Language：Japanese   Publishing type：Research paper (scientific journal)  

結晶育成技術の進展によりユウロピウム（Eu）化合物の物性が次々に明らかになってきている。Eu イオンの価数揺動に関する研究の歴史は長く，これまで半世紀以上におよび精力的に行われてきた.しかし実際に価数揺動や価数転移が報告されている物質はそれほど多くはなく，またそのほとんどが多結晶試料による研究であった.Eu化合物における価数揺動や価数転移の詳細な研究が難しい理由の一つに，試料育成の難しさがある.特にEu元素は蒸気圧が高く酸化も激しい,また対象物質は融点が高いものが多い.これまで重い電子系化合物の研究で蓄積された知識や技術をEu化合物の単結晶育成に適用しEu化合物の純良単結晶試料が最近多く育成されるようになってきた.また原子間距離を精密に制御可能な高圧力発生技術や圧力下での測定技術の進歩により，微妙に相互作用を変化させ,結晶育成だけでは探索できない次元でのEu化合物の電子物性の研究が可能になった.おもに著者らの最近の研究結果をレビューした.

DOI： https://doi.org/10.11316/butsuri.78.1_28

Publisher：Journal of the Physical Society of Japan  

We report the re-measurement of the a-axis spin susceptibility component in an early-stage sample of the spin-triplet superconductor UTe2 with the transition temperature of TSC = 1.6 K.Using Knight-shift measurements along the b axis and at a 10-degree tilt from the b axis towards the a axis, we accurately determined the a-axis component without directly measuring the a-axis Knight shift.Our results reveal a decrease of approximately 3% in the a-axis spin susceptibility in the superconducting state under a-axis magnetic field μ0 Ha ∼ 0.1 T, indicating that the spin susceptibility decreases similarly in both early-stage and ultraclean samples with TSC = 2.1 K.The previously reported absence of the reduction in Knight shift is attributed to the missing of signal from the superconducting region and to the detection of residual signals from the non-superconducting region instead.We also found that the decrease in the a-axis spin susceptibility is immediately suppressed with increasing the a-axis magnetic field and is estimated to be completely suppressed at around 1.5 T due to superconducting spin rotation.

DOI： 10.7566/JPSJ.93.123701

Scopus

Publisher：Journal of the Physical Society of Japan  

We succeeded in growing single crystals of Eu2Ga3Ir by the Bridgman method using a sealed Mo crucible, and measured the electrical resistivity, specific heat, magnetic susceptibility, magnetization, Mössbauer spectrum, and electrical resistivity under pressure, revealing a Eu2+-antiferromagnetic state with a Néel temperature TN = 18K.

DOI： 10.7566/JPSJ.93.115001

Scopus

Publisher：Physical Review Materials  

We demonstrate a close connection between the quantum critical point (QCP) and superconducting upper critical field Hc2 in the Ni-doped heavy-fermion superconductor CeCoIn5. Temperature variations of electrical resistivity ρ(T) exhibit a crossover between the non-Fermi liquid and the Fermi liquid states, whose boundary for T→0, regarded as the QCP, coincides with Hc2, while Hc2 decreases to zero with increasing Ni concentrations up to 25%. Furthermore, the A coefficient of the T2 term in ρ(T) estimated in the Fermi liquid region shows the diverging behavior with decreasing the magnetic field H toward Hc2. These experimental results suggest that the emergence of the QCP is always accompanied by the breakdown of the superconducting state by H in Ni-doped CeCoIn5.

DOI： 10.1103/PhysRevMaterials.8.L081801

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Scopus

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7566/jpscp.38.011029

Other Link： https://journals.jps.jp/doi/10.7566/JPSCP.38.011029

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7566/jpscp.38.011108

Other Link： https://journals.jps.jp/doi/10.7566/JPSCP.38.011108

Publisher：Journal of the Physical Society of Japan  

We studied in detail the electrical and magnetic properties of the Eu-divalent antiferromagnet EuTe2 with a tetragonal crystal structure using single crystals grown by the Te self-flux method. The observed anisotropic magnetization curves in the antiferromagnetic state below TN = 11.1K can be understood in terms of the magnetization processes of the two-sublattice model of an antiferromagnet with uniaxial magnetic anisotropy. A characteristic feature of this compound is that it becomes an insulator with decreasing temperature at zero magnetic field, but changes to a metal with a relatively low number of carriers in magnetic fields. From the results of magnetization, magnetoresistance, and Hall resistivity measurements in magnetic fields up to μ0H = 40T, the insulator–metal transition was found to occur when the magnetization reaches ∼2μB=Eu for both H k ½110] and [001] at measurement temperatures above 50K. Energy band calculations revealed that only the up-spin band, which is mainly composed of Te-5p electrons, crosses the Fermi level in the ferromagnetic state, although the energy band possesses a band gap in the paramagnetic and antiferromagnetic states.

DOI： 10.7566/JPSJ.93.044708

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Scopus

Publisher：Physical Review B  

The electrical resistivity of the unconventional superconductor UTe2 shows very anisotropic behavior in the normal state depending on the current direction. In this paper we show that the maximum in the resistivity ρc for current applied along the c axis at Tρcmax≈14.75 K follows the minimum in the thermal expansion Tα★ along the b axis. Under a magnetic field applied along the b axis, Tρcmax can be tracked up to the critical point of the first-order metamagnetic transition, which is located near 6 K and 34.5 T. Surprisingly, at the metamagnetic field Hm the resistivity ρc shows a steplike decrease while the resistivities ρa and ρb, for current along the a and b axes, respectively, show a steplike increase. Under hydrostatic pressure Tρcmax and Hm decrease significantly up to the critical pressure pc at which superconductivity is suppressed and a long-range antiferromagnetic order appears. We show that the phase diagram at different pressures can be scaled by Tρcmax in field and temperature, suggesting that this temperature scale is governing the main interactions in the normal state.

DOI： 10.1103/PhysRevB.109.155103

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physics and Chemistry of Minerals  

The characteristic behavior of magnetic remanence correlated with mineralogical textures and composition was observed using low-temperature magnetometry, microscopy, and chemical analysis of three isocubanite samples collected from hydrothermal deposits in the Okinawa Trough and a sample transformed from natural cubanite via heating. Both zero-field remanence acquired at 5 K and field cooling remanence acquired at 300–5 K of all samples sharply decreased with increasing temperature at approximately 100 K. In addition, low-temperature cycling of isothermal remanence at 300 K exhibited a transition at approximately 100 K; remanence increased with decreasing temperature and vice versa. The intensity of remanence at low temperature and sharpness of the transition varied across samples with different compositions and microscopic textures, that is, the presence or absence of chalcopyrite lamellae and their widths. The sample obtained from a hydrothermal chimney, in which the magnetic transition was most clearly observed, was also subjected to X-ray diffraction, Mössbauer spectroscopy, electrical resistivity, and magnetic hysteresis measurements. The obtained results were generally consistent with those reported previously for unnamed mineral CuFe3S4 with an ordered cation arrangement. The low-temperature magnetic behavior of isocubanite possibly depends on the degree of cation ordering and can be regarded as an indicator of chemical composition and cooling history. Therefore, low-temperature magnetometry is useful for the detection of isocubanite and a potentially powerful technique for the prompt estimation of its composition and texture, contributing to our understanding of the formation process of hydrothermal deposits.

DOI： 10.1007/s00269-023-01264-3

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Scopus

Other Link： https://doi.org/10.1007/s00269-023-01264-3

Language：English   Publishing type：Research paper (scientific journal)  

We studied in detail the electrical and magnetic properties of the Eu-divalent antiferromagnet EuTe2 with a tetragonal crystal structure using single crystals grown by the Te self-flux method. The observed anisotropic magnetization curves in the antiferromagnetic state below TN = 11.1 K can be understood in terms of the magnetization processes of the two-sublattice model of an antiferromagnet with uniaxial magnetic anisotropy. A characteristic feature of this compound is that it becomes an insulator with decreasing temperature at zero magnetic field, but changes to a metal with a relatively low number of carriers in magnetic fields. From the results of magnetization, magnetoresistance, and Hall resistivity measurements in magnetic fields up to μ0H = 40 T, the insulator–metal transition was found to occur when the magnetization reaches ∼2 μB/Eu for both 𝐻∥[110]
and [001] at measurement temperatures above 50 K. Energy band calculations revealed that only the up-spin band, which is mainly composed of Te-5p electrons, crosses the Fermi level in the ferromagnetic state, although the energy band possesses a band gap in the paramagnetic and antiferromagnetic states.

DOI： doi.org/10.7566/JPSJ.93.044708

Other Link： https://journals.jps.jp/doi/10.7566/JPSJ.93.044708

Language：English   Publisher：Springer  

The characteristic behavior of magnetic remanence correlated with mineralogical textures and composition was observed using low-temperature magnetometry, microscopy, and chemical analysis of three isocubanite samples collected from hydrothermal deposits in the Okinawa Trough and a sample transformed from natural cubanite via heating. Both zero-field remanence acquired at 5 K and field cooling remanence acquired at 300–5 K of all samples sharply decreased with increasing temperature at approximately 100 K. In addition, low-temperature cycling of isothermal remanence at 300 K exhibited a transition at approximately 100 K; remanence increased with decreasing temperature and vice versa. The intensity of remanence at low temperature and sharpness of the transition varied across samples with different compositions and microscopic textures, that is, the presence or absence of chalcopyrite lamellae and their widths. The sample obtained from a hydrothermal chimney, in which the magnetic transition was most clearly observed, was also subjected to X-ray diffraction, Mössbauer spectroscopy, electrical resistivity, and magnetic hysteresis measurements. The obtained results were generally consistent with those reported previously for unnamed mineral CuFe_3S_4 with an ordered cation arrangement. The low-temperature magnetic behavior of isocubanite possibly depends on the degree of cation ordering and can be regarded as an indicator of chemical composition and cooling history. Therefore, low-temperature magnetometry is useful for the detection of isocubanite and a potentially powerful technique for the prompt estimation of its composition and texture, contributing to our understanding of the formation process of hydrothermal deposits.

CiNii Research

Publisher：New Physics: Sae Mulli  

Electronic properties of a new ternary f-electron system RPt3Al5 (R: rare earth elements) have been investigated. RPt3Al5 crystalizes in the CePt3Al5-type orthorhombic structure where R atoms form 1-dimensional chains along the b-axis. LaPt3Al5 shows superconductivity below 0.4 K, while others show magnetic ordering. CePt3Al5 orders antiferromagnetically below TN = 1.2 K with spontaneous moment and shows successive magnetic transition at Tm = 0.9 K. The nearly divalent antiferromagnet EuPt3Al5 indicates an unusual valence cross-over behavior into the nearly trivalent state under high pressure of 9 GPa. It is also found that most of RPt3Al5 orders antiferromagnetically and, in some cases, shows characteristic features in magnetic suscep- tibility, where the broad maximum appears slightly above TN, reecting the low-dimensional nature.

DOI： 10.3938/NPSM.73.1135

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Electronic Structure  

The electronic structure of the f-based superconductor C e I r 3 was studied by photoelectron spectroscopy. The energy distribution of the C e 4 f states were revealed by the C e 3 d − 4 f resonant photoelectron spectroscopy. The C e 4 f states were mostly distributed in the vicinity of the Fermi energy, suggesting the itinerant character of the C e 4 f states. The contribution of the C e 4 f states to the density of states (DOS) at the Fermi energy was estimated to be nearly half of that of the I r 5 d states, implying that the C e 4 f states have a considerable contribution to the DOS at the Fermi energy. The C e 3 d core-level and C e 3 d x-ray absorption spectra were analyzed based on a single-impurity Anderson model. The number of the C e 4 f states in the ground state was estimated to be 0.8 − 0.9 , which is much larger than the values obtained in the previous studies (i.e. 0 − 0.4 ).

DOI： 10.1088/2516-1075/ad0a3d

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Scopus

Other Link： https://iopscience.iop.org/article/10.1088/2516-1075/ad0a3d

Language：English   Publisher：Science Advances  

Superconducting (SC) state has spin and orbital degrees of freedom, and spin-triplet superconductivity shows multiple SC phases because of the presence of these degrees of freedom. However, the observation of spindirection rotation occurring inside the SC state (SC spin rotation) has hardly been reported. Uranium ditelluride, a recently found topological superconductor, exhibits various SC phases under pressure: SC state at ambient pressure (SC1), high-temperature SC state above 0.5 gigapascal (SC2), and low-temperature SC state above 0.5 gigapascal (SC3). We performed nuclear magnetic resonance (NMR) and ac susceptibility measurements on a single-crystal uranium ditelluride. The b axis spin susceptibility remains unchanged in SC2, unlike in SC1, and decreases below the SC2-SC3 transition with spin modulation. These unique properties in SC3 arise from the coexistence of two SC order parameters. Our NMR results confirm spin-triplet superconductivity with SC spin parallel to b axis in SC2 and unveil the remaining of spin degrees of freedom in SC uranium ditelluride.

DOI： 10.1126/sciadv.adg2736

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PubMed

Language：English   Publisher：American Association for the Advancement of Science (AAAS)  

Superconducting (SC) state has spin and orbital degrees of freedom, and spin-triplet superconductivity shows multiple SC phases because of the presence of these degrees of freedom. However, the observation of spin-direction rotation occurring inside the SC state (SC spin rotation) has hardly been reported. Uranium ditelluride, a recently found topological superconductor, exhibits various SC phases under pressure: SC state at ambient pressure (SC1), high-temperature SC state above 0.5 gigapascal (SC2), and low-temperature SC state above 0.5 gigapascal (SC3). We performed nuclear magnetic resonance (NMR) and ac susceptibility measurements on a single-crystal uranium ditelluride. The b axis spin susceptibility remains unchanged in SC2, unlike in SC1, and decreases below the SC2-SC3 transition with spin modulation. These unique properties in SC3 arise from the coexistence of two SC order parameters. Our NMR results confirm spin-triplet superconductivity with SC spin parallel to b axis in SC2 and unveil the remaining of spin degrees of freedom in SC uranium ditelluride.

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Physical Society of Japan  

Spin susceptibility in the superconducting (SC) state was measured in the higher-quality sample of uranium-based superconductor UTe2 by using Knight-shift measurements for a magnetic field H along all three crystalline axes. In the higher-quality sample, the SC transition temperature Tc is about 2.1 K, and the residual electronic term in the specific heat is almost zero. The NMR linewidth becomes narrower and is almost half of that in the previous sample with Tc ∼ 1.6 K when H ∥ a and c. Although the Knight-shift behavior was not so different from the previous results for H ∥ b, and c, a large reduction in Knight shift along the a axis was observed, in contrast with the previous a-axis Knight shift result. We discuss the origin of the difference between the previous and present results, and the possible SC state derived from the present results.

DOI： 10.7566/JPSJ.92.063701

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Other Link： https://journals.jps.jp/doi/10.7566/JPSJ.92.063701

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Physical Society of Japan  

In this study, we observed bulk superconductivity in LaNiZn below Tc = 1.5 K, as confirmed by its electrical transport and specific heat capacity (ΔCel=γTc = 1.41). The upper critical fields along the hexagonal crystallographic c-axis and in the basal plane at 30 mK were found to be 0.36 and 0.24 T, respectively, suggesting mainly an orbital mechanism for field-induced depairing and a negligible spin triplet component in the superconducting order parameter. The angular dependence of Hc2 is explained by an effective mass model with an oblate-shaped effective Fermi surface. Our experimental and band calculation under local density approximation results suggested that LaNiZn is a Bardeen– Cooper–Schrieffer s-wave-type superconductor in the dirty limit, possibly involving multiple bands.
Letters

DOI： 10.7566/JPSJ.92.043703

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Scopus

Language：Japanese   Publisher：The Physical Society of Japan  

<p>Recent technological advances in growing single crystal samples of Eu compounds have boosted progress in the research field on valance fluctuation and /or transition of the Eu compounds. Here, we review the electronic states of single-crystalline EuT₂X₂ (T: transition metal, X: Si or Ge) and related compounds, together with the effect of pressure on these compounds. The rare-earth ions are usually trivalent, but a divalent (Eu²⁺) electronic state is more stable than a trivalent (Eu³⁺) one in the Eu-based metallic compounds. The energy difference between the Eu²⁺ and Eu³⁺ states is, however, not very large. Therefore, it is possible to change the Eu valence from nearly divalent (Eu²⁺) to nearly trivalent (Eu³⁺) by applying pressure. Here we show several characteristic features of Eu compounds under pressure: the magnetic order is suppressed, as revealed by the Doniach phase diagram, the magnetic order changes to the first-order valence transition above a critical pressure, and the moderate heavy-fermion state appears around the magnetic quantum critical point. Recently, a new phase diagram for the Eu compounds was found under pressure, which might be due to a sharp valence crossover induced by pressure.</p>

DOI： 10.11316/butsuri.78.1_28

CiNii Research

Publisher：Journal of Magnetism and Magnetic Materials  

The results of ac and dc susceptibilities, magnetization, magnetic relaxation, electrical resistivity, and specific heat measurements performed on a hexagonal AlB2-type single-crystalline U2PtSi3 are reported. The previously reported spin-glass transition in polycrystalline U2PtSi3 was confirmed to also occur in the single-crystalline sample with spin freezing temperature Tf=12.4 K. It is newly found that the spin-glass effect and magnetic behavior of U2PtSi3 measured along and perpendicular to the hexagonal c-axis show different magnetic field responses. Along the hard magnetization axis (c-axis), both the rate of change of Tf with the magnetic field and the detected magnetic viscosity coefficient are much smaller than those obtained in the c-plane. On the other hand, the low-temperature specific heat measurement yields an enhanced coefficient of the linear temperature term, and the temperature dependence of electrical resistivity illustrates a shallow minimum at the temperature much larger than Tf. The possible mechanisms for these phenomena are discussed by comparing with the corresponding properties observed in other ternary 2:1:3 uranium intermetallic compounds.

DOI： 10.1016/j.jmmm.2022.169820

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Physical Society of Japan  

We report the single-crystal growth and comparative Fermi surface studies of LaPd2Si2 via de Haas–van Alphen (dHvA) experiments and theoretical band structure calculations, as a non-magnetic reference for pressure-induced heavy-fermion superconductor CePd2Si2. We grew the single crystals of LaPd2Si2 using the Czochralski and floating zone method. High-quality single crystals of LaPd2Si2 were obtained using the floating zone method, and clear dHvA signals were detected. We detected main Fermi surfaces in angular dependence measurements of the dHvA frequencies, revealing a good agreement with the result of band structure calculations based on the localized-4f electron model. From our dHvA measurements using the high-quality single crystal, as well as our theoretical band structure calculations, we conclude that the 4f electrons in CePd2Si2 are itinerant rather than localized in an intermediate antiferromagnetic state.

DOI： 10.7566/JPSJ.91.114708

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Scopus

Other Link： https://journals.jps.jp/doi/abs/10.7566/JPSJ.91.114708

Publisher：Journal of Magnetism and Magnetic Materials  

We investigated the electronic properties of Yb4Ru7As6 using single crystalline samples grown by the Bi-flux method. Yb4Ru7As6 crystallizes in the cubic U4Re7Si6-type structure. From the electrical resistivity, magnetic susceptibility, and specific heat measurements, we have found that Yb4Ru7As6 orders antiferromagnetically below the Néel temperature of 2.5 K with the moderately enhanced electronic specific heat coefficient of 120 mJ/(Yb-mol⋅K2). A rapid increment in magnetization of about 0.25 μB/Yb has been detected at low magnetic field below 4 K, implying a weak ferromagnetic component.

DOI： 10.1016/j.jmmm.2022.169327

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Language：English   Publishing type：Research paper (scientific journal)  

We investigated the electronic properties of Yb4Ru7As6 using single crystalline samples grown by the Bi-flux method. Yb4Ru7As6 crystallizes in the cubic U4Re7Si6-type structure. From the electrical resistivity, magnetic susceptibility, and specific heat measurements, we have found that Yb4Ru7As6 orders antiferromagnetically below the Néel temperature of 2.5 K with the moderately enhanced electronic specific heat coefficient of 120 mJ/(Yb-mol K2). A rapid increment in magnetization of about 0.25μB/Yb has been detected at low magnetic field below 4 K, implying a weak ferromagnetic component.

DOI： https://doi.org/10.1016/j.jmmm.2022.169327

Other Link： https://www.sciencedirect.com/science/article/pii/S0304885322002712?casa_token=yg-FUjSU-ocAAAAA:3BMd2NSF2fRPGXlki-I4IxzDCee4xba_wOrHkTGhInXvaTK3QWJGuaTSE8hgVDPUr8c4HgJUGQ

Language：English   Publishing type：Research paper (scientific journal)  

The results of ac and dc susceptibilities, magnetization, magnetic relaxation, electrical resistivity, and specific heat measurements performed on a hexagonal AlB2-type single-crystalline U2PtSi3 are reported. The previously reported spin-glass transition in polycrystalline U2PtSi3 was confirmed to also occur in the single-crystalline sample with spin freezing temperature 𝑇𝑓 =12.4 K. It is newly found that the spin-glass effect and magnetic behavior of U2PtSi3 measured along and perpendicular to the hexagonal 𝑐-axis show different magnetic field responses. Along the hard magnetization axis (𝑐-axis), both the rate of change of 𝑇𝑓 with the magnetic field and the detected magnetic viscosity coefficient are much smaller than those obtained in the 𝑐-plane. On the other hand, the low-temperature specific heat measurement yields an enhanced coefficient of the linear temperature term, and the temperature dependence of electrical resistivity illustrates a shallow minimum at the temperature much larger than 𝑇𝑓 . The possible mechanisms for these phenomena are discussed by comparing with the corresponding properties observed in other ternary 2:1:3 uranium intermetallic compounds.

DOI： https://doi.org/10.1016/j.jmmm.2022.169820

Other Link： https://www.sciencedirect.com/science/article/pii/S0304885322007120

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Physical Society of Japan  

The link between the metamagnetic transition and novel spin-triplet superconductivity of UTe2 was discussed thermodynamically through magnetostriction measurements in a pulsed-magnetic field. We revealed a discontinuous magnetostriction across the metamagnetic transition at μ0Hm ≈ 35 T for the applied magnetic fields along the crystallographic b axis in the orthorhombic structure. The resultant volume magnetostriction of ΔV/V ≈ −5.9 × 10-4 gives the initial pressure dependence of Hm by employing the Clausius–Clapeyron’s equation, which agrees with previous pressure experiments. Further, significant anisotropic magnetostriction (AMS), derived by subtracting the averaged linear magnetostriction, was revealed. Contrary to the weakly field-dependent AMS along the a axis, those along the b and c axes show strong field dependences with a similar magnitude but with opposite signs, indicating its lattice instability. The relationship between characteristic energy scales of magnetic fields and temperatures was discussed in terms of the Grüneisen parameters compared to the other f-electron systems. The volume shrinkage in UTe2 at Hm, contrary to the volume expansion in typical heavy fermion metamagnets, pushes to invoke the link with the valence instability related to the itinerant-localized dual nature of the U magnetism.

DOI： 10.7566/JPSJ.91.063703

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Scopus

Other Link： https://journals.jps.jp/doi/full/10.7566/JPSJ.91.063703

Publisher：Journal of the Physical Society of Japan  

This study investigates the spin susceptibility in U-based superconductor UTe2 in the superconducting (SC) state by using Knight shift measurements for a magnetic field H along the a axis, which is the magnetic easy axis of UTe2. Although a tiny anomaly ascribed to the SC diamagnetic effect was observed just below the SC transition temperature Tc, the a-axis Knight shift in the SC state shows no significant decrease, following the extrapolation from the normal-state temperature dependence. This indicates that the spin susceptibility is nearly unchanged below Tc. Considering the previous Knight shift results for H ∥ b and H ∥ c, the dominant SC state is determined to be B3u in the spin-triplet pairing, which is consistent with the spin anisotropy in the normal state. The present result shows that UTe2 is a spin-triplet superconductor with spin degrees of freedom.

DOI： 10.7566/JPSJ.91.043705

Scopus

Publisher：Journal of the Physical Society of Japan  

We successfully grew single crystals of a new ternary Eu-divalent compound, EuPt3Al5, with an orthorhombic structure (Pnma, #62) using the Bridgman method. EuPt3Al5 orders antiferromagnetically below TN = 12.4 K. TN increases monotonically with increasing pressure up to 8.0 GPa, decreases slightly at 8.5 GPa, and suddenly becomes zero above 9.5 GPa. From the results of low-temperature dependences of electrical and residual resistivities, a sudden disappearance of the antiferromagnetic ordering occurs with a dramatic change in the Eu electronic states from the nearly divalent state to the valence fluctuating state at Pc ≈ 9 GPa. EuPt3Al5 is most likely the second material exhibiting an abrupt valence crossover in Eu compounds after EuCu2Ge2

DOI： 10.7566/JPSJ.91.043704

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Scopus

Publisher：Physical Review B  

To investigate the normal-state magnetic properties of UTe2 under pressure, we perform Te125 nuclear magnetic resonance (NMR) measurements up to 2 GPa. Below 1.2 GPa, the b-axis NMR Knight shift shows a broad maximum at the so-called Tχmax on cooling, which is consistent with the magnetization measurement under pressure. Tχmax decreases with increasing pressure and disappears at the critical pressure Pc = 1.7 GPa, above which superconductivity is destroyed. This tendency is also observed in the temperature dependence of the nuclear spin-lattice relaxation rate 1/T1. At low pressures, 1/T1 shows a conventional Fermi-liquid behavior (1/T1T=const) at low temperatures, indicating the formation of the heavy-fermion state. Above Pc, 1/T1T follows a 1/T behavior without any crossover to the heavy-fermion state down to the lowest temperature (∼3 K). In addition, the NMR signals disappear below 3 K, due to the influence of the magnetically ordered moments. From the pressure dependence of the Tχmax and Knight shift, it was found that the Fermi surface character is abruptly changed at Pc, and that superconductivity is observed only in the heavy-fermion state.

DOI： 10.1103/PhysRevB.105.L140502

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1103/PhysRevB.105.L140502

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.7566/JPSJ.91.043705

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://journals.jps.jp/doi/10.7566/JPSJ.91.043704

Publisher：Journal of the Physical Society of Japan  

125Te NMR experiments in field (H) applied along the easy magnetization axis (the a-axis) revealed slow electronic dynamics developing in the paramagnetic state of UTe2. The observed slow fluctuations are concerned with a successive growth of long-range electronic correlations below 30-40 K, where the spin susceptibility along the hard magnetization axis (the b-axis) shows a broad maximum. The experiments also imply that tiny amounts of disorder or defects locally disturb the long-range electronic correlations and develop an inhomogeneous electronic state at low temperatures, leading to a low temperature upturn observed in the bulk-susceptibility in H Π a. We suggest that UTe2 would be located on the paramagnetic side near an electronic phase boundary, where either magnetic or Fermi-surface instability would be the origin of the characteristic fluctuations.

DOI： 10.7566/JPSJ.91.023707

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://journals.jps.jp/doi/10.7566/JPSJ.91.023707

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Physics Condensed Matter  

It is unexpected that a spin-glass (SG) transition, which generally occurs only in systems with some form of disorder, was observed in the ThCr2Si2-type compound PrAu2Si2 at a temperature of ∼3 K. This puzzling phenomenon was later explained based on a novel dynamic frustration model that does not involve static disorder. We present the results of re-verification of the reported SG behaviors by measuring the physical properties of three polycrystalline PrAu2Si2 samples annealed under different conditions. Indeed, in the sample annealed at 827 °C for one week, a SG transition does occur at a temperature of T f ∼2.8 K as that reported previously in the literature. However, it is newly found that the SG effect is actually more pronounced in the as-cast sample, and almost completely disappears in the well-annealed (at 850 °C for four weeks) sample. The annealing effect observed in PrAu2Si2, that is, SG to paramagnetism transition is discussed by comparing with earlier results reported on the same system and other isomorphic compounds.

DOI： 10.1088/1361-648X/ac49c7

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PubMed

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.7566/JPSJ.90.103702

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7566/JPSJ.90.064709

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.7566/JPSJ.90.073707

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.7566/JPSJ.90.074705

Language：English   Publishing type：Research paper (scientific journal)  

We report the magnetic susceptibility and the magnetization under pressures up to 1.7 GPa above the critical pressure,
Pc ∼ 1.5 GPa, for H ∥ a, b, and c-axes in the novel spin triplet superconductor UTe2. The anisotropic magnetic susceptibility
at low pressure with the easy magnetization a-axis changes to the quasi-isotropic behavior at high pressure,
revealing a rapid suppression of the susceptibility for a-axis, and a gradual increase of the susceptibility for the b-axis. At
1.7 GPa above Pc, magnetic anomalies are detected at TMO ∼ 3K and TWMO ∼ 10 K. The former anomaly corresponds to
long-range magnetic order, most likely antiferromagnetism, while the latter shows a broad anomaly, which is probably
due to the development of short range order. The unusual decrease and increase of the susceptibility below TWMO for
H ∥ a and b-axes, respectively, indicate the complex magnetic properties at low temperatures above Pc. This is related to
the interplay between multiple fluctuations dominated by antiferromagnetism, ferromagnetism, valence and Fermi
surface instabilities.

DOI： https://doi.org/10.7566/JPSJ.90.073703

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1103/PhysRevB.103.L100503

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevMaterials.5.034411

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DOI： 10.1103/PhysRevB.103.014511

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DOI： 10.1103/PhysRevB.102.174503

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DOI： 10.1016/j.jallcom.2021.158753

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DOI： 10.7566/JPSJ.89.102001

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DOI： 10.7566/JPSJ.89.094703

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DOI： 10.1103/PhysRevB.102.125114

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DOI： 10.1103/PhysRevB.102.134411

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DOI： 10.1103/PhysRevResearch.2.032014

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DOI： 10.7566/JPSJ.89.053705

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DOI： 10.7566/JPSJ.89.053707

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DOI： https://doi.org/10.1080/14786435.2019.1708498

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DOI： https://doi.org/10.1038/s42005-019-0248-z

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7566/JPSJ.88.113703

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1103/PhysRevB.100.165137

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DOI： https://doi.org/10.7566/JPSJ.88.094705

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.7566/JPSJ.88.094702

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DOI： https://doi.org/10.1103/PhysRevB.100.014401

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DOI： https://doi.org/10.7566/JPSJ.88.073701

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DOI： 10.7566/JPSJ.88.063706

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DOI： 10.7566/JPSJ.88.043702

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DOI： https://doi.org/10.1016/j.jallcom.2019.02.213

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevB.99.054408

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DOI： https://doi.org/10.3390/ma12040575

Event date： 2023.3

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Venue：東京工業大学   Country：Japan  

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Venue：東京工業大学   Country：Japan  

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Venue：東京工業大学   Country：Japan  

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Venue：東京工業大学   Country：Japan  

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Pressure induced structural transition of a spin triplet superconductor UTe2

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Pressure induced structural transition of a spin triplet superconductor UTe2

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Pressure induced structural transition of a spin triplet superconductor UTe2

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Pressure induced structural transition of a spin triplet superconductor UTe2

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Pressure induced structural transition of a spin triplet superconductor UTe2

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Pressure induced structural transition of a spin triplet superconductor UTe2

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Pressure induced structural transition of a spin triplet superconductor UTe2

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Pressure induced structural transition of a spin triplet superconductor UTe2

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Pressure induced structural transition of a spin triplet superconductor UTe2

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Pressure induced structural transition of a spin triplet superconductor UTe2

Event date： 2021.3

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Venue：オンライン   Country：Japan  

Pressure induced structural transition of a spin triplet superconductor UTe2

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