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

Abstract

Measurements of the temperature dependence of the infrared conductivity of the ${\mathrm{CuO}}_2$ planes in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ in the superconducting state are reported. Remarkably, we find that the temperature dependence of ${\mathrm{\sigma }}_1$(ω,T) is independent of ω for ω≲500 ${\mathrm{cm}}^{\mathrm{-}1}$, and that it is the same as that of the nuclear Korringa product, 1/${\mathit{T}}_1$T. These observations indicate that for the best-characterized high-temperature superconductor, ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$, the phenomenology of dynamic properties is fundamentally different from that of conventional superconductors.