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SUMMARY:Unconventional superconductivity originating from disconnected Fer
 mi surfaces in the iron-based compounds - Hideo Aoki (Dept of Physics\, Un
 iversity of Tokyo):
DTSTART:20081031T111500Z
DTEND:20081031T121500Z
UID:TALK14196@talks.cam.ac.uk
CONTACT:Michael Sutherland
DESCRIPTION:The iron-based oxypnictide compound recently discovered\nby Ho
 sono is theoretically challenging as a new class of superconductors. Here 
 we study the pairing mechanism in two steps: We first construct an effecti
 ve model for the material from first principles in terms of the maximally 
 localized Wannier functions\, where the model turns out to involve all the
  five Fe 3d bands.  We then examine the Eliashberg equation with the five-
 band RPA.  A disconnected Fermi surface\, comprising two sets of Fermi poc
 kets\, has multiple nesting vectors\, which in turn give rise to an unconv
 entional pairing\, where the pairing symmetry is roughly an extended s wit
 h a sign\nchange between the pockets\, but the gap function is in fact a 5
  by 5 matrix.  We shall discuss the implications of the matrix gap functio
 n and the material/pressure dependence. This work is a collaboration with 
 K. Kuroki\, S. Onari\, R. Arita\, H. Usui\, Y. Tanaka and H. Kontani.
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
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