Sign change of the anomalous Hall effect and the anomalous Nernst effect in Weyl semimetal CeAlSi

Abstract

We report the anomalous Hall effect (AHE) and the anomalous Nernst effect (ANE) data for the non-collinear Weyl semimetal CeAlSi. The anomalous Hall conductivity (σ_ij^A) was measured for two different orientations of the magnetic field (B), namely σ_yz^A for B II a and σ_xy^A for B II c, where a and c denote the crystallographic axes. We find that σ_xy^A and σ_yz^A are of opposite sign and both are large below the Curie temperature (T_C). In the paramagnetic phase, σ_xy^A raises even more and goes through a maximum at T ~ 170 K, whereas the absolute value of σ_yz^A decreases with increasing temperature. The origin of the sign difference between σ_xy^A and σ_yz^A was attributed to the reconstruction of the band structure under the variation of the spin orientation. Further, in a system where humps in the AHE are present and scalar spin chirality is zero, we show that the k-space topology plays an important role to determine the transport properties at both low and high temperatures. We also observed the anomalous contribution in the Nernst conductivity (α_xy^A) measured for B II c. α_xy^A/T turns out to be sizeable in the magnetic phase and above T_C slowly decreases with temperature. We were able to recreate the temperature dependences of σ_xy^A and α_xy^A/T in the paramagnetic phase using a single band toy-model assuming a non-zero Berry curvature in the vicinity of the Weyl node. A decisive factor appears to be a small energy distance between the Fermi level and a Weyl point.

37 pages, 11 figures

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• Nonlinear optical diode effect in a magnetic Weyl semimetal
• Gravitational anomaly in the ferrimagnetic topological Weyl semimetal NdAlSi
• Sign competing sources of Berry curvature and anomalous Hall conductance humps in topological ferromagnets
• Structural characterization of the candidate Weyl semimetal CeGaGe
• Large circular photogalvanic effect in the noncentrosymmetric magnetic Weyl semimetal CeAlSi
• Incommensurate magnetic order drives singular angular magnetoresistance in a Weyl semimetal
• Accessing quasi-flat $\text{f}$-bands to harvest large Berry curvature in NdGaSi
• Design Principles for Topological Thermoelectrics