THE TRANSITION FROM THE D-STATE TO S-STATE DUE TO THERMAL FLUCTUATIONFOR HIGH-T-C, SUPERCONDUCTORS AS AN EVIDENCE FROM THE MICROWAVE PENETRATION-DEPTH MEASUREMENT

A temperature dependence of the penetration depth lambda(T) measuremen t for the high-T-c superconductors YBa2CU3O7 - delta and Tl2Ba2CaCu2O7 thin films elucidates a T-2 dependence at low temperatures and an exp onential dependence at high temperatures. The transition temperature f or the shift from T-2 to exponential dependence decreases as the durat ion for the samples exposed to air increases. An impurity scattered me chanism to fluctuate a pure d-wave to the s-wave by thermal fluctuaion is proposed for the pairing states of these high-T-c superconducting films.