Coexistence of low-moment magnetism and superconductivity in tetragonal FeS and suppression ofTcunder pressure

Abstract

We report local probe (µSR) measurements on the recently discovered tetragonal FeS superconductor which has been predicted to be electronically very similar to superconducting FeSe. Most remarkably, we find that low moment (10 −2 − 10 −3 µB) disordered magnetism with a transition temperature of TN ≈ 20 K microscopically coexists with bulk superconductivity below Tc = 4.3(1) K. From transverse field µSR we obtain an in-plane penetration depth λ ab (0) = 223(2) nm for FeS. The temperature dependence of the corresponding superfluid density λ −2 ab (T ) indicates a fully gapped superconducting state and is consistent with a two gap s-wave model. Additionally, we find that the superconducting Tc of FeS continuously decreases for hydrostatic pressures up to 2.2 GPa. 74.62.Fj, 76.75.+i arXiv:1602.01987v1 [cond-mat.supr-con]

Robustness of superconductivity to competing magnetic phases in tetragonal FeS

“…We observe a slight increase of relaxation as T approaches T c , but this is not as drastic a change as reported in Ref. 20. [Note that in Fig.…”

“…Our data only covers the low-field region, but is entirely consistent with that obtained in Ref. 20. Fitting both datasets with this correction to Eq.…”

“…20, the magnetic properties have been found to be markedly different. Sample ZF-µSR spectra above and below T c are given in Fig.…”

“…It has been suggested that a low-moment magnetic phase with T N ≈ 20 K coexists with superconductivity in t-FeS. 20 There has also been evidence that a magnetic anomaly exists below 15 K, while commensurate antiferromagnetic order exists below 116 K.…”

Electronic structure of FeS

“…Moreover, the gap structure of FeS is currently under debate. Muon spin rotation (µSR) measurements favor the fully-gapped superconductivity coexisting with a low-moment magnetic state at low temperature in polycrystalline FeS [18,19]. On the contrary, thermal conductivity and specific heat measurements support the existence of a nodal gap [20,21], while scanning tunneling spectroscopy indicates a highly anisotropic or nodal superconducting gap structure [22].…”