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

Abstract

C-rare earth structure lutetium sesquioxide Lu₂O₃ has been recognized as a high-<i>k</i> widegap insulator with closed shell Lu³⁺ ions. In this study, rock-salt structure lutetium monoxide LuO with unusual valence of Lu²⁺ (4f¹⁴5d¹), 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 Lu₂O₃, LuO possessed a dark-brown color and high electrical conductivity concomitant with strong spin-orbit coupling as a manifestation of Lu 5d electron carriers.