Evidence for Weyl fermions at low temperatures in the heavy fermion state of YbPtBi. (a) Anomalous contribution to the Hall resistivity, after subtracting the normal contribution from the charge carriers. (b) Topological Hall angle at different temperatures after subtracting a contribution from the Hall resistivity proportional to the magnetization. The significant value at low temperatures arises from the Berry curvature generated by the Weyl nodes. (c) Temperature dependence of the specific heat as C_p/T in various applied fields. The solid line shows a fit to a Kondo model, which cannot describe the low temperature data. (d) C_p/T vs. T² in various applied fields. The linear relationship reveals a cubic temperature dependence of the specific heat, which is a signature of the linear dispersion of heavy fermion bands expected in the vicinity of Weyl points. Figure reproduced from Guo et al., Ref. [32].