Properties of optical features in YBa2Cu3O7−δ

Abstract

Characteristic optical features in the far-infrared conductivity of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ crystals have been studied as a function of doping. We focus particularly on a reflectivity ‘‘edge’’ near 435 ${\mathrm{cm}}^{\mathrm{-}1}$ which we find to be both insensitive to carrier concentration (i.e., $T_c$), and present in the normal state of some samples. These results place tight constraints on possible interpretations of this feature.