Doping dependence of the pseudogap in the ab plane infrared spectra of Bi2Sr2Ca1-xYxCu2O8+delta

The ab plane optical spectrum of underdoped Bi2S2Ca1-xYxCu2O8+delta has bee n studied as a function of temperature. The gaplike suppression in scatteri ng rate 1/tau(omega) observed below and above T-c is found to be related to the shoulder structure in reflectivity R(omega) and the broad peak or down ward suppression from Drude-like shape in conductivity sigma(1)(omega). We conclude that the superconducting gap, which is visible in sigma(1)(omega) evolves smoothly into the pseudogap. The results obtained are consistent wi th recent electron tunneling and photoemission measurements. [S0163-1829(99 )05201-7].