Temperature dependence of tunneling spectra in YBa₂Cu₃O_7−δ and Bi₂Sr₂CaCu₂O_8+δ single crystals

During past years, scanning tunneling spectroscopy (STS) investigations of high temperature superconductors have revealed unusual characteristics of the superconducting gap. We present here the temperature dependence of the tunneling conductance spectra on YBa2Cu3O7-delta and Bi2Sr2CaCu2O8+delta single crystals. We discuss similarities and differences between these two compounds. In particular we note that while in Bi2Sr2CaCu2O8+delta a pseudogap is observed above the critical temperature, even in overdoped samples, we find no indication of a pseudogap in optimally doped YBa2Cu3O7-delta above T-c. This is consistent with other striking differences between the two systems and supports the interpretation of the pseudogap in terms of strong superconducting correlations