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SUMMARY:THE FLUCTUATING BOND MODEL – A WAY TO UNDERSTAND CUPRATE SUPERCO
 NDUCTORS? - Dennis Newns\, IBM T.J. Watson Research Center
DTSTART:20080625T101500Z
DTEND:20080625T111500Z
UID:TALK11957@talks.cam.ac.uk
CONTACT:Michael Sutherland
DESCRIPTION:The cuprate high temperature superconductivity problem has res
 isted solution for over 20 years. The experimental challenge comprises not
  only Tc’s of up to 150 K\, but exotic features such as d-wave pairing s
 ymmetry and the existence of a pseudogap above Tc. Conventional electron-p
 honon coupling seems too weak to provide the pairing mechanism\, while the
  Hubbard model has recently been shown not to be a high temperature superc
 onductor. What is it about the CuO2 plane\, known to be the active element
  in HiTc superconductors\, that is driving these systems? Chemists are fam
 iliar with the strong vibrational excitation and anomalous scattering when
  electrons hop into the antibonding orbital of a molecule. We propose a si
 milar scenario for itinerant electrons coupling into the Cu-O-Cu bond. Tak
 ing into account symmetry restrictions\, the result is a model - supported
  by ab initio calculations - with a novel strong\, local\, nonlinear inter
 action between electrons and the O-coordinate. In mean field\, the model l
 eads to the pseudogap and its characteristic temperature T* via an unusual
  symmetry-breaking that has been recently observed. The pairing interactio
 n supports strong d-wave pairing\, and is also in accord with various expe
 riment regarding other properties including isotope shifts. 
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
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