Room-temperature annealing of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ observed by optical measurements

Using rotating-analyzer ellipsometry we have measured the dielectric function of quenched ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ samples (with intermediate oxygen content) as a function of the time τ the samples spent in laboratory atmosphere. We find an increasing concentration of Cu(I${)}^{+}$ ions with τ, in accordance with previous explanations of the rise of ${\mathit{T}}_{\mathit{c}}$ with τ.