Observation of high electron mobility with significant spin-orbit coupling in rock-salt YbO epitaxial thin film

We report the optical and electrical properties of ytterbium monoxide (YbO) epitaxial thin films with unusual valence state of Yb²⁺ (4f¹⁴5d⁰) [1]. Consistent with the chemical trends of ytterbium monochalcogenides, YbO thin films exhibited the narrow bandgap of 0.25 eV and the large crystal field splitting of 5d orbitals. Electrical resistivity was tunable by electron doping to 5d conduction band via the introduction of oxygen vacancies. Also, electron mobility at 300 K increased up to 13 cm²V^–1s^–1 with increasing electron carrier density.The weak antilocalization at low temperature observed in the heavily electron-doped YbO suggests significant spin-orbit coupling owing to the heavy Yb nucleus. [1] T. Yamamoto et al., Appl. Phys. Lett. 114, 162104 (2019). Selected as Featured.