Three-dimensional bulk Fermi surfaces and Weyl crossings of Co2MnGa thin films underneath a protection layer

Angle-resolved photoelectron spectroscopy utilizing soft x-ray synchrotron radiation was applied to Heusler-type Co2MnGa thin films that have a 1-nm Al capping layer. The bulk Fermi surfaces and band structures varied along the out-of-plane momentum, stemming from the three-dimensional crystal structure, in the absence of any in situ surface treatment. In addition, there were characteristic intersecting bands (Weyl cones), with crossing points near the Fermi level, which were consistent with computed results. The Weyl cones are of bulk origin and are responsible for the high anomalous Nernst and the anomalous Hall coefficients. A close comparison of the experimental band structures in Co2MnGe and Co2MnGa indicated that the rigid band picture is valid in both alloys and that fine carrier tuning is possible by replacing Ga with Ge to improve the anomalous conductivity.