A. I. AKIMENKO, N. M. PONOMARENKO, V. A. GUDIMENKO, I. K. YANSON, P. SAMUELI, and P. KUS, Gap harmonic structure in the point-contact spectra of SmBa₂Cu₃O_7-d films, Low Temp. Phys. 16, (1990) [Fiz. Nizk. Temp. 16, 584-585, (1990)].