Charge Dynamics Near the Electron-Correlation Induced Metal-Insulator Transition in Pyrochlore-Type Molybdates

摘要

The systematics of the bandwidth controlled metal-insulator transition (MIT) are investigated for R_2Mo_2O_7 (R = Nd, Sm, Gd, Dy, and Ho) by measurements of dc and optical conductivity. The substantial role of electron correlation in driving the MIT is verified. With changing the R ionic radius (r) or equivalently the one-electron bandwidth, the T = 0 K MIT occurs at r_c ≈ r(R = Gd). The T = 0 K gap continuously vanishes as Δ ∝ (r_c - r), while at the metallic side the decrease of Drude weight is followed towards r_c. A high-temperature incoherent state is approached through crossover regions both from the metallic and the insulating state.