Influence of the quasiparticle lifetime effect on local tunneling spectra of high-Tc superconductors

The local electronic states of optimally doped Bi2Sr2CaCu2O8−δ and Ln-doped Bi2Sr2CuO6−δ (Ln-Bi2201, Ln = La, Gd) were measured by low-temperature scanning tunneling spectroscopy. The spectra showed enhanced coherence peaks when the gap amplitude was relatively small, while the peaks in the spectra were gradually suppressed as the gap amplitude became larger. In the case of Ln-Bi2201, the spectra showed the enhancements of residual conductance reflecting the impurity scattering due to doped Ln ions. We demonstrate that these trends are systematically reproduced based on the conductance formula that takes account of the energy dependent damping factor corresponding to the quasiparticle lifetime. The consistency suggests that one of the main factors dominating the spectral line shapes is the energy dependence of the quasiparticle lifetime.