BIHARMONIC PUMPING TECHNIQUE FOR Y-BA-CU-O ENERGY-SPECTRUM RESEARCH IN THE VICINITY OF THE PHASE-TRANSITION

The temperature dependence of eta(OMEGA) (here eta is the self-diffrac tion process efficiency, OMEGA is the frequency detuning of the biharm onic pumping components) for HTSC Y-Ba-Cu-O thin films in the vicinity of the superconductive transition point THETA(C) has been investigate d. It is shown that the specific ''dip'' in eta(OMEGA) for temperature s THETA < THETA(C) associated with the sample nonlinear susceptibility is due to electron-electron interaction processes and contains full i nformation about the electron (quasiparticle) bath spectrum. On the as sumption that the BCS temperature dependence of the superconductive pp width DELTA(THETA)=Ak(B)THETA(C)x (1-THETA/THETA(C))1/2 (here k(B) is the Boltzmann constant) for the temperature range 80 K less-than-or-e qual-to THETA less-than-or-equal-to THETA(C) is correct A=3.12(+0.22/0 .26) consistent with the BCS weak-coupling limit (A congruent-to 3.06) and THETA(C)=91.0(+1.3/-0.9) K have been found.