ab-plane tunneling and Andreev spectroscopy of the superconducting gap and pseudogap in (Bi,Pb){sub}2Sr{sub}2Ca{sub}2Cu{sub}3O{sub}(10+δ) and Bi{sub}2Sr{sub}2CaCu{sub}2O{sub](8+δ)

摘要

We have measured the temperature dependence of gap features revealed by Andreev reflection (Δ{sub}s) and by tunneling (Δ) in the ah plane of optimally and slightly overdoped microcrystals of (BiPb){sub}2Sr{sub}2Ca{sub}2Cu{sub}3O{sub}(10+δ) (Bi2223) with critical temperature T{sub}c = 110-115 K, and Bi{sub}2Sr{sub}2CaCu{sub}2O{sub}(8+δ) (Bi2212) with T{sub}c= 80-84 K. The tunneling conductance of a Bi2223-insulator-Bi2223 junction shows peaks at the 2Δ gap voltage, as well as dips and broad humps at other voltages. In Bi2223, similarly to the well-known Bi2212 spectra, the energies corresponding to 2Δ, to the dip, and to the hump structure are in the ratio 2:3:4. This confirms that the dip and hump features are generic to the high-temperature superconductors, irrespective of the number of CuO{sub}2 layers or the BiO superstructure. On the other hand, in both compounds the Δ(T) and Δ{sub}s(T) dependences are completely different, and we conclude that the two entities are of different natures.