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Nakayama, Katsumasa*; Suzuki, Kei
Physics Letters B, 843, p.138017_1 - 138017_7, 2023/08
Times Cited Count：0 Percentile：0.02(Astronomy & Astrophysics)The Casimir effect is a quantum phenomenon induced by the zero-point energy of relativistic fields confined in a finite-size system. This effect for photon fields has been studied for a long time, while the realization of counterparts for fermion fields in Dirac/Weyl semimetals is an open question. We theoretically demonstrate the typical properties of the Casimir effect for relativistic electron fields in Dirac/Weyl semimetals and show the results from an effective Hamiltonian for realistic materials such as Cd
As
and NaBi. We find an oscillation of the Casimir energy as a function of the thickness of the thin film, which stems from the existence of Dirac/Weyl nodes in momentum space. Experimentally, such an effect can be observed in thin films of semimetals, where the thickness dependence of thermodynamic quantities is affected by the Casimir energy.
Nakayama, Katsumasa*; Suzuki, Kei
Physical Review Research (Internet), 5(2), p.L022054_1 - L022054_6, 2023/06
The Casimir effect is a fundamental quantum phenomenon induced by the zero-point energy for a quantum field. It is well-known for relativistic fields with a linear dispersion relation, while its existence or absence for nonrelativistic fields with a quadratic dispersion is an unsettled question. Here, we investigate the Casimir effects for various dispersion relations on the lattice. We find that Casimir effects for dispersions proportional to an even power of momentum are absent in a long distance under some types of boundary conditions, while a remnant of the Casimir effect survives in a short distance. The concepts of such absence and remnants of Casimir effect help us to understand observables in finite-size materials with quantum fields on the lattice, such as thin films, narrow nanoribbons, and short nanowires. In terms of this effect, we also give a reinterpretation of the Casimir effect for massive fields.
Lee, S.*; Nakata, Koki; Tchernyshyov, O.*; Kim, S. K.*
Physical Review B, 107(18), p.184432_1 - 184432_12, 2023/05
Times Cited Count：5 Percentile：87.72(Materials Science, Multidisciplinary)We theoretically investigate the interaction between magnons and a Skyrmion-textured domain wall in a two-dimensional antiferromagnet and elucidate the resultant properties of magnon transport. Using supersymmetric quantum mechanics, we solve the scattering problem of magnons on top of the domain wall and obtain the exact solutions of propagating and bound magnon modes. Then, we find their properties of reflection and refraction in the Skyrmion-textured domain wall, where magnons experience an emergent magnetic field due to its non-trivial spin texture-induced effective gauge field. Finally, we show that the thermal transport decreases as the domain wall's chirality increases. Our results suggest that the thermal transport of an antiferromagnet is tunable by modulating the Skyrmion charge density of the domain wall.
Nakayama, Katsumasa*; Suzuki, Kei
Proceedings of Science (Internet), 430, p.379_1 - 379_9, 2023/04
The conventional Casimir effect has been studied in the continuous spacetime, but to elucidate its counterpart in the lattice space is an important subject. Here, we discuss various types of Casimir effects for quantum fields on the lattice. By using a definition of the Casimir energy on the lattice, we show that the Casimir effect for the Wilson fermion is similar to that for the continuous Dirac fermion. We apply our definition to an effective Hamiltonian describing Dirac semimetals, such as CdAs and NaBi, and find an oscillatory behavior of the Casimir energy as a function of film thickness of semimetals. We also study contributions from Landau levels under magnetic fields and the Casimir effect for nonrelativistic particle fields on the lattice.
Nakata, Koki; Suzuki, Kei
Physical Review Letters, 130(9), p.096702_1 - 096702_6, 2023/03
Times Cited Count：3 Percentile：76.59(Physics, Multidisciplinary)Quantum fluctuations of quantum fields induce a zero-point energy shift under spatial boundary conditions. This quantum phenomenon, called the Casimir effect, has been attracting much attention beyond the hierarchy of energy scales, whereas its application to spintronics has not yet been investigated enough, particularly to ferrimagnetic thin films. Here we fill this gap. Using the lattice field theory, we investigate the Casimir effect induced by quantum fields for magnons and find that the magnonic Casimir effect can arise not only in antiferromagnets but also in ferrimagnets (e.g., YIG). Thus, we pave the way for magnonic Casimir engineering.
Nakata, Koki; Onuma, Yuichi*; Kim, S. K.*
Physical Review B, 105(18), p.184409_1 - 184409_7, 2022/05
Times Cited Count：2 Percentile：32.25(Materials Science, Multidisciplinary)We show that the ratio of the thermal to spin transport coefficient of magnons in insulating magnets exhibits a different behavior from the linear response and the universal law breaks down in the strong nonlinear regime.
3(111) and 5(0-13) grain boundaries of 
-ironEbihara, Kenichi; Suzudo, Tomoaki
Metals, 12(4), p.662_1 - 662_10, 2022/04
Times Cited Count：2 Percentile：30.25(Materials Science, Multidisciplinary)Phosphorus atoms in steels accumulate at grain boundaries via thermal and/or irradiation effects and induce grain boundary embrittlement. Quantitative prediction of phosphorus segregation at grain boundaries under various temperature and irradiation conditions is therefore essential for preventing embrittlement. To develop a model of grain boundary phosphorus segregation in -iron, we studied the migration of a phosphorus atom in two types of symmetrical tilt grain boundaries (3[1-10](111) and 5[100](0-13) grain boundaries) using molecular dynamics simulations with an embedded atom method potential. The results revealed that, in the 3 grain boundary, phosphorus atoms migrate three-dimensionally mainly in the form of interstitial atoms, whereas in the 5 grain boundary, these atoms migrate one-dimensionally mainly via vacancy-atom exchanges. Moreover, de-trapping of phosphorus atoms and vacancies was investigated.
Nakata, Koki; Onuma, Yuichi*
Physical Review B, 105(14), p.144436_1 - 144436_7, 2022/04
Times Cited Count：0 Percentile：0(Materials Science, Multidisciplinary)Using a junction of the ferromagnetic insulators irradiated by linearly polarized laser, we propose a method for the generation of dc and ac spin currents of magnons across the junction interface, and provide an analytical formula for magnon transport induced by the inversion symmetry breaking.
Imai, Nobuaki*; Otsu, Hideaki*
JAEA-Conf 2021-001, 236 Pages, 2022/03
JAEA-Conf-2021-001.pdf:48.06MB
The 2020 Symposium on Nuclear Data was held on-site at RIBF Conference Hall in RIKEN Wako campus on November 26 to 27, 2020, combined with on-line connection conference. The symposium was organized by the Nuclear Data Division of the Atomic Energy Society of Japan (AESJ) in cooperation with Sigma Investigative Advisory Committee of AESJ, Nuclear Science and Engineering Center of Japan Atomic Energy Agency (JAEA), RIKEN Nishina Center, Center for Nuclear Study, The University of Tokyo (CNS), KEK Wako Nuclear Science Center (WNSC), School of Science, The University of Tokyo. In the symposium, six sessions were proposed and held: "Reactor theory and experiments" as a tutorial, "Accelerator Facilities and Nuclear Data", "Deep/Machine Learning and Nuclear Physics, Application to Nuclear Data", "Nuclear Medicine and Nuclear Pharmacy", "Fission, Heavy Ion Nuclear Spectroscopy", and "Nuclear Reaction Data" as lecture and discussion sessions. In addition, recent research progress on experiments, nuclear theory, evaluation, benchmark and applications were presented in the poster session. The total number of participants was 119, of which 62 were on-site participants. Each oral and poster presentation was followed by an active question and answer session. This report consists of total 40 papers including 15 oral and 25 poster presentations.
Nakata, Koki
Physical Review B, 104(10), p.104402_1 - 104402_12, 2021/09
Times Cited Count：1 Percentile：7.51(Materials Science, Multidisciplinary)Combining advanced technologies of optics and antiferromagnetic spintronics, we present a method to realize ultrafast Josephson spin currents through the optomagnonic Barnett effect by using macroscopic coherence of magnon condensates.
Nakata, Koki; Kim, S. K.*
Journal of the Physical Society of Japan, 90(8), p.081004_1 - 081004_10, 2021/08
Times Cited Count：2 Percentile：29.32(Physics, Multidisciplinary)This article reviews the past works on topological Hall effects of magnons in insulating magnets with a particular focus on ferrimagnets.
Nakata, Koki
Kotai Butsuri, 56(8), p.429 - 439, 2021/08
We review the thermomagnetic relation of bosons, the Wiedemann-Franz law for magnon transport, and discuss the universality.
Nakata, Koki; Onuma, Yuichi*
Physical Review B, 104(6), p.064408_1 - 064408_8, 2021/08
Times Cited Count：9 Percentile：64.95(Materials Science, Multidisciplinary)Using the quantum Boltzmann equation for Bose systems, we have developed the formula for thermal transport of bosons and found a difference from the conventional, with a particular focus on magnons.
Fukasawa, Yuto*; Kaneko, Masashi; Nakashima, Satoru*
Journal of Radioanalytical and Nuclear Chemistry, 329(1), p.77 - 84, 2021/07
Times Cited Count：1 Percentile：15.7(Chemistry, Analytical)Density functional theory calculations were applied to understand the selectivity between Am
and Eu ions with the crown ethers type ligands. 18C6 is predicted to form the most stable complex with Eu and show the higher stability for Am over Eu, being consistent with previously reported Am/Eu selectivity. We modeled N- and S-donor complexes by using framework of 18C6 complex and analyzed the complexation Gibbs energies, indicating that 18C6 with N-donor atoms is suitable for both complexation and higher Am stability over Eu due to the stronger covalent interaction.
Kano, Koichi*; Hagiwara, Satoshi*; Igarashi, Takahiro; Otani, Minoru*
Electrochimica Acta, 377, p.138121_1 - 138121_10, 2021/05
Times Cited Count：17 Percentile：69.94(Electrochemistry)We investigated the free corrosion potential at an interface between an Al electrode and an aqueous NaCl solution under acidic conditions via density functional theory combined with the effective screening medium and reference interaction site model (ESM-RISM). The electrode potentials for the anodic and cathodic corrosion reactions were obtained from the grand potential profile as a function of the electron chemical potential at the interface. Thereafter, we determined the free corrosion potential using the Tafel extrapolation method. The results of the free corrosion potential were consistent with previous experimental data. By controlling the pH, we determined the pH dependence of the free corrosion potential, and the results agreed well with the experimental results. Our results indicated that the ESM-RISM method duly described the environmental effect of an acidic solution and precisely determined the free corrosion potential.
Araki, Yasufumi; Suenaga, Daiki*; Suzuki, Kei; Yasui, Shigehiro*
Physical Review Research (Internet), 3(1), p.013233_1 - 013233_12, 2021/03
We investigate two different types of relativistic Kondo effects, distinguished by heavy-impurity degrees of freedom, by focusing on the energy-momentum dispersion relations of the ground state with condensates composed of a light Dirac fermion and a nonrelativistic impurity fermion. Heavy fermion degrees of freedom are introduced in terms of two types of heavy-fermion effective theories, in other words, two heavy-fermion limits for the heavy Dirac fermion, which is known as the heavy-quark effective theories (HQETs) in high-energy physics. While the first one includes only the heavy-particle component, the second one contains both the heavy-particle and heavy-antiparticle components, which are opposite in their parity. From these theories, we obtain two types of Kondo effects, in which the dispersions near the Fermi surface are very similar, but they differ in the structure at low momentum. We also classify the possible forms of condensates in the two limits. The two Kondo effects will be examined by experiments with Dirac/Weyl semimetals or quark matter, lattice simulations, and cold-atom simulations.
anomalyKawakami, Yohei*; Harada, Masayasu*; Oka, Makoto; Suzuki, Kei
Physical Review D, 102(11), p.114004_1 - 114004_9, 2020/12
Times Cited Count：7 Percentile：46.51(Astronomy & Astrophysics)We study strong and radiative decays of excited singly heavy baryons using an effective chiral Lagrangian based on the diquark picture. The effective Lagrangian contains a anomaly term, which is found to suppress the decay width of 
.
Kim, Y.*; Hiyama, Emiko*; Oka, Makoto; Suzuki, Kei
Physical Review D, 102(1), p.014004_1 - 014004_9, 2020/07
Times Cited Count：17 Percentile：75.31(Astronomy & Astrophysics)Applying the chiral effective theory of diquarks, we analyze the spectrum and structure of singly heavy baryons. We introduce the phenomenological quark-model potentials for the confinement. We predict the charmed and bottom baryon spectrum showing the inverse mass hierarchy.
Araki, Yasufumi; Misawa, Takahiro*; Nomura, Kentaro*
Physical Review Research (Internet), 2(2), p.023195_1 - 023195_11, 2020/05
anomalyHarada, Masayasu*; Liu, Y.-R.*; Oka, Makoto; Suzuki, Kei
Physical Review D, 101(5), p.054038_1 - 054038_11, 2020/03
Times Cited Count：16 Percentile：73.39(Astronomy & Astrophysics)Using a chiral effective theory of diquarks, we analyze the spectrum and structure of diquark and heavy baryons consisting of diquarks. anomaly is considered in the chiral Lagrangian and its effects are studied.
