Regensburg 2002 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 16: Neue und unkonventionelle Supraleiter II

TT 16.9: Vortrag

Mittwoch, 13. März 2002, 16:30–16:45, H18

Electronic structure and weak electron-phonon coupling in RB₂ (R=Zr,Nb, Ta) — •H. Rosner¹, J.M. An¹, W.E. Pickett¹, S.-L. Drechsler², A. Handstein², G. Behr², S. Otani³, G. Fuchs², K. Nenkov², K.-H. Müller², and H. Eschrig² — ¹University of California, Davis, CA, 95616, USA — ²Institut für Festkörper- und Werkstofforschung Dresden e.V., Postfach 270116, D-01171 Dresden — ³National Institute for Materials Science 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan

We present electronic structure calculations together with thermodynamic measurements on single crystals for RB₂ to search for the contradictorily reported superconductivity in these compounds and to study related normal state properties. We ascribe the absence of superconductivity, or superconductivity at very low temperatures only, to the generally weak electron phonon coupling, in combination with the orbital character of the electronic states at the Fermi surface. For the E_2g and the B_1g Γ point phonons we derive from the calculated deformation potentials small electron phonon couplings for these modes, opposite to the strong coupling of the E_2g mode in MgB₂, probably responsible for its high T_c. In comparison to MgB₂, we discuss the origin of the quite different features in the density of states and of the Fermi surfaces. The differences are mainly due to the strong hybridization between R-d and B-2p states outside the hexagonal basis plane.