Search for circular dichroism in high-Tcsuperconductors

We report observation of circular dichroism in reflection from various cuprate superconducting materials, including ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_2$ ${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ films, an etched ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ crystal, and a ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$ crystal. This signal develops as T is lowered below 200 K and exhibits little change near ${\mathit{T}}_{\mathit{c}}$. The exact onset temperatures differ for the various materials.