Observation of Weyl Cones in Ferromagnetic Heusler Alloy Films Co_2MnGa by Spin-and Angle-Resolved Photoemission Spectroscopy

摘要

When topological materials meet magnetism, extremely large anomalous transport properties such as anomalous Hall (AHE) and Nernst effects (ANE) would emerge. Recently, the highest ANE thermopowerï½6.0 µV/K has been realized at room temperature in bulk ferromagnet Co2MnGa, which is one order of magnitude larger than those of the other conventional ferromagnets . It is theoretically predicted that an intrinsic Berry curvature mechanism emerging from band structures in the vicinity of the Fermi energy (EF) plays an important role for these large transverse properties . A very recent photoemission study has reported that the bulk Co_2MnGa possesses several mirror-symmetry-protected nodal loops . However, since the Berry curvature becomes zero with the nodal loop structure , the observed large ANE cannot be explained. Moreover, in the application point of view, since the remanent magnetization of the bulk sample is negligibly small, an external magnetic field must be applied to obtain a huge output. Conversely, the film form having full remanent magnetization is promising for practical applications;namely, the large thermopower can be obtained without the external magnetic field, although the reported output is still insufficient (<2.0 µV/K) . Therefore, it is highly demanded to elucidate the spin-dependent topological band structures and enhance the thermopower in the films.