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  Autore, M.; Di Pietro, P.; Calvani, P.; Schade, U.; Pyon, S.; Takayama, T.; Takagi, H.; Lupi, S.: Phase diagram and optical conductivity of La_1.8-xEu_0.2Sr_xCuO₄. Physical Review B 90 (2014), p. 035102/1-6

10.1103/PhysRevB.90.035102
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Abstract:
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 TMIT ≈ 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∗ ≈ 5me. 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.