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Topological Weyl magnets are characterized by a magnetic semimetallic state that harbors Weyl fermions near the Fermi energy. As a parent state of such a magnetic Weyl state, we first introduce a new class of semimetals with quadratic band touchings, the “Luttinger semimetal” [1,2]. We demonstrate the case in pyrochlore iridium oxides that exhibit various exotic phenomena, including a spontaneous Hall effect without magnetization in a spin liquid state [3]. Then, we discuss a new type of frustrated antiferromagnets, Mn3X (X = Sn and Ge) as the examples of a topological Weyl magnet [4,5,6]. We show that the cluster multipole order on the kagome lattice of Mn moments can be easily controlled and allows the system to exhibit a variety of new functions at room temperature that have never been seen in antiferromagnetic metals. These include the large anomalous Hall and Nernst effects [4,5,7], large magnetic optical Kerr effect [8] and a novel type of spin Hall effect (magnetic spin Hall effect). Finally, we show that they should be significantly useful for designing antiferromagnetic spintronics, and energy harvesting technology. [1] T. Kondo et al., Nature Communications 6, 10042 (2015). [2] B. Cheng et al., Nature Communications 8, 2097 (2017). [3] Y. Machida, S. Nakatsuji, S. Onoda, T. Tayama, and T. Sakakibara, Nature 463, 210 (2010). [4] S. Nakatsuji, N. Kiyohara and T. Higo, Nature 527, 212 (2015). [5] N. Kiyohara, T. Tomita, S. Nakatsuji, Phys. Rev. Applied 5, 064009 (2016). [6] K. Kuroda, T. Tomita et al., Nature Materials 16, 1090 (2017). [7] M. Ikhlas, T. Tomita et. al., Nature Physics 13, 1085 (2017). [8] T. Higo et al., Nature Photonics, 12, 73 (2018).

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Satoru Nakatsuji, University of Tokyo
Seminar Room of the Institute of Physics II
Contact: Simon Trebst