Thursday, May 3, 2007, 1:30 pm — Small seminar room, Bldg. 510
D.M. Newns and C.C. Tsuei
IBM T.J. Watson Research Center, Yorktown Heights, NY 10598
Twenty years of extensive research have yet to produce a general consensus on the origin of high temperature superconductivity (HTS). In a novel approach [1], we attribute the coupling responsible for pairing in the cuprates to the dependence of the stability of the oxygen atom in the planar Cu-O-Cu bond on the electronic state of the bond; this stability is critical in cuprates because the O 2p and Cu 3d orbitals involved in forming the bond are nearly filled, and the bond strength can be transiently eliminated by local electron number fluctuations. This coupling is modeled by making the oxygen’s harmonic potential a (negative) constant plus a linear function of the electronic bond strength, together with a stabilizing quartic potential. The Fermi liquid nature of the d-wave superconducting ground state supports a weak-coupling treatment of this 2-phonon coupling. The resulting electron-electron interaction is dressed at long wavelengths to form an attractive interaction in the d-symmetry channel. Pairing via this interaction is d-wave with the usual dome for Tc, and an isotope shift which is very low at maximum Tc, but anomalously large on the underdoped side, as observed. The phonon softening below Tc is derived in mean field. The dominant contribution to a CDW instability is quadrupolar (d-wave) in character (dCDW). Anomalous scattering by dCDW fluctuations – tending to eliminate the Fermi surface at the antinodal points – is related to the d-wave pseudogap.
[1] D.M. Newns and C.C. Tsuei, Nature Physics 3, 184 (2007).
Hosted by: Jim Misewich
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