Berlin 2005 – scientific programme

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TT: Tiefe Temperaturen

TT 23: Posters Superconductivity, Solids at Low Temperature

TT 23.2: Poster

Monday, March 7, 2005, 14:00–18:00, Poster TU D

In-situ synthesis of MgB₂ thin films for tunnel junctions — •R. Schneider, J. Geerk, F. Ratzel, A.G. Zaitsev, R. Heid, and K.-P. Bohnen — Forschungszentrum Karlsruhe, Institut für Festkörperphysik, P.O.B. 3640, D-76021 Karlsruhe

A novel approach to the in-situ preparation of as-grown MgB₂ thin films is presented. It comprises a conventional B sputter gun and a special Mg evaporator that provides a high Mg vapor pressure at the position of the substrate. Thin films deposited on r-plane sapphire substrates at a temperature of 440^∘C had a zero resistance T_c of 33 K and a residual resistivity of approximately 100 µΩcm. Sandwichtype tunnel junctions with a natural MgB₂ oxide as the potential barrier were prepared for superconducting tunneling spectroscopy. Conductance measurements up to 500 mV revealed estimates of the barrier thickness of 1.5 nm and height of 1.6 eV. The slowly varying conductance between ±100 mV allowed us to determine the tunneling density of states. The inversion of the tunnel data using the standard single-band Eliashberg equations yielded an effective electron-phonon spectral function accounting for the smaller energy gap. The features of the tunneling spectrum were analyzed by ab-initio LDA calculations and the two-band Eliashberg equations.