Epitaxial growth and electronic properties of mixed valence YbAl3 thin films

TL;DR

This study demonstrates the successful epitaxial growth of high-quality YbAl3 thin films on MgO and investigates their electronic properties, revealing mixed valence behavior and a Kondo resonance similar to bulk crystals.

Contribution

It presents a novel method for growing epitaxial YbAl3 thin films with detailed structural and electronic characterization, advancing thin film synthesis of mixed valence compounds.

Findings

Epitaxial (001) YbAl3 films with sub-nm roughness were grown on MgO.

Films exhibit a coherence temperature of 37 K, similar to bulk crystals.

Photoelectron spectroscopy confirms mixed valence state and Kondo resonance presence.

Abstract

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.