TUNNELING DENSITY OF STATES IN CUPRATE AND BISMUTHATE SUPERCONDUCTORS

SIN and SIS tunnel junction characteristics in the energy gap region are reported for several superconducting oxides including Ba1-xBxBiO3 (BKBO), Nd2-xCexCuO4 (NCCO), and the 2212 and 2201 phases of the BiSrCaCuO (BSCCO) system. A pattern has emerged which suggests that the tunneling density of states of cuprates has a broadened BCS shape, but with distinctive features which cannot be explained by the addition of an imaginary term, GAMMA, to the BCS quasiparticle energy. A particular feature is a dip in the density of states at E>DELTA which, in die case of 2212 BSCCO, agrees with the dip found in photoemission data. While such features may be suggestive of a novel pairing state, we also observe structures in the high bias data of NCCO which have the characteristics of conventional phonon effects. The measured alpha2F(omega)) displays peaks and valleys which are in good agreement with F(omega) from neutron scattering.