Tunneling measurement of the energy gaps in the superconductors Y-Ba-Cu-O and Tl-Ba-Ca-Cu-O

Reported here are the results of point-contact electron-tunneling measurements in the high-Tc superconductors YBa₂{Cu}₃O_7-δ and Tl₂{Ba}₂Ca₂{Cu}₃O_10+δ. The ratio 2{Δ}/kTc is 4.0--5.8 (probability maximum near 4.8) for Y-Ba-Cu-O and 4.6 for Tl-Ba-Ca-Cu-O. Both are consistent with strong-coupling superconductivity. The measurements at 600 different locations of the same sample of YBa₂{Cu}₃O_7-δ were performed. The energy distribution of energy gaps with the regularity of the ratio 1:3:5 reported by Kirk et al. have not been seen in our experiment.