Topological tunability from even-odd order parameter mixing of monolayer 1T-TiSe2 charge density wave

Ming-Chien Hsu^1*, Shin-Ming Huang¹, Bahadur Singh^2,3, Chuang-Han Hsu^4,5, 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, email:mingchienh@gmail.com

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