Topological insulating phase in nonsymmorphic bulk AX2 (A = Ca, Sr, or Ba; and X = As, Sb, or Bi) compounds

Winda Purwitasari^1*, Ali Sufyan¹, Rovi Angelo B. Villaos¹, Zhi-Quan Huang¹, Arun Bansil^2,3, Hsin Lin⁴, Feng-Chuan Chuang^1,5,6,7

¹Department of Physics, National Sun Yat Sen University, Kaohsiung, Taiwan
²Department of Physics, Northeastern University, Boston, Massachusetts, USA
³Quantum Materials and Sensing Institute, Northeastern University, Burlington, MA, USA
⁴Institute of Physics, Academia Sinica, Taipei, Taiwan
⁵Physics Division, National Center for Theoretical Sciences, Taipei, Taiwan
⁶Center for Theoretical and Computational Physics, National Sun Yat Sen University, Kaohsiung, Taiwan
⁷Department of Physics, National Tsing Hua University, Hsincu, Taiwan

* Presenter:Winda Purwitasari, email:windapurwita@g-mail.nsysu.edu.tw

Owing to their unique topologically protected gapless boundary states, topological insulators (TIs) are attracting substantial interest in spintronics and quantum computing. Here we discuss the structural, electronic, and topological properties of bulk alkaline earth di-pnictides AX2 (where A= Ca, Sr, or Ba and X= As, Sb, or Bi) using first-principles calculations under the hybrid functional approach. Our structural analysis based on phonon dispersion and molecular dynamics calculations establishes the thermodynamic stability of these materials and indicates their potential for synthesis. All investigated compounds are shown to host nontrivial phases upon including spin-orbit coupling. CaAs2, SrSb2, and BaSb2 are found to be strong TIs with sizable bandgaps of up to 213 meV. Nontrivial topology in the case of SrSb2 was further confirmed through surface state computations which showed the presence of gapless surface states. In addition, we demonstrate that using the hybrid functional approach can enhance the accuracy of the calculations to predict experimental findings. Finally, our study suggests that the alkaline earth di-pnictide family would provide a promising materials platform for developing applications of TIs.

Keywords: alkaline earth di-pnictides, topological insulators, first-principles calculations