Comparison of the electrodynamic properties of sinteredYBa2Cu3O7−yandLa1.85Sr0.15CuO4−y

Abstract

The reflectivity in the superconducting and normal states of $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-y}$ has been reproduced with the effective-medium theory plus an anisotropic dielectric function and the Mattis-Bardeen conductivity with a gap value $\frac{2\Delta }{k_B{T}_c}=2.5\mathrm{} \mathrm{to} 2.7$. We find that the lowest ir-active phonon polarized in the high-conductivity plane produces structure in the superconducting gap, the lowest-frequency phonon perpendicular to the plane is overdamped, and the electronic susceptibility is more isotropic for $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-y}$ than for ${\mathrm{La}}_{1.85}{\mathrm{Sr}}_{0.15}\mathrm{Cu}{\mathrm{O}}_{4-y}$.