Andreev bound states in high temperature superconductors |
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Authors: | L Alff S Kleefisch U Schoop M Zittartz T Kemen T Bauch A Marx R Gross |
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Institution: | Physikalisches Institut, Universit?t zu K?ln, Zülpicherstrasse 77, 50937 K?ln, Germany, DE
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Abstract: | Andreev bound states at the surface of superconductors are expected for any pair potential showing a sign change in different
k-directions with their spectral weight depending on the relative orientation of the surface and the pair potential. We report
on the observation of Andreev bound states in high temperature superconductors (HTS) employing tunneling spectroscopy on bicrystal
grain boundary Josephson junctions (GBJs). The tunneling spectra were studied as a function of temperature and applied magnetic
field. The tunneling spectra of GBJ formed by YBa2Cu3O (YBCO), Bi2Sr2CaCu2O(BSCCO), and La1.85Sr0.15CuO4 (LSCO) show a pronounced zero bias conductance peak that can be interpreted in terms of Andreev bound states at zero energy
that are expected at the surface of HTS having a d-wave symmetry of the order parameter. In contrast, for the most likely s-wave HTS Nd1.85Ce0.15CuO4-y (NCCO) no zero bias conductance peak was observed. Applying a magnetic field results in a shift of spectral weight from zero
to finite energy. This shift is found to depend nonlinearly on the applied magnetic field. Further consequences of the Andreev
bound states are discussed and experimental evidence for anomalous Meissner currents is presented.
Received: 17 February 1998 / Revised: 27 April 1998 / Accepted: 23 June 1998 |
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Keywords: | PACS 74 25 Fy Transport properties [:AND:] 74 50 +r Proximity effects weak links tunneling phenomena and Josephson effects - 74 72 -h High-Tc compounds - 74 76 Bz High-Tc films |
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