

Stable organic radicals integrated into molecular junctions represent a practical realization of the single-orbital Anderson impurity model. Motivated by recent experiments for perchlorotriphenylmethyl (PTM) molecules contacted to gold electrodes, we develop a method that combines density functional theory (DFT), quantum transport theory, numerical renormalization group (NRG) calculations and renormalized super-perturbation theory (rSPT) to compute both equilibrium and non-equilibrium properties of strongly correlated nanoscale systems at low temperatures effectively from first principles. We determine the possible atomic structures of the interfaces between the molecule and the electrodes, which allow us to estimate the Kondo temperature and the characteristic transport properties, which compare well with experiments. By using the non-equilibrium rSPT results we assess the range of validity of equilibrium DFT + NRG-based transmission calculations for the evaluation of the finite voltage conductance. The results demonstrate that our method can provide qualitative insights into the properties of molecular junctions when the molecule–metal contacts are amorphous or generally ill-defined, and that it can further give a fully quantitative description when the experimental contact structures are well characterized.

У оквиру семинара Центра за фотонику, у уторак 6. новембра 2018. године у 11 часова, у читаоници Института за физику „Др Драган Поповић“, Dr. Juan José Alvarado-Gil (Institut Pprime, CNRS, Université de Poitiers, ISAE-ENSMA), одржаће предавање:

„Photothermal techniques: versatile multipurpose methodologies for the study of composite materials“

САЖЕТАК:

Photothermal techniques are based on the generation of trains of thermal waves in a material, induced by its illumination with an adequate light source. Due to its intrinsic nature, thermal waves involve a myriad of intertwined physical process related to transport phenomena, mechanical vibration, phase transitions and chemical reactions, among others. Their behavior is strongly influenced by the geometry, the presence of interfaces, and by the micro and nanostructure. The way in which the thermal wave phenomena are induced as well as the way of detecting them define the type of phenomena and the spatial and temporal resolution which can be achieved. Those characteristics make photothermal techniques very well suited for the study of a wide variety of composite materials. In this talk, we present results for the measurement of physical properties of layered, composite, granular and smart materials using different photothermal techniques. Results using photoacoustics, thermal wave cavity, photothermal radiometry, thermography, flash radiometry and transient grating are presented. It is shown that the technique can provide reliable results in a wide range of densities, thermal properties as well as in the study of time dependent phenomena.

ИЗАБРАНЕ ПУБЛИКАЦИЈЕ:

[1] NW Pech-May, C Vales-Pinzon, A Vega-Flick, A Oleaga, A Salazar, JM Yanez-Limon, JJ Alvarado-Gil
Heat transport in epoxy and polyester carbonyl iron microcomposites: The effect of concentration and temperature
Journal of Composite Materials, 52(10), 1331-1338, (2018), https://doi.org/10.1177/0021998317723694

[2] JD Macias, J Bante-Guerra, F Cervantes-Alvarez, G Rodrìguez-Gattorno, O Arés-Muzio, H Romero-Paredes,
CA Arancibia-Bulnes, V Ramos-Sánchez, HI Villafán-Vidales, J Ordonez-Miranda, R Li Voti, JJ Alvarado-Gil
Thermal Characterization of Carbon Fiber-Reinforced Carbon Composites
Applied Composite Materials, (2018)https://doi.org/10.1007/s10443-018-9694-0

[3] Jose Ordonez-Miranda, Ronggui Yang, Juan Jose Alvarado-Gil
Thermal Conductivity of Particulate Nanocomposites
Nanoscale Thermoelectrics, Lecture Notes in Nanoscale Science and Technology, 16, 93-139, (2014), https://doi.org/10.1007/978-3-319-02012-9_3

[4] J Ordonez-Miranda, Ronggui Yang, JJ Alvarado-Gil
On the thermal conductivity of particulate nanocomposites
Applied Physics Letters, 98 (23), 233111, (2011), https://doi.org/10.1063/1.3593387

[5] Jose Ordonez-Miranda, Younès Ezzahri, Karl Joulain, Jérémie Drevillon, JJ Alvarado-Gil
Modeling of the electrical conductivity, thermal conductivity, and specific heat capacity of VO 2
Physical Review B, 98(7), 075144, (2018) https://doi.org/10.1103/PhysRevB.98.075144

[6] Jose Ordonez-Miranda, Ronggui Yang, Sebastian Volz, Juan Jose Alvarado-Gil
Steady state and modulated heat conduction in layered systems predicted by the analytical solution of the phonon Boltzmann transport equation
Journal of Applied Physics, 118(7), 075103, (2015), https://doi.org/10.1063/1.4928770

[7] Jose Ordonez-Miranda, Ronggui Yang, JJ Alvarado-Gil
A constitutive equation for nano-to-macro-scale heat conduction based on the Boltzmann transport equation
Journal of Applied Physics, 109(8), 084319, (2011), https://doi.org/10.1063/1.3573512

[8] Jose Ordonez-Miranda, Juan Jose Alvarado-Gil
On the stability of the exact solutions of the dual-phase lagging model of heat conduction
Nanoscale research letters, 6(1), 321, (2011) doi: 10.1186/1556-276X-6-327

У оквиру семинара Центра за физику чврстог стања и нове материјале, у петак 2. новембра 2018. године у 14 часова, у читаоници Института за физику „Др Драган Поповић“, др Алберто Помар, Институт за науку о материјалима у Барселони, одржаће предавање:

„Strain tuned magnetic behavior in oxide thin films“

САЖЕТАК:

Transition metal oxides are known by their remarkable functional properties spanning a wide range of phenomena such as ferroelectricity and magnetism, as well as colossal magnetoresistance (CMR) and high temperature superconductivity. The mechanisms behind such extraordinary properties lie on the subtle balance between competing energies in the system. In particular, the extreme sensitivity of these properties to structural distortions and crystal chemistry offers many routes for controlling and engineering new functionalities. Interestingly, epitaxial growth of thin films introduces a new degree of freedom in the equation due to the elastic energy involved to fir the different lattice parameter and structure of film and substrate. In this way, it has been demonstrated that a fine tuning of strain relaxation mechanisms may lead to unexpected properties.
In this talk, I will review some of the results of our grupo on the growth and properties of several perovskite manganese thin films. First, i will show that both, antiferromagnetic or ferromagnetic behavior may be achieved in LaMnO3 thin films by careful tuning the strain state of the film. The possible origin of this magnetic ordering will be discussed as well as its implications in the electronic properties. Furthermore, results on the magnetic anisotropy of oxide films will also be presented and their potential applications in electronic devices will be shown.

ФОТО: Институт за науку о материјалима у Барселони

У оквиру обновљеног семинара посвећеног историји науке и теорији сазнања у уторак, 30. октобра 2018. године у 13 часова у читаоници библиотеке „Др Драган Поповић“ Института за физику у Београду биће одржано предавање:

Неке епистемолошке паралеле поводом доделе Нобелових награда 2017. и 2018. године: Признања идејним решењима или Награде за резултате који су већ употребљиви

Предавање ће одржати проф. Миленко Б. Плавшић са Технолошко–металуршког факултета Универзитета у Београду.

У петак, 26. октобра 2018. године у 12 часова на Институту за физику у Београду у сали 360, др Дејан Симић ће одржати семинар
под насловом:

Асимптотске симетрије и софт теореме

САЖЕТАК:

Обрадићемо симетрију безмасене Електродинамике у светлосној бесконачности и њену везу са софт теоремом за фотоне. Предавање ће бити више описног него техничког типа, а више детаља биће на следећем семинару ако постоји интересовање публике.

У оквиру СЦЛ семинара Центра за изучавање комплексних система, у четвртак, 25. октобра 2018. у 14 часова у читаоници библиотеке „Др Драган Поповић“ Андреас Вех (Institute of physics in Augsburg) ће одржати предавање:

„Charge reconstruction and Friedel sum rule in heterostructures“

САЖЕТАК:

We present a self-consistent method for using real space dynamical mean-field theory (r-DMFT) to address local and intersite Coulomb interactions in heterostrcutures. The local in-plane many-body problem is solved using the continuous-time quantum Monte Carlo approach for the Hubbard model in hybridization expansion (CT-Hyb). The mean-field interlayer Coulomb potential generates a classical electrostatic problem solved by the Poisson equation for the multilayered geometry. Using this method we study half-metallic heterostructures made of coupled layers of single-band Hubbard models. A similar setup for non-magnetic heterostructures turns out to be a useful playground to investigate the validity of the Friedel sum rule.