Type-II Dirac point in RbAg5Se3

Using first-principles calculations and low-energy effective model analysis, we propose that silver selenide-based RbAg₅Se₃ compound is an ideal type-II Dirac semimetal. There is a pair of Dirac points appearing at about 25.68 meV below the Fermi energy. The Dirac points existing on the k_z axis are protected by C_{4 z} rotation symmetry in addition to PT symmetry. Meanwhile, the system is also characterized by a nontrivial Z₂ topological invariant. The long clean Fermi arcs exist on the (010) surface, connecting the projections of the Dirac points. In addition, the Landau levels of the type-II Dirac points under magnetic field are also calculated. Our discovery not only adds one promising candidate into the type-II Dirac semimetals family but also provides an ideal platform for the study of topological phase transitions.