ab-plane tunneling and Andreev spectroscopy of superconducting gap and pseudogap in (Bi,Pb)2Sr2Ca2Cu3O10 and Bi2Sr2CaCu2O8

摘要

We have measured the temperature dependence of gap features revealed byAndreev reflection Delta_s and by tunneling Delta in the ab-plane of optimaland slightly overdoped microcrystals of (BiPb)2Sr2Ca2Cu3O10 (Bi2223) withcritical temperature Tc=110-115 K, and Bi2Sr2CaCu2O8 (Bi2212) with Tc=80-84 K.The tunneling conductance of Bi2223-Insulator-Bi2223 junction shows peaks atthe 2Delta gap voltage, as well as dips and broad humps at other voltages. InBi2223, similarly to the well known Bi2212 spectra, the energies correspondingto 2Delta, to the dip, and to the hump structure are in the ratio of 2:3:4.This confirms that the dip and hump features are generic to the hightemperature superconductors, irrespective of the number of CuO2 layers or theBiO superstructure. On the other hand, in both compounds Delta(T) andDelta_s(T) dependences are completely different, and we conclude that the twoentities have different nature.