CPT

Calendar of Physics Talks Vienna

Absorbing State Phase Transition with Competing Quantum and Classical Fluctuations
Speaker:Michael Buchhold (California Institute of Technology, Pasadena, CA., USA)
Abstract:Stochastic processes with absorbing states feature examples of nonequilibrium universal phenomena. While the classical regime has been thoroughly investigated in the past, relatively little is known about the behavior of these nonequilibrium systems in the presence of quantum fluctuations. Here, we theoretically address such a scenario in an open quantum spin model which, in its classical limit, undergoes a directed percolation phase transition. By mapping the problem to a nonequilibrium field theory, we show that the introduction of quantum fluctuations stemming from coherent, rather than statistical, spin flips alters the nature of the transition such that it becomes first order. In the intermediate regime, where classical and quantum dynamics compete on equal terms, we highlight the presence of a bicritical point with universal features different from the directed percolation class in a low dimension. We finally propose how this physics could be explored within gases of interacting atoms excited to Rydberg states.
Date: Mon, 13.11.2017
Time: 11:00
Location:Atominstitut, Bibliothek
Contact:Peter Rabl

New Materials for a New Age
Speaker:Nicola Spaldin (The Faculty of Physics at the University of Vienna and the Austrian Physical Society (ÖPG))
Abstract:Every advance in human civilization, from the Stone Age to today’s Silicon Age, has been driven by a development in materials. I will present a new class of materials – multiferroics – that are both a playground for exploring exciting fundamental physics, and a potential enabler of transformative beyond-silicon technologies.
Date: Mon, 13.11.2017
Time: 16:30
Location:Lise Meitner Hörsaal, Strudlhofgasse 4, 1st floor, Vienna
Contact:VPC Team

Cosmic Ray Physics — a short overview from the discovery to Dark Matter
Speaker:Prof. Pierre Salati (LAPTH)
Abstract:The discovery of cosmic rays has been the starting point of high-energy physics. A century later, their study is still a very active field with connections to cosmology. After a brief historical introduction, I will present the Leaky Box model which provides a very simple yet pedagogical framework to understand how charged particles propagate within the Milky Way. Probes of cosmic ray propagation, such as the boron-to-carbon ratio, readily point toward diffusive transport on which modern numerical codes such as Galprop, Dragon or Usine are based. After a presentation of how diffusion is implemented, I will discuss how cosmic rays are accelerated inside the Galaxy by violent events such as supernova explosions. I will finally discuss a few recent hot topics, in connection to Dark Matter searches.
Date: Tue, 14.11.2017
Time: 14:00
Duration: 60 min
Location:HEPHY Library
Contact:Suchita Kulkarni

Calabi-Yau manifolds and sporadic groups
Speaker:Abhiram Kidambi (TU Wien)
Abstract:One of the recent topics of interest in mathematical string theory is the study of the Mathieu moonshine and how it is realised in a string theoretic framework. It was shown by Eguchi, Ooguri and Tachikawa that the elliptic genus of the K3 surface has connections to the dimensions of the irreducible representations of the M_24 Mathieu group. In this talk, I shall give an overview of the (Mathieu) moonshine and present the results of a study of the (twined) elliptic genera expansion of CY 5-folds and relations to sporadic groups.
Date: Tue, 14.11.2017
Time: 14:00
Duration: 60 min
Location:Schrodinger lecture hall (5th floor), University Vienna, Strudlhofgasse 4/Boltzmanngasse 5
Contact:Daniel Grumiller and Stefan Fredenhagen

Epitaxial fcc Fe thin films for application in spin-wave devices
Speaker:Lukáš Flajšman (CEITEC BUT, Brno University of Technology, Brno/Czech Republic)
Abstract:The first part of the talk will serve as an introductory guide to spin-wave related phenomena. The second part will introduce recent advances in the growth and characterization of the metastable fcc Fe layers of Cu(100), and will show some concepts and ideas of application of the material for spin-wave related phenomena.
Date: Tue, 14.11.2017
Time: 16:00
Location:TU Wien, Institut für Angewandte Physik, E134 1040 Wien, Wiedner Hauptstraße 8-10 Yellow Tower „B“, 5th floor, SEM.R. DB gelb 05 B
Contact:Univ.Prof. Dr. Ulrike Diebold

Non-Abelian Discrete Groups and Neutrino Flavor Symmetry
Speaker:Morimitsu Tanimoto (Niigata University)
Date: Tue, 14.11.2017
Time: 16:15
Location:Erwin Schrödinger-Hörsaal, Boltzmanngasse 5, 5. Stock
Contact:W. Grimus, H. Neufeld

2D nanoscale optics and (opto‐)electronics
Speaker:Thomas Mueller (Institute of Photonics, Vienna University of Technology)
Abstract:The materials that have enabled the information technology revolution over the past decades will soon reach their physical limits. Novel nanomaterials nd technologies have therefore become a major focus of current solid‐state device research, with two‐dimensional (2D) atomic crystals being one of the most promising candidates. Graphene, a 2D structure of carbon atoms with unorthodox electronic properties, is the most prominent representative of the 2D material family. More recently, transition metal dichalcogenides (TMDs) have come into the focus of interest, as these offer properties that complement those of graphene. Some TMDs are semiconductors with a sizable bandgap, which allows the construction of logic transistors, light emitters, photovoltaic solar cells, and other devices. In the first part of this talk, I will present some of our spectroscopic studies on linear and nonlinear...
Date: Wed, 15.11.2017
Time: 14:15
Location:Seminar room FH DB gelb 10, Institute for Theoretical Physics – Vienna University of Technology, Wiedner Hauptstraße 8 – 10, 10th floor, B (yellow tower)
Contact:Univ.Prof. Dr. Joachim Burgdörfer

A globally stable blowup profile for supercritical wave maps
Speaker:Roland Donninger (Vienna)
Abstract:im Rahmen des joint relativity-geometric analysis seminars: Supercritical wave maps into spheres exhibit blowup via explicit self-similar solutions. I will present a recent stability result of the blowup profile which is valid in a large region of spacetime up to the Cauchy horizon of the singularity. This is joint work with P. Biernat (Bonn) and B. Schörkhuber (Vienna).
Date: Thu, 16.11.2017
Time: 14:00
Duration: 60 min
Location:Arbeitsgruppe Gravitation, Währinger Strasse 17, Raum 218, 2. Stock, 1090 Wien
Contact:P.T. Chrusciel, S. Fredenhagen

Colloquium: The Enigma of the Highest Energy Particles in the Universe
Speaker:Günter Sigl (DESY)
Abstract:Cosmic rays have been observed up to several 10^20 eV through the showers of secondary particles they induce in the atmosphere. This is a macroscopic energy of up to 50 Joules, presumably in one elementary particle. The existence of such particles and their propagation through the highly structured Universe pose formidable challenges and exciting prospects at the same time: Their origin and sources have not been identified yet, but they already allow to test physics at center of mass energies unattained in the laboratory, albeit in a rather indirect way. We will give an overview over possible sources and acceleration mechanisms, issues related to cosmic ray mass composition, and other open questions and future prospects, including the role of secondary gamma-rays and neutrinos produced in primary cosmic ray interactions.
Date: Fri, 17.11.2017
Time: 10:30
Duration: 60 min
Location:Wohllebengasse 12-14
Contact:Suchita Kulkarni, Josef Pradler