
Calendar of Physics Talks Vienna
Unconventional superconductivity originating from disconnected Fermi surfaces in the ironbased oxypnictide 
Speaker:  Hideo Aoki ( (Dept of Physics, University of Tokyo)) 
Abstract:  The ironbased 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$_{1x}$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
fiveband 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. 810 
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. 810/136 
Contact:  grumil@hep.itp.tuwien.ac.at 
