Topological $p_z$-wave nodal-line superconductivity with flat surface bands in the AH$_{x}$Cr${_3}$As${_3}$ (A=Na, K, Rb, Cs) superconductors

TL;DR

This paper predicts a topological pz-wave nodal-line superconducting state in hydrogen-doped ACr3As3 compounds, featuring flat surface bands and potential for experimental detection via STM, based on first-principles calculations and RPA analysis.

Contribution

It introduces a novel triplet pz-wave pairing state in ACr3As3 superconductors, revealing its topological properties and surface flat bands through theoretical modeling.

Findings

Triplet pz-wave pairing is dominant across doping regimes.

The superconducting state is topologically nontrivial with flat surface bands.

Surface flat bands can be observed by scanning tunneling microscopy.

Abstract

We study the pairing symmetry and the topological properties of the hydrogen-doped ACr$_3$As$_3$ superconductors. Based on our first-principle band structure with spin-orbit-coupling (SOC), we construct 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 pz-wave pairing in the ($\left(\uparrow\downarrow+\downarrow\uparrow\right)$) 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 (kx; ky), 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.