Absence of circular dichroism in high-temperature superconductors

We have repeated and improved upon the experiment of Lyons et al., in which the observation of circular dichroism in high-${\mathit{T}}_{\mathit{c}}$ superconductors was reported. We found a simple extension to the previous technique which makes the apparatus exclusively sensitive to T-violating circular dichroism. We find no evidence for a temperature-dependent signal in all ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ samples studied. We establish sensitivity of the apparatus to surface roughness and ascribe the previously observed signal to possible surface contamination.