Condensed Matter Physics Seminar
2006/2007 | 2007/2008 | 2008/2009 | 2009/2010 | 2010/2011 | 2011/2012 | 2012/2013 | 2013/2014 | 2014/2015 | 2015/2016 | 2016/2017 | 2017/2018 | 2018/2019 | 2019/2020 | 2020/2021 | 2021/2022 | 2022/2023 | 2023/2024 | 2024/2025
2021-01-22 (Friday)
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Jan Kunes (TU Wien)Thermal damping of spinful excitons in LaCoO3: theory and experiment
LaCoO3 is a classic material that has been studied since 1950's and still hosts new surprises.Recent RIXS experiments, which allowed for the first time a direct observation ofso called intermediate spin (IS) excitations, revealed their unexpectedly large mobility.Repeated RIXS measurements with the state-of-art energy resolution allowed us not onlyto map out the IS dispersion more precisely, but also to study the damping of IS excitations at elevated temperatures. I will derive an effective strong-coupling model of LaCoO3 and present its treatmentusing bosonic dynamical mean-field theory (B-DMFT). To account for the local hard-core constraintson the bosonic particles we have introduced HB-DMFT (DMFT for hard-core bosons) approach, whichis analogous to the concept of extremely correlated Fermi liquid introduced by Shastry to treatthe fermionic t-J model. I will discuss possible further developments of the method and its potentialto answer the remaining open questions concerning LaCoO3. Join Zoom Meetinghttps://us02web.zoom.us/j/83686899432?pwd=RXNtZkhtZFpLazVmMVRFY1BtVlI0Zz09Meeting ID: 836 8689 9432Passcode: cond-matt
2021-01-15 (Friday)
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Marek Napiórkowski (IFT UW)Wetting transitions on soft substrates
Within the mean-field type of analysis I will discuss the influence of the substrate's elasticity on wetting transitions. Join Zoom Meeting https://us02web.zoom.us/j/83686899432?pwd=RXNtZkhtZFpLazVmMVRFY1BtVlI0Zz09Meeting ID: 836 8689 9432Passcode: cond-matt
2020-12-18 (Friday)
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Waldemar Kłobus (University of Gdansk)Cooperation and dependencies in multipartite systems
We propose an information-theoretic quantifier for the advantage gained from cooperation that captures the degree of dependency between subsystems of a global system. The quantifier is distinct from measures of multipartite correlations despite sharing many properties with them. It is directly computable for classical as well as quantum systems and reduces to comparing the respective conditional mutual information between any two subsystems. Secret sharing provides an exemplary cooperation task where this quantifier is beneficial. Based on the new quantifier we prove an inequality characterizing the lack of monotonicity of conditional mutual information under local operations and provide intuitive understanding for it. Join Zoom Meeting https://us02web.zoom.us/j/83686899432? pwd=RXNtZkhtZFpLazVmMVRFY1BtVlI0Zz09 Meeting ID: 836 8689 9432Passcode: cond-matt
2020-12-11 (Friday)
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Marcin Mierzejewski (Wrocław University of Science and Technology)Charge, spin and energy transport in strongly disordered quantum chains
Dynamics of quantum systems is typically a few orders of magnitude faster than the time-scales which are relevant for our everyday experience. In particular, the relaxation times in solids with strong electronic correlations may be of the order of a few tens of femtoseconds. At longer time, quantum systems typically approach their thermal equilibrium. Yet, for some systems the relaxation may be slowed down or even completely frozen. Approaching the thermal equilibrium unavoidably implies the loss of information concerning the initial quantum state. Therefore, methods of avoiding or slowing down the thermalization might be important for the future applications. During the talk I will discuss the basic concepts concerning thermalization in quantum systems and discuss transport in disordered chains with many-body interactions where thermalization may be eliminated or at least significantly slowed down. Join Zoom Meetinghttps://us02web.zoom.us/j/83686899432?pwd=RXNtZkhtZFpLazVmMVRFY1BtVlI0Zz09Meeting ID: 836 8689 9432Passcode: cond-matt
2020-12-04 (Friday)
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Anna Kauch (TU Wien)Pi-ton contributions to optical conductivity in correlated electron systems
The interaction of light with solids gives rise to new bosonic quasiparticles, with the exciton being the most famous one. While excitons are the generic excitations of semiconductors, we show that for strongly correlated systems another polariton is prevalent -- originating from the dominant antiferromagnetic or charge density wave fluctuations in these systems. As these are usually associated with a wave vector (π,π,...) or close to it, we call these excitations π-tons. These π-tons yield the leading vertex correction to the optical conductivity in all correlated models studied: the Hubbard, the extended Hubbard model, the Falicov-Kimball, and the Pariser-Parr-Pople model, both in the insulating and in the metallic phase. Join Zoom Meetinghttps://us02web.zoom.us/j/83686899432?pwd=RXNtZkhtZFpLazVmMVRFY1BtVlI0Zz09 Meeting ID: 836 8689 9432Passcode: cond-matt
2020-11-27 (Friday)
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Krzysztof Jachymski (IFT UW)Charged impurity in a Bose-Einstein condensate
An impurity immersed in a quantum environment can be viewed as a fundamental building block for many-body problems and can give insight into the transport properties of various materials. Ultracold atoms provide here an excellent playground, allowing for precise control of experimental conditions and reaching a wide regime of system parameters. An intriguing possibility is to make use of charged impurities such as atomic ions, which interact more strongly with the background gas. It turns out that the ground state of such a system can be vastly different from the case of neutral particles. I will discuss both static and dynamic properties of ion-atom systems, highlighting the role of the long range of the interaction potential. Join Zoom Meeting https://us02web.zoom.us/j/83686899432? pwd=RXNtZkhtZFpLazVmMVRFY1BtVlI0Zz09Meeting ID: 836 8689 9432Passcode: cond-matt
2020-11-20 (Friday)
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Vincenzo Alba (University of Amsterdam)Hydrodynamic framework for out-of-equilibrium entangled many-body systems
Entanglement and entropy are key concepts standing at the foundations of quantum and statistical mechanics, respectively. In the last decade the study of quantum quenches revealed that these two concepts are intricately intertwined. For integrable models, novel hydrodynamic approaches based on a quasiparticle picture emerged as a new platform allowing for a quantitative understanding of quantum information dynamics in quantum many-body systems. Remarkably, this gives fresh insights on how thermodynamics emerges in isolated out-of-equilibrium quantum systems.I will start by reviewing this new unifying framework. I will then discuss several applications to entanglement-related quantities, such as entanglement entropies, mutual information, logarithmic negativity. I will also show how the framework allows to study the interplay between quantum information dynamics and transport of local conserved quantities. Finally, I will derive some simple bounds on the quantum information scrambling in out-of-equilibrium systems.To attend, please follow the link attached below on Friday at 12.15. Witold Bardyszewski Paweł Jakubczyk Marek Napiórkowski//---------------------------Join Zoom Meetinghttps://us02web.zoom.us/j/83686899432?pwd=RXNtZkhtZFpLazVmMVRFY1BtVlI0Zz09Meeting ID: 836 8689 9432Passcode: cond-matt
2020-11-13 (Friday)
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Jacek Herbrych (Wrocław University of Science and Technology)Interaction-induced topological phase transition and Majorana edge states in low-dimensional orbital-selective Mott insulators
Topological phases of matter are among the most intriguing research directions in Condensed Matter Physics. It is known that superconductivity induced on a topological insulator’s surface can lead to exotic Majorana modes, the main ingredient of many proposed quantum computation schemes. In this context, iron-based high critical temperature superconductors are among the main candidates to host such exotic phenomenon. Moreover, it is commonly believed that the Coulomb interaction is vital for the magnetic and superconducting properties of these systems. This work bridges these two perspectives and shows that the Coulomb interaction can also drive a trivial superconductor with orbital degrees of freedom into the topological phase. Namely, we show that above some critical value of the Hubbard interaction, identified by the change in entropy behaviour, the system simultaneously develops spiral spin order, a highly unusual triplet amplitude in superconductivity, and, remarkably, Majorana fermions at the edges of the system. Join Zoom Meetinghttps://us02web.zoom.us/j/83686899432?pwd=RXNtZkhtZFpLazVmMVRFY1BtVlI0Zz09Meeting ID: 836 8689 9432Passcode: cond-matt
2020-11-06 (Friday)
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Piotr Nowakowski (Max Planck, Stuttgart)Casimir-like interaction of inclusions on two-component membrane
I will present a simple, exactly solvable model of a membrane described by two fluctuating fields: height above a flat surface and chemical composition. Close to the critical demixing the membrane behaves as a flat sheet, while away from the criticality the composition degrees of freedom can be neglected. For this system I will consider two immobile inclusions (modelling proteins on biological membrane) and study their Casimir-like interaction mediated by the membrane. Zoom Meeting ID: 836 8689 9432Passcode: cond-matt
2020-10-30 (Friday)
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Felipe Sant'Ana (IFT UW)A study on quantum gases: bosons in optical lattices and the one-dimensional interacting Bose gas
Bosonic atoms confined in optical lattices are described by the Bose-Hubbard model and can exist in two different phases, Mott insulator or superfluid, depending on the strength of the system parameters. In the vicinity of the phase boundary, there are degeneracies that occur between every two adjacent Mott lobes. Because of this, nondegenerate perturbation theory fails to give meaningful results for the condensate density: it predicts a phase transition at a point of the phase diagram where no transition occurs. Motivated by such a misleading calculation, we develop two different degenerate perturbative methods to solve the degeneracy-related problems.Moreover, we study the one-dimensional repulsively interacting Bose gas under harmonic confinement, with special attention to the asymptotic behavior of the momentum distribution, which is a universal k−4 decay characterized by the Tan's contact. The latter constitutes a direct signature of the short-range correlations in such an interacting system and provides valuable insights about the role of the interparticle interactions. We investigate the system constituted of N interacting particles in the strongly interacting limit. In such a regime, the strong interparticle interaction makes the bosons behave similarly to the ideal Fermi gas. Because of the difficulty in analytically solving the system for N particles at finite interaction, the Tonks-Girardeau regime provides a favorable scenario to probe the contact. Therefore, we are able to provide an analytical formula for the Tan's contact. Furthermore, we analyze the scaling properties of the Tan's contact in terms of N in the high-temperature regime as well as in the strongly interacting regime. Finally, we compare our analytical calculations of the Tan's contact to quantum Monte Carlo simulations and discuss some fundamental differences between the canonical and the grand-canonical ensembles.To attend, please follow the link attached below on Friday at 12.15. Witold Bardyszewski Paweł Jakubczyk Marek Napiórkowski//---------------------------Join Zoom Meetinghttps://us02web.zoom.us/j/83686899432?pwd=RXNtZkhtZFpLazVmMVRFY1BtVlI0Zz09Meeting ID: 836 8689 9432Passcode: cond-matt