Quasiparticle Tunneling into High-T, Mercury-Cuprate Superconductors: Effects of dx^2-y^2 Order Parameter Symmetry and a Two-Dimensional van Hove Singularity

J. Y. T. Wei ； P. J. M. van Bentum ； M. Rupp ； A. Gupta ； Q. Xiong ； C. C. Tsuei ； C. W. Chu ； M. K. Wu

《Chinese Journal of Physics》 34卷2S期 (1996/04) Pp. 450-454

並列摘要

Quasiparticle tunneling measurements of the high-T, superconductors Hg1Ba2Can-1CunO2n+2+δ (n = 1,2,3) are considered in the context of dx^2-y^2 symmetry of the superconducting orderparameter and a 2-D van Hove singularity related to saddle-points in the bandstructure. We present tunneling spectra taken with a low-temperature scanning tunneling microscope on Hg-1212 epitaxial films and on polycrystalline Hg-1201 and Hg-1223. The data is analyzed with elastic tunneling formalism, using the nodal gap-function Cl(k) =Δ0 (cos kr - cos ky)/2 and the 2D electronic dispersion E(k) = -2t(cos kx + cos ky) + 4t'(cos kx cos ky). Our analysis accounts for all the generic spectral features: Gap-anisotropy introduces spectral smearing. Breakdown of the WKB-approximation near band extrema gives rise to a quasi-linear conductance background. Doping-dependence and next-nearest-neighbor interaction produce spectral asymmetry. Low c-axis dispersion enables enhancement of the spectral peaks by the van Hove singularity.