Martensitic laminate geometry controls electronic phase transitions in a Mott insulator

Symmetry-lowering structural phase transitions result in multiple degenerate structures whose coexistence is determined by macroscopic strain compatibility. In quantum materials, these structural transformations often couple to electronic degrees of freedom, yet how the structural arrangements influence electronic phase transitions remains poorly understood. By analyzing hundreds of diffraction peaks from X-ray reciprocal space mapping, we determine the lattice basis vectors and mutual orientations of all coexisting phases in epitaxial V2O3 thin films after a symmetry-lowering transformation coincident with a metal-insulator transition. We identify the orientations of interfaces between all coexisting structures using the theory of martensitic phase transformations and find that the low temperature structure comprises finely tuned layered mixtures of alternating twin variants, akin to metal alloys. By comparing films grown on various substrate orientations, we show that the metal-insulator transition temperature increases monotonically with the degree to which these layered mixtures satisfy macroscopic strain compatibility imposed by the substrate.