A charge density wave (CDW) of a nonzero ordering vector q couple electronic states at k and k+q statically, giving rise to a reduced Brillouin zone (RBZ) due to the band folding effect. Its structure, in terms of an irreducible representation of the little group of q, would change the symmetry of the system and electronic structure accompanying possible change of band inversion, offering a chance of the topological phase transition. Monolayer 1\textit{T}-TiSe2 is investigated for it shows an unconventional CDW phase having a triple-qM1− structure. Moreover, the coupling between the triple-q component of the M1− CDW will inevitably produce a small M1+ CDW. The CDW yields a band inversion in 1\textit{T}-TiSe2 but different types of CDW can affect the electronic structure and system topology differently. The impact of CDW of different types was studied by utilizing a symmetrization-antisymmetrization technique to extract the M1− and M1+ CDW contributions in the DFT-based tight-binding model and study their effects. The results are consistent with the parity consideration, improving understanding of topology for a CDW system with and without parity.
@article{arxiv.2109.01390,
title = {Topological theory of inversion-breaking charge-density-wave monolayer 1\textit{T}-TiSe$_2$},
author = {Ming-Chien Hsu and Bahadur Singh and Chuang-Han Hsu and Su-Yang Xu and Hsin Lin and Shin-Ming Huang},
journal= {arXiv preprint arXiv:2109.01390},
year = {2021}
}