Pairing Symmetry in Iron-Pnictide Superconductor KFe$_2$As$_2$

TL;DR

This paper investigates the pairing symmetry in KFe$_2$As$_2$ superconductors using a combined first-principles and $J_1$-$J_2$ model approach, concluding it exhibits a nodal $d_{xy}$-wave symmetry consistent with experimental observations.

Contribution

It introduces a phase diagram of pairing symmetries based on a low-energy effective model tailored for KFe$_2$As$_2$, identifying the nodal $d_{xy}$-wave as the pairing symmetry.

Findings

Identifies nodal $d_{xy}$-wave pairing symmetry in KFe$_2$As$_2$.

Provides a phase diagram linking $J_1$-$J_2$ parameters to pairing symmetry.

Finds good agreement with experimental nodal order parameters.

Abstract

The pairing symmetry is one of the major issues in the study of iron-based superconductors. We adopt a low-energy effective kinetic model based on the first-principles band structure calculations combined with the $J_1$-$J_2$ model for KFe$_2$As$_2$, the phase diagram of pairing symmetries is constructed. Putting the values of $J_1$ and $J_2$ of the $J_1$-$J_2$ model obtained by the first-principles calculations into this phase diagram, we find that the pairing symmetry for KFe$_2$As$_2$ is a nodal $d_{xy}$-wave in the folded Brillouin zone with two iron atoms per unit cell. This is in good agreement with experiments observed a nodal order parameter.