  Transition metal (TM) oxide heterostructure superlattices have attracted
great attention in research communities because of their emergent interfacial
phenomena that do not exist in the bulk form. In order to understand the
mechanisms that cause these phenomena, it is important to use depth-resolved
spectroscopies to study the electronic structure across the buried oxide
interfaces. In this review, we focus on the recent applications of standing
wave (SW) photoemission (SW-XPS) and resonant inelastic x-ray scattering
(SW-RIXS) spectroscopy to study the depth profiles of electronic structure or
carriers around the polar-nonpolar oxide interfaces. Using the incident photon
energies near the TM x-ray absorption resonance, the created SW excitation can
enhance the spectral response and certain electronic transitions, providing
important insight into the interfacial electronic structure in the energy and
real space regimes. Following the background introductions, we describe two SW
experiments and demonstrate that the combination of SW-XPS and SW-RIXS has the
potential to obtain the depth distribution of electronic/orbital states around
the buried interfaces with Angstrom precision.
