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論文

Electronic structure and correlation in $$beta$$-Ti$$_3$$O$$_5$$ and $$lambda$$-Ti$$_3$$O$$_5$$ studied by hard X-ray photoelectron spectroscopy

小林 啓介*; 田口 宗孝*; 小畠 雅明; 田中 健司*; 所 裕子*; 大門 寛*; 岡根 哲夫; 山上 浩志; 池永 英司*; 大越 慎一*

Physical Review B, 95(8), p.085133_1 - 085133_7, 2017/02

AA2017-0038.pdf:0.98MB

 被引用回数:12 パーセンタイル:58.54(Materials Science, Multidisciplinary)

We have conducted hard X-ray photoelectron spectroscopy investigations of the electronic structure changes and electron correlation phenomena which take place upon the photoinduced reversible phase transition between $$beta$$- and $$lambda$$-Ti$$_3$$O. From valence band spectra of $$beta$$- and $$lambda$$-Ti$$_3$$O$$_5$$, we have identified the bipolaron caused by the $$sigma$$-type bonding of $$d_{xy}$$ orbitals in $$beta$$-Ti$$_3$$O$$_5$$ and the $$pi$$ stacking between the $$d_{xy}$$ orbitals between different Ti sites in $$lambda$$-Ti$$_3$$O$$_5$$, previously predicted by $textit{ab initio}$ calculations. On the other hand, the Ti $$2p$$ and Ti $$1s$$ core level spectra exhibit nonlocal screening satellite features, which are typical spectroscopic signs of strong electron correlation in the coherent Ti $$t_{2g}$$ states. Correlation in the valence band also manifests to reduce the plasmon energy, which results in an enhancement of the valence electron mass by a factor of 2.7.

口頭

Volume collapse transition in TmTe; Competition between strong correlation and $$f$$-$$d$$ hybridization at high pressure

Jarrige, I.; Rueff, J.-P.*; Shieh, S.*; 田口 宗孝*; 大石 泰生*; 松村 隆*; 石井 啓文*; 平岡 望*; Cai, Y.*

no journal, , 

The pressure-induced mixed-valent state in TmTe is investigated up to 10.6 GPa using resonant inelastic X-ray scattering (RIXS) and the Anderson impurity model (AIM). The volume collapse transition (VCT) which takes place over the 2-4.3 GPa range is accompanied by a strong increase in the 4$$f$$-5$$d$$ hybridization. The valence in the collapsed state is found to be 2.5, showing that the VCT is inconsistent with the commonly accepted picture of Tm$$^{2+}$$ to Tm$$^{3+}$$ conversion. At 6 GPa, a transition in both magnetic and electronic ground states occurs at constant valence and hybridization. This could be indicative of a non-trivial instability of the 4$$f$$ ground state such as a non Fermi liquid behavior.

口頭

Competition between multi-channel Kondo effect and f delocalization in TmTe at high pressure

Jarrige, I.; Rueff, J.-P.*; Shieh, S.*; 田口 宗孝*; 石井 啓文*; Cai, Y. Q.*

no journal, , 

Identifying the mechanism of Kondo phenomena is arguably one of the most exciting and widely studied issues in condensed matter physics. Intermediate-valent Tm compounds stand out as potential candidates for multichannel Kondo (ncK) effect, since both integer valences Tm$$^{2+}$$ and Tm$$^{3+}$$ are magnetic. Using resonant inelastic X-ray scattering and the Anderson impurity model, we probed the Tm valence and 4f-5d hybridization in the high-pressure intermediate-valent TmTe compound. Our results reveal that the f delocalization is discontinuous, characterized by a previously unobserved plateau-like behavior over the 4.3$$sim$$6.5 GPa range. This is at odds with the usual, continuous Kondo-like f delocalization, and is interpreted as an experimental observation of the effect of culminating ncK scattering of d electrons from local moments on the electronic structure.

口頭

Competition between multi-channel Kondo effect and f delocalization in TmTe at high pressure

Jarrige, I.; Rueff, J.-P.*; Cai, Y. Q.*; Shieh, S.*; 石井 啓文*; 田口 宗孝*

no journal, , 

Among numerous f electron systems which present Kondo properties, intermediate-valent Tm compounds stand out as potential candidates for multichannel Kondo (ncK) effect, since both integer valences Tm2+ and Tm3+ are magnetic. Using resonant inelastic X-ray scattering and the Anderson impurity model, we probed the Tm valence and 4f-5d hybridization in the high-pressure intermediate-valent TmTe compound. Our results reveal that the f delocalization is discontinuous, characterized by a previously unobserved plateau-like behavior between the volume collapse transition and the structural transition (4.3$$sim$$6.5 GPa), with an associated valence (2.55) at odds with the near-trivalency previously reported. This is at odds with the usual, continuous Kondo-like f delocalization, and is interpreted as an experimental observation of the effect of culminating ncK scattering of d electrons from local moments on the electronic structure.

口頭

Single-channel vs multi-channel Kondo effects; SmTe and TmTe studied via resonant inelastic X-ray scattering under high pressure

Jarrige, I.; Rueff, J.-P.*; Shieh, S.*; 田口 宗孝*; 大石 泰生*; 松村 武*; 石井 啓文*; 平岡 望*; Cai, Y. Q.*

no journal, , 

Using resonant inelastic X-ray scattering and the Anderson impurity model, we estimated the pressure dependence of the Sm and Tm valence and 4 f -5d hybridization in the respectively single and multi-channel Kondo compounds SmTe and TmTe. We observed a usual, continuous Kondo-like f delocalization for SmTe as a function of pressure. On the contrary, our results reveal that the f delocalization in TmTe is discontinuous, characterized by a previously unobserved plateau-like behavior between 4.3 and 6.5 GPa. This is interpreted as an experimental observation of the effect of culminating multi-channel Kondo scattering of d electrons from local moments on the electronic structure. Our study raises the interesting possibility that an NCK effect realized in a compressed mixed-valent f system could impede the concomitant electron delocalization.

口頭

X線発光分光を用いた無限層構造を持つA(A=Sr,Ca)FeO$$_{2}$$のFeの3d電子状態に関する研究

水牧 仁一朗*; 田口 宗孝*; 安居院 あかね; 河村 直己*; Tassel, C.*; 辻本 吉廣*; 陰山 洋*

no journal, , 

Fe酸化物としては非常に珍しい平面四配位をとるSrFeO$$_{2}$$は2次元構造を持つにもかかわらず、磁気秩序は3次元的であり、特異な電子配置をとる興味深い物質である。今回われわれはFeの3p$$rightarrow$$1s発光を用いて、Feの電子状態を調べた。SrをCaに置換したCaFeO$$_{2}$$と比較し、Feの電子構造と局所対称性の相関と3次元磁気構造におけるFe-3d電子の役割を報告する。

口頭

X-ray Raman scattering study on the valence transition of EuPd$$_2$$Si$$_2$$

稲見 俊哉; 石井 賢司; 吉田 雅洋; 光田 暁弘*; 田口 宗孝*; Shin, S.*

no journal, , 

X線吸収分光法(XAS)による、希土類のM吸収端やN吸収端での内殻励起スペクトルは、4f電子の価数や空間対称性,混成の程度などを検出できる有力な手法として知られている。しかしながら、軟X線を用いるこの手法は物質に対する侵入長が短いため、例えば、高圧下の実験等は不可能である。X線ラマン分光法はX線の非弾性過程を利用する手法で、X線吸収スペクトルを得る代替法として知られている。硬X線を用いるので、バルク敏感で極限環境の実現も比較的たやすく、近年、希土類やアクチノイド化合物の電子構造の研究に用いられ始めている。今回は、このX線ラマン散乱法の物性研究への適用可能性を確認するため、150K近傍で急峻でかつ大きな価数転移を示すEuPd$$_2$$Si$$_2$$を試料としてテスト実験を行い、エネルギー損失スペクトルに、130eV近傍にEuの$$4drightarrow4f$$遷移に対応する明瞭な構造を観測することに成功した。

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