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
2018-01-26 (Friday)
room 1.02, Pasteura 5 at 12:15 
Thomas Sturges (IFT WF UW)Unconventional Dirac Polaritons in Cavity-Embedded Honeycomb Metasurfaces
This talk will highlight non-trivial effects induced by a photonic environment on the Dirac polaritons that exist in a honeycomb array of meta-atoms embedded in a planar cavtity. In addition to the conventional Dirac points arising due to the matter symmetries, the photonic environment generates additional satellite Dirac points with ∓π Berry flux. Reducing the cavity height induces the merging of the satellite Dirac points with the conventional ones, forming a quadratic band-degeneracy with combined ∓2π Berry flux. As a result, the massless Dirac polaritons with a linear spectrum morph into massive ones with a parabolic spectrum. Remarkably, this merging is not followed by Dirac point annihilation, but instead, massless Dirac polaritons re-emerge with an unprecedented inversion of chirality which has no analog in real or artificial graphene systems. This novel tunability could open up a new realm of unexplored Dirac-related physics, such as unconventional tunnelling and pseudo-magnetic related phenomena, in readily realizable experimental set-ups.
2018-01-19 (Friday)
room 1.02, Pasteura 5 at 12:15
Mario Cuoco (University of Salerno)Exploring novel quantum platforms for spinorbitronics and superconducting spintronics
This talk will deal with the presentation of quantum materials platforms with potential impact in the area of spinorbitronics and superconducting spintronics which combine spin-orbit coupling, superconductivity and topological effects. We have theoretically considered the interplay between geometric curvature effects on the electronic properties and the topological properties of the quantum states in low-dimensional nanomaterials. I will discuss how geometric effects in low-dimensional nanomaterials can lead to metal-insulator transition and promote the generation of topological states of matter, for instance upon the application of a rotating magnetic field one can realize the topological pumping protocol in an entirely novel fashion. Then, I will present the intricate twist between spin texture and spin transport in shape deformed nanostructures including the superconducting case. Finally, I will consider the interplay of superconductivity and magnetism in heterostructures with a special focus on topological superconductors.
2018-01-12 (Friday)
room 1.02, Pasteura 5 at 12:15
Filip Dutka (IFT UW)Semiliquid chains pulled out of a sea of microparticles
One-dimensional conductive particle assembly holds promise for a variety of practical applications, in particular for a new generation of electronic devices. However, synthesis of such chains with programmable shapes outside a liquid environment has proven difficult. A route to simply 'pull' flexible granular and colloidal chains out of a dispersion by combining field-directed assembly and capillary effects will be reported. These chains are automatically stabilized by liquid bridges formed between adjacent particles, without the need for continuous energy input or special particle functionalization. They can further be deposited onto any surface and form desired conductive patterns, potentially applicable to the manufacturing of simple electronic circuits.
2017-12-22 (Friday)
room 1.02, Pasteura 5 at 12:15
Dimitri Efremov (Institute for Solid State and Material Research, Dresden)Interplay of charge and spin degrees of freedom in unconventional superconductors and interaction driven topological insulators
2017-12-15 (Friday)
room 1.02, Pasteura 5 at 12:15
Jan Guzowski (IChF PAN)Formation, structure and mechanical properties of droplet aggregates: from small clusters to elongated threads and large tissue-like aggregates
2017-12-01 (Friday)
room 1.02, Pasteura 5 at 12:15
Anna Kauch (TU Wien)Parquet equations for the Hubbard model -- two-particle quantities in parquet and dynamical vertex approximations
The parquet equations provide a framework for self-consistent determination of the self-energy and the vertex corrections. In the context of many-body theory they were first introduced by de Dominicis and Martin alredy in the 1960th. However, the computational effort needed for two-particle self-consistent calculations limited their use only to impurity models or implied applying strong approximations to the equations. Recent advances in computational infrastructure make now calculations for lattice models feasible.In the talk I will shortly introduce parquet decomposition of two-particle vertex functions and the various approximations made to the irreducible vertices which are input to the parquet equations. I will also present preliminary results obtained with the our new implementation for the 2D Hubbard model on a square lattice in the so-called parquet approximation and within the dynamical vertex approximation scheme.
2017-11-24 (Friday)
room 1.02, Pasteura 5 at 12:15
Marek Napiórkowski (IFT UW)Thermodynamic equivalence of two-dimensional imperfect attractive Fermi and repulsive Bose gases
I shall present conditions under which thermodynamics of an imperfect Fermi gas exists and is equivalent to thermodynamics of an imperfect repulsive Bose gas.
2017-11-17 (Friday)
room 1.02, Pasteura 5 at 12:15
Mitchell D. Anderson (École Polytechnique Fédérale de Lausanne)Quantum Dynamics of Microcavity-Polaritons in Engineered Confinement Potentials
Microcavity polaritons are a hybrid photonic system arising from the strong coupling of confined photons to quantum-well excitons. Due to their light-matter nature, polaritons inherit a Kerr-like nonlinearity while being easily accessible by standard optical means. The ability to engineer confinement potentials in microcavities makes polaritons a very convenient system to study spatially localized bosonic populations in for example 0D dots, 1D chains, 2D lattices. A good example of this is the polariton Josephson junction which consists of two localized polariton populations coupled via tunneling. Careful engineering of this system is predicted to induce Gaussian squeezing, a phenomenon that lies at a heart of the so-called unconventional photon blockade associated with single photon emission. We reveal a manifestation of the predicted squeezing by measuring the ultrafast time-dependent second-order correlation function g(2)(0). The light emitted by the microcavity oscillates between Poissonian and super-Poissonian in phase with the Josephson dynamics. This behavior is remarkably well explained by quantum simulations, which predict a dynamical evolution of the squeezing parameters. Beyond this, we study in depth the dephasing mechanisms of the polariton populations and are beginning to explore a wide range of artificial structures.
2017-11-10 (Friday)
room 1.02, Pasteura 5 at 12:15
Piotr Deuar (IF PAN)The Wigner stochastic Gross-Pitaevskii equation: a scalar complex-valued field theory that retains quantum fluctuations
Classical-field calculations are a mainstay of simulations of the dynamics and stationary properties of ultracold atomic and polariton gases at nonzero temperature. They allow for temperatures too high to treat with other methods, strong fluctuations and defects, open systems, as well as the study of single experimental realisations and distribution functions. They do however omit any quantum fluctuations.We have derived an extended version of the stochastic GPE (SGPE) that preserves quantum fluctuations. So far, for the case of ultracold Bose gases. Thus, a very tractable, nonlinear description of the system has been obtained that also includes quantum fluctuations, depletion, shot noise, antibunching, and similar effects, and makes no assumptions of a condensate. In contrast to the usual ``truncated Wigner'' approach of adding virtual vacuum noise into the initial conditions, this method preserves quantum fluctuations even into the long-time stationary state.I will first describe the stochastic GPE model for an ultracold gas that allows for a stable but classical wave field description of the system with a set temperature, before presenting the newly derived extended version and briefly speculating about further generalisations.
2017-10-20 (Friday)
room 1.02, Pasteura 5 at 12:15
Katarzyna Sznajd-Weron (Department of Theoretical Physics, Wroclaw University of Science and Technology)Phase transitions in models of opinion dynamics
During this talk I will present an idea of modeling opinion dynamics and show what could be the source of phase transitions in such a models from the perspective of social psychology. Then I will present one of the most interesting models of binary opinions, the q-voter model, and discuss phase transitions that are observed within this model. Finally, I will show what kind of questions, inspired by social theories and experiments, can be asked within the model.