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The European Physical Journal B
ISSN: 1434-6028 (printed version)
ISSN: 1434-6036 (electronic version)
Abstract Volume 5 Issue 3 (1998) pp 423-438
Andreev bound states in high temperature superconductors
L. Alff, S. Kleefisch, U. Schoop, M. Zittartz, T. Kemen, T. Bauch, A. Marx, R. Gross
Physikalisches Institut, Universität zu Köln, Zülpicherstrasse 77, 50937 Köln, Germany
Received: 17 February 1998 / Revised: 27 April 1998 / Accepted: 23 June 1998
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$_{7-\delta}$ (YBCO), Bi2Sr2CaCu2O$_{8+\delta}$(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.
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
Article in PDF format (3288 KB)
Online publication: October 26, 1998
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