Observation of an anomalous heat current in GdPtBi.

In condensed matter Weyl systems, it is predicted that the generation of a heat current by the mixed axial-gravitational anomaly leads to a negative magnetothermal resistivity (MTR), locked to the parallel alignment of the applied temperature gradient $\nabla T$ and magnetic field $\mathbf{H}$. Here, we show magnetothermal transport experiments on the semimetal GdPtBi, which has previously been reported to host Weyl fermions. For collinear temperature gradients and magnetic fields ($\nabla T\parallel\mathbf{H}$), we observe a negative MTR, which diminishes at high magnetic fields, when $\nabla T$ is aligned perpendicular to $\mathbf{H}$. This observation is consistent with the generation of an anomalous heat current. At low fields, however, we also observe a negative MTR for $\nabla T\perp\mathbf{H}$, suggesting a more complex origin of the magnetothermal transport properties of GdPtBi.