Ferroelectric-induced charge modulation at multiferroic interfaces

Understanding the complex interplay between the charge, spin, lattice and orbital degrees of freedom in transition metal oxides is a prerequisite to engineering new properties in oxide heterostructures. Artificial oxide multiferroic interfaces extract their functionality from the cross coupling of different ferroic orders active in the joining materials (ferroelectric, ferromagnetic, ferroelastic). Staying confined to a few unit cells around the contact region, the coupling mechanisms between the ferroelectric and ferromagnetic phases may involve each of the mentioned degrees of freedom. Here we use soft X-ray angle resolved photoelectron spectroscopy correlated with X-ray absorption measurements to elucidate the interplay of strain, termination and ferroelectric state at the electronic properties of LaSrMnO3 - LSMO doped in the ideal half metal, fully spin polarized phase, buried under ferroelectric PbZrTiO3 and BaTiO3. By adjusting the energy of the incoming energy to probe the electrons or the hole states, we derive the carrier concentrations from the experimental Fermi wavevectors and establish the evolution of the band filling as a function of strain and termination. Then, the ferroelectric-induced changes in the interface electronic structure are extracted from X-ray absorption measurements, revealing the connection between the ferroelectric state of the top layer and the strain - dependent orbital occupations of the eg states in LSMO.