EVIDENCE OF D(X(2)-Y(2)) SYMMETRY IN THE TUNNELING CONDUCTANCE DENSITY-OF-STATES OF TL2BA2CUO6

Tunnel junctions have been made on-single crystals of Tl2Ba2CuO6 with a T-c similar to 91 K using a mechanical point-contact method. Both su perconductor-insulator-normal-metal (SIN) and superconductor-insulator -superconductor (SIS) junctions were obtained using Au and Nb tips, re spectively. The tunneling conductances obtained are reproducible, with sharp, well-defined energy gap structures and are characterized by a cusplike feature at zero bias. These conductances can be fit to a simp le, momentum-averaged density of states (DOS) obtained from a supercon ducting order parameter with d(x2-y2) symmetry. The SIS data display a weak Nb gap feature which is consistent with the subgap DOS observed in the SIN data.