Evidence of nematic order and nodal superconducting gap along [110] direction in RbFe2As2

Xi Liu,Ran Tao,Mingqiang Ren,Donglai Feng,Qi Yao,Yajun Yan,Wei Chen,Tong Zhang,Thomas Wolf

doi:10.1038/s41467-019-08962-z

Abstract

Unconventional superconductivity often intertwines with various forms of order, such as the nematic order which breaks the rotational symmetry of the lattice. Here we report a scanning tunneling microscopy study on RbFe2As2, a heavily hole-doped Fe-based superconductor (FeSC). We observe significant symmetry breaking in its electronic structure and magnetic vortex which differentiates the (π, π) and (π, -π) directions of the unfolded Brillouin zone. It is thus a novel nematic state, distinct from the nematicity of undoped/lightly-doped FeSCs which breaks the (π, 0)/(0, π) equivalence. Moreover, we observe a clear V-shaped superconducting gap. The gap is suppressed on surface Rb vacancies and step edges, and the suppression is particularly strong at the [110]-oriented edges. This is possibly due to a {{d}}_{{{x}}^2 - {{y}}^2} like pairing component with nodes along the [110] directions. Our results thus highlight the intimate connection between nematicity and superconducting pairing in iron-based superconductors.

Highlights

Unconventional superconductivity often intertwines with various forms of order, such as the nematic order which breaks the rotational symmetry of the lattice
In most undoped and lightly-doped Fe-based superconductor (FeSC), the Fe ions are close to 3d6 configuration, which favor a stripe-like collinear antiferromagnetic (AFM) order or spin density wave (SDW), with a wave vector Q = (π, 0) or (0, π) (an exception is FeTe, which has an bicollinear AFM state with Q = (π/2, π/2))
The pairing symmetry of FeSC is predicted to vary with doping3,4,17

Summary

Introduction

Unconventional superconductivity often intertwines with various forms of order, such as the nematic order which breaks the rotational symmetry of the lattice. We perform surface K dosing on RbFe2As2 and demonstrate that the (π, π) nematic state can be suppressed by electron doping, while the superconductivity is subsequently enhanced.

Results

Conclusion