Absence of a pseudogap in the in-plane infrared response of Bi2Sr2CaCu2O(8+d)

Abstract

The ab-plane reflectance of Bi2Sr2CaCu2O(8+d) thin films was measured in the 30-25000 cm^(-1) range for one underdoped (Tc = 70 K), and one overdoped sample (Tc = 63 K) as a function of temperature (10-300 K). We find qualitatively similar behaviors in the temperature dependence of the normal-state infrared response of both samples. Above Tc, the effective spectral weight, obtained from the integrated conductivity, does not decrease when T decreases, so that no opening of an optical pseudogap is seen. We suggest that these are consequences of the pseudogap opening first in the k=(0, pi) direction, according to ARPES, and of the in-plane infrared conductivity being mostly sensitive to the k=(pi, pi) direction.