Mass enhancement and metal-nonmetal transition driven by d-f hybridization in perovskite La1−xPrxCuO3

We report the large electron-mass enhancement and the metal to nonmetal transition upon the Pr doping in perovskite-type La1-xPrxCuO3. With increasing the Pr content x around 0.6, the LaCuO3-type three-dimensional structure with trivalent Cu ions changes to the quasi-one-dimensional structure with nearly divalent Cu ions, which accompanies significant changes in the electronic properties. Based on the resistivity, optical conductivity, specific heat measurements and the first-principles calculations, we discuss the formation of a nearly localized nonmetallic state stabilized by the hybridization between Cu 3d, O 2p, and Pr 4f orbitals in the quasi-one-dimensional lattice. The present perovskite-type cuprates offer a unique opportunity to explore novel quantum phases of correlated electrons in low-dimensional lattice, where the spin/charge/orbital degrees of freedom of A- and B-site ions are entangled.