Daichi Ueta

High Energy Accelerator Research Organization

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H. Yoshizawa

The University of Tokyo

Takatsugu Masuda

The University of Tokyo

Yoichi Ikeda

University of Toyama

Masahiro Yoshida

Kyoto University

Shinichi Itoh

Japan Proton Accelerator Research Complex

Yoshinori Okada

Okinawa Institute of Science and Technology Graduate University

Tetsuya Yokoo

High Energy Accelerator Research Organization

T. Sato

Tohoku University

Riki Kobayashi

University of the Ryukyus

Yuita Fujisawa

Okinawa Institute of Science and Technology Graduate University

Cooperative Institutions

The University of Tokyo

Japan Atomic Energy Agency

Osaka University

Tohoku University

High Energy Accelerator Research Organization

Okinawa Institute of Science and Technology Graduate University

Japan Proton Accelerator Research Complex

Kyoto University

Ibaraki University

Oak Ridge National Laboratory

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Superconductivity and Non-Fermi-Liquid Behavior in the Heavy-Fermion Compound CeCo₁₋_xNi_xIn₅

Journal of the Physical Society of Japan (2016)

Ryo Otaka M. Yokoyama Hiroaki Mashiko Takeshi Hasegawa Yusei Shimizu

The effect of off-plane impurity on superconductivity and non-Fermi-liquid (NFL) behavior in the layered heavy-fermion compound CeCo1−xNixIn5 is investigated by specific heat, magnetization, and electrical resistivity measurements. These measurements reveal that the superconducting (SC) transition temperature Tc monotonically decreases from 2.3 K (x = 0) to 0.8 K (x = 0.20) with increasing x, and then the SC order disappears above x = 0.25. At the same time, the Ni substitution yields the NFL behavior at zero field for x = 0.25, characterized by the −ln T divergence in specific heat divided by temperature, Cp/T, and magnetic susceptibility, M/B. The NFL behavior in magnetic fields for x = 0.25 is quite similar to that seen at around the SC upper critical field in pure CeCoIn5, suggesting that both compounds are governed by the same antiferromagnetic quantum criticality. The resemblance of the doping effect on the SC order among Ni-, Sn-, and Pt-substituted CeCoIn5 supports the argument that the doped carriers are primarily responsible for the breakdown of the SC order. The present investigation further reveals the quantitative differences in the trends of the suppression of superconductivity between Ce(Co,Ni)In5 and the other alloys, such as the rates of decrease in Tc, dTc/dx, and specific heat jump at Tc, d(ΔCp/Tc)/dx. We suggest that the occupied positions of the doped ions play an important role in the origin of these differences.

Critical field

Heavy fermion superconductor

Metamagnetism

10.7566/jpsj.85.094713

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Uncovering hidden Fermi surface instabilities through visualizing unconventional quasiparticle interference in CeTe3

Physical Review Materials (2024)

B. R. M. Smith Yuita Fujisawa Ping Wu Tomonori Nakamura N. Tomoda

The charge density wave (CDW) state is a widespread phenomenon in low-dimensional metals/semimetals. The spectral weight of the associated folded bands (shadow bands) can be an intriguing trigger leading to additional Fermi surface instability and unexplored phase transitions. The rare earth tri-telluride CeTe3 exhibits a single CDW stabilized below ~400 K and antiferromagnetism below ~3 K. The distinct periodicities between the Te-square net, the CeTe block layer, and the CDW give rise to rich shadow band formations. In this work, we reveal the predominant scattering between the original and shadow bands at 4 K, with the scattering within the original bands being relatively suppressed at Fermi energy. This unconventional quasi-particle scattering collectively underscores the vital role of the shadow bands' spectral weight and the hidden matrix element effect, which are crucial for controlling electronic properties in this system. Furthermore, our finding points to the existence of rich and unexplored Fermi surface instabilities, which potentially play a role in controlling the nature of long-range antiferromagnetism at lower temperatures in the presence of finite charge-spin interaction.

10.1103/physrevmaterials.8.104004

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Magnetism of pseudospin-1/2 pyrochlore antiferromagnet Na₃Co(CO₃)₂Cl

Journal of Physics Condensed Matter (2024)

Kazuhiro Nawa Ryo Murasaki Shinichi Itoh Hiraku Saito Hiroyuki Nojiri

Abstract Pyrochlore magnets have attracted interest as systems for realizing critical phenomena, rich magnetic structures, associated topological band structures, and nontrivial quantum phases. Na 3 Co(CO 3 ) 2 Cl is a pseudospin-1/2 antiferromagnet in which the Co 2+ ions form a pyrochlore network. Its structural and magnetic properties were investigated using magnetization, heat capacity, ESR, single-crystal x-ray diffraction, powder neutron diffraction and powder inelastic neutron scattering. Magnetization and heat capacity measurements indicated a ground-state doublet, which is regarded as pseudospin 1/2, dominated the magnetic properties at low temperatures, with a magnetic exchange of 9.6 K. As the temperature decreases, a magnetic transition is observed at 1.6 K, which is confirmed to be an all-in-all-out magnetic order. The crystal field excitations observed by inelastic neutron scattering experiments indicated the Ising nature of the ground-state doublet. This thorough study revealed that Na 3 Co(CO 3 ) 2 Cl can be regarded as a pseudospin-1/2 pyrochlore lattice antiferromagnet with dominant Ising-type interactions.

Magnetism

10.1088/1361-648x/ad7182

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Quantum oscillations with magnetic hysteresis observed in CeTe$_{3}$ thin films

arXiv (Cornell University) (2020)

Mori Watanabe Sanghyun Lee Takuya Asano Takashi Ibe Masashi Tokuda

We have performed magnetotransport measurements in CeTe$_{3}$ thin films down to $0.2~{\rm K}$. It is known that CeTe$_{3}$ has two magnetic transitions at $T_{\rm N1} \approx 3~{\rm K}$ and $T_{\rm N2} \approx 1~{\rm K}$. A clear Shubnikov-de-Haas (SdH) oscillation was observed at $4~{\rm K}$, demonstrating the strong two-dimensional nature in this material. Below $T_{\rm N2}$, the SdH oscillation has two frequencies, indicating that the Fermi surface could be slightly modulated due to the second magnetic transition. We also observed a magnetic hysteresis in the SdH oscillation below $T_{\rm N1}$. Especially, there is a unique spike in the magnetoresistance at $B \approx 0.6~{\rm T}$ only when the magnetic field is swept from a high enough field (more than $2~{\rm T}$) to zero field.

Oscillation (cell signaling)

Hysteresis

10.48550/arxiv.2006.14955

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Zero-point entropies of spin-jam and spin-glass states in a frustrated magnet

arXiv (Cornell University) (2023)

Chairote Piyakulworawat Asiri Thennakoon J. Yang H. Yoshizawa Daichi Ueta

Thermodynamics studies of a prototypical quasi-two-dimensional frustrated magnet Ba$_2$Sn$_2$ZnCr$_{7p}$Ga$_{10-7p}$O$_{22}$ where the magnetic Cr$^{3+}$ ions are arranged in a triangular network of bipyramids show that the magnetic zero-point entropy for $p=0.98$ is 55(1)\% of the entropy expected when the Cr$^{3+}$ moments are fully disordered. Furthermore, when combined with a previous neutron scattering study and the perimeter scaling entropy of a spin jam, the analysis reveals that with decreasing $p$, i.e., doping of the nonmagnetic Ga$^{3+}$ ions, the variation in the magnetic zero-point entropy can be well explained by the combined effects of the zero-point entropy of the spin jam state and that of weakly coupled orphan spins, shedding light on the coexistence of the two types of spin states in quantum magnetism.

Zero (linguistics)

10.48550/arxiv.2303.17871

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Massive Dirac magnons in the three-dimensional honeycomb magnetic oxide $$\hbox {FeTiO}_3$$

Scientific Reports (2025)

Jae-Ho Chung Kwangwoo Shin Tetsuya Yokoo Daichi Ueta Masaki Imai

Two dimensional honeycomb ferromagnets host massless Dirac magnons which are a bosonic analogue of Dirac fermions in graphene. The Dirac magnons may become massive and topological when the time reversal symmetry breaks and an energy gap opens up at the Dirac point, which was experimentally observed in $$\hbox {Cr}^{3+}$$ -based van der Waals magnets. Here, we investigate the spin wave excitations in the 3d magnetic oxide $$\hbox {FeTiO}_3$$ with $$\hbox {Fe}^{2+}$$ electrons ( $$3d^4$$ ). Using inelastic neutron scattering, we observe two magnon bands separated by a 1.2-meV gap at the Dirac points indicating that its Dirac magnons are massive. Using the linear spin-wave and density functional theory calculations, we find that the spin-orbit-coupled antisymmetric Dzyaloshinskii-Moriya exchanges can best account for the observed Dirac gap opening. The associated Berry curvature and Chern number ( $$C^\pm = \pm 1$$ ) indicate that $$\hbox {FeTiO}_3$$ hosts topological spin excitations via time-reversal symmetry breaking of Dirac magnons.

Magnon

Honeycomb

10.1038/s41598-025-90478-2

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Shubnikov-de-Haas oscillation and possible modification of effective mass in CeTe₃ thin films

AIP Advances (2021)

Mori Watanabe Ryoya Nakamura Sanghyun Lee Takuya Asano Takashi Ibe

Magnetoresistance measurements have been performed in CeTe3 thin film devices in a temperature range from 2.1 to 20 K up to 8 T. A clear Shubnikov-de-Haas oscillation was observed in the whole temperature range. The temperature dependence of the oscillation amplitude was found to deviate from the Lifshitz–Kosevich formula below the magnetic transition temperature at TN1 ≈ 3 K. This indicates a significant interplay between the magnetic ordering and the conduction electrons, which could lead to a modification of the effective cyclotron mass. By analyzing the temperature dependence of the oscillation amplitude, we have estimated the effective mass, quantum lifetime and quantum mobility of the material both in the paramagnetic and antiferromagnetic states.

Oscillation (cell signaling)

Shubnikov–de Haas effect

Atmospheric temperature range

10.1063/9.0000074

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Anisotropic Pressure Effects on Superconductivity in Fe₁₊_yTe₁₋_xS_x

Journal of the Physical Society of Japan (2018)

Kazunori Yamamoto Teruo Yamazaki Takayoshi Yamanaka Daichi Ueta H. Yoshizawa

We have investigated uniaxial and hydrostatic pressure effects on superconductivity in Fe1.07Te0.88S0.12 through magnetic-susceptibility measurements down to 1.8 K. The superconducting transition temperature Tc is enhanced by out-of-plane pressure (uniaxial pressure along the c-axis); the onset temperature of the superconductivity reaches 11.8 K at 0.4 GPa. In contrast, Tc is reduced by in-plane pressure (uniaxial pressure along the ab-plane) and hydrostatic pressure. Taking into account these results, it is inferred that the superconductivity of Fe1+yTe1-xSx is enhanced when the lattice constant c considerably shrinks. This implies that the relationship between Tc and the anion height for Fe1+yTe1-xSx is similar to that applicable to most iron-based superconductors. We consider the reduction of Tc by hydrostatic pressure due to suppression of spin fluctuations because the system moves away from antiferromagnetic ordering, and the enhancement of Tc by out-of-plane pressure due to the anion height effect on Tc.

Hydrostatic pressure

Lattice constant

Ambient pressure

Lattice (music)

Transition temperature

10.7566/jpsj.87.054705

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Crystal Structure and Magnetic Properties of the Breathing Kagome Ising Antiferromagnet Yb₃Ni₁₁Ge_4.63

Journal of the Physical Society of Japan (2020)

Mitsuru Takahashi Kazuhiro Nawa Daisuke Okuyama Hiroyuki Nojiri Matthias Frontzek

We have investigated magnetic properties of the rare-earth based intermetallic compound Yb3Ni11Ge4.63 (YNG), where Yb3+ ions form a breathing-kagome lattice. Single-site 4f electron wavefunctions of the ground-state doublet are deduced from magnetization and heat capacity measurements. The Weiss temperatures are quite anisotropic as Θa = −0.01(2) K (H ∥ a) and Θc = −0.67(2) K (H ∥ c), indicating Ising-like spin–spin interactions dominating in this compound. Low-temperature neutron diffraction confirms absence of magnetic Bragg peaks down to 0.05 K, whereas enhancement of broad peaks below 0.8 K was observed, a signature of short-range spin correlations. Competing interactions on the breathing-kagome lattice would suppress a magnetic long-range order in YNG.

10.7566/jpsj.89.094704

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Weak Ferromagnetism and Multiple Metamagnetic Transitions in the Non-centrosymmetric Tetragonal Compound CePdSi₃

Journal of the Physical Society of Japan (2016)

Daichi Ueta Yoichi Ikeda H. Yoshizawa

We have succeeded in growing single crystalline samples of CePdSi3 with the BaNiSn3-type non-centrosymmetric structure. Specific heat, magnetic susceptibility, and magnetization measurements were carried out, which revealed three successive magnetic transitions at TI = 4.85(5) K, TII = 2.78(5) K, and TIII = 2.30(5) K at zero field. Below TII, a weak ferromagnetic component was observed, indicating a canted antiferromagnetic ground state in CePdSi3. The observed large magnetic anisotropy in CePdSi3 was explained in terms of a simple crystalline-electric-field model. From the magnetization measurements, we identified five (three) magnetic states in the H–T phase diagrams for the H || [100] ([001]) direction. Interestingly, only three magnetization steps were observed for H || [110], suggesting the existence of the in-plane magnetic anisotropy in CePdSi3. We discuss a possible nature of the complex magnetic properties of CePdSi3.

Tetragonal crystal system

Metamagnetism

10.7566/jpsj.85.104703

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Citations (11)