Extended dx2 - y2-wave superconductivity. Flat nodes in the gap and the low-temperature asymptotic properties of high-Tc superconductors
Dipartimento di Fisica e Astronomia dell'Università di Catania and Istituto Nazionale di
Fisica della Materia, U.d.R.
di Catania, 57, Corso Italia, 95129 Catania, Italy
2 Institutt for Fysikk, Norges Teknisk-Naturvitenskapelige Universitet NTNU, Sem Sæ landsvei 9, Gløshaugen, 7491 Trondheim, Norway
Published online: 15 May 2000
Remarkable anisotropic structures have been recently observed in the order parameter of the underdoped superconductor Bi2Sr2CaCu2O. Such findings are strongly suggestive of deviations from a simple -wave picture of high-Tc superconductivity, i.e. . In particular, flatter nodes in are observed along the directions in -space, than within this simple model for a d-wave gap. We argue that nonlinear corrections in the -dependence of near the nodes introduce new energy scales, which would lead to deviations in the predicted power-law asymptotic behaviour of several measurable quantities, at low or intermediate temperatures. We evaluate such deviations, either analytically or numerically, within the interlayer pair-tunneling model, and within yet another phenomenological model for a d-wave order parameter. We find that such deviations are expected to be of different sign in the two cases. Moreover, the doping dependence of the flatness of the gap near the nodes is also attributable to Fermi surface effects, in addition to possible screening effects modifying the in-plane pairing kernel, as recently proposed.
PACS: 74.25.-q – General properties; correlations between physical properties in normal and superconducting states / 74.25.Jb – Electronic structure / 74.20.Mn – Nonconventional mechanisms / 74.72.Hs – Bi-based cuprates
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2000