67 results on '"Hitoshi Sugawara"'
Search Results
2. Observation of multigap and coherence peak in the noncentrosymmetric superconductor CaPtAs: As75 nuclear quadrupole resonance measurements
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Yuya Nagase, Masahiro Manago, Junichi Hayashi, Keiki Takeda, Hideki Tou, Eiichi Matsuoka, Hitoshi Sugawara, Hisatomo Harima, and Hisashi Kotegawa
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- 2023
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3. Possible antiferroquadrupolar order in the Kondo semiconductor CeOs4Sb12
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Hitoshi Sugawara, Yusuke Kani, Takashi Tayama, Yuta Kanai, and Momota Imai
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Physics ,Semiconductor ,Condensed matter physics ,business.industry ,Order (business) ,business - Published
- 2021
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4. Noncollinear spin structure with weak ferromagnetism in NbMnP
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Masaaki Matsuda, Depei Zhang, Hitoshi Ohta, Takahiro Sakurai, Qiang Zhang, Keiki Takeda, Hisashi Kotegawa, Hitoshi Sugawara, Yoshiki Kuwata, and Junichi Hayashi
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Materials science ,Ferromagnetism ,Condensed matter physics ,Spin structure - Published
- 2021
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5. Isotropic parallel antiferromagnetism in the magnetic field induced charge-ordered state of SmRu4P12 caused by p−f hybridization
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Kengo Fushiya, Ryuji Higashinaka, Masaichiro Mizumaki, C. H. Lee, Naomi Kawamura, M. Matsuda, Y. Aoki, Shinji Michimura, Takeshi Matsumura, Tatsuma D. Matsuda, Toshiya Inami, Satoshi Tsutsui, H. Nakao, Hitoshi Sugawara, and M. Tsukagoshi
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Physics ,Condensed matter physics ,Thomson scattering ,Magnetic circular dichroism ,Scattering ,Neutron diffraction ,Resonance ,Order (ring theory) ,Charge (physics) ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,0103 physical sciences ,Antiferromagnetism ,010306 general physics ,0210 nano-technology - Abstract
Nature of the field-induced charge-ordered phase (phase II) of $\mathrm{Sm}{\mathrm{Ru}}_{4}{\mathrm{P}}_{12}$ has been investigated by resonant x-ray diffraction (RXD) and polarized neutron diffraction (PND), focusing on the relationship between the atomic displacements and the antiferromagnetic (AFM) moments of Sm. From the analysis of the interference between the nonresonant Thomson scattering and the resonant magnetic scattering, combined with the spectral function obtained from x-ray magnetic circular dichroism, it is shown that the AFM moment of Sm prefers to be parallel to the field (${\mathbit{m}}_{\text{AF}}\ensuremath{\parallel}\mathbit{H}$), giving rise to large and small moment sites around which the ${\mathrm{P}}_{12}$ and Ru cage contract and expand, respectively. This is associated with the formation of the staggered ordering of the ${\mathrm{\ensuremath{\Gamma}}}_{7}$-like and ${\mathrm{\ensuremath{\Gamma}}}_{8}$-like crystal-field states, providing a strong piece of evidence for the charge order. PND was also performed to obtain complementary and unambiguous conclusion. In addition, isotropic and continuous nature of phase II is demonstrated by the field-direction invariance of the interference spectrum in RXD. Crucial role of the $p\ensuremath{-}f$ hybridization is shown by resonant soft x-ray diffraction at the P $K$ edge ($1s\ensuremath{\leftrightarrow}3p$), where we detected a resonance due to the spin polarized $3p$ orbitals reflecting the AFM order of Sm.
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- 2020
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6. Insight into Kondo screening in the intermediate-valence compound SmOs4Sb12 uncovered by soft x-ray magnetic circular dichroism
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Shin Imada, Daisuke Kikuchi, Yuichi Saitoh, Akira Sekiyama, Hitoshi Sugawara, Shigemasa Suga, Akira Yasui, Toshiharu Kadono, Atsushi Yamasaki, Hideyuki Sato, and Hideki Fujiwara
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Physics ,Soft x ray ,Valence (chemistry) ,Condensed matter physics ,Magnetic circular dichroism ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter::Materials Science ,Paramagnetism ,Heavy fermion ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Quantum ,Multiplet - Abstract
Through a high-precision soft x-ray magnetic circular dichroism (XMCD) study of the intermediate-valence compound $\mathrm{Sm}{\mathrm{Os}}_{4}{\mathrm{Sb}}_{12}$, we show our successful approach of revealing unprecedented details of Kondo screening below a characteristic temperature of ${T}_{0}\ensuremath{\sim}20$ K in the paramagnetic phase. The multiplet XMCD structure at the Sm ${M}_{5}$ edge sensitive to the $4f$ configuration enabled us to observe a clear difference between the temperature evolution above and below ${T}_{0}$ with one- and two-component behavior, respectively. Our findings are in strong contrast to the conventional Kondo crossover that coincides with the valence transition, but are qualitatively accounted for by theoretical XMCD predictions combined with the two-fluid phenomenology recently proposed. This work contributes to the large context of Kondo physics that is closely related to quantum criticality in heavy fermion systems.
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- 2020
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7. Optical and photoelectrical studies on anisotropic metal-insulator transition of RuAs
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Hiroshi Watanabe, Hitoshi Sugawara, Shin-ichi Kimura, Yoshiyuki Ohtsubo, Hisashi Kotegawa, Yuki Nakajima, Hideki Tou, Zenjiro Mita, and Takahiro Ito
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Physics ,Phase transition ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,Band gap ,Transition temperature ,FOS: Physical sciences ,02 engineering and technology ,Electronic structure ,021001 nanoscience & nanotechnology ,01 natural sciences ,Omega ,Optical conductivity ,Condensed Matter - Strongly Correlated Electrons ,Phase (matter) ,0103 physical sciences ,Metal–insulator transition ,010306 general physics ,0210 nano-technology - Abstract
The anisotropic changes in the electronic structure of a metal-to-insulator transition (MIT) material, RuAs, with two-step phase transition are reported by using polarized optical conductivity [$\sigma(\omega)$] spectra, angle-integrated photoelectron (PE) spectra, and band calculations based on local density approximation (LDA). Both the PE and $\sigma(\omega)$ spectra not only in the high-temperature (HT) phase but also in the low-temperature (LT) phase as well as the energy gap formation owing to the MIT were almost consistent with those derived from the LDA band calculations, so the fundamental electronic structure in the HT and LT phases can be explained without electron correlations. However, the electronic structure in the middle phase between the HT and LT phases has not been clarified. The polarized $\sigma(\omega)$ spectra revealed not only the anisotropic energy gap formation but also the anisotropic gap-opening temperature, i.e., the energy gap along the $c$ axis in the HT phase starts to open near the higher transition temperature, but that along the $b$ axis opens below the lower transition temperature. The finding suggests that the two-step MIT originates from the anisotropic energy gap formation., Comment: 7 pages, 7 figures
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- 2019
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8. Magnetic correlations in the pressure-induced superconductor CrAs investigated by As75 nuclear magnetic resonance
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Jun Kaneyoshi, Hisashi Kotegawa, Hideki Tou, Hitoshi Sugawara, Takahiro Sakurai, Kei Matsushima, Hisatomo Harima, Yoshiki Kuwata, Eiichi Matsuoka, and Hitoshi Ohta
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Superconductivity ,Physics ,Condensed matter physics ,Knight shift ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter::Materials Science ,Paramagnetism ,Zigzag ,Condensed Matter::Superconductivity ,0103 physical sciences ,Quadrupole ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,Cuprate ,010306 general physics ,0210 nano-technology ,Spin (physics) - Abstract
We report $^{75}\mathrm{As}$-NMR results for CrAs under pressure, which shows superconductivity adjoining a helimagnetically ordered state. We successfully evaluated the Knight shift from the spectrum, which is strongly affected by the quadrupole interaction. The Knight shift shows the remarkable feature that the uniform spin susceptibility increases toward low temperatures in the paramagnetic state. This is in sharp contrast to CrAs at ambient pressure, and also to cuprates and Fe pnictides, where antiferromagnetic correlations are dominant. Superconductivity emerges in CrAs under unique magnetic correlations, which probably originate in the three-dimensional zigzag structure of its nonsymmorphic symmetry.
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- 2019
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9. Atomic displacements and lattice distortion in the magnetic-field-induced charge-ordered state of SmRu4P12
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Tatsuma D. Matsuda, Shinji Michimura, Takeshi Matsumura, Kengo Fushiya, Ryuji Higashinaka, Yuji Aoki, Hitoshi Sugawara, and Toshiya Inami
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Diffraction ,Physics ,Magnetic moment ,Condensed matter physics ,Order (ring theory) ,Nanotechnology ,Charge (physics) ,Electron ,01 natural sciences ,010305 fluids & plasmas ,Magnetic field ,Phase (matter) ,0103 physical sciences ,010306 general physics ,Bar (unit) - Abstract
Structural properties of SmRu$_4$P$_{12}$ in the anomalous magnetic ordered phase between $T^*\sim 14 $ K and $T_{\text{N}}=16.5$ K in magnetic fields has been studied by x-ray diffraction. Atomic displacements of Ru and P, reflecting the field-induced charge order of the $p$ electrons, have been deduced by analyzing the intensities of the forbidden Bragg peaks, assuming a cubic space group $Pm\bar{3}$. Also, by utilizing high-resolution x-ray diffraction experiment, we observed a splitting of fundamental Bragg peaks, clarifying that the unit cell in the magnetic ordered phase is rhombohedral elongated along the $[1\, 1\, 1]$ axis. Responses of the rhombohedral domains to the magnetic field, which reflects the direction of the magnetic moment, is studied in detail.
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- 2016
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10. Superlattice formation lifting degeneracy protected by nonsymmorphic symmetry through a metal-insulator transition in RuAs
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Hisatomo Harima, Takahiro Sakurai, Hisashi Kotegawa, Junichi Hayashi, Keiki Takeda, Yoshiki Kuwata, Hitoshi Sugawara, Hitoshi Ohta, and Hideki Tou
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Materials science ,Strongly Correlated Electrons (cond-mat.str-el) ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Superlattice ,Fermi level ,Crystal system ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter - Strongly Correlated Electrons ,symbols.namesake ,0103 physical sciences ,Density of states ,symbols ,Condensed Matter::Strongly Correlated Electrons ,General Materials Science ,Orthorhombic crystal system ,010306 general physics ,0210 nano-technology ,Ground state ,Nuclear quadrupole resonance ,Charge density wave - Abstract
The single crystal of RuAs obtained by Bi-flux method shows obvious successive metal-insulator transitions at T_MI1~255 K and T_MI2~195$ K. The X-ray diffraction measurement reveals a formation of superlattice of 3x3x3 of the original unit cell below T_MI2, accompanied by a change of the crystal system from the orthorhombic structure to the monoclinic one. Simple dimerization of the Ru ions is nor seen in the ground state. The multiple As sites observed in nuclear quadrupole resonance (NQR) spectrum also demonstrate the formation of the superlattice in the ground state, which is clarified to be nonmagnetic. The divergence in 1/T_1 at T_MI1 shows that a symmetry lowering by the metal-insulator transition is accompanied by strong critical fluctuations of some degrees of freedom. Using the structural parameters in the insulating state, the first principle calculation reproduces successfully the reasonable size of nuclear quadrupole frequencies for the multiple As sites, ensuring the high validity of the structural parameters. The calculation also gives a remarkable suppression in the density of states (DOS) near the Fermi level, although the gap opening is insufficient. A coupled modulation of the calculated Ru d electron numbers and the crystal structure proposes a formation of charge density wave (CDW) in RuAs. Some lacking factors remain, but it shows that a lifting of degeneracy protected by the non-symmorphic symmetry through the superlattice formation is a key ingredient for the metal-insulator transition in RuAs., Comment: 10 pages, 10 figures
- Published
- 2018
11. Detection of an Unconventional Superconducting Phase in the Vicinity of the Strong First-Order Magnetic Transition in CrAs UsingAs75-Nuclear Quadrupole Resonance
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Hisatomo Harima, Hideki Tou, Hitoshi Sugawara, Rui Akamatsu, Hisashi Kotegawa, and Shingo Nakahara
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Superconductivity ,Physics ,Condensed Matter::Materials Science ,Paramagnetism ,Condensed matter physics ,Field (physics) ,Quantum critical point ,Phase (matter) ,General Physics and Astronomy ,Unconventional superconductor ,First order ,Nuclear quadrupole resonance - Abstract
Pressure-induced superconductivity was recently discovered in the binary helimagnet CrAs. We report the results of measurements of nuclear quadrupole resonance for CrAs under pressure. In the vicinity of the critical pressure P(c) between the helimagnetic (HM) and paramagnetic (PM) phases, a phase separation is observed. The large internal field remaining in the phase-separated HM state indicates that the HM phase disappears through a strong first-order transition. This indicates the absence of a quantum critical point in CrAs; however, the nuclear spin-lattice relaxation rate 1/T(1) reveals that substantial magnetic fluctuations are present in the PM state. The absence of a coherence effect in 1/T(1) in the superconducting state provides evidence that CrAs is the first Cr-based unconventional superconductor.
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- 2015
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12. Phase diagram of CeRuPO under pressure investigated byP31-NMR: Comparison between CeRuPO under pressure and theCe(Ru1−xFex)POsystem
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Ryota Yamauchi, Hideki Tou, Hisashi Kotegawa, Shunsaku Kitagawa, Hitoshi Sugawara, and Eiichi Matsuoka
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NMR spectra database ,Physics ,Condensed matter physics ,Ferromagnetism ,Magnetic structure ,Antiferromagnetism ,Order (ring theory) ,Condensed Matter::Strongly Correlated Electrons ,Strongly correlated material ,Condensed Matter Physics ,Ground state ,Electronic, Optical and Magnetic Materials ,Phase diagram - Abstract
We have performed $^{31}\mathrm{P}$-NMR measurements on single-crystalline CeRuPO under pressure in order to understand the variation in magnetic character against pressure. The nuclear magnetic resonance (NMR) spectra for $\text{H}\ensuremath{\perp}c$ and $\text{H}\ensuremath{\parallel}c$ at 2.15 GPa split below the ordered temperature, which is microscopic evidence of the change in the magnetic ground state from the ferromagnetic state at ambient pressure to the antiferromagnetic (AFM) state under pressure. The analysis of NMR spectra suggests that the magnetic structure in the AFM state is the stripe-type AFM state with the AFM moment ${m}_{\mathrm{AFM}}\ensuremath{\perp}c$ axis, and it changes with a magnetic field perpendicular to the $c\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.16em}{0ex}}\mathrm{axis}$. In addition, the dimensionality of magnetic correlations in the spin and $k$ space is estimated. We reveal that three-dimensional magnetic correlations in CeRuPO are robust against pressure, which is quite different from the suppression of the magnetic correlations along the $c\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.16em}{0ex}}\mathrm{axis}$ by Fe substitution in $\text{Ce}({\mathrm{Ru}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x})\text{PO}$.
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- 2014
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13. Magnetic-field-induced charge order in the filled skutteruditeSmRu4P12: Evidence from resonant and nonresonant x-ray diffraction
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Shinji Michimura, Takeshi Matsumura, Hitoshi Sugawara, Yuya Hayashi, Yuji Aoki, Tatsuma D. Matsuda, Kengo Fushiya, Ryuji Higashinaka, and Toshiya Inami
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Materials science ,Condensed matter physics ,X-ray crystallography ,engineering ,Nanotechnology ,Strongly correlated material ,Skutterudite ,engineering.material ,Electrostatic induction ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Magnetic field - Abstract
This work was supported by Grants-in-Aid for Scientific Research (No. 21204456, No. 21102515, and No. 2430087) from JSPS and MEXT, and by a Basic Science Research Grant from the Sumitomo Foundation.
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- 2014
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14. Anomalous transport properties ofRFe4P12(R= La, Ce, Pr, and Nd)
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Hideyuki Sato, K. Abe, H Okada, Tatsuma D. Matsuda, Y. Abe, Yuji Aoki, and Hitoshi Sugawara
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Physics ,Condensed matter physics ,Hall effect ,Electrical resistivity and conductivity ,Seebeck coefficient ,Kondo effect ,Ground state - Abstract
We have investigated the resistivity $(\ensuremath{\rho}),$ thermoelectric power (TEP), and Hall coefficient ${(R}_{H})$ on high-quality single crystals of $R{\mathrm{Fe}}_{4}{\mathrm{P}}_{12}.$ TEP in ${\mathrm{CeFe}}_{4}{\mathrm{P}}_{12}$ is extremely large $(\ensuremath{\sim}0.5$ mV/K at 290 K) with a peak of $\ensuremath{\sim}0.75$ mV/K at around 65 K. The Hall mobility also shows a peak at $\ensuremath{\sim}65$ K, suggesting carriers with heavy masses developed at lower temperatures related to the f-hybridized band. Both Pr and Nd systems exhibit an apparent increase of $\ensuremath{\rho}$ with decreasing temperature far above their magnetic transition temperatures. In the same temperature ranges, TEP exhibits unusually large absolute values of $\ensuremath{-}50 \ensuremath{\mu}\mathrm{V}/\mathrm{K}$ for ${\mathrm{PrFe}}_{4}{\mathrm{P}}_{12}$ and $\ensuremath{-}15 \ensuremath{\mu}\mathrm{V}/\mathrm{K}$ for ${\mathrm{NdFe}}_{4}{\mathrm{P}}_{12},$ respectively. For ${\mathrm{PrFe}}_{4}{\mathrm{P}}_{12},$ such anomalous transport properties suggest an unusual ground state, possibly related to the quadrupolar Kondo effect.
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- 2000
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15. Transport properties of the anisotropic itinerant-electron metamagnet UCoAl
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Tatsuma D. Matsuda, Yohei Shiokawa, Hitoshi Sugawara, Hideyuki Sato, Yuji Aoki, A. V. Andreev, Vladimir Sechovsky, and Ladislav Havela
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Materials science ,Condensed matter physics ,Magnetoresistance ,Scattering ,Hall effect ,Electrical resistivity and conductivity ,Seebeck coefficient ,Condensed Matter::Strongly Correlated Electrons ,Electron ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Anisotropy ,Electronic band structure - Abstract
Magnetoresistance (MR), Hall resistivity, and thermoelectric power in UCoAl, which exhibits a metamagnetic transition (MT) at low temperatures, have been investigated. Across MT, the MR shows a steplike decrease and increase for the transverse and longitudinal geometries, respectively. The temperature dependence of MR indicates that the magnetic scattering due to the spin fluctuations largely contributes to the electrical resistivity around 17 K. The Hall coefficient and the thermoelectric power show drastic changes associated with MT. Both in the low- and high-field states, the extraordinary Hall effect dominates in the temperature dependence of Hall coefficient. The temperature dependence of thermoelectric power can be qualitatively explained by an extended $s\ensuremath{-}d$ model considering the $5f$ band structure.
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- 2000
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16. Magnetic, thermal, and transport properties of single crystals of antiferromagnetic Kondo-latticeCe2PdSi3
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E. V. Sampathkumaran, Hitoshi Sugawara, Tatsuma D. Matsuda, Shanta Saha, Hideyuki Sato, and Yuji Aoki
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Physics ,Magnetization ,Condensed matter physics ,Seebeck coefficient ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,Fermi surface ,Kondo effect ,Ground state ,Heat capacity ,Magnetic susceptibility - Abstract
Magnetization, heat capacity, electrical resistivity, thermoelectric power, and Hall effect have been investigated on single-crystalline ${\mathrm{Ce}}_{2}{\mathrm{PdSi}}_{3}.$ This compound is shown to order antiferromagnetically below N\'eel temperature ${(T}_{N})\ensuremath{\sim}3\mathrm{K}.$ The Sommerfeld coefficient far below ${T}_{N}$ is found to be about $110{\mathrm{m}\mathrm{J}/\mathrm{K}}^{2}\mathrm{mol}\mathrm{Ce},$ which indicates the heavy-fermion character of this compound. The transport and magnetic properties exhibit large anisotropy with an interplay between crystalline-electric-field (CEF) and Kondo effects. The sign of thermoelectric power is opposite for different directions at high temperatures and the ordinary Hall coefficient is anisotropic with opposite sign for different geometries, indicating the anisotropic Fermi surface. The CEF analysis from the temperature dependence of magnetic susceptibility suggests that the ground state is $|\ifmmode\pm\else\textpm\fi{}\frac{1}{2}〉.$ The first and the second excited CEF doublet levels are found to be located at about 30 and 130 K, respectively. The Kondo temperature is estimated to be the same order as ${T}_{N},$ indicating the presence of a delicate competition between the Kondo effect and magnetic order.
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- 2000
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17. Thermal conductivity ofCeAuAl3:Evidence of phonon scattering by Ce magnetic moment fluctuations
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Yuji Aoki, Hitoshi Sugawara, Hideyuki Sato, M. A. Chernikov, and H. R. Ott
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Physics ,Tetragonal crystal system ,Thermal conductivity ,Phonon scattering ,Neutron magnetic moment ,Magnetic moment ,Condensed matter physics ,Phonon ,Condensed Matter::Superconductivity ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,Spin magnetic moment - Abstract
We have measured the thermal conductivity $\ensuremath{\lambda}(T)$ on tetragonal ${\mathrm{CeAuAl}}_{3}$ single crystals along both the a and c axes between 0.4 and 40 K. For comparison, the same measurement has been made on a polycrystalline sample of ${\mathrm{LaAuAl}}_{3}.$ The thermal conductivity of the Ce compound is lower than for the La compound and only weakly anisotropic. No distinct anomalies in $\ensuremath{\lambda}(T)$ of ${\mathrm{CeAuAl}}_{3}$ are observed at the antiferromagnetic transition and, far below the N\'eel temperature, the Wiedemann-Franz law is almost fulfilled. For both compounds a maximum in $\ensuremath{\lambda}/T,$ owing to the phonon contribution, has been observed in the vicinity of 10 K. The data are interpreted by considering phonon scattering processes involving the localized $4f$ electron states on the Ce ions.
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- 2000
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18. Local magnetization rotation in NiFe wire monitored by multiple transverse probes
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Teruo Ono, Yuji Aoki, Hideki Miyajima, Hideyuki Sato, Teruya Shinjo, Hitoshi Sugawara, and R. Hanada
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Condensed Matter::Materials Science ,Magnetization ,Transverse plane ,Materials science ,Ferromagnetism ,Condensed matter physics ,Magnetoresistance ,Electrical resistivity and conductivity ,Field dependence ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Rotation ,Voltage - Abstract
We have simultaneously measured the field dependence of transverse voltages at two pairs of transverse probes along with the magnetoresistance to detect the motion of ferromagnetic domain walls in a thin NiFe wire. We observed sharp steplike changes of the transverse voltage correlated with the jumps in magnetoresistance, which have been reported previously in thin ferromagnetic wires. The field dependence is explained in terms of the rotation of local magnetization near the transverse probes. This fact suggests that such a local magnetization rotation might contribute to some of the negative domain-wall resistivity reported in recent papers.
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- 2000
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19. Magnetic anisotropy, first-order-like metamagnetic transitions, and large negative magnetoresistance in single-crystalGd2PdSi3
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Tatsuma D. Matsuda, E. V. Sampathkumaran, Hideyuki Sato, Hitoshi Sugawara, Shanta Saha, and Roop Mallik
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Condensed Matter::Materials Science ,Magnetic anisotropy ,Magnetization ,Materials science ,Magnetoresistance ,Condensed matter physics ,Electrical resistivity and conductivity ,Seebeck coefficient ,Anisotropy ,Single crystal ,Ion - Abstract
Electrical resistivity (\ensuremath{\rho}), magnetoresistance (MR), magnetization, thermopower, and Hall-effect measurements on the single-crystal ${\mathrm{Gd}}_{2}{\mathrm{PdSi}}_{3},$ crystallizing in an ${\mathrm{AlB}}_{2}$-derived hexagonal structure, are reported. The well-defined minimum in \ensuremath{\rho} at a temperature above N\'eel temperature ${(T}_{N}=21\mathrm{K})$ and large negative MR below $\ensuremath{\sim}{3T}_{N},$ reported earlier for the polycrystals, are reproducible even in single crystals. Such features are generally uncharacteristic of Gd alloys. In addition, we also found interesting features in other data, e.g., two-step first-order-like metamagnetic transitions for the magnetic field along [0001] direction. The alloy exhibits anisotropy in all these properties, though Gd is an $S$-state ion.
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- 1999
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20. Hall effect inY1−xUxPd3andCeNi2Ge2
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J. Urakawa, T. Fukuhara, Yuji Aoki, Kunihiko Maezawa, Hitoshi Sugawara, Hideyuki Sato, and Yoshichika Onuki
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Materials science ,Condensed matter physics ,Hall effect ,Strongly correlated material - Published
- 1998
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21. Anisotropy of the superconducting gap inCeCo2s
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Hideyuki Sato, Yuji Aoki, T. Nishigaki, and Hitoshi Sugawara
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Physics ,Superconductivity ,Condensed matter physics ,Ferromagnetism ,Specific heat ,Band gap ,Electrical resistivity and conductivity ,Condensed Matter::Superconductivity ,Transition temperature ,Anisotropy ,Spin-½ - Abstract
We find extraordinary superconducting characteristics in the low-temperature specific heat of high quality ${\mathrm{CeCo}}_{2}$ single crystals, suggesting that the superconducting gap is highly anisotropic. The electronic specific-heat jump at the superconducting transition temperature (${\mathrm{T}}_{\mathrm{c}}$ =1.5 K) is \ensuremath{\Delta}${\mathrm{C}}_{\mathrm{e}}$ /\ensuremath{\gamma}${\mathrm{T}}_{\mathrm{c}}$ =0.85, which is reduced compared to the BCS value of 1.43. At low temperatures (0.13/${\mathrm{T}}_{\mathrm{c}}$ \ensuremath{\ll}1), ${\mathrm{C}}_{\mathrm{e}}$ varies approximately as ${\mathrm{T}}^{2}$ , indicating a possibility of lines of nodes in the gap. A possible correlation of the gap anisotropy with the ferromagnetic spin fluctuation is discussed.
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- 1997
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22. Magnetic state of Ce in thin layers
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S. Hashimoto, T. Yokoyama, Yuji Aoki, Y. Komaba, Hideyuki Sato, T. Hanyu, Hitoshi Sugawara, and Y. Kobayashi
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Magnetization ,Cerium ,Crystallography ,Materials science ,chemistry ,Condensed matter physics ,Hall effect ,Electrical resistivity and conductivity ,Tantalum ,chemistry.chemical_element ,Thin film ,Magnetic susceptibility ,Amorphous solid - Abstract
We have fabricated Ce/Ta multilayers under ultrahigh vacuum to investigate the magnetic state of Ce in thin layers. The magnetization, electrical resistivity, and Hall effect have been measured for Ce layer thicknesses between 5 and 100 \AA{}. Results of x-ray analysis indicate that Ce atoms crystallize as bulk Ce for ${\mathit{d}}_{\mathrm{Ce}}$=100 \AA{}, and are amorphous for ${\mathit{d}}_{\mathrm{Ce}}$\ensuremath{\leqslant}15 \AA{}. For ${\mathit{d}}_{\mathrm{Ce}}$=100 \AA{}, the Ce \ensuremath{\gamma}-\ensuremath{\alpha} transition observed in the resistivity and reduced magnetization at 2 K suggest the stabilization of \ensuremath{\alpha}-phase Ce at low temperatures. For ${\mathit{d}}_{\mathrm{Ce}}$\ensuremath{\leqslant}15 \AA{}, in contrast, the magnetic susceptibility and extraordinary Hall effect indicate the existence of magnetic Ce down to 1 K. We speculate that the transition to the nonmagnetic state of Ce at low temperatures for ${\mathit{d}}_{\mathrm{Ce}}$\ensuremath{\leqslant}15 \AA{} is prevented by the amorphous structure. \textcopyright{} 1996 The American Physical Society.
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- 1996
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23. Atomic dynamics of low-lying rare-earth guest modes in heavy fermion filled skutteruditesROs4Sb12(R=light rare-earth)
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Alfred Q. R. Baron, Hiroshi Uchiyama, Takumi Hasegawa, John P. Sutter, Akira Ochiai, Tomoya Uruga, Jun-ichi Yamaura, Hideyuki Sato, Norio Ogita, Masayuki Udagawa, Satoshi Tsutsui, Naomi Kawamura, Hitoshi Sugawara, and Masaichiro Mizumaki
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Physics ,Condensed matter physics ,Heavy fermion ,Rare earth ,Strongly correlated material ,Atomic physics ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials - Published
- 2012
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24. Suppression of time-reversal symmetry breaking superconductivity in Pr(Os1−xRux)4Sb12and Pr1−yLayOs4Sb12
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M. B. Maple, Adrian D. Hillier, K. Ohishi, S. Sanada, Yuji Aoki, Ryosuke Kadono, Wataru Higemoto, Akihiro Koda, D. E. MacLaughlin, Takashi U. Ito, Hideyuki Sato, Kenji Ishida, Y. Tunashima, Oscar Bernal, Y. Yonezawa, Daisuke Kikuchi, Hitoshi Sugawara, and Lei Shu
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Physics ,Superconductivity ,Condensed matter physics ,Relaxation (NMR) ,Doping ,02 engineering and technology ,Muon spin spectroscopy ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,T-symmetry ,Pairing ,0103 physical sciences ,Strongly correlated material ,010306 general physics ,0210 nano-technology - Abstract
Zero-field muon spin relaxation experiments have been carried out in the Pr(Os${}_{1\ensuremath{-}x}$Ru${}_{x}$)${}_{4}$Sb${}_{12}$ and Pr${}_{1\ensuremath{-}y}$La${}_{y}$Os${}_{4}$Sb${}_{12}$ alloy systems to investigate broken time-reversal symmetry (TRS) in the superconducting state, signaled by the onset of a spontaneous static local magnetic field ${B}_{s}$. In both alloy series ${B}_{s}$ initially decreases linearly with solute concentration. Ru doping is considerably more efficient than La doping, with a $~$50% faster initial decrease. The data suggest that broken TRS is suppressed for Ru concentration $x\ensuremath{\gtrsim}0.6$ but persists for essentially all La concentrations. Our data support a crystal-field excitonic Cooper pairing mechanism for TRS-breaking superconductivity.
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- 2011
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25. Comment on 'Pronounced Enhancement of the Lower Critical Field and Critical Current Deep in the Superconducting State ofPrOs4Sb12'
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Adrian D. Hillier, D. E. MacLaughlin, Daisuke Kikuchi, Lei Shu, Hitoshi Sugawara, Y. Tunashima, Yuji Aoki, Hideyuki Sato, and J. M. Mackie
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Superconductivity ,Physics ,Phase transition ,Condensed matter physics ,Transition temperature ,General Physics and Astronomy ,Muon spin spectroscopy ,01 natural sciences ,Vortex state ,010305 fluids & plasmas ,Condensed Matter::Superconductivity ,0103 physical sciences ,Strongly correlated material ,010306 general physics ,Penetration depth ,Critical field - Abstract
Cichorek et al. [Phys. Rev. Lett. 94, 107002 (2005)] reported enhancements of the lower critical field Hc1(T) and critical current in superconducting PrOs4Sb12 below a transition temperature Tc3 ~ 0.6 K, and speculated that this reflects a transition between superconducting phases. Features have been observed near Tc3 in other properties, but not in the specific heat. We report muon spin rotation measurements of the penetration depth in the vortex state of PrOs4Sb12 near Hc1(T), that to high accuracy exhibit no anomaly Tc3 and therefore cast doubt on the putative phase transition.
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- 2010
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26. Thermal conductivity measurements of the energy-gap anisotropy of superconducting LaFePO at low temperatures
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Kenichiro Hashimoto, Hitoshi Sugawara, S. Tonegawa, Norihito Nakata, Y. Senshu, Minoru Yamashita, Yuji Matsuda, Takasada Shibauchi, and K. Ikada
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Physics ,Superconductivity ,Thermal conductivity ,Condensed matter physics ,Field (physics) ,Band gap ,Condensed Matter Physics ,Anisotropy ,Penetration depth ,Curvature ,Critical field ,Electronic, Optical and Magnetic Materials - Abstract
The superconducting gap structure of LaFePO $({T}_{c}=7.4\text{ }\text{K})$ is studied by thermal conductivity $(\ensuremath{\kappa})$ at low temperatures in fields $H$ parallel and perpendicular to the $c$ axis. A clear two-step field dependence of $\ensuremath{\kappa}(H)$ with a characteristic field ${H}_{s}(\ensuremath{\sim}350\text{ }\text{Oe})$ much lower than the upper critical field ${H}_{c2}$ is observed. In spite of the large anisotropy of ${H}_{c2}$, $\ensuremath{\kappa}(H)$ in both $H$ directions is nearly identical below ${H}_{s}$. Above ${H}_{s}$, $\ensuremath{\kappa}(H)$ grows gradually with $H$ with a convex curvature, followed by a steep increase with strong upward curvature near ${H}_{c2}$. These results indicate multigap superconductivity with active two-dimensional (2D) and passive three-dimensional bands having contrasting gap values. Together with the recent penetration depth results, we suggest that the 2D bands consist of nodal and nodeless ones, consistent with extended $s$-wave symmetry.
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- 2009
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27. Electronic hybridization effect on4felectron crystal field states ofPrOs4P12
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Kazuaki Iwasa, Hitoshi Sugawara, Kotaro Saito, and Youichi Murakami
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Physics ,education.field_of_study ,Condensed matter physics ,Computer Science::Information Retrieval ,Population ,Computer Science::Computation and Language (Computational Linguistics and Natural Language and Speech Processing) ,Neutron scattering ,Inelastic scattering ,Mott scattering ,Condensed Matter Physics ,Coupling (probability) ,Inelastic neutron scattering ,Electronic, Optical and Magnetic Materials ,Resonant inelastic X-ray scattering ,Strongly correlated material ,Atomic physics ,education - Abstract
Crystal-field excitation spectra of $\text{Pr}\text{ }4f$ electron state in the filled skutterudite ${\text{PrOs}}_{4}{\text{P}}_{12}$ measured by inelastic neutron scattering experiment evolve distinctly with temperature variation. The spectral widths of excitations from the ground-state singlet to the two triplets and their temperature dependences are well reproduced by the theory based on the exchange coupling between $4f$ and conduction electrons. The shift of level energies by around 1 meV below 60 K indicates modification of crystal-field potential with variation of thermal population of $4f$ electron crystal-field states. The spectral evolution is consistent with the specific heat data that deviates from the calculated one for the well-localized $4f$ electron. The result supports the effect of $p\text{\ensuremath{-}}f$ hybridization between $\text{Pr}\text{ }4f$ and $\text{P}\text{ }p$ states in ${\text{PrOs}}_{4}{\text{P}}_{12}$.
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- 2009
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28. Anomalous Duality of4fElectrons in Filled SkutteruditeCeOs4Sb12
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Ritsuko Eguchi, C. T. Chen, Masaharu Matsunami, Takayuki Kiss, Keiichiro Yamamoto, Yasunori Senba, Hiromichi Ohashi, Ashish Chainani, Hitoshi Sugawara, Koji Horiba, Shuntaro Watanabe, Hisatomo Harima, Tadashi Togashi, Shik Shin, X. Y. Wang, Hideyuki Sato, and M. Taguchi
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Physics ,Condensed matter physics ,Photoemission spectroscopy ,Inverse photoemission spectroscopy ,Fermi level ,General Physics and Astronomy ,Angle-resolved photoemission spectroscopy ,Electronic structure ,engineering.material ,symbols.namesake ,engineering ,symbols ,Condensed Matter::Strongly Correlated Electrons ,Strongly correlated material ,Skutterudite ,Pseudogap - Abstract
We study the electronic structure of the filled skutterudite CeOs 4 Sb 12 using photoemission spectroscopy (PES). Soft x-ray excited Ce 3d-4f resonant PES confirms the existence of Ce 4f states at the Fermi level (E F ). Temperature dependent high-resolution laser-PES spectra reveal a pseudogap formation around E F , which can be explained in terms of the hybridization gap. Simultaneously, a sharp feature is formed just above E F with decreasing temperature. The heavy-fermion-like specific heat is attributed to the occupation of this feature. The results identify the origin of the anomalous coexistence of heavy-fermion and pseudogap behavior in terms of a symmetry dependent hybridization.
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- 2009
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29. Fermi surface of the Pr-based filled skutterudite compoundPrOs4P12
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Ko-ichi Magishi, Hideyuki Sato, Toyoaki Endo, Yoshichika Ōnuki, Yoshinori Iwahashi, Rikio Settai, Hisatomo Harima, Hitoshi Sugawara, Kuniyuki Koyama, Daisuke Kikuchi, and Takahito Saito
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Physics ,Condensed matter physics ,Heavy fermion ,engineering ,Fermi surface ,Fermi liquid theory ,Skutterudite ,engineering.material ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Effective mass (spring–mass system) - Abstract
We have investigated the Fermi-surface (FS) properties in the Pr-based filled skutterudite ${\text{PrOs}}_{4}{\text{P}}_{12}$ and its reference compound ${\text{LaOs}}_{4}{\text{P}}_{12}$ by means of de Haas--van Alphen experiments and the band-structure calculations. The topology of FS in ${\text{PrOs}}_{4}{\text{P}}_{12}$ is close to that in the reference compound ${\text{LaOs}}_{4}{\text{P}}_{12}$, indicating a localized nature of $4f$ electrons in ${\text{PrOs}}_{4}{\text{P}}_{12}$. Whereas the localized nature of $4f$ electrons, we have confirmed a highly enhanced cyclotron effective mass of up to $18{m}_{0}$ in ${\text{PrOs}}_{4}{\text{P}}_{12}$, which is enhanced about 3.8 times compared to that in ${\text{LaOs}}_{4}{\text{P}}_{12}$. No nesting property with $q=(1,0,0)$ in the FS of ${\text{PrOs}}_{4}{\text{P}}_{12}$ has been confirmed in contrast to good nesting properties in ${\text{PrFe}}_{4}{\text{P}}_{12}$ and ${\text{PrRu}}_{4}{\text{P}}_{12}$ which exhibit unusual ordered states at low temperatures. A role of both the $4f$ electron's contributions and the FS nesting property for unusual phase transitions are discussed.
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- 2009
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30. S123b-NQR study of unconventional superconductivity in the filled skutterudite heavy-fermion compoundPrOs4Sb12under high pressure up to 3.82 GPa
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Shinji Kawasaki, Kouta Katayama, Guo-Qing Zheng, Hitoshi Sugawara, Daisuke Kikuchi, and Hideyuki Sato
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Superconductivity ,Physics ,Condensed matter physics ,engineering.material ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Excited state ,Quadrupole ,engineering ,Strongly correlated material ,Singlet state ,Skutterudite ,Ground state ,Nuclear quadrupole resonance - Abstract
We report $^{123}$Sb nuclear quadrupole resonance (NQR) measurements of the filled skutterudite heavy-fermion superconductor PrOs$_4$Sb$_{12}$ under high pressure. The temperature dependence of NQR frequency and the spin-lattice relaxation rate $1/T_1$ indicate that the crystal-electric-field splitting $\Delta_{\rm CEF}$ between the ground state $\Gamma_1$ singlet and the first excited state $\Gamma_4^{(2)}$ triplet decreases with increasing pressure. Ac-susceptibility measurements indicate that the superconducting transition temperature ($T_{\rm c}$) also decreases with increasing pressure. However, above $P$ $\sim$ 2 GPa, both $\Delta_{\rm CEF}$ and $T_{\rm c}$ do not depend on external pressure up to $P$ = 3.82 GPa. These pressure dependences of $\Delta_{\rm CEF}$ and $T_{\rm c}$ suggest an intimate relationship between quadrupole excitations associated with the $\Gamma_4^{(2)}$ level and unconventional superconductivity in PrOs$_4$Sb$_{12}$. In the superconducting state, 1/$T_1$ below $T_{\rm c}$ = 1.55 and 1.57 K at $P$ = 1.91 and 2.63 GPa shows a power-law temperature variations and are proportional to $T^5$ at temperatures considerably below $T_{\rm c}$. These data can be well fitted by the gap model $\Delta(\theta) = \Delta_0\sin\theta$ with $\Delta_0$ = 3.08 $k_{\rm B}T_{\rm c}$ and 3.04 $k_{\rm B}T_{\rm c}$ for $P$ = 1.91 and 2.63 GPa, respectively. The results indicate there exists point nodes in the gap function.
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- 2008
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31. Double superconducting transition in the filled skutteruditePrOs4Sb12and sample characterizations
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Jean-Pascal Brison, Daniel Braithwaite, Marie-Aude Méasson, Pierre Bordet, Jacques Flouquet, Paul C. Canfield, Gérard Lapertot, and Hitoshi Sugawara
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Superconductivity ,Diffraction ,Materials science ,Condensed matter physics ,02 engineering and technology ,engineering.material ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Heat capacity ,Electronic, Optical and Magnetic Materials ,Thermal conductivity ,0103 physical sciences ,X-ray crystallography ,engineering ,Strongly correlated material ,Skutterudite ,010306 general physics ,0210 nano-technology ,Phase diagram - Abstract
Through the characterization of many samples of the filled skutterudite compound PrOs4Sb12, we found that even though the double superconducting transition in the specific heat (Tc1 ~1.89 K and Tc2 ~ 1.72 K) appears in samples of good quality, there are various pieces of evidence that cast doubt on its intrinsic nature. First, three samples exhibit a single sharp transition of ~15 mK width at Tc~1.7 K. The quality of the samples exhibiting a single transition is clearly better; the width of the transition is smallest and the normalized specific heat jump ((C-Cnormal)/Cnormal)Tc is larger than the sum of the two specific heat jumps when a double transition exists. Second, the ratio of the two specific heat jumps Delta C(Tc1)/Delta C(Tc2) exhibits a wide variation with samples not only among different batches but also even within a batch. Finally, this ratio was strongly reduced by polishing a sample down to ~100 µm, which points to bulk inhomogeneities as an origin of the spurious transition. Our x-ray diffraction analysis points to Pr-vacancy problem in the samples, but it does not show that they are the origin of the double transition. We provide the superconducting phase diagram under magnetic field of a sample exhibiting a single transition and fit the curve Hc2(T) with a two-band model taking into account the appropriate values for the gap as deduced from thermal conductivity measurements.
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- 2008
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32. Stability of electronic states across the metal-insulator transition inPrRu4P12
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Akira Sekiyama, G. Funahashi, Takayuki Muro, Akira Sugimura, Atsushi Yamasaki, T. Ishikawa, J. Yamaguchi, Kenji Tamasaku, Hideyuki Sato, Shin Imada, H. Kobori, Hitoshi Sugawara, Shigemasa Suga, Hideki Fujiwara, M. Yano, Atsushi Higashiya, Makina Yabashi, Hisatomo Harima, and Daisuke Kikuchi
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Physics ,Mixed states ,Condensed matter physics ,Inverse photoemission spectroscopy ,Angle-resolved photoemission spectroscopy ,Metal–insulator transition ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Electronic states - Abstract
We have investigated the exotic metal-insulator (M-I) transition in $\mathrm{Pr}{\mathrm{Ru}}_{4}{\mathrm{P}}_{12}$ by using hard-x-ray and soft-x-ray photoemission spectroscopies. The significantly large hybridization strength between conduction and $\mathrm{Pr}\phantom{\rule{0.2em}{0ex}}4f$ electrons $(c\text{\ensuremath{-}}f)$ is found not to change much between the metal and insulating phases. These results suggest that the M-I transition does not noticeably affect the $c\text{\ensuremath{-}}f$ hybridization nature and $\mathrm{P}\phantom{\rule{0.2em}{0ex}}3p--\mathrm{Pr}\phantom{\rule{0.2em}{0ex}}4f$ mixed states are highly stable.
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- 2008
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33. Electronic structure of semiconductingCeFe4P12: Strong hybridization and relevance of single-impurity Anderson model
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Yoshinori Nishino, K. Horiba, Masaharu Matsunami, M. Taguchi, T. Ishikawa, Y. Takata, Hideyuki Sato, Hisatomo Harima, Kenji Tamasaku, Makina Yabashi, Shik Shin, Hitoshi Sugawara, Eiji Ikenaga, Daigo Miwa, Kensuke Kobayashi, Hiromichi Ohashi, Yasunori Senba, Keiichiro Yamamoto, and Ashish Chainani
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Physics ,Valence (chemistry) ,Condensed matter physics ,Photoemission spectroscopy ,Fermi level ,Electronic structure ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,symbols.namesake ,symbols ,Density of states ,Strongly correlated material ,Atomic physics ,Electronic band structure ,Anderson impurity model - Abstract
Semiconducting skutterudite $\mathrm{Ce}{\mathrm{Fe}}_{4}{\mathrm{P}}_{12}$ is investigated by synchrotron x-ray photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS). $\mathrm{Ce}\phantom{\rule{0.2em}{0ex}}3d$ core-level PES and $3d\text{\ensuremath{-}}4f$ XAS, in combination with single-impurity Anderson model (SIAM) calculations, confirm features due to ${f}^{0}$, ${f}^{1}$, and ${f}^{2}$ configurations. The $\mathrm{Ce}\phantom{\rule{0.2em}{0ex}}3d\text{\ensuremath{-}}4f$ resonant-PES spectra provide the $\mathrm{Ce}\phantom{\rule{0.2em}{0ex}}4f$ density of states (DOS), which indicates the absence of a Kondo resonance at the Fermi level, but can still be explained by SIAM with a small gap in non-$f$ DOS. While $\mathrm{Ce}\phantom{\rule{0.2em}{0ex}}4f$ partial DOS from band structure calculations is consistent with the main $\mathrm{Ce}\phantom{\rule{0.2em}{0ex}}4f$ DOS, the importance of SIAM for core-level PES and XAS spectra quantifies the mixed valence for semiconducting $\mathrm{Ce}{\mathrm{Fe}}_{4}{\mathrm{P}}_{12}$, derived from strong hybridization between non-$f$ conduction and $\mathrm{Ce}\phantom{\rule{0.2em}{0ex}}4f$ DOS.
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- 2008
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34. Gap opening with ordering inPrFe4P12studied by local tunneling spectroscopy
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Daisuke Kikuchi, Hermann Suderow, Isabel Guillamón, V. Crespo, Kamran Behnia, Yuji Aoki, Hitoshi Sugawara, Hideyuki Sato, and Sebastian Vieira
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Physics ,Local density of states ,Condensed matter physics ,Fermi level ,Fermi surface ,Condensed Matter Physics ,Spectral line ,Electronic, Optical and Magnetic Materials ,symbols.namesake ,Phase (matter) ,symbols ,Density of states ,Spectroscopy ,Quantum tunnelling - Abstract
We present measurements of the local tunneling density of states in the low temperature ordered state of $\mathrm{Pr}{\mathrm{Fe}}_{4}{\mathrm{P}}_{12}$. The temperature dependencies of the Fermi level density of states and of the integrated density of states at low bias voltages show anomalies at $T\ensuremath{\simeq}6.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the onset of multipolar ordering as detected by specific heat and other macroscopic measurements. In the ordered phase, we find a local density of states with a V-shape form, indicating a partial gap opening over the Fermi surface. The size of the gap according to the tunneling spectra is about $2\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$.
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- 2008
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35. Low-lying excitations at the rare-earth site due to the rattling motion in the filled skutteruditeLaOs4Sb12revealed byLa139NMR andSb121∕123NQR
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Kenji Ishida, Hitoshi Sugawara, Yusuke Nakai, Hideyuki Sato, and Daisuke Kikuchi
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Physics ,Condensed matter physics ,Phonon ,Anharmonicity ,Relaxation (NMR) ,Rare earth ,Electronic structure ,engineering.material ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,engineering ,Strongly correlated material ,Skutterudite ,Nuclear quadrupole resonance - Abstract
We report experimental results of nuclear magnetic resonance (NMR) at the La site and nuclear quadrupole resonance (NQR) at the Sb site in the filled skutterudite $\mathrm{La}{\mathrm{Os}}_{4}{\mathrm{Sb}}_{12}$. We found that the nuclear spin-lattice relaxation rate divided by temperature $1∕{T}_{1}T$ at the La site exhibits a different temperature dependence from that at the Sb site. Although $1∕{T}_{1}T$ at the Sb site is explained by the Korringa mechanism, $1∕{T}_{1}T$ at the La site exhibits a broad maximum around $50\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, showing the presence of an additional contribution at the La site. The additional low-lying excitations observed at the La site can be understood with the relaxation from anharmonic phonons due to the rattling motion of the La atoms.
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- 2008
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36. Soft x-ray spectroscopy of the possibly heavy-fermion compoundNdOs4Sb12
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Shigemasa Suga, Takayuki Muro, Shin Imada, Daisuke Kikuchi, Hitoshi Sugawara, A. Yamasaki, H. Higashimichi, M. Yano, Akira Sekiyama, and Hitoshi Sato
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Physics ,Soft x ray ,Condensed matter physics ,Photoemission spectroscopy ,Heavy fermion ,Science and engineering ,Strongly correlated material ,Angle-resolved photoemission spectroscopy ,Soft X-ray emission spectroscopy ,Condensed Matter Physics ,Spectroscopy ,Electronic, Optical and Magnetic Materials - Abstract
S. Imada,1 H. Higashimichi,1 A. Yamasaki,2 M. Yano,1 T. Muro,3 A. Sekiyama,1 S. Suga,1 H. Sugawara,4 D. Kikuchi,5 and H. Sato5 1Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan 2Department of Physics, Faculty of Science and Engineering, Konan University, Kobe 658-8501, Japan 3Spring-8/JASRI, Sayo 579-5198, Japan 4Faculty of the Integrated Arts and Sciences, The University of Tokushima, Minami-jyousanjima-machi 1-1, Tokushima 770-8502, Japan 5Graduate School of Science, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan Received 1 June 2007; revised manuscript received 3 September 2007; published 24 October 2007
- Published
- 2007
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37. Connection between Charge Fluctuations and the Coherent Temperature in the Heavy-Fermion SystemSmOs4Sb12: ASb121, 123NQR Study
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Hitoshi Sugawara, Hideyuki Sato, Hisashi Kotegawa, Daisuke Kikuchi, H. Hidaka, and Tatsuo C. Kobayashi
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Physics ,Condensed matter physics ,Relaxation rate ,Heavy fermion ,Kinetic isotope effect ,General Physics and Astronomy ,Charge (physics) ,Strongly correlated material ,Kondo effect ,Connection (algebraic framework) ,Nuclear quadrupole resonance - Abstract
We report {121, 123}Sb nuclear quadrupole resonance measurements under pressure in a novel heavy fermion (HF) system SmOs4Sb12. The nuclear spin-spin relaxation rate 1/T{2} exhibits a distinct peak near the coherent temperature of the Kondo effect. The isotope effect of 121Sb and 123Sb indicates that the peak in 1/T{2} is electrical in origin. The connection between the peak in 1/T{2} and the development of coherency of the Kondo effect is robust even under pressure. It is conjectured that charge fluctuation plays an important role in forming the HF state in SmOs4Sb12.
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- 2007
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38. Muon spin relaxation and hyperfine-enhancedPr141nuclear spin dynamics inPr(Os,Ru)4Sb12and(Pr,La)Os4Sb12
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Ryosuke Kadono, Takashi U. Ito, W. M. Yuhasz, R. H. Heffner, Akihiro Koda, Y. Yonezawa, Hideyuki Sato, M. B. Maple, Adrian D. Hillier, Hitoshi Sugawara, Oscar Bernal, Kenji Ishida, N. A. Frederick, S. Sanada, Yuji Aoki, Lei Shu, D. E. MacLaughlin, Tatsuya Yanagisawa, Daisuke Kikuchi, K. Ohishi, T. A. Sayles, Y. Tunashima, and Wataru Higemoto
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Physics ,Muon ,Spins ,Condensed matter physics ,Relaxation (NMR) ,02 engineering and technology ,Muon spin spectroscopy ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Magnetic field ,Excited state ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,Strongly correlated material ,010306 general physics ,0210 nano-technology ,Hyperfine structure - Abstract
Zero- and longitudinal-field muon spin relaxation experiments have been carried out in the alloy series $\mathrm{Pr}{({\mathrm{Os}}_{1\ensuremath{-}x}{\mathrm{Ru}}_{x})}_{4}{\mathrm{Sb}}_{12}$ and ${\mathrm{Pr}}_{1\ensuremath{-}y}{\mathrm{La}}_{y}{\mathrm{Os}}_{4}{\mathrm{Sb}}_{12}$ to elucidate the anomalous dynamic muon spin relaxation observed in these materials. The damping rate $\ensuremath{\Lambda}$ associated with this relaxation varies with temperature, applied magnetic field, and dopant concentrations $x$ and $y$ in a manner consistent with the ``hyperfine enhancement'' of $^{141}\mathrm{Pr}$ nuclear spins first discussed by Bleaney [Physica (Utrecht) 69, 317 (1973)]. This mechanism arises from Van Vleck-like admixture of magnetic ${\mathrm{Pr}}^{3+}$ crystalline-electric-field-split excited states into the nonmagnetic singlet ground state by the nuclear hyperfine coupling, thereby increasing the strengths of spin-spin interactions between $^{141}\mathrm{Pr}$ and muon spins and within the $^{141}\mathrm{Pr}$ spin system. We find qualitative agreement with this scenario and conclude that electronic spin fluctuations are not directly involved in the dynamic muon spin relaxation.
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- 2007
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39. Coexistence of Strongly Mixed-Valence and Heavy-Fermion Character inSmOs4Sb12Studied by Soft- and Hard-X-Ray Spectroscopy
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T. Ishikawa, Atsushi Yamasaki, Shigemasa Suga, T. Saita, Shin Imada, Atsushi Higashiya, Kenji Tamasaku, Hitoshi Sugawara, T. Miyamachi, Makina Yabashi, Hidenori Fujiwara, Daigo Miwa, Hideyuki Sato, Daisuke Kikuchi, H. Higashimichi, and Akira Sekiyama
- Subjects
Physics ,X-ray spectroscopy ,Valence (chemistry) ,Condensed matter physics ,Photoemission spectroscopy ,Inverse photoemission spectroscopy ,General Physics and Astronomy ,Angle-resolved photoemission spectroscopy ,Strongly correlated material ,Atomic physics ,Soft X-ray emission spectroscopy ,Spectroscopy - Abstract
Sm-based heavy-fermion compound ${\mathrm{SmOs}}_{4}{\mathrm{Sb}}_{12}$ has been investigated by soft x-ray ($h\ensuremath{\nu}=1070--1600\text{ }\text{ }\mathrm{eV}$) and hard x-ray (HX; $h\ensuremath{\nu}=7932\text{ }\text{ }\mathrm{eV}$) spectroscopy. The HX photoemission spectroscopy clearly demonstrates that the strongly mixed-valence state and the heavy-fermion state coexist in the bulk. It is found that the Sm valence decreases below 100 K, indicating that the Kondo coherence develops with approaching the proposed Kondo temperature. Our theoretical analyses suggest that the origin of the coexistence in ${\mathrm{SmOs}}_{4}{\mathrm{Sb}}_{12}$ is the coincidence of two conditions, namely, (i) the energy difference between Sm divalent and trivalent states is very small and (ii) the hybridization between Sm $4f$ and conduction electrons is weak.
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- 2007
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40. Elastic properties of the non-Fermi-liquid metalCeRu4Sb12and dense Kondo semiconductorCeOs4Sb12
- Author
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Yoshiki Nakanishi, Hitoshi Sugawara, T. Kumagai, Masahito Yoshizawa, Hideyuki Sato, T. Tanizawa, and Masafumi Oikawa
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Materials science ,Condensed matter physics ,Band gap ,Fermi level ,Condensed Matter Physics ,Coupling (probability) ,Electronic, Optical and Magnetic Materials ,symbols.namesake ,symbols ,Quasiparticle ,Strongly correlated material ,Fermi liquid theory ,Ground state ,Electronic band structure - Abstract
We have investigated the elastic properties of the Ce-based filled skutterudite antimonides CeRu$_{4}$Sb$_{12}$ and CeOs$_{4}$Sb$_{12}$ by means of ultrasonic measurements. CeRu$_{4}$Sb$_{12}$ shows a slight increase around 130 K in the temperature dependence of the elastic constants $C$$_{11}$, ($C$$_{11}$-$C$$_{12}$)/2 and $C$$_{44}$. No apparent softening toward low temperature due to a quadrupolar response of the 4$f$-electronic ground state of the Ce ion was observed at low temperatures. In contrast CeOs$_{4}$Sb$_{12}$ shows a pronounced elastic softening toward low temperature in the longitudinal $C$$_{11}$ as a function of temperature ($T$) below about 15 K, while a slight elastic softening was observed in the transverse $C$$_{44}$ below about 1.5 K. Furthermore, CeOs$_{4}$Sb$_{12}$ shows a steep decrease around a phase transition temperature of 0.9 K in both $C$$_{11}$ and$ C$$_{44}$. The elastic softening observed in $C$$_{11}$ below about 15 K cannot be explained reasonably only by the crystalline electric field effect. It is most likely to be responsible for the coupling between the elastic strain and the quasiparticle band with a small energy gap in the vicinity of Fermi level. The elastic properties and the 4$f$ ground state of Ce ions in CeRu$_{4}$Sb$_{12}$ and CeOs$_{4}$Sb$_{12}$ are discussed from the viewpoint of the crystalline electric field effect and the band structure in the vicinity of Fermi level.
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- 2007
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41. Spin-triplet superconductivity inPrOs4Sb12probed by muon Knight shift
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Hitoshi Sugawara, A. Koda, Subir Saha, Hideyuki Sato, Ryosuke Kadono, Y. Aoki, Wataru Higemoto, and K. Ohishi
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Superconductivity ,Physics ,Muon ,Condensed matter physics ,Condensed Matter::Superconductivity ,Condensed Matter::Strongly Correlated Electrons ,Knight shift ,Heavy fermion superconductor ,Muon spin spectroscopy ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Spin-½ - Abstract
We report a muon spin rotation study in single-crystalline samples of the heavy fermion superconductor $\mathrm{Pr}{\mathrm{Os}}_{4}{\mathrm{Sb}}_{12}$. The muon Knight shift is independent of temperature passing through ${T}_{c}$ down to $20\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$ at 3 and $17\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$, indicating that the local spin susceptibility does not decrease in the superconducting state. This result is evidence that spin-triplet superconductivity is realized in $\mathrm{Pr}{\mathrm{Os}}_{4}{\mathrm{Sb}}_{12}$.
- Published
- 2007
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42. Drastic Change in Transport of Entropy with Quadrupolar Ordering inPrFe4P12
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Kamran Behnia, Alexandre Pourret, Daisuke Kikuchi, Hitoshi Sugawara, Yuji Aoki, and Hideyuki Sato
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Thermoelectric transport ,Materials science ,Condensed matter physics ,General Physics and Astronomy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,7. Clean energy ,Lattice thermal conductivity ,Metal ,symbols.namesake ,Charge-carrier density ,visual_art ,0103 physical sciences ,Thermal ,symbols ,visual_art.visual_art_medium ,Condensed Matter::Strongly Correlated Electrons ,Nernst equation ,Strongly correlated material ,010306 general physics ,0210 nano-technology ,Entropy (order and disorder) - Abstract
The antiferroquadrupolar ordering of ${\mathrm{PrFe}}_{4}{\mathrm{P}}_{12}$ is explored by probing thermal and thermoelectric transport. The lattice thermal conductivity drastically increases with the ordering, as a consequence of a large drop in carrier concentration and a strong electron-phonon coupling. The low level of carrier density in the ordered state is confirmed by the anomalously large values of the Seebeck and Nernst coefficients. The results are reminiscent of ${\mathrm{URu}}_{2}{\mathrm{Si}}_{2}$ and suggest that both belong to the same class of partial metal-insulator transitions. The magnitude of the Nernst coefficient, larger than in any other metal, indicates a new route for Ettingshausen cooling at Kelvin temperatures.
- Published
- 2006
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43. Ultrasonic study of the filled skutterudite compoundPrRu4P12
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T. Tanizawa, T. Kumagai, Yoshiki Nakanishi, O. Masafumi, Masahito Yoshizawa, Hitoshi Sugawara, Hideyuki Sato, and Shanta Saha
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Materials science ,Condensed matter physics ,engineering ,Strongly correlated material ,Ultrasonic sensor ,Skutterudite ,engineering.material ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials - Published
- 2006
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44. Multiband Superconductivity in the Heavy Fermion CompoundPr Os4Sb12
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Jean-Pascal Brison, Hideyuki Sato, Jacques Flouquet, Koichi Izawa, Hitoshi Sugawara, Marie-Aude Méasson, Yuji Matsuda, and Gabriel Seyfarth
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Superconductivity ,Physics ,Condensed matter physics ,General Physics and Astronomy ,02 engineering and technology ,Tourbillon ,Heavy fermion superconductor ,021001 nanoscience & nanotechnology ,01 natural sciences ,Vortex state ,Vortex ,Magnetic field ,Thermal conductivity ,Condensed Matter::Superconductivity ,Heavy fermion ,0103 physical sciences ,010306 general physics ,0210 nano-technology - Abstract
The thermal conductivity of the heavy fermion superconductor PrOs4Sb12 was measured down to Tc/40 throughout the vortex state. At lowest temperatures and for magnetic fields H ~ 0.07Hc2, already 40% of the normal state thermal conductivity is restored. This behaviour (similar to that observed in MgB2) is a clear signature of multiband superconductivity in this compound.
- Published
- 2005
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45. Direct Observation of Quadrupolar Excitons in the Heavy-Fermion SuperconductorPrOs4Sb12
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Yuji Aoki, M. Kohgi, Stéphane Raymond, Naoto Metoki, Keitaro Kuwahara, Jacques Flouquet, Hideyuki Sato, Hitoshi Sugawara, Kazuaki Iwasa, Koji Kaneko, and Marie-Aude Méasson
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Superconductivity ,Physics ,Condensed matter physics ,Exciton ,General Physics and Astronomy ,Heavy fermion superconductor ,Inelastic neutron scattering ,Modulation ,Condensed Matter::Superconductivity ,Dispersion relation ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,Atomic physics ,Excitation - Abstract
We report inelastic neutron scattering experiments performed to investigate the low energy magnetic excitations on single crystals of the heavy-fermion superconductor PrOs(4)Sb(12). The observed excitation clearly softens at a wave vector Q=(1,0,0), which is the same as the modulation vector of the field-induced antiferro-quadrupolar ordering, and its intensity at Q=(1,0,0) is smaller than that around the zone center. This result directly evidences that this excitonic behavior is derived mainly from nonmagnetic quadrupolar interactions. Furthermore, the narrowing of the linewidths of the excitations below the superconducting transition temperature indicates the close connection between the superconductivity and the excitons.
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- 2005
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46. Evolution of4felectron states in the metal-insulator transition ofPrRu4P12
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Shanta Saha, Kazuaki Iwasa, Keitaro Kuwahara, Toshiro Sakakibara, Hideyuki Sato, Takashi Tayama, Masahumi Kohgi, Hitoshi Sugawara, Yuji Aoki, and Lijie Hao
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Physics ,Condensed matter physics ,Electron ,Electronic structure ,engineering.material ,Inelastic scattering ,Condensed Matter Physics ,Inelastic neutron scattering ,Spectral line ,Electronic, Optical and Magnetic Materials ,engineering ,Skutterudite ,Metal–insulator transition ,Atomic displacement - Abstract
Magnetic excitations of the filled skutterudite $\mathrm{Pr}{\mathrm{Ru}}_{4}{\mathrm{P}}_{12}$ exhibiting a metal-insulator (M-I) transition at ${T}_{\mathrm{M}\text{\ensuremath{-}}\mathrm{I}}=63\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ were studied by inelastic neutron scattering experiment. The spectra at temperatures much lower than ${T}_{\mathrm{M}\text{\ensuremath{-}}\mathrm{I}}$ are described as well-defined crystal-field excitations. With approaching ${T}_{\mathrm{M}\text{\ensuremath{-}}\mathrm{I}}$, the excitation peaks broaden and shift considerably together with the temperature variation of the carrier number and the atomic displacement in the transition. The $4f$ electron states evolve from the well-localized state in the insulator phase to the strongly hybridized itinerant state by $p\text{\ensuremath{-}}f$ mixing near ${T}_{\mathrm{M}\text{\ensuremath{-}}\mathrm{I}}$. The hybridization is responsible for the M-I transition of $\mathrm{Pr}{\mathrm{Ru}}_{4}{\mathrm{P}}_{12}$.
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- 2005
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47. Fermi surface ofLaRu4P12: A clue to the origin of the metal-insulator transition inPrRu4P12
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Hiroaki Shishido, Yoshihiko Inada, Yoshichika Ōnuki, Shanta Saha, Hitoshi Sugawara, Yuji Aoki, Hisatomo Harima, Hideyuki Sato, and Rikio Settai
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Mass enhancement ,Physics ,Superconductivity ,Magnetoresistance ,Condensed matter physics ,Fermi surface ,Strongly correlated material ,Metal–insulator transition ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials - Abstract
We report the de Haas--van Alphen (dHvA) effect and magnetoresistance in the filled-skutterudite superconductor ${\mathrm{LaRu}}_{4}{\mathrm{P}}_{12}$, which is a reference material of ${\mathrm{PrRu}}_{4}{\mathrm{P}}_{12}$ that exhibits a metal-insulator (M-I) transition at ${T}_{\mathrm{MI}}\ensuremath{\simeq}60\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The observed dHvA branches for the main Fermi surface (FS) are well explained by the band-structure calculation, using the full potential linearized augmented-plane-wave method with the local-density approximation, suggesting a nesting instability with $\mathbf{q}=(1,0,0)$ in the main multiply connected FS as expected also in ${\mathrm{PrRu}}_{4}{\mathrm{P}}_{12}$. Observed cyclotron effective masses of $(2.6\ensuremath{-}11.8){m}_{0}$, which are roughly twice the calculated masses, indicate the large mass enhancement even in the La-skutterudites. Comparing the FS between ${\mathrm{LaRu}}_{4}{\mathrm{P}}_{12}$ and ${\mathrm{PrRu}}_{4}{\mathrm{P}}_{12}$, an essential role of $c\text{\ensuremath{-}}f$ hybridization cooperating with the FS nesting in driving the M-I transition in ${\mathrm{PrRu}}_{4}{\mathrm{P}}_{12}$ is clarified.
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- 2005
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48. Transport properties inCeOs4Sb12: Possibility of the ground state being semiconducting
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Miki Kobayashi, S. Osaki, Hideyuki Sato, Shanta Saha, T. Namiki, Hitoshi Sugawara, and Yuji Aoki
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Physics ,Phase transition ,Condensed matter physics ,Magnetoresistance ,Hall effect ,Spin density wave ,Strongly correlated material ,Kondo effect ,Condensed Matter Physics ,Ground state ,Electronic, Optical and Magnetic Materials ,Phase diagram - Abstract
We have measured both magnetoresistance and Hall effect in $\mathrm{Ce}{\mathrm{Os}}_{4}{\mathrm{Sb}}_{12}$ to clarify the large resistivity state ascribed to the Kondo insulating one and the origin of the phase transition near $0.9\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ reported in the specific-heat measurement. We found unusual temperature $(T)$ dependence both in the electrical resistivity $\ensuremath{\rho}\ensuremath{\sim}{T}^{\ensuremath{-}1∕2}$ and the Hall coefficient ${R}_{H}\ensuremath{\sim}{T}^{\ensuremath{-}1}$ over the wide temperature range of about two orders of magnitude below $\ensuremath{\sim}30\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, which can be explained as a combined effect of the temperature dependences of carrier density and carrier scattering by spin fluctuation. An anomaly related with the phase transition has been clearly observed in the transport properties, from which the $H\text{\ensuremath{-}}T$ phase diagram is determined up to $14\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. Taking into account the small entropy change, the phase transition is most probably the spin density wave one. Both the electrical resistivity and Hall resistivity at $0.3\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is largely suppressed about an order of magnitude by magnetic fields above $\ensuremath{\sim}3\phantom{\rule{0.3em}{0ex}}\mathrm{T}$, suggesting a drastic change of electronic structure and a suppression of spin fluctuations under magnetic fields.
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- 2005
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49. Pressure-induced metal-insulator transition in the filled skutteruditePrFe4P12
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Ikuma Ando, Tatsuo C. Kobayashi, Miki Kobayashi, H. Hidaka, Hideyuki Sato, Hisatomo Harima, Hisashi Kotegawa, and Hitoshi Sugawara
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Superconductivity ,Physics ,Condensed matter physics ,engineering.material ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Electrical resistivity and conductivity ,engineering ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,Strongly correlated material ,Kondo effect ,Skutterudite ,Metal–insulator transition ,Phase diagram - Abstract
We have studied the electrical resistivity of the filled skutterudite compound $\mathrm{Pr}{\mathrm{Fe}}_{4}{\mathrm{P}}_{12}$ under high pressure. The antiferroquadrupolar ordering temperature ${T}_{Q}$ decreases monotonically with increasing pressure up to $2.4\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. Above $2.4\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, we have found that a metal-insulator $(M\text{\ensuremath{-}}I)$ transition appears. The insulating state is easily suppressed by a magnetic field. The observed Kondo effect and a field-induced heavy-fermion state at high pressure suggest that the quadrupolar interactions survive in the insulating region. The quadrupolar interactions might play an essential role in the $M\text{\ensuremath{-}}I$ transition. $\mathrm{Pr}{\mathrm{Fe}}_{4}{\mathrm{P}}_{12}$ is an unusual compound in that it shows a pressure-induced transition from a metal to an insulator.
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- 2005
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50. Static and dynamical properties in the Pr-based filled skutterudite compoundPrFe4P12revealed by aP31-NMR study
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Ben-Li Young, M. S. Rose, D. E. MacLaughlin, Yasuo Kitaoka, Hisatomo Harima, Kentaro Kitagawa, H. Kotegawa, Keiichi Ishida, Mamoru Yogi, Hitoshi Sugawara, Yoshihiko Ihara, Tatsuma D. Matsuda, Hideyuki Sato, Hiroshi Murakawa, and Yuji Aoki
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Physics ,Condensed matter physics ,Magnetism ,Spin–lattice relaxation ,Antiferromagnetism ,Kondo effect ,Condensed Matter Physics ,Ground state ,Coupling (probability) ,Critical field ,Hyperfine structure ,Electronic, Optical and Magnetic Materials - Abstract
$^{31}\mathrm{P}$-NMR studies have been carried out to investigate magnetic properties in the Pr-based filled skutterudite compound $\mathrm{Pr}{\mathrm{Fe}}_{4}{\mathrm{P}}_{12}$. This compound shows an unusual phase transition at ${T}_{A}\ensuremath{\sim}6.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, which is now regarded as antiferroquadrupole (AFQ) ordering from neutron-diffraction experiments. Splitting of the P-NMR spectrum due to the appearance of two P sites with different hyperfine fields was observed below ${T}_{A}$. From the field dependence, the splitting seems to disappear in zero magnetic field, indicating that the different hyperfine fields are not due to magnetic order, but to the appearance of two inequivalent P sites below ${T}_{A}$. This is ascribed to the distortion of the P cage surrounding a Pr ion below ${T}_{A}$, which is associated with the Pr orbital ordering. The nuclear spin-lattice relaxation rate $(1∕{T}_{1})$ shows the typical behavior of Kondo systems, where onset of local-moment screening due to the coupling between conduction and localized $\mathrm{Pr}\text{\ensuremath{-}}4f$ electrons is observed below $50\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Far above a critical field ${H}_{A}\ensuremath{\sim}50\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$, the Korringa behavior ${T}_{1}T=\mathrm{const}$ is observed below $2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in $100\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$. The Korringa value below $2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is one order of magnitude larger than that in $\mathrm{La}{\mathrm{Fe}}_{4}{\mathrm{P}}_{12}$, which has no $4f$ electrons. Our NMR experiment shows that the heavy-fermion state is realized far above ${H}_{A}$ in $\mathrm{Pr}{\mathrm{Fe}}_{4}{\mathrm{P}}_{12}$. The magnetic fluctuations in $\mathrm{Pr}{\mathrm{Fe}}_{4}{\mathrm{P}}_{12}$ are discussed from a comparison with typical heavy-fermion compounds. In magnetic fields below ${H}_{A}$, $1∕{T}_{1}$ shows a sharp decrease below ${T}_{A}$, however, in smaller magnetic fields less than $10\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$, $1∕{T}_{1}$ stays constant far below ${T}_{A}$ with a relatively large value. The temperature and field dependence of $1∕{T}_{1}$ reveals the presence of low-energy spin fluctuations in the low-temperature and low-field region. These unusual magnetic fluctuations are considered to originate from the magnetic dynamics of Pr-nuclear spins since the fluctuating magnetic field $\ensuremath{\sim}1.4\phantom{\rule{0.3em}{0ex}}\mathrm{Oe}$ and frequency $\ensuremath{\sim}3.5\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$ are so small. The nuclear ordering temperature is estimated to be $\ensuremath{\sim}0.08\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$ using the nuclear exchange fluctuations derived from the observed $1∕{T}_{1}$ of P. We show that $\mathrm{Pr}{\mathrm{Fe}}_{4}{\mathrm{P}}_{12}$ is a quite unique compound in which nuclear magnetism can be detected by P NMR thanks to the nonmagnetic ground state of the $\mathrm{Pr}\text{\ensuremath{-}}4f$ moments.
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- 2005
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