Anisotropic vortex lattice structures in the FeSe superconductor

TL;DR

This paper investigates the anisotropic vortex lattice structures in FeSe superconductors, linking experimental observations of nodal superconductivity and anisotropy to theoretical calculations involving orbital ordering and symmetry breaking.

Contribution

It introduces a self-consistent Bogoliubov-de Gennes approach to model anisotropic vortex structures considering orbital ordering effects in FeSe.

Findings

Orbital ordering breaks $C_4$ symmetry to $C_2$ in FeSe.

Theoretical vortex structures match experimental anisotropy.

Nodal superconductivity explained by mixed s-wave pairing.

Abstract

In the recent work by Song et al. [Science 332, 1410 (2011)], the scanning tunneling spectroscopy experiment in the stoichiometric FeSe reveals evidence for nodal superconductivity and strong anisotropy. The nodal structure can be explained with the extended s-wave pairing structure with the mixture of the $s_{x^2+y^2}$ and $s_{x^2y^2}$ pairing symmetries. We calculate the anisotropic vortex structure by using the self-consistent Bogoliubov-de Gennes mean-field theory. In considering the absence of magnetic ordering in the FeSe at the ambient pressure, orbital ordering is introduced, which breaks the $C_4$ lattice symmetry down to $C_2$, to explain the anisotropy in the vortex tunneling spectra.