Anomalous Nernst and Seebeck coefficients in epitaxial thin film Co₂MnAl_xSi_1-x

We have measured the Seebeck and anomalous Nernst coefficients and corresponding transverse and longitudinal thermoelectric conductivities from 2 to 400 K in thin film (∼ 10 nm) Co₂MnAl_xSi_1-x (0≤x≤1) grown by molecular beam epitaxy (MBE). A large (-14 A*m^-1K^-1 at 300 K) anomalous transverse thermoelectric conductivity α_xy^A is observed in Co₂MnAl, which is 50 times larger than α_xy^A of Co₂MnSi (0.28 A*m^-1K^-1 at 300 K), as well as a significant enhancement in the anomalous Hall conductivity (6 times larger at 300K). This enhancement is likely due to the appearance of Weyl points in the band structure of Co₂MnAl close to the Fermi level. As a result of the high sensitivity to the Weyl points near the Fermi level, we propose α_xy^A as a helpful tool to capture Weyl points that are too far from the Fermi level to produce significant effect in the anomalous Hall conductivity.