Topological tunability from even-odd order parameter mixing of monolayer 1T-TiSe2 charge density wave
Ming-Chien Hsu1*, Shin-Ming Huang1, Bahadur Singh2,3, Chuang-Han Hsu4,5, Su-Yang Xu6, Hsin Lin7, Chenliang Su2, Arun Bansil3
1Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan
2SZU-NUS Collaborative Center and International Collaborative Laboratory of 2D Materials for Optoelectronic Science & Technology, Shenzhen University, Guangdong Province, China
3Department of Physics, Northeastern University, Massachusetts, USA
4Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore
5Department of Physics, National University of Singapore, Singapore
6Department of Physics, Massachusetts Institute of Technology, Massachusetts, USA
7Institute of Physics, Academia Sinica, Taipei, Taiwan
* Presenter:Ming-Chien Hsu,
Monolayer 1T-TiSe2 has been found to have charge density wave (CDW) experimentally. The primary CDW order parameter takes the M1− symmetry having odd parity and will change parity of electronic states of the system. Due to the coexistence of three q vectors from the primary order parameter, a secondary order parameter of even parity is induced inevitably. The mixture of the two opposite-parity order parameters will break inversion symmetry, which fails connection between symmetry and topology. Here we propose a method to decouple the parity-odd and parity- even CDW gaps, so that we can perform continuously the inversion-asymmetric CDW state into an inversion-symmetric one. In this way it helps to understand topological phase transitions in inversion asymmetric systems from the inversion-symmetry point of view.

Keywords: TiSe2, charge density wave, inversion asymmetry, topological phase transition, monolayer