Calendar of Physics Talks Vienna

Quantum Monte Carlo simulations of ultracold fermions on optical lattices within dynamical mean-field theory
Speaker:Prof. Nils Blümer (Uni Mainz)
Abstract:Within the last few years, ultracold fermionic atoms on optical lattices have been established as highly tunable model systems for strongly correlated materials. Most notably, the prototypical Mott metal-insulator transition has been detected recently in binary mixtures of 40K, based on signals in the double occupancy of lattice sites and on cloud compressibilities. However, despite significant efforts, low-temperature ordered phases could not yet be seen in cold-atom systems. In my talk, I will first introduce the systems of interest and the corresponding Hubbard-like models and characterize the relevant theoretical approaches. In particular, I will discuss recent developments in quantum Monte Carlo (DMFT) methods for solving the impurity problems arising within the dynamical mean-field theory (DMFT). I will, then, present results for Mott transitions in ternary fermionic mixtures on an optical lattice, including signatures of an unforeseen semi-compressible phase [1]. Finally, I will turn to our recent studies of antiferromagnetic order in harmonically trapped lattice fermions at low temperatures. As we have shown, the Néel transition is clearly signaled, in the strong-coupling regime, by an enhanced double occupancy. The detailed quantitative predictions possible using our QMC based implementation of real-space DMFT should provide essential guidance for experimentalists. [1] E. V. Gorelik, N. Blümer, Phys. Rev. A 80, 051602(R) (2009).
Date: Mon, 03.05.2010
Time: 16:00
Duration: 45 min
Location:Josef-Stefan-Hoersaal Boltzmanngasse 5, 3rd floor, 1090 Wien
Contact:Karsten Held

The non-extendibility of quantum theory
Speaker:Renato Renner (ETH Zurich)
Abstract:The fact that quantum theory is not deterministic has been the cause of a great debate since the birth of the theory. A crucial contribution to this discussion came from Kochen and Specker, and from Bell, who showed that it is, under certain reasonable assumptions, impossible to extend quantum theory in order to make it deterministic. These arguments do, however, not exclude the possibility that there may be an extension to quantum mechanics that would allow one to predict the outcomes of measurements with higher accuracy than is possible with the current theory. In this talk I will show that such an extension cannot exist.
Date: Mon, 03.05.2010
Time: 17:30
Duration: 60 min
Location:TU Wien, Schütte-Lihotzky-Hörsaal (HS7), Karlsplatz 13, Hof 2, 1040 Wien
Contact:Prof. Caslav Brukner

Geometric Langlands duality and physics
Speaker:Karl-Georg Schlesinger (University of Vienna)
Abstract:We review the approach to the geometric Langlands program for algebraic curves via S-duality of an N=4 supersymmetric four dimensional gauge theory, initiated by Kapustin and Witten in 2006. We sketch some of the central further developments. Placing this four dimensional gauge theory into a six dimensional framework, as advocated by Witten, holds the promise to lead to a formulation which makes geometric Langlands duality a manifest symmetry (like coavariance in differential geometry). Furthermore, it leads to an approach toward geometric Langlands duality for algebraic surfaces, reproducing and extending the recent results of Braverman and Finkelberg.
Date: Tue, 04.05.2010
Time: 12:30
Duration: 60 min
Location:University of Vienna, Boltzmanngasse 5, 5th Floor, Large Seminar Room
Contact:Theo Adaktylos, David Burke, Andreas Gabriel, Niklas Johansson & Christoph Spengler

Modulare Lokalisierung in der Quantenfeldtheorie, II
Speaker:Bernhard Reiter (Univ. Wien) (Fakultät für Physik)
Abstract:im Rahmen des Seminars für Mathematische Physik
Date: Tue, 04.05.2010
Time: 14:15
Duration: 60 min
Location:Erwin Schrödinger-Hörsaal, Boltzmanngasse 5, 5. Stock
Contact:J. Yngvason

Spin- and angle-resolved photoemission on low dimensional Rashba systems
Speaker:Dr. Hugo Dil (Physik-Institut, Universität Zürich/CH)
Abstract:Combining an angle-resolved photoelectron spectrometer equipped with a three-dimensional spin polarimeter [1] and a new two-step fitting routine [2] we can measure absolute spin polarization vectors for individual bands intersected in a particular set of ARPES data[3]. This procedure is crucial when analyzing strongly overlapping peaks or weak signals sitting on a large unpolarized background, especially in the presence of non-collinear spins. It is robust against strong intensity variations due to matrix element effects because it references the spin polarization contribution of each band to the measured peak intensity. The method is applied to two-dimensional systems where spin-orbit effects lead to spin splittings and complex momentum-dependent spin structures. Presented case studies include surface alloys of Bi and Pb on Ag(111) that show a giant Rashba effect [2], as well as ultrathin Pb layers on Si(111) [4], where by introducing the electron spin as an additional tag Rashba splittings of less than 10 meV could be resolved. Further it will be shown how this powerful technique can be applied to increasingly complex systems, such as topological insulators [5] or their one-dimensional parent compounds [6]. References: [1] M. Hoesch et al., J. Elec. Spec. Rel. Ph. 124, 263 (2002) [2] F. Meier et al., PRB 77, 165431 (2008) [3] For a review see: J. H. Dil, Journal of Physics: Cond. Mat. 21, 403001 (2009) [4] J. H. Dil et al. PRL 101, 266802 (2008) [5] D. Hsieh et al. Science 323, 919 (2009) [6] J. W. Wells et al. PRL 102, 096802 (2009)
Date: Tue, 04.05.2010
Time: 16:00
Location:Technische Universität Wien, Institut für Angewandte Physik, Seminarraum 134A, Turm B (gelbe Leitfarbe), 5. OG, 1040 Wien, Wiedner Hauptstraße 8-10
Contact:Prof. Dr. Ulrike Diebold

The Search for Electric Dipole Moments
Speaker:Peter Fierlinger (TU München) (Fakultät für Physik)
Abstract:im Rahmen des Teilchenphysikseminars
Date: Tue, 04.05.2010
Time: 16:15
Duration: 60 min
Location:Erwin-Schrödinger-Hörsaal, Boltzmanngasse 5, 5. Stock
Contact:G.Ecker, H. Neufeld

The boundary of the space of the gravitational degrees of freedom
Speaker:Prof. Niall O´Murchadha (Univ. College Cork, Irland) (Fakultät für Physik)
Abstract:im Rahmen des Literaturseminars
Date: Thu, 06.05.2010
Time: 13:30
Duration: 60 min
Location:Währinger Straße 17, 1. Stock, Zimmer 118
Contact:R. Beig

A Multiplex View of Organization and Social Balance in Large-scale Social Networks und Lattice Models as Algebraic Dynamical systems, part II
Speaker:Micheal Szell (Med.Uni Wien) und Martin Göll (Uni Wien) (Fakultät für Physik)
Abstract:im Rahmen der gemeinsam veranstalteten Seminare "Komplexe Stochastische Systeme(Uni Wien) und "Analyse Komplexer Systeme" (Med. Uni Wien)
Date: Fri, 07.05.2010
Time: 14:30
Duration: 90 min
Location:Erwin Schrödinger-Hörsaal, Boltzmanngasse 5, 5. Stock