Superconducting gap in the tunneling spectra of high-T-c cuprates

In Bi2212 and La214, the low-T (T << T-c) superconducting gap magnitude 2 D elta(0) and the temperature dependence of in-plane resistivity rho were exa mined over a wide carrier-doping range. In both systems, 2 Delta(0) increas es with lowering doping level and rho starts decreasing faster around a tem perature T*, comparable to the mean-field T-c or the onset temperature of a spin-channel singlet formation in the mean-field RVB theory, each of which is given by similar to Delta(0)/2k(B).