Researchers demonstrated that superlattices of alternating TiO2 and VO2 layers dramatically expand the tunability range of the metal–insulator transition (MIT) in the strongly correlated VO2.1 The demonstration of a wide tunability range for the electronic properties by heterostructuring suggests new approaches for the developing novel electronic devices using strongly correlated oxides.
The TiO2/VO2 superlattices were fabricated by pulsed laser deposition. The binary oxide superlattices of alternating slices of variable TiO2 and VO2 thickness are prototypes for exploring novel phenomena in reduced dimensionality systems of strongly correlated oxides. The approach for tuning the electronic structure is based on the ability to create and transform occupied and unoccupied electronic states produced by interface coupling and lattice distortions. The population of electronic states was deduced from X-ray absorption spectroscopy and resonant inelastic X-ray scattering. The wide range of MIT temperatures were observed by electrical transport measurements, while the X-ray spectroscopy results revealed the evolution of electronic states originating from changes in the oxygen off stoichiometry tunable by the dimensionality control. This result ultimately suggests that superlattice fabrication is capable of tuning oxygen concentration while still affording a wide tunability range of the MIT—highly desirable for technological applications of strongly correlated oxides. The solid navy color (near 0 eV) of the RIXS data in the figure overflows beyond 0 eV, so you may crop the data a bit to end at 0 eV.
