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SUMMARY:Common behaviors of unconventional superconductors indicating non-
 BCS condensation and spin-mediated resonant pairing - Yasutomo J. Uemura\,
  Columbia University\, New York\, USA
DTSTART:20100922T101500Z
DTEND:20100922T111500Z
UID:TALK26307@talks.cam.ac.uk
CONTACT:Michael Sutherland
DESCRIPTION:In unconventional suprconductors\, including high-Tc cuprates\
 , FeAs\, organic BEDT\, A3C60 and heavy-fermion CeCoIn5 systems\, we notic
 e a few common behaviors which point towards novel condensation and pairin
 g mechanisms.  They include:  (1) superconducting phase emerging adjacent 
 to the competing antiferromagnetic / SDW states\; (2) scaling of resonance
 -mode energy with Tc analogous to rotons in superfluid He\; (3) scaling of
  the spin fluctuation energy scale with Tc\; (4) scaling of the superfluid
  density with Tc in the underdoped region\; (5) scaling of the superfluid 
 density with Tc in the overdoped / pressurized region\; (6) scaling of the
  specific heat jump C/T at Tc with Tc in the overdoped  / pressurized regi
 on. \n\nTogether with accumulated results\, we show our new data on (Sr\,C
 a)2RuO4 for (1) and CeCo(In\,Sn)5 and Ba(Fe\,Co)2As2 for (5).\n\nWhile (3)
  is expected for a BCS-like condensation\, (2)\, (4)\, (5) and (6) point t
 owards Bose-Einstein condensation where Tc is governed by the condensing b
 oson density and mass.  In particular\, we notice that the spin fluctuatio
 n (mediating boson) energy scale is comparable to condensing charge energy
  scale (derived from superfluid density) in many of these systems\, sugges
 ting a resonant behavior in condensation and pairing.  This may be a key c
 oncept to understand highly unusual non-BCS like behaviors (5) and (6) in 
 the overdoped / pressurized regions of these unconventional superconductor
 s. Scaling of Tc on the soft-mode energy (2)\, in addition to superfluid d
 ensity (4) and (5)\, may be understood by BE condensation and BE-BCS cross
 over in the vicinity of magnetic competing states (1).\n\n
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
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