  The breaking of orbital degeneracy on a transition metal cation and the
resulting unequal electronic occupations of these orbitals provide a powerful
lever over electron density and spin ordering inmetal oxides. Here, we use ab
initio calculations to show that reversibly modulating the orbital populations
on Mn atoms can be achieved at ferroelectric/manganite interfaces by the
presence of ferroelectric polarization on the nanoscale. The change in orbital
occupation can be as large as 10%, greatly exceeding that of bulk manganites.
This reversible orbital splitting is in large part controlled by the
propagation of ferroelectric polar displacements into the interfacial region, a
structural motif absent in the bulk and unique to the interface. We use
epitaxial thin film growth and scanning transmission electron microscopy to
verify this key interfacial polar distortion and discuss the potential of
reversible control of orbital polarization via nanoscale ferroelectrics.
