start-ver=1.4
cd-journal=joma
no-vol=94
cd-vols=
no-issue=11
article-no=
start-page=113801
end-page=
dt-received=
dt-revised=
dt-accepted=
dt-pub-year=2025
dt-pub=20251115
dt-online=
en-article=
kn-article=
en-subject=
kn-subject=
en-title=
kn-title=Magnetically Enhanced Thermoelectric Effect Driven by Martensitic Transformation in the Weak Itinerant Ferromagnet Co2NbSn
en-subtitle=
kn-subtitle=
en-abstract=
kn-abstract=We investigated the magnetic and thermoelectric properties of the full Heusler alloy Co2NbSn, which exhibits a martensitic transformation at 240 K. Magnetization measurements reveal weak itinerant ferromagnetism in the martensitic phase, which is well described by Takahashi’s spin fluctuation theory. The characteristic spin fluctuation parameters were estimated to be T0 = 1.0 × 103 K and TA = 7.2 × 103 K. Seebeck coefficient measurements under magnetic fields up to 9 T show complex temperature and field dependence, which we decomposed into electron diffusion, spin fluctuation drag, and magnon drag components. A significant magnon-drag contribution was identified in both austenite and martensitic phases. Remarkably, this contribution is strongly enhanced in the martensitic phase compared to the austenite phase, despite a smaller magnetic moment. These findings provide evidence for robust low-energy spin excitations and highlight the potential of martensitic transformation in enhancing the thermoelectric performance of itinerant ferromagnetic alloys.
en-copyright=
kn-copyright=

en-aut-name=KiharaTakumi
en-aut-sei=Kihara
en-aut-mei=Takumi
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=1
ORCID=

en-aut-name=XuXiao
en-aut-sei=Xu
en-aut-mei=Xiao
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=2
ORCID=

en-aut-name=OgiYuki
en-aut-sei=Ogi
en-aut-mei=Yuki
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=3
ORCID=

en-aut-name=AdachiYoshiya
en-aut-sei=Adachi
en-aut-mei=Yoshiya
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=4
ORCID=

en-aut-name=RoyTufan
en-aut-sei=Roy
en-aut-mei=Tufan
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=5
ORCID=

en-aut-name=MatsuuraRyuji
en-aut-sei=Matsuura
en-aut-mei=Ryuji
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=6
ORCID=

en-aut-name=KanomataTakeshi
en-aut-sei=Kanomata
en-aut-mei=Takeshi
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=7
ORCID=

affil-num=1
en-affil=Research Institute for Interdisciplinary Science, Okayama University
kn-affil=

affil-num=2
en-affil=Department of Materials Science, Tohoku University
kn-affil=

affil-num=3
en-affil=Graduate School of Science and Engineering, Yamagata University
kn-affil=

affil-num=4
en-affil=Graduate School of Science and Engineering, Yamagata University
kn-affil=

affil-num=5
en-affil=Center for Science and Innovation in Spintronics (CSIS), Core Research Cluster (CRC), Tohoku University
kn-affil=

affil-num=6
en-affil=Faculty of Engineering, Tohoku Gakuin University
kn-affil=

affil-num=7
en-affil=Research Institute for Engineering and Technology, Tohoku Gakuin University
kn-affil=
END

start-ver=1.4
cd-journal=joma
no-vol=89
cd-vols=
no-issue=1
article-no=
start-page=012001
end-page=
dt-received=
dt-revised=
dt-accepted=
dt-pub-year=2019
dt-pub=20191212
dt-online=
en-article=
kn-article=
en-subject=
kn-subject=
en-title=
kn-title=Sparse Modeling in Quantum Many-Body Problems
en-subtitle=
kn-subtitle=
en-abstract=
kn-abstract=This review paper describes the basic concept and technical details of sparse modeling and its applications to quantum many-body problems. Sparse modeling refers to methodologies for finding a small number of relevant parameters that well explain a given dataset. This concept reminds us physics, where the goal is to find a small number of physical laws that are hidden behind complicated phenomena. Sparse modeling extends the target of physics from natural phenomena to data, and may be interpreted as “physics for data”. The first half of this review introduces sparse modeling for physicists. It is assumed that readers have physics background but no expertise in data science. The second half reviews applications. Matsubara Green’s function, which plays a central role in descriptions of correlated systems, has been found to be sparse, meaning that it contains little information. This leads to (i) a new method for solving the ill-conditioned inverse problem for analytical continuation, and (ii) a highly compact representation of Matsubara Green’s function, which enables efficient calculations for quantum many-body systems.
en-copyright=
kn-copyright=

en-aut-name=OtsukiJunya
en-aut-sei=Otsuki
en-aut-mei=Junya
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=1
ORCID=

en-aut-name=OhzekiMasayuki
en-aut-sei=Ohzeki
en-aut-mei=Masayuki
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=2
ORCID=

en-aut-name=ShinaokaHiroshi
en-aut-sei=Shinaoka
en-aut-mei=Hiroshi
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=3
ORCID=

en-aut-name=YoshimiKazuyoshi
en-aut-sei=Yoshimi
en-aut-mei=Kazuyoshi
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=4
ORCID=

affil-num=1
en-affil=Research Institute for Interdisciplinary Science, Okayama University
kn-affil=

affil-num=2
en-affil=Graduate School of Information Sciences, Tohoku University
kn-affil=

affil-num=3
en-affil=Department of Physics, Saitama University
kn-affil=

affil-num=4
en-affil=4Institute for Solid State Physics, University of Tokyo
kn-affil=
END

start-ver=1.4
cd-journal=joma
no-vol=89
cd-vols=
no-issue=6
article-no=
start-page=064401
end-page=
dt-received=
dt-revised=
dt-accepted=
dt-pub-year=2020
dt-pub=20200519
dt-online=
en-article=
kn-article=
en-subject=
kn-subject=
en-title=
kn-title=Energy Transfer to Resonant Zonal Rossby Modes in Two-Dimensional Turbulence on a Rotating Sphere
en-subtitle=
kn-subtitle=
en-abstract=
kn-abstract=The transfer of energy by the nonlinear interaction of Rossby waves in two-dimensional turbulence on a rotating sphere was investigated in this study. Although it has been suggested that three-wave resonant interaction dominates nonlinear interactions when the rotation rate of the sphere is sufficiently high, resonant interactions do not transfer energy to zonal Rossby waves, resulting in the nonresonant interaction of Rossby waves being responsible for the generation of zonal flows [Reznik, Piterbarg, and Kartashova, Dyn. Atmos. Oceans 18, 235 (1993); Obuse and Yamada, Phys. Rev. Fluids 4, 024601 (2019)]. The resonant and nonresonant interactions of Rossby waves were investigated in this study, and it was found that although energy is transferred to the zonal Rossby modes by the nonresonant three-wave interaction of Rossby waves, the target of this nonresonant energy transfer is only the resonant zonal Rossby waves.
en-copyright=
kn-copyright=

en-aut-name=ObuseKiori
en-aut-sei=Obuse
en-aut-mei=Kiori
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=1
ORCID=

en-aut-name=YamadaMichio
en-aut-sei=Yamada
en-aut-mei=Michio
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=2
ORCID=

affil-num=1
en-affil=Graduate School of Environmental and Life Science, Okayama University
kn-affil=

affil-num=2
en-affil=Research Institute for Mathematical Sciences, Kyoto University
kn-affil=
END