Observation of a neutron spin resonance in the bilayered superconductor CsCa2Fe4As4F2

D T Adroja,H Luo,S J Blundell,G-H Cao,Z-C Wang,F Lang

doi:10.1088/1361-648x/aba28f

Abstract

We report inelastic neutron scattering (INS) investigations on the bilayer Fe-based superconductor CsCa2Fe4As4F2 above and below its superconducting transition temperature Tc ≈ 28.9 K to investigate the presence of a neutron spin resonance. This compound crystallises in a body-centred tetragonal lattice containing asymmetric double layers of Fe2As2 separated by insulating CaF2 layers and is known to be highly anisotropic. Our INS study clearly reveals the presence of a neutron spin resonance that exhibits higher intensity at lower momentum transfer (Q) at 5 K compared to 54 K, at an energy of 15 meV. The energy ER of the observed spin resonance is broadly consistent with the relationship ER = 4.9kBTc, but is slightly enhanced compared to the values observed in other Fe-based superconductors. We discuss the nature of the electron pairing symmetry by comparing the value of ER with that deduced from the total superconducting gap value integrated over the Fermi surface.

Highlights

The discovery of iron-based superconductors in 2006 by Kamihara et al [1] has attracted considerable interest in condensed matter physics
This paper reports the discovery of a spin resonance mode in a powder sample of CsCa2Fe4As4F2 using inelastic neutron scattering (INS)
The presence of multiple spin resonances has been supported by a random phase approximation (RPA) calculation on CaKFe4As4 that reproduces the broad spectral features of the spin resonance anticipated as a result of multiple superconducting gaps on the different Fermi surface sheets in CaKFe4As4 [36]

Summary

Introduction

The discovery of iron-based superconductors in 2006 by Kamihara et al [1] has attracted considerable interest in condensed matter physics. The mechanism driving superconductivity in the iron-based materials is currently thought to involve spin fluctuations which mediate the electron pairing These spin fluctuations, mainly arising from the excitations between electron and hole pockets, may give rise to a neutron spin resonance centred around an energy (ER) which scales linearly with the superconducting transition temperature Tc with the relationship ER ∼ 4.9kBTc in iron-based superconductors [4, 8]. This has been tested using a variety of iron-based superconductors which fall into the well-known 1111-, 111-, 11-, 112- or 122-type families [4, 9, 10]. Heavy fermion superconductors, which have very low transition temperatures (below 3 K), exhibit a neutron spin resonance [13, 14]

Results

Discussion

Conclusion