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

We report the anomalous Hall effect (AHE) and the anomalous Nernst effect (ANE) data for the noncollinear Weyl semimetal CeAlSi. The anomalous Hall conductivity (sigma iAj) was measured for two different orientations of the magnetic field (B), namely sigma yzA for B||a and sigma xAy for B||c, where a and c denote the crystallographic axes. We find that sigma xAy and sigma yzA are of opposite sign and both are large below the Curie temperature (TC). In the paramagnetic phase, sigma xAy rises even more and goes through a maximum at T approximate to 170 K, whereas the absolute value of sigma yzA decreases with increasing temperature. The origin of the sign difference between sigma xAy and sigma yzA 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 (alpha xAy) measured for B||c. alpha xAy/T turns out to be sizeable in the magnetic phase and above TC slowly decreases with temperature. We were able to recreate the temperature dependencies of sigma xAy and alpha xAy/T in the paramagnetic phase using a single band toy model assuming a nonzero 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.