Weyl monopoles dance with the spin waves
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nuary 2021 Vol. 64 No. 1: 217063 https://doi.org/10.1007/s11433-020-1605-8
Editor’s Focus
Editor’s Focus
Weyl monopoles dance with the spin waves *
BingHai Yan
Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 760001, Israel Received July 21, 2020; accepted July 29, 2020; published online August 24, 2020
Citation:
B. H. Yan, Weyl monopoles dance with the spin waves, Sci. China-Phys. Mech. Astron. 64, 217063 (2021), https://doi.org/10.1007/s11433-020-1605-8
In a Weyl semimetal (WSM), the conduction and valence bands cross each other near the Fermi energy, and the crossing points, called Weyl points, exhibit a monopole-like distribution of the Berry curvature. The Berry curvature is a fictitious magnetic field in the momentum-space and induces the anomalous velocity to the real-space electron motion. Therefore, Weyl monopoles play essential roles in the charge transport, for example, the anomalous Hall effect (AHE). The anomalous Hall conductivity (AHC) is nearly proportional to the distance between the Weyl point pairs with opposite chirality. The magnetic order and spin structure sensitively modify Weyl point positions and energies. Recently, Co3Sn2S2 has been extensively studied as a prototype of magnetic WSM [1] with increasing attention. This compound hosts Weyl points at only 60 meV above the Fermi energy and by a low charge carrier density. The wide separation of Weyl points induces a giant AHE with the AHC −1 −1 ~1130 Ω cm and the Hall angle up to 20% [1]. The existence of Weyl points in the bulk and Fermi arc states on the surface were verified by surface spectroscopic probes [1]. The WSM also exhibits other topology-induced phenomena such as surface Fermi arcs [1], the anomalous Nernst effect (ANE) [2] and possible chiral edge states [3]. Because Co atoms form a magnetic Kagome lattice, this compound also provokes interests in flat-bands and the frustrated physics [4]. It is even studied to catalyze the water splitting [5]. Theoretically, the Weyl points also influence the spin dynamics in a magnetic WSM. The spin orientation sensitively *Corresponding author (email: [email protected])
tunes the band structure and subsequently manipulates the positions and energies of Weyl points (as illustrated in Figure 1), leading to modified AHE. At the finite temperature, the collective motion of magnetic moments forms spin waves. One can imagine that spin waves can modify the static scenario of Weyl points and the AHE. Because of the strong coupling between the spin and motion in Weyl materials, the modified AHE shakes the spin waves, too. Such effect establishes an intimate relationship between the AHC and spin dynamics, where both the spin stiffness and the spin wave gap are modified away from the behaviors of the conventional ferromagnetic spin wave [6]. Very recently, Liu et al. [7] presented a comprehensive neutron scattering study on high-quality single-crystals of Co3Sn2S2. By mapping the dispersions of spin waves up to 18 meV both in plane and out of plane, Liu et a
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