Dirac and Weyl semimetals display a host of novel properties. In ${\mathrm{Cd}}_3{\mathrm{As}}_2$, the Dirac nodes lead to a protection mechanism that strongly suppresses backscattering in a zero magnetic field, resulting in ultrahigh mobility ($\sim {10}^7{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$). In an applied magnetic field, an anomalous Nernst effect is predicted to arise from the Berry curvature associated with the Weyl nodes. We report the observation of a large anomalous Nernst effect in ${\mathrm{Cd}}_3{\mathrm{As}}_2$. Both the anomalous Nernst signal and transport relaxation time ${\tau }_{\mathrm{tr}}$ begin to increase rapidly at $\sim 50\mathrm{K}$. This suggests a close relation between the protection mechanism and the anomalous Nernst effect. In a field, the quantum oscillations of bulk states display a beating effect, suggesting that the Dirac nodes split into Weyl states, allowing the Berry curvature to be observed as an anomalous Nernst effect.

• Received 7 October 2016

DOI:https://doi.org/10.1103/PhysRevLett.118.136601