Regensburg 2000 – scientific programme

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TT: Tiefe Temperaturen

TT 22: Postersitzung III: Supraleitende Anwendungen (1-4) Massive HTSL, Bandleiter, Filme (5-26), Transport in HTSL (27-30), Elektronenstruktur in Supraleitern (31-43), Borkarbide (44-50), Quantenphasen- und Metall-Isolator-Überg
änge (51-69)

TT 22.35: Poster

Thursday, March 30, 2000, 14:00–17:30, A

Effects of impurities and surface disorder on the surface properties of electron-doped cuprates — •Andreas Poenicke and Mikael Fogelström — Institut für Theoretische Festkörperphysik, Universität Karlsruhe, 76128 Karlsruhe

It is well established, that the order parameter in hole-doped high temperature superconductors has a d-wave symmetry. In the case of electron-doped cuprate superconductors like Nd_2−xCe_xCuO_4−y, the order parameter symmetry is still an open question. In tunneling experiments the hallmark of a d-wave order parameter, the zero bias conduction peak, was never observed. The absence of these peaks disfavors an order parameter with sign changes around the Fermi surface. However, it is not yet clear whether the order parameter is of isotropic or anisotropic s-wave symmetry. Tunneling measurements indicate anisotropic s-wave pairing, while penetration depth measurements are in agreement with an isotropic s-wave symmetry.
We study surface properties like the local density of states and the tunneling conductivity as well as the London penetration depth for the discussed order parameters. Emphasis is put on the role of bulk impurities and local surface disorder. Surface disorder, from chemical or structural defects, is modelled by a layer of either magnetic or non-magnetic impurities. The impurity scattering is calculated in the self-consistent t-matrix approximation. The results are compared with recent experiments.