We have shown by means of measurements of the current-phase relationship I(phi) of YBCO grain boundary Josephson junctions (GBJJs) that GBJJs with misorientation angles theta greater than or equal to 24degrees are in the tunnel limit. The properties of 45degrees GBJJs are known to be anomalous: both symmetric and asymmetric junctions exhibit a substantial second harmonic of I(phi) and, in symmetric 45degrees GBJJs, a temperature-controlled sign change of the first harmonic of I(phi) has been observed. We have shown that in the tunnel limit these anomalous properties follow from the d-wave pairing symmetry of YBCO, provided the interface is sufficiently rough, (C) 2001 Elsevier Science B.V. All rights reserved. [References: 8]
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