Effect of disorder on the metal-insulator transition of vanadium oxides: Local versus global effects

In this paper we investigate the effect of disorder on highly correlated electron systems, which exhibit metal-insulator transition (MIT) and structural-phase transition (SPT). We show that the effect of ion irradiation is strikingly different between V₂O₃ and VO₂, two otherwise similar materials. Upon irradiation, the MIT and SPT temperatures in V₂O₃ decrease drastically at low absolute dosages, much lower than for VO₂. At a low threshold dose, the insulating state of V₂O₃ drastically collapses into a metallic state. Contrary to this, irradiation of VO₂ leads to a much milder reduction of the MIT and SPT temperatures and to a weak, gradual decrease of the insulating state resistivity-not suppressed even at one order of magnitude higher doses than the V₂O₃ threshold. These major differences imply that the phase transition in V₂O₃ arises from global (rather than local as in VO₂) physical mechanisms that are extremely sensitive to disorder. This shows that the MIT and SPT may have substantially different physical origins in different systems, with the consequent major implications for theoretical descriptions of the MIT in highly correlated electron systems. (authors)