Dynamic properties of a high-Tc superconductor: Direct evidence for non-BCS behavior

Measurements of the temperature dependence of the infrared conductivity of the CuO2 planes in YBa2Cu3O7 in the superconducting state are reported. Remarkably, we find that the temperature dependence of 1(,T) is independent of for 500 cm-1, and that it is the same as that of the nuclear Korringa product, 1/T1T. These observations indicate that for the best-characterized high-temperature superconductor, YBa2Cu3O7, the phenomenology of dynamic properties is fundamentally different from that of conventional superconductors. © 1991 The American Physical Society.