  Thickness driven electronic phase transitions are broadly observed in
different types of functional perovskite heterostructures. However, uncertainty
remains whether these effects are solely due to spatial confinement, broken
symmetry or rather to a change of structure with varying film thickness. Here,
we present direct evidence for the relaxation of oxygen 2p and Mn 3d orbital
(p-d) hybridization coupled to the layer dependent octahedral tilts within a
La2/3Sr1/3MnO3 film driven by interfacial octahedral coupling. An enhanced
Curie temperature is achieved by reducing the octahedral tilting via interface
structure engineering. Atomically resolved lattice, electronic and magnetic
structures together with X-ray absorption spectroscopy demonstrate the central
role of thickness dependent p-d hybridization in the widely observed
dimensionality effects present in correlated oxide heterostructures.
