Optical conductivity of V4O7 across its metal-insulator transition

The optical properties of a V4O7 single crystal have been investigated from the high-temperature metallic phase down to the low-temperature antiferromagnetic insulating phase. The temperature-dependent behavior of the optical conductivity across the metal-to-insulator (MIT) transition can be explained in a polaronic scenario. Charge carriers form strongly localized polarons in the insulating phase, as suggested by a far-infrared charge gap abruptly opening at T-MIT approximate to 237 K. In the metallic phase, instead, the presence of a Drude term is indicative of fairly delocalized charges with a moderately renormalized mass m* approximate to 5m,. The electronic spectral weight is almost recovered on an energy scale of 1 eV, which is much narrower than in the VO2 and V2O3 cases. Those findings suggest that electron-lattice interaction rather than electronic correlation is the driving force for the V4O7 metal-insulator transition.