Octahedral Symmetry Modification Induced Orbital Occupancy Variation in VO 2 .

Octahedral symmetry is one of the parameters to tune the functional properties of complex oxides. VO 2 , a complex oxide with a 3 d 1 electronic system, exhibits an insulator-metal transition (IMT) near room temperature (∼68 °C), accompanying a change in the octahedral structure from asymmetrical to symmetrical. However, the role of octahedral symmetry in VO 2 on the IMT characteristics is unclear. Crystal and electronic structure analyses combined with density-functional-theory calculations showed the bandwidth-controlled IMT characteristics of monoclinic VO 2 with high octahedral symmetry. The expanded apical V-O length for a high octahedral symmetry of a VO 2 film increased the bandwidth of the conduction band by depressing V 3 d -O 2 p hybridization. As a result, the interdimer hopping energy increased and thereby decreased the IMT temperature, although the short V-V chain enhanced electron correlation. These findings suggest that octahedral symmetry can control the IMT characteristics of VO 2 by changing the orbital occupancy.