Bandwidth control in a perovskite-type 3 d 1 -correlated metal Ca 1 − x Sr x VO 3 . I. Evolution of the electronic properties and effective mass

Single crystals of the perovskite-type ${3d}^{1}$ metallic alloy system ${\mathrm{Ca}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{VO}}_{3}$ were synthesized in order to investigate metallic properties near the Mott transition. The substitution of a ${\mathrm{Ca}}^{2+}$ ion for a ${\mathrm{Sr}}^{2+}$ ion reduces the bandwidth $W$ due to a buckling of the V-O-V bond angle from $\ensuremath{\sim}180\ifmmode^\circ\else\textdegree\fi{}$ for ${\mathrm{SrVO}}_{3}$ to $\ensuremath{\sim}160\ifmmode^\circ\else\textdegree\fi{}$ for ${\mathrm{CaVO}}_{3}.$ Thus, the value of $W$ can be systematically controlled without changing the number of electrons making ${\mathrm{Ca}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{VO}}_{3}:$ one of the most ideal systems for studying bandwidth effects. The Sommerfeld-Wilson ratio $(\ensuremath{\simeq}2),$ the Kadowaki-Woods ratio (in the same region as heavy fermion systems), and a large ${T}^{2}$ term in the electric resistivity, even at 300 K, substantiate a large electron correlation in this system, though the effective mass, obtained by thermodynamic and magnetic measurements, shows only a systematic but moderate increase in going from ${\mathrm{SrVO}}_{3}$ to ${\mathrm{CaVO}}_{3},$ in contrast to the critical enhancement expected from the Brinkmann-Rice picture. It is proposed that the metallic properties observed in this system near the Mott transition can be explained by considering the effect of a nonlocal electron correlation.