Electrically conducting rock-salt LuO epitaxial thin film*

Lutetium sesquioxide Lu₂O₃ is known as a widegap insulator with the highly stable closed shell trivalent ions. On the other hand, lutetium monoxide LuO has been recognized as gaseous phase. In this study, solid-phase rock-salt LuO was synthesized in a form of epitaxial thin film by pulsed laser deposition method for the first time [1]. LuO possesses unusual valence of Lu²⁺ (4f¹⁴5d¹). In contrast with transparent and highly insulating Lu₂O₃, LuO exhibited dark-brown color and metallic conduction with high electrical conductivity at room temperature (~60 S.cm^–1). A cusp-shaped positive magnetoresistance originating from the weak antilocalization effect suggested a significant spin-orbit coupling in LuO manifested by Lu 5d electron carriers. [1] K. Kaminaga et al., ACS Omega 3, 12501-12504 (2018).