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

Measurements of the temperature dependence of the infrared conductivity of the CuO{sub 2} planes in YBa{sub 2}Cu{sub 3}O{sub 7} in the superconducting state are reported. Remarkably, we find that the temperature dependence of {sigma}{sub 1}({omega},{ital T}) is independent of {omega} for {omega}{approx lt}500 cm{sup {minus}1}, and that it is the same as that of the nuclear Korringa product, 1/{ital T}{sub 1}{ital T}. These observations indicate that for the best-characterized high-temperature superconductor, YBa{sub 2}Cu{sub 3}O{sub 7}, the phenomenology of dynamic properties is fundamentally different from that of conventional superconductors.