Observation of bound surface states in grain-boundary junctions of high-temperature superconductors

L. Alff, A. Beck, R. Gross, A. Marx, S. Kleefisch, Th. Bauch, H. Sato, M. Naito, and G. Koren
Phys. Rev. B 58, 11197 – Published 1 November 1998
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Abstract

We have performed a detailed study of the tunneling spectra of bicrystal grain-boundary junctions (GBJ’s) fabricated from the high-temperature superconductors (HTS) YBa2Cu3O7δ (YBCO), Bi2Sr2CaCu2O8+δ (BSCCO), La1.85Sr0.15CuO4 (LSCO), and Nd1.85Ce0.15CuO4y (NCCO). In all experiments the tunneling direction was along the CuO2 planes. With the exception of NCCO, for all materials a pronounced zero bias conductance peak (ZBCP) was observed that decreases with increasing temperature and disappears at the critical temperature. These results can be explained by the presence of a dominating d-wave symmetry of the order parameter resulting in the formation of zero-energy Andreev bound states at surfaces and interfaces of HTS. The absence of a ZBCP for NCCO is consistent with a dominating s-wave symmetry of the pair potential in this material. The observed nonlinear shift of spectral weight to finite energies by applying a magnetic field is in qualitative agreement with recent theoretical predictions.

  • Received 10 February 1998

DOI:https://doi.org/10.1103/PhysRevB.58.11197

©1998 American Physical Society

Authors & Affiliations

L. Alff

  • II. Physikalisches Institut, Universität zu Köln, Zülpicherstrasse 77, D-50937 Köln, Germany

A. Beck

  • IBM Research Division, Zürich Research Laboratory, Säumerstrasse 4, 8803 Rüschlikon, Switzerland

R. Gross, A. Marx, S. Kleefisch, and Th. Bauch

  • II. Physikalisches Institut, Universität zu Köln, Zülpicherstrasse 77, D-50937 Köln, Germany

H. Sato and M. Naito

  • NTT Basic Research Laboratories, 3-1 Morinosato Wakamiya, Atsugi-shi, Kanagawa 243, Japan

G. Koren

  • Physics Department, Technion, Israel Institute of Technology, 32000 Haifa, Israel

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Vol. 58, Iss. 17 — 1 November 1998

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