Bandwidth control in a perovskite-type ${3d}^1$-correlated metal ${\mathrm{Ca}}_{1-x}{\mathrm{Sr}}_x{\mathrm{VO}}_3.$ I. Evolution of the electronic properties and effective mass

Single crystals of the perovskite-type ${3d}^1$ metallic alloy system ${\mathrm{Ca}}_{1-x}{\mathrm{Sr}}_x{\mathrm{VO}}_3$ 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 $\sim 180°$ for ${\mathrm{SrVO}}_3$ to $\sim 160°$ for ${\mathrm{CaVO}}_3.$ Thus, the value of $W$ can be systematically controlled without changing the number of electrons making ${\mathrm{Ca}}_{1-x}{\mathrm{Sr}}_x{\mathrm{VO}}_3:$ one of the most ideal systems for studying bandwidth effects. The Sommerfeld-Wilson ratio $\left(\simeq 2\right),$ 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.