Abstract
The charge density wave (CDW) in 1T–TiSe2 harbors a nontrivial symmetry configuration. It is important to understand this underlying symmetry both for gaining a handle on the mechanism of CDW formation and for probing the CDW experimentally. Here, based on first-principles computations within the framework of the density functional theory, we unravel the connection between the symmetries of the normal and CDW states and the electronic structure of 1T–TiSe2. Our analysis highlights the key role of irreducible representations of the electronic states and the occurrence of band gaps in the system in driving the CDW. By showing how symmetry-related topology can be obtained directly from the electronic structure, our study provides a practical pathway in search of topological CDW insulators.
Highlights
Transition metal dichalcogenides (TMDCs) have layered crystal structures with the weak van der Waals interaction between the adjacent layers
We have presented an in-depth analysis of the symmetries as well as the topology of the electronic structure of bulk 1T -TiSe2 charge density wave (CDW)
Our first-principles calculations show that the CDW state hosts a nodal band structure in which the nodes are protected by symmetry and topology resembling that of the Dirac nodes in the spin-density-wave phase of iron pnictides[36,37]
Summary
Transition metal dichalcogenides (TMDCs) have layered crystal structures with the weak van der Waals interaction between the adjacent layers. The L−1 CDW is nontrivial due to its anisotropic character It is reminiscent of the d-density wave in strongly correlated systems where the local rotation symmetry is broken[20,21]. The key role of symmetry, has not been hardly explored in the literature[24,25,26,27] With this motivation, we will elucidate the symmetry properties of the CDW state in 1T -TiSe2 and their connections with the electronic structure and the band topology of the system. [For a commensurate CDW the translation symmetry can be restored by enlarging the unit cell: TCDW = TM for some integer M such that TCDW, ∆ˆ = 0.] So, the symmetry group will be reduced to a subgroup G of G0 which will contain symmetry elements isomorphic to those that are left invariant under the CDW distortion in G0. −1 related to the ordering vectors for the direction of the atomic displacements[28]
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