Strain and doping-induced control of Weyl points for enhancing anomalous Nernst conductivities

The anomalous Nernst effect is a thermoelectric transport phenomenon that is governed by the Berry curvature near the Fermi level. Materials must generally have a large anomalous Nernst conductivity (ANC) to be useful in functional thermoelectric devices. We have previously used k·p models to suggest that in materials featuring Weyl points near the Fermi level, the ANC may be enhanced by tuning the Weyl positions in k-space. Here we use first-principles calculations to investigate the effectiveness of experimentally-accessible methods – namely, strain and ion doping – for Weyl point tuning and thus ANC enhancement. We demonstrate that even modest epitaxial strain can significantly increase the ANC of magnetic heusler compounds. We additionally show that an apparent violation of the Mott relation in an experimental ion-doped sample can be explained by Weyl point "migration" due to both band and Fermi level shifting.