DIRECTIONAL TUNNELING AND ANDREEV REFLECTION ON YBA2CU3O7-DELTA SINGLE-CRYSTALS - PREDOMINANCE OF D-WAVE PAIRING SYMMETRY VERIFIED WITH THEGENERALIZED BLONDER, TINKHAM, AND KLAPWIJK THEORY

We report directional tunneling and point-contact spectroscopy measure ments on the {100}, {110}, and {001} faces of YBa2Cu3O7-delta single c rystals at 4.2 K. The conductance spectra show fully developed quasipa rticle tunneling, Andreev reflection, and zero-bias peak characteristi cs, depending systematically on the junction orientation and impedance . Quantitative spectral analysis using the generalized formalism of Bl ender, Tinkham, and Klapwijk (BTK) indicates a predominantly d(x)(2)-y (2) pairing symmetry, with less than 5% s-wave component in either the d + s or d + is scenario. [S0031-9007(98)07041-0].