Optical investigation of metal-insulator transitions in V1-xWxO2 (0 <= x <= 0.33)

Abstract

We have investigated the variation of charge and lattice dynamics upon the metal-insulator transitions in V1-xWxO2 thin films by optical spectroscopy. As x increases, the charge gap steeply decreases to collapse around x(c) = 0.09, and then increases again, confirming the insulator-metal-insulator reentrant transition of the ground state with x. From the infrared-active phonon modes, we found that the monoclinic structural distortion gradually decreases with x and disappears at the V3+-based end point x = 0.33. The mechanism of the reentrant metal-insulator transitions with x is ascribed to the combined effect of the changes in the electron correlation and structural distortion (Peierls distortion), both affected by the V band-filling change via W substitution.