Damped Dirac magnon in a metallic kagome antiferromagnet FeSn
The Kagomé lattice is one of the most interesting structural motifs in condensed matter physics, potentially hosting topological nature of bosons as well as fermions [1,2]. In particular, for the case of ferromagnetic nearest-neighbor exchange interaction in the Kagomé spin-network, the magnon (boson) exhibits topological properties similar to the electronic band structure of the Kagomé metal, resulting in the band-crossing of the Dirac magnon [2]. To study the magnon band structure of the Kagomé lattice, we performed inelastic neutron scattering (INS) on the metallic Kagomé magnet FeSn [3] by using time-of-flight spectrometers, HRC and 4SEASONS at J-PARC. The measured spectra shown in the figure below exhibits the low-energy magnon dispersions of FeSn in the three-dimensional hexagonal Brillouin region. The acoustic magnons emanate from Qm=Γ(0,0,1/2) and disperse throughout the entire BZ. Strongly dispersive magnons in the HK-plane extend beyond 80 meV, whereas the magnon dispersion along the out-of-plane direction has a bandwidth of less than 20 meV, indicating the dominant spin-spin interactions are within the Kagomé-lattice plane. Moreover, the observed in-plane magnon dispersions are explained by ferromagnetic spin interactions, indicating that FeSn constitutes the ferromagnetic Kagomé lattice. The observed low-energy and high-energy spectra (not shown here) are well explained by the pure Heisenberg spin Hamiltonian model, which preserves the time-reversal symmetry of the magnons, indicating the presence of massless Dirac magnons at the K-point [4]. Through this low-energy magnon analysis, we were able to determine the Hamiltonian parameters, and by observing additional high-energy magnon spectra, we could observe the Dirac magnons in the FeSn Kagomé spin-lattice. The neutron experiment at the Materials and Life Science Experimental Facility of the J-PARC was performed under a user program (Proposals No. 2019B0248 and No.2020A0217).
[1] Linda Ye et al., Nature 555 638 (2018). [2] R. Chisnell et al., PRL 115 147201 (2015). [3] B. C. Sales, et al., PRM 3 114203(2019). [4] S.-H. Do et al., PRB 105 L180403 (2022).
Figure (a) Contour map of the INS intensity along high symmetry directions [given in (f)]. The data shown in (a),(c) were measured using HRC with Ei=153 meV. Horizontal (vertical) error bars of pink (green) circles indicate the fitted peaks full width at half maxima (FWHM), and vertical (horizontal) error bars indicate the range of energy (momentum) integration. (b) INS data (left) and spin-wave calculations (right) as described in the text along the out-of-plane direction through the zone center (ZC), measured using the 4SEASONS spectrometer with Ei=46 meV. The solid line is the calculated magnon dispersion. (c) Constant energy slice of the magnon spectra in the [H,0,L] plane and the calculated spectra. (d) Low-energy spectrum of I(Q,E) near the ZC measured using Ei=27 meV at 4SEASONS, and (e) the corresponding calculation including an easy-plane anisotropy of Dz=0.1 meV.
◆ その他（学会発表）
Daichi Ueta, Shinichi Itoh, Tetsuya Yokoo, Takatsugu Masuda, Taro Nakajima, Shinichiro Asai, Hiraku Saito, Daichi Kawana, Ryosuke Sugiura, Toshio Asami, Yoshiaki Ihata, Hiroaki Tanino, “Neutron flux and energy resolution of the HRC spectrometer at J-PARC”, The 15th Edition of the QENS series and the 10th of the WINS workshops, 23 – 27 May 2022, Miramar Palace, San Sebastián, Spain and online, oral, international.
◆ 論文等
Seung-Hwan Do, Koji Kaneko, Ryoichi Kajimoto, Kazuya Kamazawa, Matthew B. Stone, Jiao Y. Y. Lin, Shinichi Itoh, Takatsugu Masuda, German D. Samolyuk, Elbio Dagotto, William R. Meier, Brian C. Sales, Hu Miao, and Andrew D. Christianson, "Damped Dirac magnon in the metallic kagome antiferromagnet FeSn", Phys. Rev. B, 105, L180403, (2022).
(2) ソフトマターグループ
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H. Kawaura, M. Harada, Y. Kondo, M. Mizutani, N. Takahashi, and N. L. Yamada, "Effects of Lithium Bis(oxalate)borate Electrolyte Additive on the Formation of a Solid Electrolyte Interphase on Amorphous Carbon Electrode by Operando Time-Slicing Neutron Reflectometry", ACS Appl. Mater. Interfaces, 14 (2022) 24526.
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冨岡美里, 修士, 神戸大学 (2022-03) “Structure and Interactions with water of poly(substituted methylene)s with high-dense side chains/側鎖を高密度に有するポリ置換メチレンの構造と水との相互作用”
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(4) 中性子光学研究グループ
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Takashi Higuchi and on behalf of the TUCAN collaboration, "Prospects for a neutron EDM measurement with an advanced ultracold neutron source at TRIUMF", EPJ Web of Conferences, 262, 01015, (2022).
