Observing structural distortions in complex oxides by x-ray photoelectron diffraction

The observation of structural distortions in complex oxides is becoming more important in order to explain their macroscopic behavior. X-ray photoelectron diffraction is an excellent technique to study the crystal structure and potentially observe oxygen distortions in an element-specific fashion. Its surface-sensitive character opens up the possibility to perform experiments on ultra-thin films without probing the substrate underneath. For BaBiO3 thin films, for example recent experimental results point towards a suppression of an oxygen breathing mode with decreasing film thickness resulting in a decreased energy band gap. As another example, a nontrivial electronic band structure is predicted for [111]-bilayers of LaMnO3. However, the likely presence of a Jahn- Teller distortion would suppress the topological phase. Here, the working principle of x-ray photoelectron diffraction is described and the data analysis required afterwards is discussed. X-ray photoelectron diffraction interference patterns are obtained for various thicknesses of BaBiO3 and LaMnO3 thin films. Experimental results are compared with multiple-scattering simulations. Although, indications for the structural distortions are observed, we discuss limitations of the technique in quantifying the displacement of the oxygen atoms.