Momentum shift of Dirac cones in the silicene-intercalated compound CaSi2

Recent experimental realization of CaSi2 paves the way of restoring the Dirac dispersion in layered materials by means of intercalation [E. Noguchi et al., Adv. Mater. 27, 856 (2015)]. Here we investigate this new material with several possible stacking sequences within ab initio calculations. The robust Dirac dispersion, a characteristic of monolayer honeycomb lattice, moves below the Fermi energy due to electron doping of silicene layers by intercalated Ca atoms. Moreover, the Dirac cone shifts away from the high symmetric point of the hexagonal Brillouin zone with the opening of a small gap. This happens due to the sublattice symmetry breaking and consequent enhanced asymmetric interlayer hopping, enforced by the enhanced buckling of the honeycomb layers. Our further studies on Ca intercalated multilayer germanene compound provide the microscopic understanding of the Dirac electrons in intercalated buckled layered materials.