Temperature dependence of the far-infrared reflectivity spectrum of the high-TcsuperconductorYBa2Cu3O7−y

Abstract

The far-infrared spectrum of $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-y}$ shows features not typical of a conventional superconductor. Besides rich phonon structure superimposed on a Drude-like tail, we find two regions of enhanced reflectivity below $T_c$. They begin at temperature-independent edges and each appears to be associated with a phononlike peak. These results could indicate temperature-independent energy gaps at 150 and 255 ${\mathrm{cm}}^{-1\mathrm{}}$ or could be evidence of internal pair excitations strongly coupled to lattice modes. Also present are features suggestive of lattice modes which soften below $T_c$.