In a clean high-${\mathrm{T}}_{\mathrm{c}}$ superconductor you do not see the gap

The frequency-dependent conductivity of laser-deposited ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ thin films shows an onset of midinfrared absorption at ∼140 ${\mathrm{cm}}^{\mathrm{-}1}$ and structure in the 400–500-${\mathrm{cm}}^{\mathrm{-}1}$ region. These low-energy absorptions occur both above and below $T_c$, making them unlikely to be the superconducting gap in the usual BCS sense. The absorption across the gap is weak because the high-$T_c$ materials are in the clean limit; this weak absorption is masked by the midinfrared absorption.