New Lutetium Oxide: Electrically Conducting Rock-Salt LuO Epitaxial Thin Film

[Image: see text] C-rare earth structure lutetium sesquioxide Lu(2)O(3) has been recognized as a high-k widegap insulator with closed shell Lu(3+) ions. In this study, rock-salt structure lutetium monoxide LuO with unusual valence of Lu(2+) (4f(14)5d(1)), previously known as the gaseous phase, was synthesized as an epitaxial thin film by the pulsed laser deposition method. In contrast with transparent and highly insulating Lu(2)O(3), LuO possessed a dark-brown color and high electrical conductivity concomitant with strong spin–orbit coupling as a manifestation of Lu 5d electron carriers.