  Precise control of lattice mismatch accommodation and cation interdiffusion
across the interface is critical to modulate correlated functionalities in
epitaxial heterostructures, particularly when the interface composition is
positioned near a compositional phase transition boundary. Here we select
La1-xSrxMnO3 (LSMO) as a prototypical phase transition material and establish
vertical epitaxial interfaces with NiO to explore the strong interplay between
strain accommodation, stoichiometry modification, and localized electron
transport across the interface. It is found that localized stoichiometry
modification overcomes the plaguing dead layer problem in LSMO and leads to
strongly directional conductivity, as manifested by more than three orders of
magnitude difference between out-of-plane to in-plane conductivity.
Comprehensive structural characterization and transport measurements reveal
that this emerging behavior is related to a compositional change produced by
directional cation diffusion that pushes the LSMO phase transition from
insulating into metallic within an ultrathin interface region. This study
explores the nature of unusual electric conductivity at vertical epitaxial
interfaces and establishes an effective route for engineering nanoscale
electron transport for oxide electronics.
