TY - JOUR

T1 - Quasiparticle tunneling spectra of the high mercury cuprates

T2 - Implications of the-wave two-dimensional van Hove scenario

AU - Wei, J.

AU - Tsuei, C.

AU - van Bentum, P.

AU - Xiong, Q.

AU - Chu, C.

AU - Wu, M.

PY - 1998

Y1 - 1998

N2 - Quasiparticle tunneling measurements of the high-temperature superconductors (Formula presented) are considered in the context of (Formula presented) symmetry of the superconducting order parameter and a two-dimensional (2D) van Hove singularity (vHs) related to saddle points in the electronic band structure. Normal-metal-insulator-superconductor tunneling spectra taken at 4.2 K with a scanning tunneling microscope on Hg-1212 (Formula presented)-axis epitaxial films, as well as on Hg-1201 and Hg-1223 polycrystalline samples, show distinct gap characteristics which cannot be easily reconciled with the simple (Formula presented)-wave BCS density of states. The data are analyzed with the nodal (Formula presented)-wave gap function (Formula presented) and the 2D tight-binding electronic dispersion (Formula presented) using the quasiparticle tunneling formalism for elastic and specular transmission. The analysis indicates a highly directional and energy-dependent spectral weighting, related to the gap anisotropy and band-structure dependence of the tunneling matrix element (Formula presented) and successfully explains the observed gap spectra. Values for the (Formula presented)-wave gap maximum are determined to be (Formula presented) 50, and 75 meV, respectively, for optimally doped Hg-1201, Hg-1212, and Hg-1223, corresponding to reduced-gap ratios of (Formula presented) 9.5, and 13. These ratios are substantially larger than the BCS weak-coupling limit of 3.54. A comparison with data from other high-(Formula presented) cuprates indicates an overall trend of (Formula presented) rising with (Formula presented) in violation of BCS universality.

AB - Quasiparticle tunneling measurements of the high-temperature superconductors (Formula presented) are considered in the context of (Formula presented) symmetry of the superconducting order parameter and a two-dimensional (2D) van Hove singularity (vHs) related to saddle points in the electronic band structure. Normal-metal-insulator-superconductor tunneling spectra taken at 4.2 K with a scanning tunneling microscope on Hg-1212 (Formula presented)-axis epitaxial films, as well as on Hg-1201 and Hg-1223 polycrystalline samples, show distinct gap characteristics which cannot be easily reconciled with the simple (Formula presented)-wave BCS density of states. The data are analyzed with the nodal (Formula presented)-wave gap function (Formula presented) and the 2D tight-binding electronic dispersion (Formula presented) using the quasiparticle tunneling formalism for elastic and specular transmission. The analysis indicates a highly directional and energy-dependent spectral weighting, related to the gap anisotropy and band-structure dependence of the tunneling matrix element (Formula presented) and successfully explains the observed gap spectra. Values for the (Formula presented)-wave gap maximum are determined to be (Formula presented) 50, and 75 meV, respectively, for optimally doped Hg-1201, Hg-1212, and Hg-1223, corresponding to reduced-gap ratios of (Formula presented) 9.5, and 13. These ratios are substantially larger than the BCS weak-coupling limit of 3.54. A comparison with data from other high-(Formula presented) cuprates indicates an overall trend of (Formula presented) rising with (Formula presented) in violation of BCS universality.

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U2 - 10.1103/PhysRevB.57.3650

DO - 10.1103/PhysRevB.57.3650

M3 - Article

AN - SCOPUS:0000290335

VL - 57

SP - 3650

EP - 3662

JO - Physical Review B-Condensed Matter

JF - Physical Review B-Condensed Matter

SN - 1098-0121

IS - 6

ER -