Lecture abstracts
| Emilie Gaudry Univ. Lorraine CNRS UMR 7198, Institut Jean Lamour, Nancy |
| Electrons and phonons basics The atomic structure of complex intermetallic compounds, based on a giant cell containing up to several thousands of atoms, is responsible to a host of unusual physical properties – at least when judged against their chemical composition. For example, most of the Al-based complex intermetallic alloys do not have a metallic behaviour, although they are made of good metals like Al. This is usually related to the opening of a pseudogap in their electronic structure, i.e. a reduction in the density of the states at the Fermi energy. Similarly, the structures of complex intermetallics influence their vibrational properties. In this lecture, electrons and phonons basics will be presented, and applied in the case of (complex) intermetallic phases. |
| Marc de Boissieu SIMaP, Universite de Grenoble Alpes, CNRS, France |
| Complex structure reminder Structural complexity is one of the key parameter that influences physical properties. In this lecture we will give a reminder and overview of the differ ent kind of structural complexity, in particular in intermetallic compounds. The key notions are those o f order, disorder and local order. Using a selection of examples, ranging from aperiodic crystals to disordered periodic crystal we will illustrate the notion of complexity. Some of the too ls such as diffraction and diffuse scattering, used for structure determination, will be briefly introduced. Phonons in complex systems
In this lecture we will introduce the effect of structural complexity on the lattice dynamics and phonon spectrum. The lecture will be illustrated by the phonon properties of systems with increasing complexity. The notions of phonon dispersion, eigen-vectors and participation ration will be introduced. Inelastic x-ray and neutron scattering, the tools for experimental phonon measurements, will be introduced. Some of the experimental results will be compared to what can be achieved by lattice dynamic simulations.
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| Neven Barišić Institute of Solid State Physics, TU Wien, Vienna, Austria, and Department of Physics, Faculty of Science, University of Zagreb, Croatia |
| Electrons in complex systems A brief overview of the importance of material science in the past, presence and future will be given. Disorder effects on electrical properties will be introduced in the context of two classical and well-understood systems: semiconductors and metals. The important take home message is that, even in such rather simple systems, very complex behaviors can be observed. In this context, variable range hopping and quantum interference will be addressed. Magnetic impurities and their connection to correlation effects and Kondo physics will also be discussed. The Bandwidth (W) and the Coulomb repulsion (U) are the energy scales that define the behavior of electrons in complex systems. Two limits, the strong (W << U) and the weak (W >> U) coupling limit, will be addressed. In particular, in the strong coupling limit two different material classes will be discussed. Heavy Fermion systems, for which W is smaller than room temperature, constitute a beautiful demonstration of the coherent merging of quasi-localized and itinerant electrons. In this context, quantum critical behavior will be briefly addressed. In cuprate superconductors, as a second class of materials exhibiting strong coupling correlations, temperature is always smaller than W (and U). Consequently, phenomena that are usually observed only at low temperatures, such as Mott-localization, Fermi-liquid behavior and superconductivity, persist to elevated temperatures. In the opposite weak coupling limit, correlation effects are brought into play by reduced dimensionality, resulting in charge and spin density waves. These effects will be described with the help of key, real-world, examples. |
| Ivo Batistić Department of Physics, Faculty of Science, University of Zagreb, Croatia |
| Phonon properties of materials with different structural complexity Lecture will start with a brief introduction into a harmonic oscillator, its quantization, its application to a general system of coupled atoms/ions by harmonic forces and to the notion of phonons. The structural complexity of materials can be result of a long range aperiodicity, a non-commensurate lattice distortion, the defect presence (local and extended ones), etc. Usually, realistic studies of phonon properties in structurally complex systems involve numerically intense calculations and/or heavy mathematical formalism. In this lecture we shall cover only very simple cases which can be done analytically. These simple cases can be generalized in order to get an insight into more complex situations. Particular attention will be paid to long wave limit where generally complex equation of motion can be simplified. Some of these results will be applied to calculation of few thermodynamic and transport properties. Tutorial will consist of numerical calculations and simulations with already prepared python scripts. Participants would be able to investigate how calculation/simulation results depends on the parameters in the problem under consideration. Knowledge of python programming language is recommended but it is not required. |
| Yuri Grin Max-Planck-Institut für Chemische Physik fester Stoffe, Dresden, Germany |
| Introduction to thermoelectrics. Complexity of the crystal structures, chemical bonding and thermoelectric behaviour of materials
Many decades after the discovery of the Seebeck effect thermoelectric attracted rather attention in academic circles. Only with the begin of the 20th century its application potential was recognized. Today, thermoelectric is accepted as the power generation technology for the space applications and heat harvesting technology in different brunches. Thermoelectric ability of a material is described by the goodness-of-fit function ZT which is dependent on the Seebeck coefficient, the thermal and electrical conductivities. Electrical conductivity and Seebeck coefficient are – in turn – functions of the charge carrier concentration. The latter is connected with the band structure and – hence – with the atomic interactions in the material. One of the key issues in further understanding of thermoelectric behaviour of materials is complexity of their crystal structures. Structural complexity of this class of inorganic compounds may be described from the points of view of crystallographic features (number of atoms, symmetry), of chemical and crystallographic order/disorder, or of thermodynamic factors (phase diagrams, formation reactions), etc. On base of crystallographic description, even a special family of intermetallic compounds – the so-called complex metallic alloys or phases (CMA) – was defined. Neither electronic nor thermal transport of thermoelectric materials follow strictly the crystallographic understanding of structural complexity. Nevertheless, recently was shown that the reduced lattice thermal conductivity of the clathrate Ba8Ni3.5Ge42.1□0.4 with respect to clathrates without vacancies and with respect to Ba8Ge43□3with ordered vacancies suggests that disordered vacancies disturb the heat transport more efficiently as the electronic transport. Moreover, structural complexity of the clathrate Ba8Au5.25Ge40.6□0.15 may yield an explanation for its puzzling glass-like thermal conductivity. Further insights may be achieved including the spatial separation of regions with different atomic interactions into the content of the structural complexity.
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| Osor Slaven Barišić Institute of Physics, Zagreb, Croatia |
| Electron-phonon interaction
In this lecture some important aspects of electron-phonon interaction are discussed. First question to be answered is how this interaction occurs, with gradual introduction of most frequently used electron-phonon models, like the Fröhlich, the Holstein and the Barišić-Labbé-Friedel model. In the next step polaronic effects are analyzed, from both experimental and theoretical point of view. The ARPES spectra and thermal conductivity data from some recent measurements characterized by strong electron-phonon interactions are analyzed in more detail. From the theoretical side, particular attention is dedicated to two kinds of quasiparticles, polarons and bipolarons, involving coupling of dilute itinerant charge carriers to a lattice polarization (deformation). A brief overview of charge-density-waves, BCS superconductivity and the strong electron-phonon coupling scenario for high-temperature superconductivity is presented.
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| Aleksa Bjeliš Department of Physics, Faculty of Science, University of Zagreb, Croatia |
| Charge and spin density waves in one dimension The lecture will start with the historical overview and the basic theoretical elements of the charge and spin density wave C(S)DW phenomena in (quasi) one dimensional materials. Then I shall elaborate some characteristic properties of C(S)DWs which distinguish them from other long-range orders with broken symmetry, as well as some features emerging after the application of external magnetic field. Finally, I shall comment on some open questions related to the uniaxial charge orders in presently intensely investigated two dimensional materials. Orientationally the content will be organized through following short sections: – Short excursion through the history – Microscopic origins of C(S)DWs based on many body models with reduced spatial dimension – Phenomenological approaches, including the short account on the incommensurate-commensurate phase transitions and lock-ins – Collective dynamics of C(S)DWs – C(S)DWs in the external magnetic field, and magnetic field induced C(S)DWs – Charge orderings and uniaxial density waves in two dimensional conductors. |
| Eduard Tutiš Institute of Physics, Zagreb, Croatia |
| Charge density waves in two dimensions The research in two-dimensional and quasi-two-dimensional electronic systems has been gaining momentum in recent decades, with significant pushes coming from copper oxide high-temperature superconductors and new and exciting discoveries in several old and new, inorganic and organic, layered materials. Currently exploding research in atomically thin layers in the post-graphene era, particularly focused on the collective electronic states and topological phases, is often an extension of research in where the same layers are loosely stacked. Historically, the research in charge density waves (CDW) in two dimensions (2D) appeared in 1970’s as the extension of research in quasi-one-dimensional systems. Quite early, however, the study of quasi-2D electronic systems acquired a life of its own, as it became obvious that the additional dimension greatly extends the possibilities for the interplay of various electronic condensates, their coexistence or competition. This lecture covers a number of cases/materials which came into research focus in recent years, with very different mechanisms being responsible for the CDW formation. The size of super-cell produced by the ordering ranges from several atoms to several hundred atoms. We start from the extension of the Peierls mechanism to the systems isotropic in two dimensions, then embark to the example where charge density waves combine with metallic phase, or superconducting phase, in a regular nano-array, and the example where, once established, the charge density wave phase serves as the substrate for the appearance of the Mott-insulator phase. Another mechanism to be reviewed is the excitonic – insulator condensation, argued to appear in several materials in recent years. This is the case where the transition is governed by the coulomb interaction in semimetals or narrow gap semiconductors. Moving towards the situation where the coulomb and electron-lattice interaction become progressively more important, we discuss the case of the 2D electron gas transforming into the collection of electronic strings, where only spin degrees of freedom survive, well described through the 1D Heisenberg S=1/2 model. All the mechanisms to be discussed have the physical realisations in particular materials whose physical behaviour often goes against the common wisdom. |
| Miroslav Požek Department of Physics, Faculty of Science, University of Zagreb, Croatia |
| Introduction to nuclear magnetic resonance A brief introduction to nuclear magnetic resonance (NMR) spectroscopy will be given. After introduction of basic Hamiltonian, semiclassical aproach will be used to describe basic phenomena. Pulsed NMR experimental technique will be described. Time-dependent evolution of magnetization will be treated through Bloch equations of motion. The power of NMR and related nuclear quadrupolar resonance (NQR) methods in gaining relevant information for solid state physis will be illustrated by several examples of recent measrements. References:
[1] Slichter C P, Principles of Magnetic Resonance, Springer, Berlin 1990. [2] Abragam A, The Principles of Nuclear Magnetism, Oxford, 1982 [3] Walsted R E, The NMR Probe of High-Tc Materials, Springer, 2008. [4] Curro N. J., Nuclear Magnetic Resonance as a Probe of Strongly Correlated Electron Systems in “Strongly Correlated Systems Experimental Techniques” (Avella A. and Mancini F., Eds.), Springer, Heidelberg, 2015. |
| Marina Ilakovac Kveder Ruđer Bošković Institute, Zagreb, Croatia |
| Introduction to electron paramagnetic resonance Electron paramagnetic resonance (EPR) spectroscopy will be introduced and compared to the nuclear magnetic resonance (NMR). Quantum physics framework will be followed in the formulation of basic concepts. Description of the quantum state of an ensemble of spins will be given in terms of density matrix formalism, appropriate for the description of time-dependent problems. The time evolution of density matrix will be introduced along with the product operator formalism in order to be able to calculate the expectation values of the observables relevant in EPR(NMR) experiments [1]. Electron-spin relaxation processes will be addressed and some examples of the involvement of phonon mechanism in energy exchange between the spin system and the lattice presented. In addition, the role of hyperfine interaction in electron-spin decoherence, called spectral diffusion, will be shown [2], [3]. The topic of multi-frequency approach will be targeted on the delineation of the mechanisms relevant for the electron-spin relaxation, apart from its importance in the spectral resolution of overlapping paramagnetic species [4]. References:
[1] Schweiger A, Jeschke G (eds.) Principles of pulse electron paramagnetic resonance, Oxford University Press 2001. [2] Zhou Y, Bowler B E, Eaton G R, Eaton S S (1999) J. Magn. Reson. 139, 165. [3] Hoffmann S K, Hilczer W,Goslar J,Massa M M, Calvo R (2001) J. Magn. Reson. 153, 92. [4] Kveder M, Merunka D, Ilakovac A, Rakvin B (2011). J. Magn. Reson. 213, 26. |
| Mihael Grbić Department of Physics, Faculty of Science, University of Zagreb, Croatia |
| How does nuclear magnetic resonance spectra observes phase transitions and what can we use it for? Nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) are spectroscopic techniques that give insight into local properties of the system as seen by a specific nucleus present in the material. The technique is sensitive to both magnetic and charge degrees of freedom, and as such can provide important information on the physical mechanisms driving the emergence of various phases of the system. To get a better sense of the important energy scales, we will have a closer look of the NMR/NQR Hamiltonian and determine the boundaries of the specific limits for which there are analytical solutions. We will present a few examples where one can observe the emergence of magnetism and/or changes in local electric fields. In particular, we will focus on a system with copper spins where a structural transition changes the symmetry of the copper sites, and where at low temperature antiferromagnetic order sets-in. The data are acquired via NQR measurements of copper sites, and at low magnetic field (Zeeman perturbed NQR) using rotational spectra acquisition. We will test the local symmetry of the sites above and below the structural transition by fitting the known functions for the angle dependence, extract the order-parameter hyperfine field of the magnetic phase, and analyse the data with regards to the existing models/theories. The calculations will be done in Matlab. |
| Dijana Žilić Ruđer Bošković Institute, Zagreb, Croatia |
| Electron paramagnetic resonance spectroscopy in material science Electron paramagnetic or spin resonance (EPR/ESR) is a spectroscopic technique that gives insight into local properties of paramagnetic centres and microscopic picture of interactions. However, for investigation of systems with spin S > 1/2 , it is often necessary to perform non-commercial EPR spectroscopy, that uses high frequencies (higher than 100 GHz) and high magnetic fields(~ 10 T) (high-field/high-frequency EPR, HF-EPR). Here, X-band (microwave frequency around 10 GHz) as well as HF-EPR studies of few transition metal complexes (Cu2+, Cr3+, Mn2+…) are presented [1-5]. Experimentally obtained EPR spectra are simulated and analyzed using EasySpin [6], a computational package based on a commercial technical computation software Matlab. For theorethical description of investigated spin systems, spin-Hamiltonian approach are used. As a conclusion, magneto-structural correlation in the investigated complexes will be discussed. References: [1] E. Garribba and G. Micera, J. Chem. Edu. 83 (2006) 1229-1232. [2] N. Novosel, D. Žilić, D. Pajić, M. Jurić, B. Perić, K. Zadro, B. Rakvin, P. Planinić, Solid State Sci. 10 (2008) 1387-1394. [3] D. Žilić, L. Androš, Lidija, Y. Krupskaya, V. Kataeva and B. Büchner, Appl. Magn. Reson. 46 (2015) 309-321. [4] M. Jurić, K. Molčanov, D. Žilić, B. Kojić-Prodić, RSC Advances 6 (2016) 62785-62796. [5] D. Žilić, K. Molčanov, M. Jurić, J. Habjanič, B. Rakvin, Y. Krupskaya, V. Kataev, S. Wurmehl, B. Büchner, Polyhedron 126 (2017) 120-126. [6] S. Stoll and A. Schweiger, J. Magn. Reson. 178 (2006) 42–55 |
| Vlasta Bonačić Koutecký Humboldt-University, Berlin, Germany, and University of Split, Croatia |
| Basics of catalysis – Role of nanoscience based on metalic nanoclusters Due to economic and environmental requirements design of new catalysts is important research field with broad applications for i) alternative fuels, ii) reduction of pollutants and iii) energetic requirements for chemical production. For this purpose, combinatorial approaches widely used are not sufficient. The knowledge about exact mechanisms of catalytic reactions and active sites should significantly improve the efficiency of catalyst design. This can be achieved by joint theoretical and experimental “smart” design of new catalysts for environmental issues, industrial production and renewable energy. Therefore, three examples illustrating knowledge driven design of new catalysts will be presented:
After introduction and explanation of examples within 90 minutes computational and experimental approaches used to obtain above results will be demonstrated by dr. Marjan Krstić within additional 90 minutes. |
| Marjan Krstić University of Split, Croatia |
| Basics of catalysis – Role of nanoscience based on metalic nanoclusters Computational and experimental approaches Catalysts are driving force of many industries (such as chemical, pharmaceutical, petrochemical, …) in the modern world. During this session, combined theoretical and experimental approach will be presented with the goal to design new catalyst from basics towards application. Focus will be on the theoretical simulations of gas phase protected metallic nanoclusters to determine catalytic cycle and reaction profiles for two distinctive catalytic reactions: 1) fuel cell feed gas purification by CO methanation mediated by ruthenium nanoclusters 2) hydrogen storage application based on liganded binuclear noble metal hydrides to catalyze extrusion of H2 and CO2 from formic acid (HO2CH). For this purpose density functional theory (DFT) will be used. Brief theoretical overview will be presented before applying DFT to the real calculations. A step by step construction of reaction profiles will be performed through optimisation of local minima and transition states along the reaction coordinates. Found geometrical structures will be confirmed by comparison of simulated UV/Vis absorption and IR spectra with the experimentally measured data. Molecular dynamics (MD) simulations will also be demonstrated to follow time evolution of catalytic reactions |