Second-Harmonic Voltage Response for the Magnetic Weyl Semimetal Co 3 Sn 2 S 2
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Second-harmonic Voltage Responce for the Magnetic Weyl Semimetal Co3 Sn2 S2 V. D. Esin, A. V. Timonina, N. N. Kolesnikov, E. V. Deviatov 1) Institute of Solid State Physics of the Russian Academy of Sciences, 142432 Chernogolovka, Russia Submitted 29 April 2020 Resubmitted 29 April 2020 Accepted 29 April 2020
We experimentally investigate longitudinal and transverse second-harmonic voltage response to ac electrical current for a magnetic Weyl semimetal Co3 Sn2 S2 . In contrast to the previously observed Berry-curvature induced non-linear Hall effect for non-magnetic Weyl and Dirac semimetals, the second-harmonic transverse voltage demonstrates sophisticated interplay of different effects for Co3 Sn2 S2 . In high magnetic fields, it is of Seebeck-like square-B law, while the low-field behavior is found to be linear and sensitive to the direction of sample magnetization. The latter can be expected both for the non-linear Hall effect and for the surface state contribution to the Seebeck effect in Weyl semimetals. Thus, thermoelectric effects are significant in Co3 Sn2 S2 , unlike non-magnetic Weyl and Dirac materials. DOI: 10.1134/S0021364020120024
Recent interest to the time-reversal-invariant nonlinear Hall (NLH) effect [1–14] is a part of a broad research area of topological systems. In zero magnetic field, a non-linear Hall-like current arises from the Berry curvature, which can be regarded as a magnetic field in momentum space. It leads to a quadratic response to ac excitation current, so NLH effect should appear as a non-zero transverse second-harmonic voltage without magnetic field. Since Berry curvature concentrates in regions where two or more bands cross [15], topological systems are the obvious candidates to observe the NLH effect [1]. It has been experimentally demonstrated for monolayer transitional metal dichalcogenides [16, 17] and for three-dimensional Weyl and Dirac semimetals [18]. Dirac semimetals host special points of Brillouin zone with three-dimensional linear dispersion [15]. In Weyl semimetals, by breaking time reversal or inversion symmetries, every Dirac point splits into two Weyl nodes with opposite chiralities. First experimentally investigated Weyl semimetals (WSMs) were noncentrosymmetric crystals with broken inversion symmetry. Even in this case, a second-harmonic quadratic signal can also originate from the thermoelectric Seebeck effect [19, 20]. When the magnetic field is perpendicular to the temperature gradient, it leads to quadratic-B correction in the Seebeck coefficient [21, 22]. In contrast to these calculations, a second-harmonic NLH voltage shows [18] odd-type dependence on the direction of the 1) e-mail:
magnetic field. Thus, the magnetic field measurements allow to distinguish the NLH effect from the thermoelectric response. There are only a few candidates [23–26] of magnetically ordered WSMs with broken time-reversal symmetry. Recently, giant anomalous Hall effect was reported [27, 28] for the kagome-lattice ferromagnet Co3 Sn2 S2 , as an indication for the existence of a magnetic Weyl phase.
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