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Inter-valence charge transfer (IVCT) is electron transfer between two metal $M$ sites differing in oxidation states through a bridging ligand: $M^{n+1} + M'^{m} \rightarrow M^{n} + M'^{m+1}$. It is considered that IVCT is related to the hopping probability of electron (or the electron mobility) in solids. Since controlling the conductivity of ferromagnetic semiconductors (FMSs) is a key subject for the development of spintronic device applications, the manipulation of the conductivity through IVCT may become a new approach of band engineering in FMSs. In Ru-doped cobalt ferrite CoFe$_2$O$_4$ (CFO) that shows ferrimagnetism and semiconducting transport properties, the reduction of the electric resistivity is attributed to both the carrier doping caused by the Ru substitution for Co and the increase of the carrier mobility due to hybridization between the wide Ru $4d$ and the Fe $3d$ orbitals. The latter is the so-called IVCT mechanism that is charge transfer between the mixed valence Fe$^{2+}$/Fe$^{3+}$ states facilitated by bridging Ru $4d$ orbital: Fe$^{2+}$ + Ru$^{4+}$ $\leftrightarrow$ Fe$^{3+}$ + Ru$^{3+}$. To elucidate the emergence of the IVCT state, we have conducted x-ray absorption spectroscopy (XAS) and resonant photoemission spectroscopy (RPES) measurements on non-doped CFO and Co$_{0.5}$Ru$_{0.5}$Fe$_2$O$_4$ (CRFO) thin films. The observations of the XAS and RPES spectra indicate that the presence of the mixed valence Fe$^{2+}$/Fe$^{3+}$ state and the hybridization between the Fe $3d$ and Ru $4d$ states in the valence band. These results provide experimental evidence for the IVCT state in CRFO, demonstrating a novel mechanism that controls the electron mobility through hybridization between the $3d$ transition-metal cations with intervening $4d$ states., 16 pages, 5 figures, 1 table

(Ga,Fe)Sb is a promising ferromagnetic semiconductor for practical spintronic device applications because its Curie temperature ($T_{\rm C}$) is above room temperature. However, the origin of ferromagnetism with high $T_{\rm C}$ remains to be elucidated. Here, we use soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES) to investigate the valence-band (VB) structure of (Ga$_{0.95}$,Fe$_{0.05}$)Sb including the Fe-3$d$ impurity band (IB), to unveil the mechanism of ferromagnetism in (Ga,Fe)Sb. We find that the VB dispersion in (Ga$_{0.95}$,Fe$_{0.05}$)Sb observed by SX-ARPES is similar to that of GaSb, indicating that the doped Fe atoms hardly affect the band dispersion. The Fe-3$d$ resonant ARPES spectra demonstrate that the Fe-3$d$ IB crosses the Fermi level ($E_{\rm F}$) and hybridizes with the VB of GaSb. These observations indicate that the VB structure of (Ga$_{0.95}$,Fe$_{0.05}$)Sb is consistent with that of the IB model which is based on double-exchange interaction between the localized 3$d$ electrons of the magnetic impurities. The results indicate that the ferromagnetism in (Ga,Fe)Sb is formed by the hybridization of the Fe-3$d$ IB with the ligand $p$ band of GaSb., 24 pages, 6 figures

Artificially fabricated 3d/5d superlattices (SLs) involve both strong electron correlation and spin-orbit coupling in one material by means of interfacial 3d-5d coupling, whose mechanism remains mostly unexplored. In this work we investigated the mechanism of interfacial coupling in LaMnO3/SrIrO3 SLs by several spectroscopic approaches. Hard x-ray absorption, magnetic circular dichroism and photoemission spectra evidence the systematic modulation of the Ir ferromagnetism and the electronic structure with the change of the SL repetition period. First-principles calculations further reveal the mechanism of the SL-period dependence of the interfacial electronic structure and the local properties of the Ir moments, confirming that the formation of Ir-Mn molecular orbital is responsible for the interfacial coupling effects. The SL-period dependence of the ratio between orbital and spin components of the Ir magnetic moments can be attributed to the realignment of electron spin during the formation of the interfacial molecular orbital. Our results clarify the nature of interfacial coupling in this prototypical 3d/5d SL system and the conclusion will shed light on the study of other strongly correlated and spin-orbit coupled oxide heterointerfaces. Ministry of Education (MOE) Published version

To investigate the relationship between the charge redistribution and ferromagnetism at the heterointerface between perovskite transition-metal oxides LaNiO$_3$ (LNO) and LaMnO$_3$ (LMO), we performed x-ray absorption spectroscopy and x-ray magnetic circular dichroism (XMCD) measurements. In the LNO/LMO heterostructures with asymmetric charge redistribution, the electrons donated from Mn to Ni ions are confined within one monolayer (ML) of LNO at the interface, whereas holes are distributed over 3-4 ML on the LMO side. A detailed analysis of the Ni-$L_{2,3}$ and Mn-$L_{2,3}$ XMCD spectra reveals that Ni magnetization is induced only by the Ni$^{2+}$ ions in the 1 ML LNO adjacent to the interface, while the magnetization of Mn ions is increased in the 3-4 ML LMO of the interfacial region. The characteristic length scale of the emergent (increased) interfacial ferromagnetism of the LNO (LMO) layers is in good agreement with that of the charge distribution across the interface, indicating a close relationship between the charge redistribution due to the interfacial charge transfer and the ferromagnetism of the LNO/LMO interface. Furthermore, the XMCD spectra clearly demonstrate that the vectors of induced magnetization of both ions are aligned ferromagnetically, suggesting that the delicate balance between the exchange interactions occurring inside each layer and across the interface may induce the canted ferromagnetism of Ni$^{2+}$ ions, resulting in weak magnetization in the 1 ML LNO adjacent to the interface., 22 pages, 4 figures

We have elucidated the nature of the electron correlation effect in uranium compounds by imaging the partial $\mathrm{U}~5f$ density of states (pDOS) of typical itinerant, localized, and heavy fermion uranium compounds by using the $\mathrm{U}~4d-5f$ resonant photoemission spectroscopy. Obtained $\mathrm{U}~5f$ pDOS exhibit a systematic trend depending on the physical properties of compounds. The coherent peak at the Fermi level can be described by the band-structure calculation, but an incoherent peak emerges on the higher binding energy side ($\lesssim 1~\mathrm{eV}$) in the \Uf pDOS of localized and heavy fermion compounds. As the $\mathrm{U}~5f$ state is more localized, the intensity of the incoherent peak is enhanced and its energy position is shifted to higher binding energy. These behaviors are consistent with the prediction of the Mott metal-insulator transition, suggesting that the Hubbard-$U$ type mechanism takes an essential role in the $5f$ electronic structure of actinide materials., Accepted to PRB Dec. 22, 2018

本研究は、日本語を母語とする英語学習者がコントロール構文の主語として生成するPRO の先行詞を適切に解釈できるかどうかを実証的に調査し、理論的に解明しようとする試みである。高校生と大学生を対象に行った実験では、PRO の先行詞選択において、英語の子供たちに見られるような「主語」対「目的語」について有意差はなく、初級・中級・上級の学習者グループ間のみに有意差が見られた。分析では、日本語のコントール構文にもPRO 主語が存在する点を踏まえ、母語の文法知識が「拡大投射原理」（EPP）・「最少距離原理」（MDP）と共に第二言語の構造習得の手がかりとして役立つ一方、両言語間に意味構造のミスマッチがある場合、英語の動詞からの項情報を構造にマッピングするのに時間を要すると文法理論と母語転移の観点から説明する。

The electronic structures of UX$_3$ (X=Al, Ga, and In) were studied by photoelectron spectroscopy to understand the relationship between their electronic structures and magnetic properties. The band structures and Fermi surfaces of UAl$_3$ and UGa$_3$ were revealed experimentally by angle-resolved photoelectron spectroscopy (ARPES), and they were compared with the result of band-structure calculations. The topologies of the Fermi surfaces and the band structures of UAl$_3$ and UGa$_3$ were explained reasonably well by the calculation, although bands near the Fermi level ($E_\mathrm{F}$) were renormalized owing to the finite electron correlation effect. The topologies of the Fermi surfaces of UAl$_3$ and UGa$_3$ are very similar to each other, except for some minor differences. Such minor differences in their Fermi surface or electron correlation effect might take an essential role in their different magnetic properties. No significant changes were observed between the ARPES spectra of UGa$_3$ in the paramagnetic and antiferromagnetic phases, suggesting that UGa$_3$ is an itinerant weak antiferromagnet. The effect of chemical pressure on the electronic structures of UX$_3$ compounds was also studied by utilizing the smaller lattice constants of UAl$_3$ and UGa$_3$ than that of UIn$_3$. The valence band spectrum of UIn$_3$ is accompanied by a satellite-like structure on the high-binding-energy side. The core-level spectrum of UIn$_3$ is also qualitatively different from those of UAl$_3$ and UGa$_3$. These findings suggest that the U~$5f$ states in UIn$_3$ are more localized than those in UAl$_3$ and UGa$_3$., 12 pages, 8 figures

We investigate the thickness effects on charge and magnetic orderings in Fe perovskite oxide La1/3Sr2/3FeO3/SrTiO3 thin films by hard x-ray and resonant soft x-ray scattering (RSXS) with changing thin film thickness systematically. We found that the correlation lengths of the magnetic ordering along the in-plane and out-of-plane directions are comparable and proportional to the thickness, and shows stronger thickness dependence than those of charge orderg. %the thickness dependence of correlation length of charge ordering is smaller than that of magnetic orderings. The magnetic ordered states disappear when the correlation length of magnetic ordering decreases to that of charge ordering through the intrinsic thickness effects. Surface sensitive grazing-incident RSXS revealed that the orderings exist even in the surface region, which indicates that the observed orderings is not affected by surface effect like oxygen vacancies. Critical thickness is in 5-15 nm, which corresponds to 4-11 antiferromagnetic ordering period. This critical value seems to be common to other ferromagnetic oxide thin films.

Clarification of the position of the Fermi level ($E_\mathrm{F}$) is important in understanding the origin of ferromagnetism in the prototypical ferromagnetic semiconductor Ga$_{1-x}$Mn$_x$As (GaMnAs). In a recent publication, Souma $et$ $al$. [Sci. Rep. $\mathbf{6}$, 27266 (2016)], have investigated the band structure and the $E_\mathrm{F}$ position of GaMnAs using angle-resolved photoemission spectroscopy (ARPES), and concluded that $E_\mathrm{F}$ is located in the valence band (VB). However, this conclusion contradicts a number of recent experimental results for GaMnAs, which showed that $E_\mathrm{F}$ is located above the VB maximum in the impurity band (IB). Here, we show an alternative interpretation of their ARPES experiments, which is consistent with those recent experiments and supports the picture that $E_\mathrm{F}$ is located above the VB maximum in the IB., 5 pages, 1 figure

GeMn granular thin films are a unique and promising material for spintronics applications due to large positive magnetoresistance (MR). Previous studies on GeMn have suggested that the large MR is related to nanospinodal decomposition of GeMn into Mn-rich ferromagnetic nanoparticles and Mn-poor paramagnetic matrix. However, its microscopic origin of the MR has not been clarified yet. Here, using X-ray magnetic circular dichroism (XMCD), which is extremely sensitive to the local magnetic state of each atom, we investigate the magnetic properties of the nanoparticles and the matrix in GeMn separately. We find that the MR ratio is proportional to the product of the magnetizations originating from the nanoparticles and the matrix. This result indicates that spin-polarized holes in the nanoparticles penetrate into the matrix and that these holes undergo spin-disorder magnetic scattering by the paramagnetic Mn atoms in the matrix, which induces the large MR.

Ge$_{1-x}$Fe$_{x}$ (Ge:Fe) shows ferromagnetic behavior up to a relatively high temperature of 210 K, and hence is a promising material for spintronic applications compatible with Si technology. We have studied its electronic structure by soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES) measurements in order to elucidate the mechanism of the ferromagnetism. We observed finite Fe 3$d$ components in the states at the Fermi level ($E_{F}$) in a wide region in momentum space and $E_{F}$ was located above the valence-band maximum (VBM). First-principles supercell calculation also suggested that the $E_{F}$ is located above the VBM, within the narrow spin-down $d$($e$) band and within the spin-up impurity band of the deep acceptor-level origin derived from the strong $p$-$d$($t_{2}$) hybridization. We conclude that the narrow $d$($e$) band is responsible for the ferromagnetic coupling between Fe atoms while the acceptor-level-originated band is responsible for the transport properties of Ge:Fe.