Berlin 2005 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 18: Superconductivity - Properties, Electronic Structure, Order Parameter II

TT 18.2: Vortrag

Montag, 7. März 2005, 10:30–10:45, TU H2053

Interband Pairing Interaction in the Two-Band Superconductor MgB₂ Observed by Tunneling — •J. Geerk¹, R. Schneider¹, G. Linker¹, A. Zaitsev¹, R. Heid¹, K.-P. Bohnen¹, and H. v. Löhneysen^1,2 — ¹Forschungszentrum Karlsruhe, Institut für Festkörperphysik, P.O.B. 3640, D-76021 Karlsruhe — ²Physikalisches Institut, Universität Karlsruhe

The anisotropic superconductor MgB₂ was studied by tunneling spectroscopy of tunnel junctions of the sandwich type prepared on as deposited thin films with T_c values near 32 K. The tunnel junctions revealed an energy gap between 2.5 and 3 meV and phonon induced structures in the tunnelling density of states. The inversion of the tunnel data using the standard single-band Eliashberg equations yielded a so-called effective Eliashberg function with three distinct peaks at 38,58 and 85 meV which is compared to a theoretical calculated counterpart obtained by inversion of superconducting density of states data from two-band Eliashberg equations where electron-phonon spectral functions extracted from ab-initio LDA calculations were inserted. Convincing agreement is found between the experimental and calculated effective Eliashberg functions. Further evaluation reveals that the central peak a 58 meV mainly reflects the shape of the π-σ interband pairing interaction which appears in the gap function of the π-sheet in an amplified way due to the large gap of the σ-sheet. It is concluded that the superconductivity on the π-sheet is essentially generated by interband electron-phonon coupling.