Interface Structures in Ferromagnetic LaMnO$_{3}$-SrMnO$_{3}$ Superlattices

We have investigated the interfaces of LaMnO3$_{2n}$-SrMnO3$_{n}$ (LMO/SMO) superlattices. Charge density calculations have predicted a leakage of Mn e$_{g}$ electrons from LMO into SMO.\footnote{C. Aruta et al., Phys. Rev. B 80 (2009).} For n=1, these electrons are expected to be distributed throughout all films in the superlattice, while for n $>$ 3, the electrons are expected to be localized within a few layers near the interfaces. Using aberration corrected STEM coupled with EELS, we probed a LMO$_{11.8}$-SMO$_{4.4}$ superlattice at high spatial resolution to examine interfacial states. We find that the LMO on SMO interface is structurally sharper than SMO on LMO interfaces. Extra interfacial states above the Fermi level are localized to 1 unit cell of the sharp LMO/SMO interface while the states are weak or absent at the rougher SMO/LMO interfaces. The same interfaces that have extra states have an enhanced ferromagnetic moment at low temperatures.\footnote{S. May et al., Phys. Rev. B 77 (2008).}