研究者詳細 - 渡辺　真仁

論文 - 渡辺　真仁

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Dynamical and static structure factors in hedgehog-antihedgehog order in an icosahedral 1/1 approximant crystal 査読有り国際誌

Shinji Watanabe

Physical Review B 109 184404-1 - 184404-7 2024年05月

Magnetic Dynamics and Nonreciprocal Excitation in Uniform Hedgehog Order in Icosahedral 1/1 Approximant Crystal 査読有り国際誌

Shinji Watanabe

Scientific Reports 13 14438-1 - 14438-11 2023年09月

Crystalline electric field and magnetic anisotropy in Dy-based icosahedral quasicrystal and approximant 査読有り国際誌

Shinji Watanabe, Tatsuya Iwasaki

Physical Review B 108 045110-1 - 045110-6 2023年07月

Magnetism and topological property in icosahedral quasicrystal 査読有り国際誌

Shinji Watanabe

Journal of Physics: Conference Series 2461 012011-1 - 012011-8 2023年03月

Temperature Dependence of Yb Valence in an Au–Al–Yb Intermediate-Valence Quasicrystal Investigated by Yb L3-Edge X-ray Absorption Near-Edge Structure Spectroscopy 査読有り国際誌

Tetsu Watanuki, Masaichiro Mizumaki, Shinji Watanabe, Naomi Kawamura, Kiyofumi Nitta, Akihiko Machida, Tsutomu Ishimasa

MATERIALS TRANSACTIONS ( 公益社団法人日本金属学会 ) 63 ( 10 ) 1380 - 1383 2022年09月

記述言語：英語掲載種別：研究論文（学術雑誌）

In this paper, we investigate the temperature dependence of Yb valence in an Au-Al-Yb intermediate-valence quasicrystal by Yb L3-edge synchrotron X-ray absorption near-edge structure spectroscopy. The Yb valence of 2.61+ at room temperature decreases monotonically as the temperature decreases, indicating that the Yb ionic radius increases as the temperature decreases and is consistent with the anomalous suppression of the thermal shrinkage of this quasicrystal by cooling, as previously reported. The Yb valence changes by -0.053 on cooling from 298 to 2 K, and its change is more gradual on the high-temperature side than on the low-temperature side with the boundary around 200 K. Additionally, the effect of the changes in the Yb valence on the volume is quantitatively examined. The ratio of the volume changes due to the change in Yb valence per Yb atom, ΔVYb, to the amount of change in Yb valence, Δν, which is expressed as ΔVYb/Δν, was evaluated. The value of ΔVYb/Δν was estimated to be -2.8 Å3/unit Yb valence/Yb atom, whose value was close to that evaluated for YbInCu4

DOI： 10.2320/matertrans.MT-M2022064

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CiNii Research

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Magnetic dynamics of hedgehog in icosahedral quasicrystal 査読有り国際誌

Shinji Watanabe

Scientific Reports 12 ( 1 ) 15514-1 - 15514-8 2022年09月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Quasicrystals (QCs) possess a unique lattice structure without translational invariance, which is characterized by the rotational symmetry forbidden in periodic crystals such as the 5-fold rotation. Recent discovery of the ferromagnetic (FM) long-range order in the terbium-based QC has brought about breakthrough but the magnetic structure and dynamics remain unresolved. Here, we reveal the dynamical as well as static structure of the FM hedgehog state in the icosahedral QC. The FM hedgehog is shown to be characterized by the triple-Q state in the reciprocal-lattice q space. Dynamical structure factor is shown to exhibit highly structured q and energy dependences. We find a unique magnetic excitation mode along the 5-fold direction exhibiting the streak fine structure in the q-energy plane, which is characteristic of the hedgehog in the icosahedral QC. Non-reciprocal magnetic excitations are shown to arise from the FM hedgehog order, which emerge in the vast extent of the q-energy plane.

DOI： 10.1038/s41598-022-19870-6

Kyutacar

Scopus

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Magnetic dynamics of ferromagnetic long range order in icosahedral quasicrystal 査読有り国際誌

Shinji Watanabe

Scientific Reports 12 ( 1 ) 10792-1 - 10792-9 2022年06月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Quasicrystals lack translational symmetry and have unique lattice structures with rotational symmetry forbidden in periodic crystals. The electric state and physical property are far from complete understanding, which are the frontiers of modern matter physics. Recent discovery of the ferromagnetic long-range order in the rare-earth based icosahedral quasicrystal has made the breakthrough. Here, we first reveal the dynamical as well as static magnetic structure in the ferromagnetic long-range order in the terbium-based quasicrystal. The dynamical structure factor exhibits highly structured energy and wavenumber dependences beyond the crystalline-electric-field excitation. We find the presence of the magnetic excitation mode analog to magnon with unique hierarchical structure as well as the localized magnetic excitation with high degeneracy in the quasicrystal. Non-collinear and non-coplanar magnetic structure on the icosahedron is discovered to give rise to non-reciprocal magnetic excitation in the quasicrystal as well as non-reciprocal magnon in the periodic cubic 1/1 approximant. These findings afford illuminating insight into the magnetic dynamics in the broad range of the rare-earth-based quasicrystals and approximants.

DOI： 10.1038/s41598-022-14796-5

Kyutacar

Scopus

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Pressure dependence of the magnetic ground state in CePtSi2 査読有り国際誌

S. E. Dissanayake, F. Ye, W. Tian, M. Matsuda, H. Muto, S. Suzuki, T. Nakano, S. Watanabe, J. Gouchi, and Y. Uwatoko

Physical Review B 105 ( 24 ) 245111-1 - 245111-6 2022年06月

記述言語：英語掲載種別：研究論文（学術雑誌）

CePtSi2 was reported to exhibit an antiferromagnetic order below T∗=1.8 K at ambient pressure, a valence state change at ∼1.2 GPa, and superconductivity in the range between 1.4 and 2.1 GPa with a maximum transition temperature of 0.14 K [T. Nakano, Phys. Rev. B 79, 172507 (2009)1098-012110.1103/PhysRevB.79.172507]. We have performed polycrystalline and single-crystal neutron diffraction experiments to determine the magnetic structure under ambient and high pressures. We found incommensurate magnetic peaks with a magnetic propagation vector of (0.32,0,0.11) at ambient pressure below TSDW∼1.25 K. Those magnetic peaks originate from a spin-density-wave order with the easy axis along the c axis and an averaged ordered moment of 0.45(5)μB, suggesting that there may be an intermediate phase between T∗ and TSDW. Applying pressures, the magnetic propagation vector shows no change and the magnetic order disappears around 1.0 GPa, which is much lower than the critical pressure for the superconducting phase. The results suggest that other than magnetic fluctuations may play a primary role in the superconducting pairing mechanism.

DOI： 10.1103/PhysRevB.105.245111

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Topological magnetic textures and long-range orders in terbium-based quasicrystal and approximant 査読有り国際誌

Shinji Watanabe

Proceedings of the National Academy of Sciences of the United States of America 118(43) ( 43 ) e2112202118-1 - e2112202118-5 2021年10月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

The quasicrystal (QC) possesses a unique lattice structure with rotational symmetry forbidden in periodic crystals. The electric property is far from complete understanding. It has been a longstanding issue whether magnetic long-range order is realized in the QC. Here, we report our theoretical discovery of the ferromagnetic long-range order in the Tb-based QC. The difficulty in past theoretical studies on the QC was lack of the microscopic theory of the crystalline electric field (CEF), which is crucially important in the rare earth systems. By analyzing the CEF in the Tb-based QC, we clarify that magnetic anisotropy plays a key role in realizing unique magnetic textures in the Tb-based QC and approximant crystal (AC). By constructing the minimal model, we show that various magnetic textures on the icosahedron, at whose vertices Tb atoms are located, are realized. We find that the hedgehog state is characterized by the topological charge of one and the whirling-moment state is characterized by an unusually large topological charge of three. The hedgehog and whirling-moment states are shown to be realized as antiferromagnetic orders transcribed as the emergent monopole and antimonopole in the 1/1 AC. We find that these states exhibit the topological Hall effect under applied magnetic field accompanied by the topological as well as metamagnetic transition. Our model and the determined phase diagram are expected to be relevant to the broad range of the rare earth–based QCs and ACs with strong magnetic anisotropy, which are useful not only to understand magnetism but also, to explore topological properties.

DOI： 10.1073/pnas.2112202118

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Magnetism and topology in Tb-based icosahedral quasicrystal 査読有り国際誌

Shinji Watanabe

Scientific Reports 11 ( 11 ) 17679-1 - 17679-8 2021年09月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Quasicrystal (QC) possesses a unique lattice structure with rotational symmetry forbidden in conventional crystals. The electric property is far from complete understanding and it has been a long-standing issue whether the magnetic long-range order is realized in the QC. The main difficulty was lack of microscopic theory to analyze the effect of the crystalline electric field (CEF) at the rare-earth atom in QCs. Here we show the full microscopic analysis of the CEF in Tb-based QCs. We find that magnetic anisotropy arising from the CEF plays a key role in realizing unique magnetic textures on the icosahedron whose vertices Tb atoms are located at. Our analysis of the minimal model based on the magnetic anisotropy suggests that the long-range order of the hedgehog characterized by the topological charge of one is stabilized in the Tb-based QC. We also find that the whirling-moment state is characterized by unusually large topological charge of three. The magnetic textures as well as the topological states are shown to be switched by controlling compositions of the non-rare-earth elements in the ternary compounds. Our model is useful to understand the magnetism as well as the topological property in the rare-earth-based QCs and approximant crystals.

DOI： 10.1038/s41598-021-97024-w

Kyutacar

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Elastic Softening in Quantum Critical Yb-Al-Au Approximant Crystal and Quasicrystal 査読有り国際誌

Shinji Watanabe

Solid State Communications 336 ( 336 ) 114425-1 - 114425-6 2021年06月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

The elastic property of quantum critical quasicrystal (QC) Yb15Al34Au51 is analyzed theoretically on the basis of the approximant crystal (AC) Yb14Al35Au51. By constructing the realistic effective model in the AC, we evaluate the 4f-5d Coulomb repulsion at Yb as Ufd≈1.46eV realizing the quantum critical point (QCP) of the Yb-valence transition. The RPA analysis of the QCP shows that softening in elastic constants occurs remarkably for bulk modulus and longitudinal mode at low temperatures. Possible relevance of these results to the QC as well as the pressure-tuned AC is discussed.

DOI： 10.1016/j.ssc.2021.114425

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Crystalline Electronic Field in Rare-Earth Based Quasicrystal and Approximant: Analysis of Quantum Critical Au-Al-Yb Quasicrystal and Approximant 査読有り

Shinji Watanabe, Mina Kawamoto

J. Phys. Soc. Jpn. 90 ( 6 ) 063701-1 - 063701-5 2021年04月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

On the basis of the point charge model, we formulate the crystalline electronic field (CEF) Hamiltonian HCEF in rareearth based quasicrystal (QC) and approximant crystal (AC) with ligand ions located at pseudo 5-fold configurations by using the operator equivalent method. By setting the total angular momentum J = 7=2, the CEF in the quantum critical QC Au51Al34Yb15 and the 1=1 AC Au51Al35Yb14 is analyzed with consideration for the effect of Al=Au mixed sites. We find that the ratio of the valences of ligand ions x = ZAl=ZAu plays an important role in characterizing the CEF ground state. As x decreases from x = 3, the 4f wave function of the CEF ground state with the flat shape lying in the mirror plane is deformed around x ≈ 0.8 to the flat shape perpendicular to the pseudo 5-fold axis at x = 0. The formulated HCEF by J is generally applicable to rare-earth-based QCs and ACs, which is useful to analyze the CEF.

DOI： 10.7566/JPSJ.90.063701

Kyutacar

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Interplay of Valence and Semimetal-to-Insulator Transitions in SmS 査読有り

Shinji Watanabe

J. Phys. Soc. Jpn. 90 ( 2 ) 023706-1 - 023706-5 2021年01月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Recent discoveries of a new type of quantum criticality arising from Yb-valence fluctuations in Yb-based metal in periodic crystal and quasicrystal have opened a new class of quantum critical phenomena in correlated electron systems. To clarify whether this new concept can be generalized to other rare-earth-based semimetal and insulator, we study SmS which exhibits golden-black phase transition under pressure. By constructing the model for SmS, we show that Coulomb repulsion between 4 f and 5d orbitals at Sm drives first-order valence transition (FOVT) and semimetal-to-insulator transition (MIT) simultaneously, which explains the golden-black phase transition. We clarify the ground-state phase diagram for the FOVT and MIT by identifying the quantum critical point of the FOVT. We find that exciton condensates in both semimetal and insulator phases. Our result explains measured peak anomalies in the specific heat and compressibility in pressurized golden SmS and provides a cue to clarify recently-observed anomalies in black SmS.

DOI： 10.7566/JPSJ.90.023706

Kyutacar

Scopus

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Ultrasound Response in Quantum Critical β-YbAlB4 and α-YbAl0.986Fe0.014B4 査読有り

Shinji Watanabe

J. Phys. Soc. Jpn. 89 ( 7 ) 073702-1 - 073702-5 2020年06月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

We analyze the key origin of quantum valence criticality in the heavy electron metal β-YbAlB4 evidenced in the sister compound α-YbAl0.986Fe0.014B4. By constructing a realistic canonical model for β-YbAlB4, we evaluate Coulomb repulsion between the 4f and 5d electrons at Yb Ufd≈6.2 eV realizing the quantum critical point (QCP) of the Ybvalence transition. To reveal the Yb 5d contribution to the quantum critical state, we propose ultrasound measurement. We find that softening of elastic constants of not only the bulk modulus but also the shear moduli is caused by electric quadrupole fluctuations enhanced by critical 4f and 5d charge fluctuations for low temperatures at the valence QCP. Possible relevance of these results to β-YbAlB4 and also α-YbAl1-xFexB4 is discussed.

DOI： 10.7566/JPSJ.89.073702

Kyutacar

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Theory for Non-Fermi Liquid Temperature Dependence in Resistivity of CexLa1-xCu5.62Au0.38 (x=0.02-0.10) on the Local Quantum Valence Criticality of Ce Impurities 査読有り

K. Miyake, S. Watanabe

JPS Conf. Proc. 30 011027-1 - 011027-7 2020年03月

Quantum Valence Criticality in Heavy Fermions on Periodic and Aperiodic Crystals 査読有り

S. Watanabe, K. Miyake

JPS Conf. Proc. 30 011023-1 - 011023-12 2020年03月

価数転移に由来する新しい量子現象査読有り

渡辺真仁

J-Physics ニュースレター 9 2020年03月

磁気量子臨界点近傍の比熱、熱膨張係数、グリュナイゼンパラメーター招待有り査読有り

渡辺真仁

J-Physics ニュースレター 9 2020年03月

Charge Transfer Effect under Odd-Parity Crystalline Electric Field 査読有り

S. Watanabe, K. Miyake

JPS Conf. Proc. 29 014001-1 - 014001-10 2020年02月

Non-Divergent Grüneisen Parameter in Quantum Critical Quasicrystal Yb15Al34Au51: Reflection of Robustness of Quantum Criticality under Pressure 査読有り国際誌

Shinji Watanabe, Kazumasa Miyake

Solid State Communications ( ELSEVIER ) 306 113774-1 - 113774-6 2019年11月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

The mechanism of not diverging Grüneisen parameter in the quantum critical heavy-fermion quasicrystal (QC) Yb15Al34Au51 is analyzed. We construct the formalism for calculating the specific heat CV(T), the thermal-expansion coefficient α(T), and the Grüneisen parameter Γ(T) near the quantum critical point of the Yb valence transition. By applying the framework to the QC, we calculate CV(T), α(T), and Γ(T), which explains the measurements. Not diverging Γ(T) is attributed to the robustness of the quantum criticality in the QC under pressure. The difference in Γ(T) at the lowest temperature between the QC and approximant crystal is shown to reflect the difference in the volume derivative of characteristic energy scales of the critical Yb-valence fluctuation and the Kondo temperature. Possible implications of our theory to future experiments are also discussed.

DOI： 10.1016/j.ssc.2019.113774

Kyutacar

Scopus

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価数転移由来の新規量子現象の理論研究

渡辺真仁

J-Physics ニュースレター 7 24 - 25 2019年03月

Charge Transfer Effect under Odd-Parity Crystalline Electric Field: Divergence of Magnetic Toroidal Fluctuation in β-YbAlB4 査読有り

Shinji Watanabe, Kazumasa Miyake

Journal of the Physical Society of Japan 88 ( 3 ) 033701-1 - 033701-5 2019年02月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

A novel property of the quantum critical heavy fermion superconductor β-YbAlB4 is revealed theoretically. By analyzing the crystalline electronic field (CEF) on the basis of the hybridization picture, odd parity CEF is shown to exist because of sevenfold configuration of B atoms around Yb, which breaks the local inversion symmetry. This allows onsite admixture of 4f and 5d wavefunctions with a pure imaginary coefficient, giving rise to the magnetic toroidal (MT) degree of freedom. By constructing a realistic minimal model for β-YbAlB4, we show that onsite 4f-5d Coulomb repulsion drives charge transfer between the 4f and 5d states at Yb, which makes the MT fluctuation as well as the electric dipole fluctuation diverge simultaneously with the critical Yb-valence fluctuation at the quantum critical point of the valence transition.

DOI： 10.7566/JPSJ.88.033701

Kyutacar

Scopus

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Grüneisen Parameter and Thermal Expansion near Magnetic Quantum Critical Points in Itinerant Electron Systems 査読有り

Shinji Watanabe, Kazumasa Miyake

Physical Review B 99 ( 99 ) 035108-1 - 035108-25 2019年01月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Complete expressions of the thermal-expansion coefficient α and the Grüneisen parameter Γ are derived on the basis of the self-consistent renormalization (SCR) theory. By considering the zero point as well as thermal spin fluctuation under the stationary condition, the specific heat for each class of the magnetic quantum critical point (QCP) specified by the dynamical exponent z=3 [feorromagnetism (FM)] and z=2 [antiferromagnetism (AFM)] and the spatial dimension (d=3 and 2) is shown to be expressed as CV=Ca-Cb, where Ca is dominant at low temperatures, reproducing the past SCR criticality endorsed by the renormalization group theory. Starting from the explicit form of the entropy and using the Maxwell relation, α=αa+αb (with αa and αb being related to Ca and Cb, respectively) is derived, which is proven to be equivalent to α derived from the free energy. The temperature-dependent coefficient found to exist in αb, which is dominant at low temperatures, contributes to the crossover from the quantum-critical regime to the Curie-Weiss regime. For sufficiently low temperatures, the thermal-expansion coefficient at the QCP behaves as α≈αb∼T1/3 (3D FM), T1/2 (3D AFM), -lnT (2D FM), and -ln(-lnT)/ln-TlnT (2D AFM). Based on these correctly calculated CV and α, Grüneisen parameter Γ=Γa+Γb is derived, where Γa and Γb contain αa and αb, respectively. The inverse susceptibility (renormalized by the mode-mode coupling of spin fluctuations) coupled to the volume V in Γb gives rise to the divergence of Γ at the QCP for each class even though the characteristic energy scale of spin fluctuation T0 is finite at the QCP, which gives a finite contribution in Γa=-VT0∂T0∂VT=0. For TT0, the Grüneisen parameter at the QCP behaves as Γ≈Γb∼-T-2/3/lnT (3D FM), T-1/2/(const.-T1/2) (3D AFM), -T-2/3lnT (2D FM), and ln(-lnT)/[TlnTln-TlnT] (2D AFM). General properties of α and Γ including their signs as well as the relation to T0 and the Kondo temperature in temperature-pressure phase diagrams of Ce- and Yb-based heavy electron systems are discussed.

DOI： 10.1103/PhysRevB.99.035108

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The Dominant Role of Critical Valence Fluctuations on High Tc Superconductivity in Heavy Fermions 査読有り

Gernot W. Scheerer, Zhi Ren, Shinji Watanabe, Gerard Lapertot, Dai Aoki, Didier Jaccard, Kazumasa Miyake

npj Quantum Materials 3 ( 1 ) 41-1 - 41-6 2018年08月

記述言語：英語掲載種別：研究論文（学術雑誌）

Despite almost 40 years of research, the origin of heavy-fermion superconductivity is still strongly debated. Especially, the pressure-induced enhancement of superconductivity in CeCu2Si2 away from the magnetic breakdown is not sufficiently taken into consideration. As recently reported in CeCu2Si2 and several related compounds, optimal superconductivity occurs at the pressure of a valence crossover, which arises from a virtual critical end point at negative temperature Tcr. In this context, we did a meticulous analysis of a vast set of top-quality high-pressure electrical resistivity data of several Ce-based heavy fermion compounds. The key novelty is the salient correlation between the superconducting transition temperature Tc and the valence instability parameter Tcr, which is in line with theory of enhanced valence fluctuations. Moreover, it is found that, in the pressure region of superconductivity, electrical resistivity is governed by the valence crossover, which most often manifests in scaling behavior. We develop the new idea that the optimum superconducting Tc of a given sample is mainly controlled by the compound’s Tcr and limited by non-magnetic disorder. In this regard, the present study provides compelling evidence for the crucial role of critical valence fluctuations in the formation of Cooper pairs in Ce-based heavy fermion superconductors besides the contribution of spin fluctuations near magnetic quantum critical points, and corroborates a plausible superconducting mechanism in strongly correlated electron systems in general.

DOI： 10.1038/s41535-018-0111-6

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Anomalous temperature dependence of the relaxation rate measured by muon spin rotation in alpha-YbAl0.986Fe0.014B4 査読有り

Kazumasa Miyake, Shinji Watanabe

Physical Review B 98 ( 7 ) 075125-1 - 075125-6 2018年08月

記述言語：英語掲載種別：研究論文（学術雑誌）

Recently, it was reported by MacLaughlin et al. in Phys. Rev. B 93, 214421 (2016)2469-995010.1103/PhysRevB.93.214421 that α-YbAl0.986Fe0.014B4 exhibits an anomalous temperature dependence in the relaxation rate 1/T1 of μSR, and stressed that such temperature dependence cannot be understood by the scenario based on the quantum critical valence transition (QCVT) while this compound exhibits a series of the non-Fermi-liquid behaviors explained by the theory of the QCVT. In this paper, we point out that the anomalous temperature dependence in 1/T1 can be understood semiquantitatively by assuming that the attraction of a screening cloud of conduction electrons about the μ+ induces a local magnetic moment arising from a 4f hole on the Yb ion, giving rise to the Kondo effect between heavy quasiparticles.

DOI： 10.1103/PhysRevB.98.075125

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Effects of Crystalline Electronic Field and Onsite Interorbital Interaction in Yb-based Quasicrystal and Approximant Crystal 招待有り査読有り

S. Watanabe and K. Miyake

J. Phys.: Condens. Matter 30 184001-1 - 184001-11 2018年04月

Yb系準結晶・近似結晶の新しい量子臨界現象招待有り

渡辺真仁

J-Physics ニュースレター 5 10 - 13 2018年03月

Grüneisen Parameter and Thermal Expansion by the Self-Consistent Renormalization Theory of Spin Fluctuations 査読有り

S. Watanabe and K. Miyake

J. Phys. Soc. Jpn. 86 034712-1 - 034712-6 2018年02月

Coincidence of Magnetic and Valence Quantum Critical Points in CeRhIn5 under Pressure 査読有り

Z. Ren, G. W. Scheerer, D. Aoki, K. Miyake, S. Watanabe, and D. Jaccard

Phys. Rev. B 96 184524-1 - 184524-5 2017年11月

New quantum criticality revealed under pressure 招待有り査読有り

Watanabe S., Miyake K.

Japanese Journal of Applied Physics 56 ( 56 ) 05FA01-1 - 05FA01-7 2017年05月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

© 2017 The Japan Society of Applied Physics.Unconventional quantum critical phenomena observed in Yb-based periodic crystals such as YbRh2Si2 and β-YbAlB4 have been one of the central issues in strongly correlated electron systems. The common criticality has been discovered in the quasicrystal Yb15Au51Al34, which surprisingly persists under pressure at least up to P = 1.5 GPa. The T/H scaling where the magnetic susceptibility can be expressed as a single scaling function of the ratio of the temperature T to the magnetic field H has been discovered in the quasicrystal, which is essentially the same as that observed in β-YbAlB4. Recently, the T/H scaling as well as the common criticality has also been observed even in the approximant crystal Yb14Au51Al35 under pressure. The theory of critical Yb-valence fluctuation gives a natural explanation for these striking phenomena in a unified way.

DOI： 10.7567/JJAP.56.05FA01

Scopus

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Ubiquity of Unconventional Phenomena Associated with Critical Valence Fluctuations in Heavy Fermion Metals 招待有り査読有り

K. Miyake, S. Watanabe

Philos. Mag. ( 97 ) 3495 - 3516 2017年04月

Lifetime-Broadening-Suppressed X-ray Absorption Spectrum of beta-YbAlB4 Deduced from Yb 3d→2p Resonant X-ray Emission Spectroscopy 査読有り

Naomi Kawamura, Noriko Kanai, Hisashi Hayashi, Yasuhiro H. Matsuda, Masaichiro Mizumaki, Kentaro Kuga, Satoru Nakatsuji, and Shinji Watanabe

Journal of the Physical Society of Japan 86 ( 86 ) 014711-1 - 014711-7 2016年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

In this work, the Yb 3d → 2p (Yb Lα1,2) resonant X-ray emission spectrum of β-YbAlB4 was acquired using excitation energies around the Yb L3-edge, at 2K. Subsequently, the lifetime-broadening-suppressed (LBS) X-ray absorption structure (XAS) spectrum was obtained using the SIM-RIXS program. This spectrum was found to exhibit clearly resolved pre-edge and shoulder structures. Resonant La1 emission spectra were well reproduced from LBS-XAS profiles over wide ranges of excitation and emission energies. In contrast, noticeable discrepancies appeared between the experimental and simulated Lα2 emission spectra, suggesting an effect resulting from M4M5O1 Coster-Kronig transitions. LBS-XAS, in conjunction with partial fluorescence yield (PFY) XAS and transmission XAS, determined a value for the Yb valence (v) in β-YbAlB4 of 2.76 ± 0.08 at 2K. Despite this relatively large uncertainty in v, each method provided a consistent variation in valence (Sv) as the temperature was raised from 2 to 280 K: 0.060 ± 0.004 (LBS-XAS), 0.061 ± 0.005 (PFY-XAS) and 0.058 ± 0.007 (transmission XAS). The smaller δv associated with LBS-XAS demonstrates the greater precision of this method.

DOI： 10.7566/JPSJ.86.014711

Scopus

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周期系・準周期系重い電子系に普遍的な新しい量子臨界物性の解明

渡辺真仁

J-Physics ニュースレター 2 19 - 19 2016年09月

Origin of quantum criticality in Yb-Al-Au approximant crystal and quasicrystal 査読有り

Watanabe S., Miyake K.

Journal of the Physical Society of Japan 85 ( 6 ) 63703-1 - 63703-5 2016年06月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

©2016 The Physical Society of Japan.To get insight into the mechanism of emergence of unconventional quantum criticality observed in quasicrystal Yb15Al34Au51, the approximant crystal Yb14Al35Au51 is analyzed theoretically. By constructing a minimal model for the approximant crystal, the heavy quasiparticle band is shown to emerge near the Fermi level because of strong correlation of 4f electrons at Yb. We find that charge-transfer mode between 4f electron at Yb on the 3rd shell and 3p electron at Al on the 4th shell in Tsai-type cluster is considerably enhanced with almost flat momentum dependence. The modecoupling theory shows that magnetic as well as valence susceptibility exhibits χ ∼ T-0.5 for zero-field limit and is expressed as a single scaling function of the ratio of temperature to magnetic field T/B over four decades even in the approximant crystal when some condition is satisfied by varying parameters, e.g., by applying pressure. The key origin is clarified to be due to strong locality of the critical Yb-valence fluctuation and small Brillouin zone reflecting the large unit cell, giving rise to the extremely-small characteristic energy scale. This also gives a natural explanation for the quantum criticality in the quasicrystal corresponding to the infinite limit of the unit-cell size.

DOI： 10.7566/JPSJ.85.063703

Scopus

CiNii Article

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f電子系準結晶・近似結晶の量子臨界性

渡辺真仁

日本物理学会講演概要集 ( 一般社団法人日本物理学会 ) 71 ( 1 ) 1753 - 1754 2016年03月

Basic Properties of Conductivity and Normal Hall Effect in the Periodic Anderson Model 査読有り

Shinji Watanabe, Kazumasa Miyake

Journal of the Physical Society of Japan ( 85 ) 044704-1 - 044704-16 2016年03月

Quantum Criticality and Emergence of the T/B Scaling in Strongly Correlated Metals 査読有り

Shinji Watanabe, Kazumasa Miyake

Journal of Magnetism and Magnetic Materials ( 400 ) 13 - 16 2016年02月

Thermal Expansion of a Au-Al-Yb Intermediate Valence Quasicrystal 査読有り

T. Watanukia, S. Kashimoto, T. Ishimasa, A. Machida, S. Yamamoto, Y. Tanaka, M. Mizumaki, N. Kawamura, S. Watanabe

Solid State Communications ( 211 ) 19 - 22 2015年03月

Pressure-Induced Valence Crossover and Novel Metamagnetic Behavior near the Antiferromagnetic Quantum Phase Transition of YbNi3Ga9 査読有り

K. Matsubayashi, T. Hirayama, T. Yamashita, S. Ohara, N. Kawamura, M. Mizumaki, N. Ishimatsu, S. Watanabe, K. Kitagawa, Y. Uwatoko

Physical Review Letters 114 086401-1 - 086401-5 2015年02月

High Pressure Properties for Electrical Resistivity and Ce Valence State of Heavy-Fermion Antiferromagnet Ce2NiGa12 査読有り

N Kawamura, R Sasaki, K Matsubayashi, N Ishimatsu, M Mizumaki, Y Uwatoko, S Ohara and S Watanabe

Journal of Physics: Conference Series 568 042015-1 - 042015-6 2014年12月

T/B Scaling in beta-YbAlB4 査読有り

Shinji Watanabe, Kazumasa Miyake

Journal of the Physical Society of Japan 83 103708-1 - 103708-5 2014年09月

Unconventional Quantum Criticality Due to Critical Valence Transition 招待有り査読有り

三宅和正、渡辺真仁

Journal of the Physical Society of Japan 83 061006-1 - 061006-10 2014年05月

Robustness of Quantum Criticality of Valence Fluctuations 査読有り

渡辺真仁、三宅和正

Journal of the Physical Society of Japan 82 083704-1 - 083704-4 2013年07月

Multiprobe Signatures of the Valence Crossover in Heavy Fermion Superconductor CeCu2Si2 Under High Pressure 査読有り

Gabriel Seyfarth, Anna-Sabina Rüetschi, Kausik Sengupta, Antoine Georges,Shinji Watanabe, Kazumasa Miyake, Didier Jaccard

Journal of the Physical Society of Japan Supplement B 81 SB004-1 - SB004-8 2012年12月

New universality class of quantum criticality in Ce- and Yb-based heavy fermions 招待有り査読有り

S. Watanabe, K. Miyake

Journal of Physics: Condensed Matter 24 ( 29 ) 294208-1 - 294208-10 2012年06月

Heavy Fermion Superconductor CeCu2Si2 Under High Pressure: Multiprobing The Valence Crossover 査読有り

G. Seyfarth, A.-S. Rüetschi, K. Sengupta, A. Georges, D. Jaccard, S. Watanabe, K. Miyake

Physical Review B 85 205105-1 - 205105-13 2012年05月

局所相関の強い遍歴電子系における新しい量子臨界現象の解明招待有り

渡辺真仁

重い電子系の形成と秩序化　ニュースレター 4 ( 2 ) 4 - 6 2012年03月

New Frontiers of Quantum Critical End Point

渡辺真仁

Journal of the Physical Society of Japan News and Comments ( Journal of the Physical Society of Japan ) 8 12 - 12 2011年08月

Sharp Valence Change as Origin of Drastic Change of Fermi Surface and Transport Anomalies in CeRhIn5 under Pressure 査読有り

Shinji Watanabe, Kazumasa Miyake

Journal of Physics: Conference Series 273 ( 1 ) 012063-1 - 012063-4 2011年02月

Roles of Critical Valence Fluctuations in Ce- and Yb-Based Heavy Fermion Metals 招待有り査読有り

Shinji Watanabe, Kazumasa Miyake

Journal of Physics: Condensed Matter 23 ( 9 ) 094217-1 - 094217-11 2011年02月

Quantum Valence Criticality as an Origin of Unconventional Critical Phenomena 査読有り

Shinji Watanabe, Kazumasa Miyake

Physical Review Letters 105 ( 18 ) 186403-1 - 186403-2 2010年10月

Origin of Drastic Change of Fermi Surface and Transport Anomalies in CeRhIn5 under Pressure 査読有り

Shinji Watanabe, Kazumasa Miyake

Journal of the Physical Society of Japan 79 033707-1 - 033707-4 2010年03月

Influence of Quantum Critical Point of First-Order Valence Transition on Ce- and Yb-based Heavy Fermions 招待有り査読有り

Shinji Watanabe, Kazumasa Miyake

physica status solidi (b) 247 ( 3 ) 490 - 494 2010年02月

Magnetic-Field Induced Quantum Critical Points of Valence Transition in Ce- and Yb-Based Heavy Fermions 査読有り

Shinji Watanabe, Atsushi Tsuruta, Kazumasa Miyake, Jacques Flouquet

Physica B: Condensed Matter 404 ( 19 ) 2942 - 2945 2009年10月

Valence Fluctuations Revealed by Magnetic Field and Pressure Scans: Comparison with Experiments in YbXCu_4 (X=In, Ag, Cd) and CeYIn_5 (Y=Ir, Rh) 査読有り

Shinji Watanabe, Atsushi Tsuruta, Kazumasa Miyake, Jacques Flouquet

Journal of the Physical Society of Japan 78 104706-1 - 104706-13 2009年09月

On Proximity of 4/7 Solid Phase of 3He Adsorbed on Graphite -Origin of Specific Heat Anomalies in Hole-Doped Density Ordered Solid- 査読有り

Shinji Watanabe, Masatoshi Imada

Journal of the Physical Society of Japan 78 033603-1 - 033603-4 2009年02月

量子モンテカルロ法における負符号問題とその克服 : 経路積分繰り込み群法の開発とその発展

渡辺真仁

素粒子論研究 ( 素粒子論研究編集部 ) 116 F87 - F92 2009年02月

Magnetic-Field Control of Quantum Critical Points of Valence Transition 査読有り

Shinji Watanabe, Atsushi Tsuruta, Kazumasa Miyake, and Jacques Flouquet

Physical Review Letters 100 ( 23 ) 236401-1 - 236401-4 2008年06月

What is Minimal Model of 3He Adsorbed on Graphite? -Importance of Density Fluctuations in 4/7 Registered Solid- 査読有り

Shinji Watanabe, Masatoshi Imada

Journal of the Physical Society of Japan 76 113603-1 - 113603-4 2007年11月

Quantum Valence Criticality and Superconductivity 査読有り

Shinji Watanabe, Masatoshi Imada, Kazumasa Miyake

Journal of Magnetism and Magnetic Materials 310 ( 2 ) 841 - 843 2006年11月

Superconductivity Emerging near Quantum Critical Point of Valence Transition 査読有り

Shinji Watanabe, Masatoshi Imada, Kazumasa Miyake

Journal of the Physical Society of Japan 75 043710-1 - 043710-4 2006年04月

経路積分繰り込み群法のアルゴリズムとその応用

渡辺真仁

数理解析研究所講究録 ( 京都大学数理解析研究所 ) 1441 28 - 31 2005年05月

Thermodynamic Relations in Correlated Systems 査読有り

Shinji Watanabe, Masatoshi Imada

Jounrnal of the Physical Society of Japan 73 3341 - 3350 2004年12月

Precise Determination of Phase Diagram for Two-Dimensional Hubbard Model with Filling- and Bandwidth-Control Mott Transitions: Grand-Canonical Path-Integral Renormalization Group Approach 査読有り

Shinji Watanabe, Masatoshi Imada

Journal of the Physical Society of Japan 73 1251 - 1266 2004年05月

Absence of Unit Cell Doubling in Nonmagnetic Insulator Phase on Two-Dimensional Lattice with Geometrical Frustration 査読有り国際誌

Shinji Watanabe

Journal of the Physical Society of Japan 72 2042 - 2045 2003年08月

Coupled CDW and SDW Fluctuations as an Origin of Anomalous Properties of Ferromagnetic Superconductor UGe_2 査読有り

Shinji Watanabe, Kazumasa Miyake

Journal of the Physical Society of Japan 71 2489 - 2499 2002年10月

Nonmagnetic Insulating States near the Mott Transitions on Lattices with Geometrical Frustration and Implications for kappa-(ET)_2Cu_2(CN)_3 査読有り国際誌

Hidekazu Morita, Shinji Watanabe, Masatoshi Imada

Journal of the Physical Society of Japan 71 2109 - 2112 2002年09月

A Scenario for Superconductivity of UGe_2 due to Coupled Charge and Spin Fluctuations 査読有り

S. Watanabe, K. Miyake

Journal of Physics and Chemistry of Solids 63 1465 - 1468 2002年06月

Coupled charge and spin fluctuations and mechanism of superconductivity in UGe2 under pressures 査読有り

Shinji Watanabe, Kazumasa Miyake

Physica B: Condensed Matter 312-313 115 - 117 2002年03月

Partial Ferromagnetism in Semimetallic Systems: Numerical Calculation and Rigorous Proof 査読有り

Shinji Watanabe, Koichi Kusakabe, Yoshio Kuramoto

Physica B: Condensed Matter 312-313 811 - 812 2002年03月

Partial Ferromagnetism in a Two-Band Hubbard Model with Semimetallic Bands: Numerical Evidences and a Rigorous Result 査読有り

K. Kusakabe, S. Watanabe, Y. Kuramoto

Journal of the Physical Society of Japan Supplement 71 311 - 313 2002年03月

Anisotropy and Pressure Dependence of the Upper Critical Field of the Ferromagnetic Superconductor UGe_2 査読有り

I. Sheikin, A. Huxley, D. Braithwaite, J. P. Brison, S. Watanabe, K. Miyake, J. Flouquet

Physical Review B 64 220503(R)-1 - 220503(R)-4 2001年11月

UGe_2: a Ferromagnetic Superconductor 査読有り

J. Flouquet, A. Huxley, I. Sheikin, N. Kernavanois, D. Braithwaite, E. Ressouche, S. Watanabe, K. Miyake

Journal of the Physical Society of Japan Supplement 70 14 - 17 2001年03月

Magnetization Process in Heavy Electron Systems 査読有り国際誌

Shinji Watanabe

Journal of the Physical Society of Japan 69 2947 - 2952 2000年09月

Ground State and Elementary Excitations in the One-Dimensional f^2 Kondo Lattice Model 査読有り

S. Watanabe, Y. Kuramoto

Physica B: Condensed Matter 281-282 260 - 261 2000年06月

Transition from Haldane Phase to Spin Liquid and Incommensurate Correlation in Spin-1/2 Heisenberg Chains 査読有り国際誌

Shinji Watanabe, Hisatoshi Yokoyama

Journal of the Physical Society of Japan 68 2073 - 2097 1999年06月

Spin, Charge, and Quasi-Particle Gaps in the One-Dimensional Kondo Lattice with f^2 Configuration 査読有り国際誌

Shinji Watanabe, Yoshio Kuramoto, Tomotoshi Nishino, Naokazu Shibata

Journal of the Physical Society of Japan 68 159 - 165 1999年01月

Competition between Crystalline Electric Field Singlet and Itinerant States of f Electrons 査読有り国際誌

Shinji Watanabe, Yoshio Kuramoto

Zeitschrift für Physik B Condensed Matter 104 ( 3 ) 535 - 540 1997年10月

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