Ames Laboratory; Physics and Astronomy
Physics and Astronomy, Ames Laboratory
Physical Review B
We report combined experimental and theoretical analysis of superconductivity in CaK(Fe1-xNix)(4) As-4 (CaK1144) for x = 0, 0.017, and 0.034. To obtain the superfluid density rho = [1 + Delta lambda(L)(T)/lambda(K)(0)](-2), the temperature dependence of the London penetration depth Delta lambda(L)(T) was measured by using a 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 lambda(L)(T << T-c) approximate to lambda(L)(0) was measured by using MWR, lambda(L)(5 K) approximate to 170 +/- 20 nm, which agreed well with the NV centers in diamond optical magnetometry that gave lambda(L)(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.
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Iowa State University Digital Repository, Ames IA (United States)