Pseudogap features of intrinsic tunneling in Bi2212 single crystals

The c-axis intrinsic tunneling properties of Bi2212 and HgBr2-Bi2212 single crystals have been measured in the temperature range 4.2-250 K. The 7-15-u nit-cell-high mesa structures on the surfaces of these single crystals were investigated. Clear superconductor-insulator-superconductor like tunneling curves were observed for current applied in the c-axis direction. The dyna mic conductance shows both sharp peaks at the superconducting energy gap (S G), followed by dips and wide maxima at larger voltages. The maxima togethe r with depressed conductance at zero voltage persist in the whole temperatu re range, illustrating the presence of the pseudogap in the quasiparticle e xcitation spectra, while the SG peaks decrease in voltage and lose their di stinctiveness at T -->T-c The intercalation of Bi2212 with HgBr2 molecules results in a drastic increase of the c-axis lattice constant and resistivit y rho (c). Despite this, the overall shape of the rho (c)(T)-dependence and the characteristic temperature T* at which an upturn in the rho (c)(T)-dep endence sets in upon cooling do not change. This implies that T* is not aff ected by coupling between the CuO2 bilayers. (C) 2001 Elsevier Science B.V. All rights reserved.