Superconducting gap and pseudogap for overdoped Bi_(2-x)Pb_xSr_2CaCu_2O_(8+δ) using 60 ns time-scale short-pulse interlayer tunneling spectroscopy

摘要

We have measured the interlayer tunneling spectra for overdoped Bi_(2-x)Pb_xSr_2CaCu_2O_(8+δ) single crystals with a doping level p ranging from 0.20 to 0.22 and a T_c from 80 to 67 K using a small mesa structure and a 60 ns time-scale short-pulse technique. It is found that, with increasing doping, the superconducting gap decreases from 46 to 18 meV, while the pseudogap decreases from 42 to 10 meV. The result indicates the existence of the pseudogap in the overdoped region even at a doping level p higher than 0.19, at which the pseudogap is expected to disappear in some generic phase diagram models. Furthermore, the values obtained for the superconducting gap, normal tunneling resistance, and the maximum Josephson current indicate the likeliness of the inhomogeneous superconducting state even in the overdoped region.