Topological crystalline insulator states in the Ca₂As family

Journal Article · 03 December 2018 · Physical Review. B

DOI: https://doi.org/10.1103/physrevb.98.241104 · OSTI ID:1544152

Zhou, Xiaoting ^[1]; Hsu, Chuang-Han ^[2]; Chang, Tay-Rong ^[1]; Tien, Hung-Ju ^[1]; Ma, Qiong ^[3]; Jarillo-Herrero, Pablo ^[3]; Gedik, Nuh ^[3]; Bansil, Arun ^[4]; Pereira, Vitor M. ^[2]; Xu, Su-Yang ^[3]; Lin, Hsin ^[5]; Fu, Liang ^[3]

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1. National Cheng Kung Univ., Tainan City (Taiwan)
2. National University of Singapore (Singapore)
3. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
4. Northeastern Univ., Boston, MA (United States)
5. Academia Sinica, Taipei (Taiwan)

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. Here, 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. Moreover, the other family members, including Ca₂Sb, Ca₂Bi, and Sr₂Sb, feature different topological surface states due to their distinct topological invariants. We thus further propose topological phase transitions in the pseudobinary systems such as (Ca_1–xSr_x)₂As and Ca₂As_xSb_1–x. 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.

• Research Organization: Energy Frontier Research Centers (EFRC) (United States). Center for Excitonics (CE); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)
• Sponsoring Organization: Gordon and Betty Moore Foundation; Ministry of Science and Technology (MOST); National Center for Theoretical Sciences (NCTS); US Air Force Office of Scientific Research (AFOSR); USDOE; USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division
• Grant/Contract Number: AC02-05CH11231; FG02-07ER46352; SC0001088; SC0010526
• OSTI ID: 1544152
• Journal Information: Physical Review. B, Journal Name: Physical Review. B Journal Issue: 24 Vol. 98; ISSN 2469-9950
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English