Fig. 4

Evidence for Weyl fermions in the heavy fermion state of YbPtBi from the anomalous Hall effect and specific heat. a Anomalous contribution to the Hall effect of sample S6 obtained from subtracting the ordinary one band Hall resistivity. The Anomalous Hall effect contains two terms, \(\rho _{{xy}}^{\mathrm{A}}\) which is proportional to the magnetization, and the topological term \(\rho _{{xy}}^{\mathrm{T}}\). The dashed lines show just \(\rho _{{xy}}^{\mathrm{A}}\) obtained from analyzing the data together with the measured magnetization (Supplementary Fig. 8 and Supplementary Note 4). b Topological Hall angle \({\mathrm{\Delta }}\sigma _{{xy}}^{\mathrm{T}}{\mathrm{/}}\sigma _{{xx}}\) as a function of field, after subtracting \(\rho _{{xy}}^{\mathrm{A}}\). A clear peak is observed at temperatures up to at least 30 K, giving evidence for the Berry curvature induced by the Weyl points. c Specific heat as C_p/T at 5, 7, 9, and 13 T where the solid lines show the results of fitting a Kondo resonance model³⁶. The deviation from the model at low temperatures shows clear evidence for an additional low-energy contribution. For comparison the zero-field specific heat of non-magnetic LuPtBi from ref.³⁵ is also displayed. d Specific heat in-field, as C/T vs. T², showing that the low-temperature behavior is well accounted for by a T³ dependence (solid lines) which is the expected behavior for Weyl heavy fermion semimetals¹⁶