Proximity-induced superconductivity within the insulating (Li0.84Fe0.16)OH layers in (Li0.84Fe

Abstract

The superconducting and magnetic properties of single crystalline (Li 0.84 Fe 0.16)OHFe 0.98 Se with the transition temperature T c 40 K were studied by means of muon-spin rotation (μSR). The zero-field and field-shift μSR experiments confirm the homogeneity of the sample and the antiferromagnetic ordering within the (Li 0.84 Fe 0.16)OH layers below T m 10 K. The temperature dependence of the in-plane component of the magnetic penetration depth (λ ab) was found to be consistent with gap opening within the superconducting FeSe planes, and it is well described within either the single s-wave gap or two s-wave gaps scenario. The opening of an additional small superconducting gap within the insulating (Li 1−x Fe x)OH layers was detected from the temperature evolution of the out-of plane component of the magnetic penetration λ −2 c (T). The superconductivity in (Li 0.84 Fe 0.16)OH is most probably induced by the proximity to the superconducting FeSe layers.

Probing the superconducting gap structure of (Li1−xFex)OHFeSe

“…28 The gap values we obtain from fitting the in-plane superfluid density are smaller than those reported from previous measurements, particularly in the case of the smaller gap. Evidence for this smaller gap is clearly observed from our measurements of ∆λ(T ) and ρ s at low temperatures, which may be a result of the high sensitivity of the TDO-based technique.…”

“…2(a) that ∆λ(T ) for the #A samples decreases with decreasing temperature before flattening below about 0.1T c , indicating a nodeless gap structure in (Li 1−x Fe x )OHFeSe with a lack of low energy excitations, which is consistent with previous results. [24][25][26][27][28] Furthermore when fitted with a power law dependence ∆λ(T ) ∼ T n , exponents of n = 2.83 and n = 2.46 are obtained for samples #A-1 and #B-1 respectively. In the case of nodal superconductors, n = 1 for line nodes and n = 2 for point nodes is generally anticipated.…”

“…The fitted values of λ ef f (0) of 636Å and 1228Å for samples #A-1 and #B-1 respectively, are significantly different from the value of λ(0) ≈ 2800Å from µSR measurements. 28 . Such a difference is also expected for multi-gap or anisotropic superconductors.…”

“…26,27 Meanwhile the in-plane superfluid density obtained from muon-spin rotation (µSR) measurements is consistent with either one or two gaps, but very different behavior is seen in the out-of-plane component, which shows a much more rapid drop of the superfluid density with temperature. 28 Furthermore, inelastic neutron scattering (INS) measurements give evidence for the presence of a spin resonance peak, 29,30 consistent with a sign change of the order parameter across the Fermi surface, while a lack of a sign change was suggested from an STS study, on the basis of quasi-particle interference (QPI) results and the effect of impurities.…”

“…28 Since the samples from batch #A are higher quality and show a sharper su- Normalized superfluid density ρs as a function of the reduced temperature T /Tc for sample #A-1 of (Li1−xFex)OHFeSe. The dashed, dashed-dotted and solid lines show fits to models with a single isotropic s-wave gap, two isotropic gaps and the s × τ3 state respectively.…”