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 V${}_{1\ensuremath{-}x}$W${}_{x}$O${}_{2}$ thin films by optical spectroscopy. As $x$ increases, the charge gap steeply decreases to collapse around ${x}_{\mathrm{c}}=0.09$, 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 V${}^{3+}$-based end point $\mathit{x}=0.33$. 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.