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論文

Two-step Mott transition in Ni(S,Se)$$_2$$; $$mu$$SR studies and charge-spin percolation model

Sheng, Q.*; 金子 竜也*; Yamakawa, Kohtaro*; Guguchia, Z.*; Gong, Z.*; Zhao, G.*; Dai, G.*; Jin, C.*; Guo, S.*; Fu, L.*; et al.

Physical Review Research (Internet), 4(3), p.033172_1 - 033172_14, 2022/09

A pyrite system NiS$$_{2-x}$$Se$$_x$$ exhibits a bandwidth controlled Mott transition via (S,Se) substitutions in a two-step process: the antiferromagnetic insulator (AFI) to antiferromagnetic metal (AFM) transition at $$xsim$$0.45 followed by the AFM to paramagnetic metal (PMM) transition at $$xsim$$1.0. Among a few other Mott systems which exhibit similar two-step transitions, Ni(S,Se)$$_2$$ is of particular interest because a large intermediate AFM region in the phase diagram would provide unique opportunities to study the interplay between the spin and charge order. By comparing and combining our muon spin relaxation studies and previous neutron scattering studies, here we propose a picture where the spin order is maintained by the percolation of "nonmetallic" localized and dangling Ni moments surrounded by S, while the charge transition from AFI to AFM is caused by the percolation of the conducting paths generated by the Ni-Se-Ni bonds.

論文

Magnetic properties and electronic configurations of Mn ions in the diluted magnetic semiconductor Ba$$_{1-x}$$K$$_x$$(Zn$$_{1-y}$$Mn$$_y$$)$$_2$$As$$_2$$ studied by X-ray magnetic circular dichroism and resonant inelastic X-ray scattering

鈴木 博人*; Zhao, G.*; 岡本 淳*; 坂本 祥哉*; Chen, Z.-Y.*; 野中 洋亮*; 芝田 悟朗; Zhao, K.*; Chen, B.*; Wu, W.-B.*; et al.

Journal of the Physical Society of Japan, 91(6), p.064710_1 - 064710_5, 2022/06

 被引用回数:0 パーセンタイル:0(Physics, Multidisciplinary)

The magnetic properties and the electronic excitations of the new diluted magnetic semiconductor Ba$$_{1-x}$$K$$_x$$(Zn$$_{1-y}$$Mn$$_y$$)$$_2$$As$$_2$$ have been studied by X-ray magnetic circular dichroism (XMCD) and resonant inelastic X-ray scattering (RIXS). The sum rule analysis of the XMCD spectra indicates that the Mn atoms are in the high-spin configurations of $$d^5$$, whereas the presence of competing ferromagnetic and antiferromagnetic interactions between the Mn ions reduces the net spin moment. Based on a comparison of the RIXS line shapes with those of Ga$$_{1-x}$$Mn$$_x$$As, it is concluded that the ground state of Mn in Ba$$_{1-x}$$K$$_x$$(Zn$$_{1-y}$$Mn$$_y$$)$$_2$$As$$_2$$ consists of both the $$3d^5 underline{L}$$ and $$3d^5$$ electron configurations.

論文

Probing the quantum phase transition in Mott insulator BaCoS$$_{2}$$ tuned by pressure and Ni substitution

Guguchia, Z.*; Frandsen, B. A.*; Santos-Cottin, D.*; 社本 真一; Gauzzi, A.*; 植村 泰朋*; 他12名*

Physical Review Materials (Internet), 3(4), p.045001_1 - 045001_9, 2019/04

 被引用回数:6 パーセンタイル:27.49(Materials Science, Multidisciplinary)

$$mu$$SRを用いて、BaCoS$$_{2}$$を圧力とNi置換でモット転移を調整し、量子相転移の様子を調べた。その結果、ゼロ温度で両方の量子相転移が一次転移であることがわかった。

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:23 パーセンタイル:71.84(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:31 パーセンタイル:77.41(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

Diluted ferromagnetic semiconductor Li(Zn,Mn)P with decoupled charge and spin doping

Deng, Z.*; Zhao, K.*; Gu, B.; Han, W.*; Zhu, J. L.*; Wang, X. C.*; Li, X.*; Liu, Q. Q.*; Yu, R. C.*; 後神 達郎*; et al.

Physical Review B, 88(8), p.081203_1 - 081203_5, 2013/08

 被引用回数:71 パーセンタイル:91.9(Materials Science, Multidisciplinary)

We report the discovery of a diluted magnetic semiconductor, Li(Zn,Mn)P, in which charge and spin are introduced independently via lithium off-stoichiometry and the isovalent substitution of Mn$$^{2+}$$ for Zn$$^{2+}$$, respectively. Isostructural to (Ga,Mn)As, Li(Zn,Mn)P was found to be a ${it p}$-type ferromagnetic semiconductor with excess lithium providing charge doping. First-principles calculations indicate that excess Li is favored to partially occupy the Zn site, leading to hole doping. Ferromagnetism with Curie temperature up to 34 K is achieved while the system still shows semiconducting transport behavior.

論文

Li(Zn,Mn)As as a new generation ferromagnet based on a I-II-V semiconductor

Deng, Z.*; Jin, C. Q.*; Liu, Q. Q.*; Wang, X. C.*; Zhu, J. L.*; Feng, S. M.*; Chen, L. C.*; Yu, R. C.*; Arguello, C.*; 後神 達郎*; et al.

Nature Communications (Internet), 2, p.1425_1 - 1425_5, 2011/08

 被引用回数:150 パーセンタイル:93.71(Multidisciplinary Sciences)

(Ga,Mn)Asは典型的な強磁性III-V族半導体として知られている。これは3価のGa原子を2価のMnで置き換えたものであるが、化学的溶解度が限られているため準安定であり、薄膜でしか製作できないものであった。また電子ドープも行うことができなかった。この困難な条件を超えるため、Masekらは理論的にI-II-V族半導体LiZnAsを提案した。この物質では原子価が等しい(Zn,Mn)の置き換えによる磁性の発現とLi濃度を過剰あるいは不足させることによるキャリアードープを独立に制御可能である。本研究では世界で初めてバルクな状態でのLi$$_{1+y}$$(Zn$$_{1-x}$$Mn$$_x$$)Asの合成に成功した。わずかにLiを過剰にすることで、50Kまでの温度で強磁性が現れること、またp型のキャリアーを持つことが観測され、これらの結果を報告した。

論文

$$mu$$SR study of CeRhIn$$_5$$ under applied pressure

Heffner, R.*; 後神 達郎*; Andreica, D.*; 大石 一城*; 髭本 亘; 伊藤 孝; Amato, A.*; Spehling, J.*; Klauss, H. H.*; Bauer, E. D.*; et al.

Journal of Physics; Conference Series, 225, p.012011_1 - 012011_6, 2010/06

 被引用回数:1 パーセンタイル:50.39

At ambient pressure CeRhIn$$_5$$ is an incommensurate antiferromagnet with Neel temperature $$T_{rm N}$$ = 3.8 K. The application of pressure reduces $$T_{rm N}$$ and yields (1) a state in which AFM coexists with superconductivity, and then (2) a superconducting state in the absence of AFM. We report transverse-field muon spin relaxation ($$mu$$SR) measurements at pressures 2.07 and 2.26 GPa in the pure superconducting state of single-crystalline CeRhIn$$_5$$. $$mu$$SR is sensitive to the local field distribution produced by the vortex lattice in a mixed superconducting state, allowing a measurement of the magnetic field penetration depth $$lambda (T)$$. We measured $$lambda_{ab}(T)$$ for applied field along the $$c$$-axis as a function of temperature $$T$$, and find $$lambda_{ab}$$(0) = 372(5) nm and 338(6) nm for $$P$$ = 2.07 GPa and 2.26 GPa, respectively. The $$T$$-dependence of the superfluid density $$rho_s(T) propto lambda^{-2}(T)$$ was found to be $$rho_s(T) propto T^n$$ with $$n$$ = 1.9(2).

論文

Muon spin rotation measurements of heterogeneous field response in overdoped La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$

MacDougall, G. J.*; Savici, A. T.*; Aczel, A. A.*; Birgeneau, R. J.*; Kim, H.*; Kim, S.-J.*; 伊藤 利充*; Rodriguez, J. A.*; Russo, P. L.*; 植村 泰朋*; et al.

Physical Review B, 81(1), p.014508_1 - 014508_7, 2010/01

 被引用回数:10 パーセンタイル:46.2(Materials Science, Multidisciplinary)

Transverse-field muon spin rotation measurements of overdoped La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$ reveal a large broadening of the local magnetic field distribution in response to applied field, persisting to high temperatures. The field response is approximately Curie-Weiss-like in temperature and is largest for the highest doping investigated. Such behavior is contrary to the canonical Fermi-liquid picture commonly associated with the overdoped cuprates and implies extensive heterogeneity in this region of the phase diagram. A possible explanation for the result lies in regions of staggered magnetization about dopant cations, analogous to what is argued to exist in underdoped systems.

論文

Absence of broken time-reversal symmetry in the pseudogap state of the high temperature La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$ superconductor from muon-spin-relaxation measurements

MacDougall, G. J.*; Aczel, A. A.*; Carlo, J. P.*; 伊藤 利充*; Rodriguez, J.*; Russo, P. L.*; 植村 泰朋*; 脇本 秀一; Luke, G. M.*

Physical Review Letters, 101(1), p.017001_1 - 017001_4, 2008/07

 被引用回数:60 パーセンタイル:88.15(Physics, Multidisciplinary)

銅酸化物高温超伝導体に見られる擬ギャップの起源として、擬ギャップ温度以下で、時間反転対称性の破れた軌道電流パターンを持つ秩序状態が存在することが理論で提唱され、YBCOを用いた中性子回折実験によりその軌道電流から生まれるモーメントに起因すると考えられる磁気ピークが観測されている。本研究では、微小な内部磁場の観測に優れるミュウオンスピン緩和測定を用いて、La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$の組成を最適ドープから過剰ドープまで変化させて軌道電流秩序状態があるかを検証した。その結果、軌道電流秩序状態はすべての組成で存在せず、仮に存在したとしても内部磁場にして0.2G以下であり、中性子で報告されたモーメントの200分の1以下となる。よって、理論で提唱されているような時間反転対称性の破れた軌道電流パターンを持つ秩序状態は存在しないことを示した。

論文

Muon spin rotation study of field-induced magnetism in heavily overdoped La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$

MacDougall, G. J.*; Birgeneau, R. J.*; Kim, H.*; Kim, S.-J.*; Rodriguez, J.*; Russo, P. L.*; Savici, A. T.*; 植村 泰朋*; 脇本 秀一; Wiebe, C. R.*; et al.

Physica B; Condensed Matter, 374-375, p.211 - 214, 2006/03

 被引用回数:4 パーセンタイル:22.78(Physics, Condensed Matter)

高温超伝導体の研究において、単結晶試料育成や化学的ドーピングの困難から、過剰ドープ領域の研究はほとんどなされていなかった。本研究では、世界初となる過剰ドープしたLa$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$単結晶の$$mu$$SR実験の結果を報告する。縦磁場$$mu$$SRの結果から、relaxation rateの温度依存性がCurie-Weiss則に従い、そのCurie constantが磁場の関数として$$Cproptoalpha H$$と書かれることが見いだされた。この現象は、内部磁場分布の異常が磁場により誘起されていることを示している。磁場誘起の度合を表す$$alpha$$$$x=0.12$$から既に現れ、過剰ドープ領域の$$x=0.30$$まで単調増加し、ドープ量に依存することがわかった。この磁場誘起による異常な内部磁場分布の原因の解明は、今後の重要な課題である。

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