Abstract Transition metal d-electron oxides with an odd number of electrons per unit cell are expected to form metals with partially occupied energy bands, but exhibit in fact Ferrite a range of behaviors, being either insulators, or metals, or having insulator-metal transitions.Traditional explanations involved predominantly electron-electron interactions in fixed structural symmetry.The present work focuses instead on the role of symmetry breaking local structural motifs.
Viewing the previously observed V-V dimerization in VO2 as a continuous knob, reveals in density functional calculations the splitting of an isolated flat band from the broad conduction band.This leads past a critical percent dimerization to the formation of the insulating phase while lowering the total energy.In VO2 this transition is found to have a rather low energy barrier approaching the thermal energy at room temperature, suggesting energy-efficient switching in neuromorphic computing.
Interestingly, sufficient V-V dimerization suppresses magnetism, leading to the nonmagnetic insulating state, whereas magnetism appears when dimerization is reduced, forming a metallic state.This study opens the way to design novel functional quantum materials with Horse Fly Masks symmetry breaking-induced flat bands.