Intentional cation intermixing at VO2/TiO2 interfaces: Why a metallic phase with V-V dimers can exist

In its bulk form, VO2 displays an abrupt metal-to-insulator transition (MIT) accompanied by a structural phase transition involving the evolution of V-V dimers.~ One can modulate electron correlation effects by preferentially filling the d sub orbitals of VO2 by growing epitaxial films on isomorphic TiO2 substrates i.e. atomically abrupt interfaces. [1] ~ Here we report our Synchrotron spectroscopy studies of intentional cation intermixing at the VO2/TiO2 interface.~ Although the~resultant film was metallic with no evidence of a MIT, the V-V dimer intensity did vary with temperature i.e. a structural transition persisted.~ We explain our findings within a hole doping model, whereby the high concentration of Ti4$+$ ions replacing V4$+$ ions within the structure heavily reduces the V 3d electron count i.e. away from the Mott criterion.~The fact that the distortion of the lattice is still thermodynamically favored at lower temperatures indicates that electron correlations are not a prerequisite for the structural phase transition of VO2.[2]~ Taken together with our previous strain studies,[1] our data elegantly shows the importance of orbital occupancy on the MIT of VO2. [1] Phys. Rev. B 93, 241110(R) (2016) [2] to be published (2016)