Topological crystalline insulator states in the Ca₂As family

XIAOTING ZHOU^1*, Chuang-Han Hsu², Tay-Rong Chang¹, Hung-Ju Tien¹, Qiong Ma³, Pablo Jarillo-Herrero³, Nuh Gedik³, Arun Bansil⁴, Vitor Pereira², Suyang Xu³, Hsin Lin⁵, Liang Fu³

¹Physics, National Cheng Kung University, Tainan, Taiwan
²National University of Singapore, Singapore, Singapore
³Massachusetts Institute of Technology, Cambridge, USA
⁴Northeastern University, Boston, USA
⁵Academia Sinica, Taipei, Taiwan

* Presenter:XIAOTING ZHOU, email:physxtzhou@gmail.com

Topological crystalline insulators (TCIs) are insulating electronic phases of matter with nontrivial topology originating from crystalline symmetries. Recent theoretical advances have proposed new TCI states protected by rotational symmetries and provided powerful guidelines to search for TCIs in real materials. Building upon recent theoretical works, we demonstrate a feasible method to identify new TCI states based on first-principles calculations.We systematically unveil the topological properties of the TCI states in Ca2As. On both top and side surfaces, we observe topological surface states protected independently by rotational and mirror symmetries.We show that a particular lattice distortion can single out the newly proposed topological protection by the rotational symmetry. As a result, the Dirac points of the topological surface states are moved to generic locations in momentum space away from any high-symmetry lines. Such topological surface states have not been seen before. Our work reveals rich and exotic TCI physics across the Ca₂As family of materials and demonstrates a complete roadmap for uncovering TCIs topological nature based on first-principles calculations. Such a method can be broadly applied in searching for new TCIs.

Keywords: Topological Crystalline Instulator, Crystalline Symmetry, Symmetry Indicator, Topological Invariant, Dirac Surface States