Kenichi Kaminaga

A valence-selective X-ray fluorescence holography study of an yttrium oxide thin film

The first direct valence-selective structure determination by X-ray fluorescence holography is reported. The method is applied to investigate an epitaxial thin film of the rare earth monoxide YO, which has recently been synthesized by pulsed laser deposition. The surface of the sample is easily oxidized to Y2O3. In order to separate the structural information connected with the two different valence states of Y, the X-ray fluorescence holography measurements were performed close to the Y K absorption edge. Using the shift of the absorption edge for the different valence states, very different relative contributions of YO and Y2O3 are obtained. Thus, it is possible to distinguish the crystal structures of YO and Y2O3 in the thin-film sample.

Superconductivity of Rock-Salt Structure LaO Epitaxial Thin Film

We report a superconducting transition in a LaO epitaxial thin film with the superconducting transition onset temperature ( Tc) at around 5 K. This Tc is higher than those of other lanthanum monochalcogenides and opposite to their chemical trend: Tc = 0.84, 1.02, and 1.48 K for LaX (X = S, Se, Te), respectively. The carrier control resulted in a dome-shaped Tc as a function of electron carrier density. In addition, the Tc was significantly sensitive to epitaxial strain in spite of the highly symmetric crystal structure. This rock-salt superconducting LaO could be a building block to design novel superlattice superconductors.

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

C-rare earth structure lutetium sesquioxide Lu2O3 has been recognized as a high-k 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.