Epitaxial growth and electronic properties of mixed valence YbAl3 thin   films
  We report the growth of thin films of the mixed valence compound YbAl$_{3}$ on MgO using molecular-beam epitaxy. Employing an aluminum buffer layer, epitaxial (001) films can be grown with sub-nm surface roughness. Using x-ray diffraction, in situ low-energy electron diffraction and aberration-corrected scanning transmission electron microscopy we establish that the films are ordered in the bulk as well as at the surface. Our films show a coherence temperature of 37 K, comparable to that reported for bulk single crystals. Photoelectron spectroscopy reveals contributions from both $\textit{f}^{13}$ and $\textit{f}^{12}$ final states establishing that YbAl$_{3}$ is a mixed valence compound and shows the presence of a Kondo Resonance peak near the Fermi-level. 
Shouvik Chatterjee, Suk Hyun Sung, David J. Baek, Lena F. Kourkoutis,   Darrell G. Schlom and Kyle M. Shen
cond-mat.mtrl-sci