Structural, electronic and topological properties of NaCaBi and KBaBi compounds

Abstract

Topological insulators are promising candidates for potential applications in spintronics owing to their topologically protected dissipationless surface states. Here, we have investigated the structural, electronic and topological properties of NaCaBi and KBaBi compounds without and with spin-orbit coupling effect by employing density functional theory in Quantum Espresso code. Without spin-orbit coupling, NaCaBi and KBaBi compounds behave as a type-I nodal line semimetal and form a nodal loop around the Γ-point in the kz = 0 plane of Brillouin zone. When the bulk states are projected onto the (001) surface, a drumhead-like surface state is reported inside the nodal line for both compounds. The s/p band inversion in NaCaBi and KBaBi compounds are reported due to the strong spin-orbit coupling with band inversion energy of 0.87 eV and 0.32 eV respectively. The spin-orbit coupling in NaCaBi and KBaBi compounds induced the band gap of value 0.32 eV and 0.21 eV respectively. Z2 indices for NaCaBi and KBaBi are found (1; 000) which indicates that NaCaBi and KBaBi are strong topological insulators. The topological surface states and corresponding spin-texture are also calculated for both compounds which show a single Dirac cone at Γ-point with Dirac point lying below the Fermi-level. The obtained results are in good agreement with the available results reported in the literature.