Low-Temperature Anomaly in the Penetration Depth of YBCO Films:
Evidence for Andreev Bound States at Surfaces

Author(s): H. Walter, W. Prusseit, R. Semerad, H.Kinder, W. Assmann, H. Huber, H. Burkhardt, D. Rainer, and J. A. Sauls
Comments: 4 pages with 4 figures
Journal: Physical Review Letters 80, 3598 (1998) [DOI] [PDF]

We report the observation of anomalous Meissner currents in thin films of superconducting YBCO with oriented internal surfaces introduced by heavy-ion bombardment. High-precision measurements of the penetration depth (λ) reveal an upturn in the temperature dependence of λ below T* ≈ 15 K. The magnitude of the observed effect, its onset temperature and its dependence on the orientation of the surfaces are in quantitative agreement with the theory of surface effects in d-wave superconductors. The anomaly is interpreted to arise from surface currents that are carried by surface-induced Andreev bound states.

Eprint: [PDF]

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