Calendar of Physics Talks Vienna

Unconventional superconductivity originating from disconnected Fermi surfaces in the iron-based oxypnictide
Speaker:Hideo Aoki ( (Dept of Physics, University of Tokyo))
Abstract:The iron-based oxypnictide compound recently discovered by Hosono is theoretically challenging as a new class of superconductors. Here we study the pairing mechanism in two steps: We first construct an effective model for LaO$_{1-x}$F$_x$FeAs from first principles by using the maximally localized Wannier functions, where the model turns out to involve all of the five Fe 3d bands. We then examine the Eliashberg equation, where the spin and charge susceptibilities calculated with the five-band RPA are plugged. A disconnected Fermi surface, which comprises two sets ($\alpha, \beta$) of Fermi pockets, acts to develop multiple nesting vectors. This in turn gives rise to an unconventional pairing, where the superconducting gap changes sign across $\alpha$ and $\beta$ pockets leaving $\alpha$ fully gapped, but $\beta$ has nodes. We also discuss other possible pairing symmetries according as the interaction parameter is varied. This work is a collaboration with K. Kuroki, S. Onari, R. Arita, H. Usui, Y. Tanaka and H. Kontani.
Date: Mon, 04.08.2008
Time: 15:00
Location:Seminarraum 138B, 7. OG, Turm C (rot), Wiedener Hauptstr. 8-10
Contact:K. Held (13710)

Hydrodynamics and beyond in the strongly coupled N=4 plasma
Speaker:Karl Landsteiner (Madrid, IFT)
Abstract:Over the last years a new state of matter has been discovered through heavy Ion collisions at RHIC: the strongly coupled quark gluon plasma (sQGP). This by itself is an amazing fact, but probably even more amazing is that so far the best description of the sQGP is given by string theory via the AdS/CFT correspondence! I describe some properties of the basic AdS/CFT model of the plasma such as
-) return to equilibrium after an initial perturbation
-) hydrodynamic approximation and its range of validity
-) causality and hydrodynamics
-) thermalization times
Date: Thu, 07.08.2008
Time: 11:00
Duration: 60 min
Location:Seminar room e136, Institute for Theoretical Physics, Vienna University of Technology, Wiedner Hauptstr. 8-10/136