Influences of energy dependent quasiparticle lifetime effect on tunneling spectra of high-Tc superconductors

The local electronic states of optimally doped Bi2Sr2CaCu2O8+delta (Bi2212) and Ln-doped Bi(2)Sr(1.6)Ln(0.4)CuO(6+delta) (Ln-Bi2201, Ln=La, Gd) were measured by low-temperature scanning tunneling spectroscopy. Spatially inhomogeneous electronic states were detected for all samples, and the gap amplitudes were distributed in the range between 40-140meV in the case of Bi2212 and 30-200meV in the case of Ln-Bi2201.The spectra showed enhanced coherence peaks with large residual conductance when the gap amplitude was relatively small, while the peaks in the spectra were gradually broadened as the gap amplitude became larger. We demonstrate that a series of spectra with various gap amplitudes obtained on a single sample is systematically reproduced by the conductance spectra for d-wave BCS density of states which take account of the energy dependent quasiparticle lifetime broadening factor. This fact indicates the presence of serious influences of an intrinsic broadening effect due to the strong electron correlation in tunneling spectroscopy of high-T-c superconductors.