Local destruction of superconductivity by non-magnetic impurities in mesoscopic iron-based superconductors.

Jun Li,Liviu F Chibotaru,Takeshi Hatano,Tobias Schwarz,Jie Yuan,Gufei Zhang,Johan Vanacken,Paulo J Pereira,Min Ji,Kazunari Yamaura,Xiaoxing Ke,Gustaaf Van Tendeloo,R Kleiner ,Ya Hua Yuan ,D Koelle ,E Takayama‐Muromachi ,Y Huang ,Hai L Feng ,Hua Bing Wang ,Pan Wu ,Victor Moshchalkov

doi:10.1038/ncomms8614

Abstract

The determination of the pairing symmetry is one of the most crucial issues for the iron-based superconductors, for which various scenarios are discussed controversially. Non-magnetic impurity substitution is one of the most promising approaches to address the issue, because the pair-breaking mechanism from the non-magnetic impurities should be different for various models. Previous substitution experiments demonstrated that the non-magnetic zinc can suppress the superconductivity of various iron-based superconductors. Here we demonstrate the local destruction of superconductivity by non-magnetic zinc impurities in Ba0.5K0.5Fe2As2 by exploring phase-slip phenomena in a mesoscopic structure with 119 × 102 nm2 cross-section. The impurities suppress superconductivity in a three-dimensional ‘Swiss cheese'-like pattern with in-plane and out-of-plane characteristic lengths slightly below ∼1.34 nm. This causes the superconducting order parameter to vary along abundant narrow channels with effective cross-section of a few square nanometres. The local destruction of superconductivity can be related to Cooper pair breaking by non-magnetic impurities.

Highlights

The determination of the pairing symmetry is one of the most crucial issues for the iron-based superconductors, for which various scenarios are discussed controversially
According to Anderson’s theorem[5,6,7,8], a few at% of non-magnetic impurities can act as strong scattering centres and dramatically suppress superconductivity by pair breaking in the case of an anisotropic gap, for example, in a d-wave[9] or s± wave[2,3] superconductor
On the basis of these results, recent theoretical studies proposed that the suppression of superconductivity could be attributed to various effects apart from pair breaking, such as localization[12] or disorder[13,14]

Summary

Introduction

The determination of the pairing symmetry is one of the most crucial issues for the iron-based superconductors, for which various scenarios are discussed controversially. On a local-scale of suppression, the Zn ions can exclude the supercurrent of an unconventionally gapped superconductor within an area of px2ab, which results in a two-dimensional (2D) ‘Swiss cheese’-like supercurrent distribution; here xab is the in-plane coherence length of the superconductor. This model was proposed based on the in-plane Zn-doping studies of cuprate superconductors by scanning tunnelling spectroscopy (STM)[17] and muon spin relaxation experiments[18,19], while such experiments on the iron pnictides are still in progress[20]. For a one-dimensional (1D) superconducting system, it has been proposed that c may be spatially or temporally modulated along its length at finite temperature

Methods

Results

Conclusion