Tunable topological phase transition from nodal-line semimetal to Weyl semimetal by breaking symmetry

In this paper, we theoretically study the topological phase transition from nodal-line semimetal to Weyl semimetal. The nodal-line structure is protected by mirror symmetry and located on the kx-ky mirror reflection plane, and the Hamiltonian of nodal-line semimetal has an emergent chiral symmetry on this plane. When the mirror symmetry is broken, the topological nodal line opens the gap and the nodal-line semimetal transition to Weyl semimetal with Weyl points on the kx axis or the ky axis. In addition, we break the chiral symmetry and realize the Weyl semimetal with the Weyl points on the kz axis. Destruction of the chiral symmetry leads to the gradual bending of the energy bands. With the evolution of the energy bands, the type-II nodal-line semimetal, the type-II Weyl semimetal and the type-I Weyl semimetal are successively realized. Furthermore, we also study the surface states of the nodal-line semimetal and the corresponding Weyl semimetals after the phase transition. Our work provides more ways to study the phase transition between nodal-line semimetal and Weyl semimetal and helps realize possible applications in topological electronic devices in the future.