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論文

Evidence for singular-phonon-induced nematic superconductivity in a topological superconductor candidate Sr$$_{0.1}$$Bi$$_{2}$$Se$$_{3}$$

Wang, J.*; Ran, K.*; Li, S.*; Ma, Z.*; Bao, S.*; Cai, Z.*; Zhang, Y.*; 中島 健次; 河村 聖子; $v{C}$erm$'a$k, P.*; et al.

Nature Communications (Internet), 10, p.2802_1 - 2802_6, 2019/06

Superconductivity mediated by phonons is typically conventional, exhibiting a momentum-independent $$s$$-wave pairing function, due to the isotropic interactions between electrons and phonons along different crystalline directions. Here, by performing inelastic neutron scattering measurements on a superconducting single crystal of Sr$$_{0.1}$$Bi$$_{2}$$Se$$_{3}$$, a prime candidate for realizing topological superconductivity by doping the topo-logical insulator Bi$$_{2}$$Se$$_{3}$$, we found that there exist singular phonons, with the linewidths of the acoustic phonons increasing substantially at long wavelengths, but only for those along the [001] direction. This observation indicates a large and singular electron-phonon coupling at small momenta, which we propose to give rise to the exotic $$p$$-wave nematic superconducting pairing in the MxBi$$_{2}$$Se$$_{3}$$ (M = Cu, Sr, Nb) superconductor family. Therefore, we show that these superconductors may be the first examples where electron-phonon interaction can induce more exotic superconducting pairing than the $$s$$-wave.

論文

Uniaxial pressure effect on the magnetic ordered moment and transition temperatures in BaFe$$_{2-x}$$T$$_{x}$$As$$_{2}$$ ($$T$$ = Co,Ni)

Tam, D. M.*; Song, Y.*; Man, H.*; Cheung, S. C.*; Yin, Z.*; Lu, X.*; Wang, W.*; Frandsen, B. A.*; Liu, L.*; Gong, Z.*; et al.

Physical Review B, 95(6), p.060505_1 - 060505_6, 2017/02

 被引用回数:8 パーセンタイル:25.41(Materials Science, Multidisciplinary)

We use neutron diffraction and muon spin relaxation to study the effect of in-plane uniaxial pressure on the antiferromagnetic (AF) orthorhombic phase in BaFe$$_{2-x}$$T$$_{x}$$As$$_{2}$$ and its Co- and Ni-substituted members near optimal superconductivity. In the low-temperature AF ordered state, uniaxial pressure necessary to detwin the orthorhombic crystals also increases the magnetic ordered moment, reaching an 11% increase under 40 MPa for BaFe$$_{1.9}$$Co$$_{0.1}$$As$$_2$$, and a 15% increase for BaFe$$_{1.915}$$Ni$$_{0.085}$$As$$_2$$. We also observe an increase of the AF ordering temperature ($$T_N$$) of about 0.25 K/MPa in all compounds, consistent with density functional theory calculations that reveal better Fermi surface nesting for itinerant electrons under uniaxial pressure. The doping dependence of the magnetic ordered moment is captured by combining dynamical mean field theory with density functional theory, suggesting that the pressure-induced moment increase near optimal superconductivity is closely related to quantum fluctuations and the nearby electronic nematic phase.

論文

Volume-wise destruction of the antiferromagnetic Mott insulating state through quantum tuning

Frandsen, B. A.*; Liu, L.*; Cheung, S. C.*; Guguchia, Z.*; Khasanov, R.*; Morenzoni, E.*; Munsie, T. J. S.*; Hallas, A. M.*; Wilson, M. N.*; Cai, Y.*; et al.

Nature Communications (Internet), 7, p.12519_1 - 12519_8, 2016/08

 被引用回数:7 パーセンタイル:40.56(Multidisciplinary Sciences)

RENiO$$_3$$ (RE = rare-earth element) and V$$_2$$O$$_3$$ are archetypal Mott insulator systems. When tuned by chemical substitution (RENiO$$_3$$) or pressure (V$$_2$$O$$_3$$), they exhibit a quantum phase transition (QPT) between an antiferromagnetic Mott insulating state and a paramagnetic metallic state. Because novel physics often appears near a Mott QPT, the details of this transition, such as whether it is first or second order, are important. Here, we demonstrate through muon spin relaxation/rotation experiments that the QPT in RENiO$$_3$$ and V$$_2$$O$$_3$$ is first order: the magnetically ordered volume fraction decreases to zero at the QPT, resulting in a broad region of intrinsic phase separation, while the ordered magnetic moment retains its full value until it is suddenly destroyed at the QPT. These findings bring to light a surprising universality of the pressure-driven Mott transition, revealing the importance of phase separation and calling for further investigation into the nature of quantum fluctuations underlying the transition.

論文

Electronic excitations around the substituted atom in La$$_2$$Cu$$_{1-y}$$N$$_y$$O$$_4$$ as seen via resonant inelastic X-ray scattering

石井 賢司; 筒井 健二; 池内 和彦*; Jarrige, I.; 水木 純一郎; 平賀 晴弘*; 山田 和芳*; 遠山 貴己*; 前川 禎通; 遠藤 康夫*; et al.

Physical Review B, 85(10), p.104509_1 - 104509_5, 2012/03

 被引用回数:3 パーセンタイル:79.94(Materials Science, Multidisciplinary)

We perform a resonant inelastic X-ray scattering (RIXS) study of Ni-substituted La$$_2$$CuO$$_4$$ and Cu-substituted La$$_2$$NiO$$_4$$.Resonantly enhanced charge-transfer excitations are successfully observed by tuning the incident photon energy to the $$K$$-edge of the substituted element. These excitations display a very weak momentum dependence, evidencing their local character. We find a shift in the energy of the onset edge of these features compared with the non-substituted compounds La$$_2$$CuO$$_4$$ and La$$_2$$NiO$$_4$$. This shift is quantitatively reproduced by exact diagonalization calculations of the RIXS spectra. RIXS is shown to be a powerful tool to probe the electronic states of substituted elements and to understand their interaction with surrounding atoms.

論文

Resonant inelastic X-ray scattering of La$$_2$$Cu$$_{0.95}$$Ni$$_{0.05}$$O$$_4$$

石井 賢司; 池内 和彦*; Jarrige, I.; 水木 純一郎; 平賀 晴弘*; 山田 和芳*; 筒井 健二; 遠山 貴己*; 前川 禎通*; 遠藤 康夫*; et al.

Physica C, 470(Suppl.1), p.S155 - S157, 2010/12

 パーセンタイル:100(Physics, Applied)

Substitution of a specific element for a component is often used to elucidate its role in the superconductors. For a complete understanding of the substitution effect not only on the superconductivity but also on the electronic states, element-selective experiments are required. In this respect, resonant inelastic X-ray scattering (RIXS) has proven to be a powerful experimental technique enabling element-selective diagnosis of charge excitations. By tuning the incident photon energy to a given absorption edge of the element, the excitations involving the element are resonantly enhanced. In addition, RIXS has the advantage that momentum dependence can be measured. Using RIXS, we have measured the electronic excitations at the substituting sites in La$$_2$$Cu$$_{0.95}$$Ni$$_{0.05}$$O$$_4$$ and La$$_2$$Ni$$_{0.95}$$Cu$$_{0.05}$$O$$_4$$. Near the absorption edge of the substituting element, namely the Ni $$K$$-edge for La$$_2$$Cu$$_{0.95}$$Ni$$_{0.05}$$O$$_4$$ and the Cu $$K$$-edge for La$$_2$$Ni$$_{0.95}$$Cu$$_{0.05}$$O$$_4$$, charge transfer excitations from the 2$$p$$ level of neighboring oxygen to the upper Hubbard band of the substituted Ni/Cu are observed. Experimental spectra are qualitatively reproduced by a theoretical calculation based on a $$d$$-$$p$$ model.

論文

Thermally activated charge transfer in a Prussian blue derivative probed by resonant inelastic X-ray scattering

Jarrige, I.; Cai, Y. Q.*; 石井 啓文*; 平岡 望*; Bleuzen, A.*

Applied Physics Letters, 93(5), p.054101_1 - 054101_3, 2008/08

 被引用回数:9 パーセンタイル:57.34(Physics, Applied)

Charge-transfer excitation is at the source of the photoinduced magnetism observed in several Prussian blue molecule-based magnets. Using resonant inelastic X-ray scattering and X-ray absorption spectroscopy, we probe directly the thermally-activated charge transfer in a photomagnetic Fe-Co cyanide, Cs$$_{0.7}$$Co$$_{4}$$[Fe(CN)$$_{6}$$]$$_{2.9}$$[V]$$_{1.1}$$. 16H$$_{2}$$O, where [V] represents [Fe(CN)$$_{6}$$] vacancies. The temperature dependence of both Co and Fe valence ratios is estimated for the first time in one cooling run, thus yielding a more complete picture of the temperature-induced cooperative electronic modifications. This novel approach, benefiting from relatively short acquisition times, opens the possibility for realtime characterization of the photoinduced magnetism in molecule-based magnets.

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

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

Jarrige, I.; Rueff, J.-P.*; Shieh, S.*; Wang, J.*; 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$$sim$$4.3 GPa range is accompanied by a strong increase in the 4f-5d hybridization. The valence in the collapsed state is found to be $$sim$$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 4f ground state such as a non Fermi liquid behavior.

口頭

LaMnO$$_{3}$$における圧力下金属絶縁体転移のX線発光と吸収分光法の測定

Jarrige, I.; Shieh, S.*; 石井 啓文*; 平岡 望*; Cai, Y.*

no journal, , 

Here we report on a spectroscopic investigation of the intricate interplays between electronic, magnetic and structural properties of LaMnO$$_{3}$$ across its pressure-induced insulator to metal transition (IMT) at 32 GPa. We measure the Mn K-beta fluorescence line by X-ray emission spectroscopy (XES) and the Mn K-egde by X-ray absorption spectroscopy in the partial fluorescence yield mode (PFY-XAS). The XES spectra disclose a high-spin to low-spin transition accompanying the IMT that points to strongly interwoven charge and spin degrees of freedom, which is reminiscent of the Mott perspective. On the other hand, close insight is gained on the structure from the Mn K pre-edge region, where evidence is found for a complete suppression of the Jahn-Teller distortions at the IMT. This is congruent with the scenario that the gap closure results from the progressive pressure-induced degeneracy of the majority-spin eg band, thus suggesting that the IMT in LaMnO$$_{3}$$ is not a plain Mott transition.

口頭

Ni置換La$$_2$$CuO$$_4$$の共鳴非弾性X線散乱

石井 賢司; 池内 和彦; Jarrige, I.; 水木 純一郎; 平賀 晴弘*; 山田 和芳*; 筒井 健二; 遠山 貴己*; 前川 禎通*; 石井 啓文*; et al.

no journal, , 

これまでに高温超伝導体のCuをNiに置換した系は非常に数多くの研究がなされてきた。その多くはCu$$^{2+}$$($$S=1/2$$)をNi$$^{2+}$$($$S=1$$)に置換したと考え、Niを磁性不純物として着目したものであったが、Ni置換は電子状態にも何らかの影響があると予想される。今回、共鳴非弾性X線散乱(RIXS)の元素選択性を利用することによりNi周りの電子状態を抽出することに成功したのでその結果について報告する。本研究で用いた$$K$$吸収端のRIXSでは、CuまたはNiの$$1s$$-$$4p$$遷移に対応するエネルギーのX線を利用することで、電荷ギャップを越える励起が観測できる。例えば、Niの$$K$$吸収端でLa$$_2$$Cu$$_{0.95}$$Ni$$_{0.05}$$O$$_4$$の測定を行うと、中間状態で生成されたNiの$$1s$$正孔を遮蔽するために周りの酸素$$2p$$軌道からNiの$$3d$$軌道へ電子が遷移する。酸素$$2p$$軌道にできたホールはCuとZhang-Rice siglet(ZRS)を形成するので、ZRSとNi($$3d^9$$)が存在するような励起状態を観測することになる。同様に、La$$_2$$CuO$$_4$$をCuの$$K$$吸収端で測定すると、ZRSとCu($$3d^{10}$$)が生じる励起状態が観測される。今回、La$$_2$$Cu$$_{1-y}$$Ni$$_y$$O$$_4$$$$y=0.05,0.95$$の測定を行い、既に報告されている$$y=0,1$$のスペクトルと比較することで、Ni, Cuそれぞれに特徴的な電子状態の議論を行う。

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

Radiation-induced degradation of cellulose in the 1-butyl-3-methylimidazolium chloride ionic liquid

Peng, J.; Cai, D.*; Hao, Y.*; Zhai, M.*; Lin, M.; 勝村 庸介

no journal, , 

イオン液体である1-ブチル-3-メチルイミダゾリウムクロライド([Bmim]Cl)はセルロースを特別な誘導体にせずとも溶かすほど、溶解性に優れている。ここでは、[Bmim]Cl中に溶解した微結晶セルロースの$$gamma$$線照射後の分子量測定を行った。微結晶セルロースの$$gamma$$線照射分解を検討し、分解のG値,Gdを算出した。

口頭

Electronic excitations probed with resonant inelastic X-ray scattering

石井 賢司; 筒井 健二; 池内 和彦*; Jarrige, I.; 水木 純一郎; 平賀 晴弘*; 山田 和芳*; 遠山 貴己*; 前川 禎通; 石井 啓文*; et al.

no journal, , 

It is widely recognized that inelastic scattering of neutron and X-ray is a powerful tool to investigate dynamical properties of electrons in the energy-momentum space. Especially, inelastic X-ray scattering has become available in the last decade by utilizing brilliant synchrotron radiation X-rays. When the incident X-ray energy is tuned to an absorption edge of a constituent element of materials, resonantly enhanced electronic excitations are observed, which is called resonant inelastic X-ray scattering (RIXS). An additional characteristic arises from the resonant process, namely, the specific element selectively get involved in the observed excitations. While neutron scattering is predominantly sensitive to spin excitations, one can complementarily measure various excitations of electronic degrees of freedom, charge, spin, and orbital, with the RIXS technique. In our presentation, we show an explicit application of the element selectivity: resonant inelastic X-ray scattering of Ni-substituted La$$_{2}$$CuO$$_{4}$$ and Cu-substituted La$$_{2}$$NiO$$_{4}$$. Resonantly enhanced charge-transfer excitations are successfully observed by tuning the incident photon energy to the K-edge of the substituted element. Combined with theoretical calculations, we will discuss the local electronic states around the substituted element which are affected through the interaction with surrounding atoms.

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