Electronic structure and properties of BaAIGe and SrAlGe

The electronic structures of BaAlGe and SrAlGe which are superconductors with hexagonal honeycomb layers have been studied by using a first principles method. Energy bands, Fermi surfaces, and density of states are presented. The two materials have topologically different Fermi surfaces. BaAlGe has two Fermi surfaces: one has a three dimensional spinning-top-like shape and the other has a cylindrical shape with two dimensional character. SrAlGe has only one connected Fermi surface. Two gap superconductivity for BaAlGe is suggested from the inherently different character of the two Fermi surfaces. The higher Tc of SrAlGe than BaAlGe is related to the difference in both the topology of the Fermi surface and the band dispersions along the z direction.

► First principles electronic structure of BaAlGe and SrAlGe.
► Strong interlayer coupling along the z-direction.
► Different topology of Fermi surface: BaAlGe has two distinct Fermi surfaces while SrAlGe has a connected Fermi surface.