Electron or hole liquids in high-T_c cuprates: evidence for d-wave order parameter

Abstract

Phillips and Jung [J.C. Phillips and J. Jung (2002). Phil. Mag. B, 82, 1163] refute nodal properties of the gap function Δ_k and propose an isotropic s-wave picture with electron–phonon interaction as the mechanism for high-T _c superconductivity in the cuprates. Here, we compare and contrast predictions of various physical properties with the gap function Δ_k reflecting three scenarios: (i) isotropic s-wave pairing, (ii) extended s-wave with eight line nodes as championed quite recently by Zhao [G.M. Zhao (2001). Phys. Rev. B, 64, 024503], and (iii) d-wave pairing. By referring to (a) scanning tunnelling microscopy imaging of a Zn impurity, supported by our own subsequent theoretical study, (b) linear decrease of T _c with non-magnetic impurity concentration, and (c) calculations on the extended s-wave scenario applied to tunnelling conductance, strong evidence for nodal properties of Δ_k is given. The contentions of Phillips and Jung [J.C. Phillips and J. Jung (2002). Phil. Mag. B, 82, 1163] should therefore be treated with considerable caution, isotropic s-wave behaviour being truly exceptional among the high-T_c cuprates.

Keywords:

• Fermi liquids
• High-Tc cuprates
• Anisotropic superconductors
• Impurity effects
• Tunnelling

Acknowledgments

F.E. Leys thanks Professor K. Van Alsenoy for much motivation and encouragement. He also acknowledges financial support from the “Program for the Stimulation of Participation in Research Programs of the European Union” of the University of Antwerp. N.H. March and F.E. Leys thank the Department of Physics and Astronomy, University of Catania, for the stimulating environment and much hospitality.