The far-infrared c-axis conductivity of flux-grown Y$_{ 1-x}$Pr$_{ x}$Ba$_{ 2}$Cu$_{ 3}$O$_{ 7}$ single crystals with 0.2$\leq $x$\leq $0.5 has been studied by sepectral ellipsometry. We find that the c-axis response exhibits spectral features similar to deoxygenated underdoped YBa$_{ 2}$Cu$_{ 3}$O$_{ 7-\delta}$, i.e., a pseudogap develops in the normal state, the phonon mode at 320 cm$^{ -1}$ exhibits an anomalous T-dependence and an additional absorption peak forms at T. This suggests that the T$_{ c}$ suppression in flux grown Pr-substituted crystals is caused by a decrease of the hole content and/or by carrier localization rather than by pair breaking.
Categories: cond-mat.supr-con