ELECTRICAL RESPONSES OF HIGH-TC SUPERCONDUCTING THIN-FILMS TO INFRARED RADIATION

The electrical responses to both CW and pulsed infrared radiation of highly oriented thin films of various high-T(c) oxide superconductors, LnBa2Cu3Oy, La2-xSrxCuO4, and Ba1-xKxBiO3 have been investigated. All films show a clear deviation of the normalized response delta-V/(dV/dT) from a constant value at temperatures below T(c) which indicates the existence of a nonbolometric response. The responsivity and the normalized response of these materials as well as of BaPb1-xBixO3 are approximately inversely proportional to the Cooper pair density. These materials show a typical response time of 1 - 10 ns to pulsed radiation. These results can be explained on the basis of the nonequilibrium gap suppression model where the effective quasiparticle recombination time is dominated by the phonon escape time.