Local electronic structure and dynamics of hydrogen in CeO

幸田 章宏*; 伊藤 孝   ; 平石 雅俊*; 岡部 博孝*; 門野 良典*

Koda, Akihiro*; Ito, Takashi; Hiraishi, Masatoshi*; Okabe, Hirotaka*; Kadono, Ryosuke*

The local electronic states of muon (Mu) as an isotope of hydrogen (H) in high-quality single-crystalline ceria (CeO) are investigated using muon spin rotation/relaxation (SR) and first-principles density functional theory (DFT) calculations. Upon positive muon implantation, both paramagnetic (Mu) and diamagnetic (Mu) states are observed below 10 K. Magnetic field dependence of the Mu signals combined with DFT results provides evidence for the formation of a polaron state, consisting of Mu bonded to a ligand oxygen and a 4 electron localized on a nearby Ce site. The crystal-orientation dependence of the Mu signal suggests strong anisotropy of the 4 electron due to the spin-orbit coupling with lifted degeneracy. Furthermore, the Mu state exhibits transition to the Mu state that corresponds to another Mu state (exhibiting a diamagnetic response due to fast spin/charge fluctuations) at temperatures above 10 K, before disappearing above 30 K. These findings suggest rapid diffusive motion of the 4 electrons and/or Mu (as well as H) at higher temperatures.