Topological semimetal realized in a specific honeycomb lattice

As one type of the elementary particles in standard mode, the realization of Weyl fermions in condensed matter has attracted increasing interest. However, most discovered Weyl semimetals show complicate electronic structures, which lead to many confusions for their essential physics. Here we report firstly that fruitful topological phases can be realized in a specific honeycomb lattice, including ideal Weyl semimetal, 3D strong topological insulator, nodalline semimetal, and a novel semimetal consisting of both Weyl nodes and nodal-lines. Guiding by this model, we demonstrate that GdSI is the long-pursuing ideal Weyl semimetal with the least Weyl nodes residing at the Fermi level, and LuSI (YSI) is a 3D strong topological insulator with the right-handed helical surface states. Our work paves a new way to explore the ideal topological semimetals, and provides a good platform to research the physics of the Weyl semimetal and the related device design.