Abstract
Complex transition metal oxides have become key materials for new generations of electronic devices. Physical properties of such oxides are strongly correlated with their electronic structures. Based on the progress of recent technologies, much more fanscinating physical phenomena and novel functionalities, arising from the ultrathin oxide films and oxide interfaces, have been revealed. In this thesis, we mainly performed resonant soft x-ray scattering (RSXS) and hard x-ray photoemission spectroscopy (HAXPES) to study some forefront physical topics in LaAlO3/SrTiO3 heterostructure and manganite LaMnO3/SrMnO3 superlattice. Unexpected electronic and magnetic properties at interfaces between distinct transition-metal oxides have received much attention. The electronic phase at the interface of a heterostructure often di ers from those of the sandwiching bulks. In the rst part of this thesis, we present a HAXPES method under grazing incidence to probe the distribution of charge transfer at the interface of LaAlO3/SrTiO3 heterostructure. The heterostructure between LaAlO3 and SrTiO3 is one of representative systems with fascinating interfacial properties. However, dimensionality and quantitative information about the charge distribution of this system near the interface also remains unclear. The HAXPES results, which provide direct information about the pro le of electronic reconstruction, not only show the existence of Ti3+ but also reveal its finite distribution depth. By exploiting the collapse of evanescent x-ray waves and the abrupt increase of x-ray absorption at the critical incidence angle, our HAXPES study reveals a 2% electronic reconstruction from Ti4+ to Ti3+ occurring near the interface. Such an electronic reconstruction also extends from the interface into SrTiO3 with a depth of about 48 A (12 unit cells) and an estimated total charge transfer of 0.24 electrons per two-dimensional unit cell. Among the interface physics, particularly, orbital polarization is one of the most interesting topics. The second subject in this thesis, we measured directly the orbital polarization of interfacial electronic states in a system of LaMnO3/SrMnO3 superlattice. A theoretical analysis of the angular dependence of scattering yields measurements on the electronic reconstruction across the interface exhibits an in-plane orbital polarization. We for the rst time demonstrated that resonant soft x-ray scattering is a unique means to measure directly the interfacial orbital polarization of a superlattice, in contrast to the measurement of linear dichroism in x-ray absorption. At the last part of this thesis, by applying advantages of thin film synthesis on this specially designed LaMnO3/SrMnO3 superlattice, we further examine experimentally the change in Jahn-Teller distortions across a magnetic transition. Since spin and orbital orderings coexist in manganites, and the magnetic and transport properties are closely related to the orbital ordering. Yet a fundamental unresolved issue is to explain the formation of orbital ordering in manganites. As a consequence, we provide experimental evidence that the global Jahn-Teller distortion is tied up with the many-body superexchange interaction. The measured Jahn-Teller distortion is markedly enhanced upon the emergence of magnetization and strongly correlated with the spin ordering in manganites. Such a close connection sheds light on the mystery of the mechanism of orbital ordering and reveals the many-body origin of the global Jahn-Teller distortions in manganites.