Dresden 2006 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 11: Superconductivity: Heterostructures, Andreev Scattering, Proximity Effect, Coexistence
TT 11.1: Vortrag
Dienstag, 28. März 2006, 09:30–09:45, HSZ 301
Observation of Andreev bound states in YBCO/Au/Nb ramp-type Josephson junctions — •B. Chesca1, D. Doenitz1, T. Dahm2, R. P. Huebener1, D. Koelle1, R. Kleiner1, A. Ariando3, H.J.H. Smilde3, and H. Hilgenkamp3 — 1Physikalisches Institut - Experimentalphysik II, Universität Tübingen — 2Institut für Theoretische Physik, Universität Tübingen — 3Faculty of Science and Technology and Mesa+ Research, Institute, University of Twente
We present [1] temperature, magnetic field, and crystallographic orientation dependencies of the quasiparticle tunneling spectra of YBCO/Au/Nb junctions. With Nb superconducting, the proximity gap induced in the Au layer appears in the spectra as well defined coherence peaks and a dip at the center of a broadened zero-bias conductance peak (ZBCP).The data are consistent with the formation of Andreev bound states (ABS) at the junction interfaces supporting a d-wave symmetry of the order parameter in YBCO. We tested both proposed models of ABS assisted quasiparticle tunneling between two superconductors: the convolution model and the series connection of two decoupled interfaces model, and proved the first one applies to our case. In high contrast to Josephson tunneling, the quasiparticle spectra are crystallographic orientation insensitive: a ZBCP is observed no matter whether the tunneling occurs in the (100) or (110) directions consistent with microscopic roughness at the junction interface. The formation of ABS is insensitive to the twinned or untwinned character of the YBCO film. [1] B. Chesca et al., submitted to Phys. Rev. B(cond-mat/0506734, 2005)