Absence of a loss of in-plane infrared spectral weight in the pseudogap regime of Bi2Sr2CaCu2O8+δ -: art. no. 097005

The ab-plane reflectance of Bi2Sr2CaCu2O8+delta (Bi-2212) thin films was measured in the 30-25 000 cm(-1) range for one underdoped (T-c = 70 K), and one overdoped sample (T-c = 63 K) down to 10 K. We find similar behaviors in the temperature dependence of the normal-state infrared response of both samples. Above T-c, 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 in the k = (0, pi) direction and of the in-plane infrared conductivity being mostly sensitive to the k = (pi, pi) direction.