Plaquette-centered rotation symmetry and octet-nodal superconductivity in $\text{KFe}_{2}\text{As}_{2}$

Guo-Yi Zhu; Guang-Ming Zhang

paper

Plaquette-centered rotation symmetry and octet-nodal superconductivity in $KFe_{2} As_{2}$

arXiv:1707.04009

Abstract

A plaquette-centered rotation symmetry $C_{4}^{p}$ is identified to play a significant role in determining and stabilizing the Fermi-surface structure of Fe-based superconductors. Together with the $S_{4}$ symmetry previously found, we are able to sort out the tangling orbitals and solve the puzzle of pairing symmetry of superconductivity in $KFe_{2} As_{2}$ in a simple but comprehensive way. By modeling the material with a strong coupling $t - J_{1} - J_{2}$ model, we find phase transitions of pairing symmetry driven by the competition between the local spin antiferromagnetic couplings from nodal $d_{x^{2} - y^{2}} \times s_{x^{2} + y^{2}}$ -wave to nodeless -wave through the intermediate $s + i d \times s$ mixed pairing phase, which is consistent with the observation of pressure experiments. The emergent $d$ -wave form factor inevitably arises from the projection of inter-orbital Cooper pairing onto the Fermi surface and is inherited from the electronic structure in the representation of $C_{4}^{p}$ symmetry. Moreover, the $S_{4}$ symmetry dictates 2 copies of $d$ -wave pairing condensates, counting 8 nodes in total. We further show that weakly breaking $C_{4}^{p}$ naturally leads to the octet nodal gap as precisely observed in laser angle resolved photoemission spectroscopy. The octet nodes reflect the collaboration of the $C_{4}^{p}$ and $S_{4}$ symmetries, which sheds new light on the enigma of the pairing symmetry in $KFe_{2} As_{2}$ .

arXiv comment10 pages, 5 figures, revised version

Plaquette-centered rotation symmetry and octet-nodal superconductivity in KFe2​As2​

Abstract

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Plaquette-centered rotation symmetry and octet-nodal superconductivity in $KFe_{2} As_{2}$