AC JOSEPHSON EFFECT IN HIGH-TC POLYCRYSTALLINE THIN-FILM BRIDGES

We have investigated the effect of millimeter-wave electromagnetic radiation on the I-V curves of superconducting bridges made from polycrystalline YBa2Cu3O7-x films with the grain size a approximately 1-mu-m and the critical current density j(4.2K) approximately 10(4) A/cm2. When the bridge dimensions wxl were decreased from 200 x 200-mu-m2 to 5 x 5-mu-m2, the effect of radiation at T<<T changed from heating (for bridges with w, 1 greater-than-or-equal-to 100-mu-m) to(c) vortex synchronization (20-mu-m < w, l < 100-mu-m) and after that (w, 1 less-than-or-equal-to 20-mu-m) to synchronization of Josephson oscillations. Josephson behaviour of the bridges with w, 1 < 20-mu-m was shown to be related to large-scale percolation processes in the system of intergrain Josephson junctions with the characteristics percolation length L approximately 20-mu-m. In was demonstrated that bridges with w, 1 < L could have values of noise equivalent power NEP < 10(-12)W/Hz1/2 at T = 40K.