Anomalous Nernst and Righi-Leduc Effects in Mn3Sn : Berry Curvature and Entropy Flow

Abstract

We present a study of electric, thermal and thermoelectric response in noncollinear antiferromagnet Mn3Sn, which hosts a large Anomalous Hall Effect (AHE). Berry curvature generates off-diagonal thermal(Righi-Leduc) and thermoelectric(Nernst) signals, which are detectable at room temperature and invertible with a small magnetic field. The thermal and electrical Hall conductivities respect the Wiedemann-Franz law, implying that the transverse currents induced by Berry curvature are carried by Fermi surface quasi-particles. In contrast to conventional ferromagnets, the anomalous Lorenz number remains close to the Sommerfeld number over the whole temperature range of study, excluding any contribution by inelastic scattering and pointing to Berry curvature as the unique source of AHE. The anomalous off-diagonal thermo-electric and Hall conductivities are strongly temperature-dependent and their ratio is close to kB/e.The ordinary Hall effect, the transverse electric field generated by a longitudinal charge current in presence of a magnetic field, is caused by the Lorentz force exerted by magnetic field on charge carriers. In ferromagnetic solids, there is an additional component to this response (known as extraordinary or anomalous), thought to arise as a result of a sizeable magnetization. During the past decade, a clear link between the Anomalous Hall Effect (AHE) and the Berry curvature of Bloch waves has been established [1,2]. Charged carriers of entropy are also affected by the Lorenz force. Therefore, one expects a transverse component to thermal conductivity called the Righi-Leduc (or the thermal Hall) effect [3] in presence of magnetic field. This is also the case of thermoelectric conductance, which acquires an off-diagonal component, α ij , intimately linked to the Nernst coefficient, directly measurable by experiment [4]. When the Berry curvature replaces the magnetic field, counterparts of the AHE appear in the thermal and thermoelectric response of ferromagnets [5][6][7][8]. They can be an additional source of information regarding the fundamental mechanism leading to the generation of dissipationless transverse currents. Recently, following a proposition by Chen, Niu and Macdonald[9], Nakasutji et al. and Nayak et al. found a large AHE in Mn 3 Sn [10] and Mn 3 Ge [11,12], which are noncollinear antiferromagnets at room temperature. Several recent theoretical studies were devoted to this issue [13][14][15].In this letter, we present a study of Anomalous Righi-Leduc and Nernst effects (ANE) in Mn 3 Sn in order to quantify the amplitude of these coefficients compared to their Hall counterpart.We detect a large Anomalous Righi-Leduc conductivity and find that its magnitude corresponds to what is expected according to the Wiedemann-Franz (WF) Law over an extended temperature window. The result confirms a theoretical prediction by Haldane[16] with important consequences for the debate regarding the two alternative formulations of anomalous Hall effect [16][17][18]. AHE can be formulated as a property of th...

Noncollinear antiferromagnetic Mn3Sn films

“…Mn 3 Sn and Mn 3 Ge were theoretically predicted to show large AHE driven by nonvanishing Berry curvature [13], while band-structure calculations reveal that both compounds demonstrate a Weyl semimetal state with several Weyl points around the Fermi level [22,23]. In accordance with these theoretical calculations, single crystals of Mn 3 Sn and Mn 3 Ge were found to exhibit large AHE [24][25][26] and large anomalous Nernst effect [14,15], reaching the same order of magnitude as in ferromagnetic materials. These studies concern bulk single crystal, but to extend to spintronic devices thin films of these materials are required.…”

“…Among many different antiferromagnetic [7][8][9] or artificial antiferromagnetic materials [10,11], the noncollinear chiral antiferromagnets have attracted much interest, due to their remarkable structural, magnetic, and electrotransport properties. The trianglular spin structure of these compounds gives rise to a large anomalous Hall effect (AHE) [12,13], thermoelectric effect [14][15][16], magneto-optical Kerr effect [17,18], and spin Hall effect (SHE) [19]. Inspired by experimental work in Mn 3 Ir [19], ab initio calculations confirmed large anisotropic anomalous Hall current and spin Hall current in these materials [20], while predicting that charge current is also spin polarized [21].…”

Spin Hall effect emerging from a noncollinear magnetic lattice without spin–orbit coupling

“…Large AHE in room temperature has recently been reported in Mn 3 Ge and Mn 3 Sn [22,23]. These materials also exhibit other exotic phenomena including the Weyl semimetal phase [38], magneto-optical Kerr effect [39], anomalous Nernst effect [40], and topological defects [41]. Distinct from hexagonal Mn 3 X compounds, the Mn 3 Ir (space group Pm m 3 , No.…”

Large Anomalous Nernst Effect in a van der Waals Ferromagnet Fe3GeTe2

“…Furthermore, the topological nature of FGT gives rise to some intriguing phenomena, for example, the observation of large anomalous Hall effect (AHE) [12] and magnetic skyrmions [13][14][15]. Of particular interest is the anomalous Nernst effect (ANE) in topological materials because the special band topology in these materials could introduce a very large ANE [16][17][18][19], which shares some similarities with, but also differences from, the better known AHE. In AHE and ANE, the current is driven by an electric field and temperature gradient ∇ respectively, while a voltage is measured perpendicular to both the current and the magnetization M of the material.…”