Probing Momentum-Resolved Orbital Polarization at the Oxide Interfaces with SW-ARPES

Interface electronic structure is critical to the functional properties of strongly-correlated multilayer systems such as the La$_{\mathrm{0.7}}$Sr$_{\mathrm{0.3}}$MnO$_{\mathrm{3}}$/SrTiO$_{\mathrm{3}}$ heterostucture, a promising candidate for a magnetic tunnel junction. Recently it was demonstrated that for periodic superlattice samples controllable depth selectivity in angle-resolved photoemission spectroscopy (ARPES) can be accomplished by setting up an x-ray standing-wave (SW) field in the sample and translating it vertically along the surface normal by varying x-ray incidence angle. Here, by varying polarization of the incident x-rays we add orbital sensitivity to SW-ARPES, thus allowing us to distinguish momentum-resolved electronic dispersions for the electronic states of different symmetries (e.g. x$^{\mathrm{2}}$-y$^{\mathrm{2}}$ and 3z$^{\mathrm{2}}$-r$^{\mathrm{2}})$. Distinctly different momentum-resolved orbital polarization maps are obtained for the bulk-like and interface-like Mn 3d electronic states. The results are compared to state-of-the-art first-principles calculations. Future directions and applications are discussed.