Doping dependence of the pseudogap in theabplane infrared spectra ofBi2Sr2Ca1−xYxCu2O8+δ

The ab plane optical spectrum of underdoped ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{Ca}}_{1-x}{\mathrm{Y}}_x{\mathrm{Cu}}_2{\mathrm{O}}_{8+\mathrm{\delta }}$ has been studied as a function of temperature. The gaplike suppression in scattering rate 1/τ(ω) observed below and above $T_c$ is found to be related to the shoulder structure in reflectivity $R\left(\omega \right)$ and the broad peak or downward suppression from Drude-like shape in conductivity ${\sigma }_1\left(\omega \right).\mathrm{}$ We conclude that the superconducting gap, which is visible in ${\sigma }_1\left(\omega \right),$ evolves smoothly into the pseudogap. The results obtained are consistent with recent electron tunneling and photoemission measurements.