Search for circular dichroism in high-${\mathit{T}}_{\mathit{c}}$ superconductors

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.