Topological p_z-wave nodal-line superconductivity with flat surface bands in the AH_xCr₃As₃ (A = Na, K, Rb, Cs) superconductors

¹ School of Physics, Beijing Institute of Technology - Beijing 100081, China
² CAS Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences Beijing 100190, China
³ Max-Planck-Institut für Festkörperforschung - Heisenbergstrasse 1, D-70569 Stuttgart, Germany

^(b) yangfan_blg@bit.edu.cn (corresponding author)

Received: 25 January 2022
Accepted: 11 April 2022

Abstract

We study the pairing symmetry and the topological properties of the hydrogen-doped ACr₃As₃ superconductors. Based on our first-principle band structure with spin-orbit coupling (SOC), we construct a tight-binding model including the on-site SOC terms, equipped with the multi-orbital Hubbard interactions. Then using the random-phase-approximation (RPA) approach, we calculate the pairing phase diagram of this model. Our RPA results yield the triplet p_z-wave pairing in the spin channel to be the leading pairing symmetry all over the experiment relevant hydrogen-doping regimes. This pairing state belongs to the spin-U(1)-symmetry–protected time-reversal–invariant topological nodal-line superconductivity. Determined by the momentum-dependent topological invariant Z(k_x, k_y), the whole (001) surface Brillouin zone is covered with topological flat bands with different regimes covered with different numbers of flat surface bands, which can be detected by the scanning tunneling microscope experiments.