Tunneling spectroscopy of YBCO "break junctions"

We present measurements at break junctions prepared of polycrystalline and textured YBCO pellets with different resistances. The higher-ohmic junctions show the well known behaviour of HTSC tunnel contacts with gap-like structures.in their dI/dV(V) characteristics. Lower-ohmic junctions show the behaviour of point contacts. Their I(V) and dI/dV(V) characteristics indicate all properties of the Andreev reflection corresponding to the theory of Kümmel et al. Ä1Ü for BCS superconductors. For correcting the characteristics we took into consideration the influence of granular capacitive coupling; so we are able to compare the characteristics dicectly with theoretical calculations. We studied the influence of magnetic fields up to 8 T.