Andrey Chubukov
University of Wisconsin
FeAs based superconductors are the "stars of 2008".
A year ago nobody heard about them, but this summer
the number of publications per week exceeded the rate for the high Tc
cuprates at their peak.
All essential players in FeAs are the same as in the cuprates: antiferromagnetism of undoped cumpounds, unconventional superconductivity, unusual feedbacks from the pairing. Yet, the
interaction driven insulating behavior so typical for the cuprates
is likely absent in the pnictides as measurements show that even the parent compounds are reasonably good metals.
In the talk, I review recent experimental and theoretical works on
Fe-based pnictides and discuss the mechanisms for magnetism and
superconductivity, the symmetry of the superconducting gap and the role
of disorder. I show that FeAs are compensated matals, with
hole and electron Fermi surfaces of almost equal sizes.
I argue that the pairing symmetry is an $s-$wave, but
not a conventional one, as in Al or Hg, but an extended s-wave, when the
gap does not vary along a Fermi surface, but changes sign between hole
and electron Fermi surfaces.
Friday, November 7th at 4:00 PM
Room L211, Technological Institute
Refreshments are served at 3:30 PM
