2019/09/10 by D. Torsello, K. Cho, K. R. Joshi +10 · 1 citation
Physics and Astronomy · #cond-mat.mtrl-sci #cond-mat.supr-con
paper · pdf · doi:10.1103/physrevb.100.094513
published as Phys. Rev. B 100, 094513 (2019) · 8 pages, 5 figures
arxiv created 2019/09/10 · arxiv updated 2019/09/12
We report combined experimental and theoretical analysis of superconductivity in CaK(Fe1-xNix)4As4 (CaK1144) for x=0, 0.017 and 0.034. To obtain the superfluid density, ρ=(1+ΔλL(T)/λL(0) )-2, the temperature dependence of the London penetration depth, ΔλL (T), was measured by using tunnel-diode resonator (TDR) and the results agreed with the microwave coplanar resonator (MWR) with the small differences accounted for by considering a three orders of magnitude higher frequency of MWR. The absolute value of λL (T ≪ Tc) ≈ λL(0) was measured by using MWR, λL (5~K) ≈ 170 ± 20 nm, which agreed well with the NV-centers in diamond optical magnetometry that gave λL (5~K) ≈ 196 ± 12 nm. The experimental results are analyzed within the Eliashberg theory, showing that the superconductivity of CaK1144 is well described by the nodeless s± order parameter and that upon Ni doping the interband interaction increases.