Effects of disorder induced by heavy-ion irradiation on (Ba1−x K x )Fe2As2 single crystals, within the three-band Eliashberg s± wave model

Abstract

One of the open issues concerning iron-based superconductors is whether the s± wave model is able to account for the overall effects of impurity scattering, including the low rate of decrease of the critical temperature with the impurity concentration. Here we investigate Ba1−xKxFe2As2 crystals where disorder is introduced by Au-ion irradiation. Critical temperature, T c, and London penetration depth, λ L, were measured by a microwave resonator technique, for different values of the irradiation fluence. We compared experimental data with calculations made on the basis of the three-band Eliashberg equations, suitably accounting for the impurity scattering. We show that this approach is able to explain in a consistent way the effects of disorder both on T c and on λ L(T), within the s± wave model. In particular, a change of curvature in the low-temperature λ L(T) curves for the most irradiated crystals is fairly well reproduced.

Microwave analysis of the interplay between magnetism and superconductivity in EuFe2(As1−xPx)2Ghigo1, Torsello2, Gozzelino3 et al. 2019Phys. Rev. ResearchSelf Cite241290View full textAdd to dashboardCite

“…In particular, it has been shown that magnetic moments in the FeAs layers of iron-based pnictides have a tendency to order antiferromagnetically and it has been theorized that AFM spin fluctuations can induce the s ± pairing at the origin of superconductivity in these compounds [1]. This picture, although not completely accepted, has been suggested for several compounds of the so-called 122 family, i.e., BaFe 2 As 2 with various substitutions, isovalent or inducing electron or hole doping [2][3][4]. Within this framework, systems also containing magnetic rare-earth-metal elements are of interest, since at low temperatures they develop additional magnetic ordering of local moments.…”

Analysis of the London penetration depth in Ni-doped CaKFe4As4

“…The complete characterization of the London penetration depth (absolute value and temperature dependence) can also be carried out by means of a microwave resonator (MWR) technique that has already been applied to other IBS crystals [20][21][22]28,29]. In this case the measurement system consists of an YBa 2 Cu 3 O 7−x coplanar waveguide resonator (with resonance frequency f 0 of about 8 GHz) to which the sample is coupled.…”

“…It should be noted that this approach is only an effective one. The Ni atoms introduced in the structure are scattering centers, but their scattering potential cannot be a priori modeled within a simple scheme as in the case of irradiation induced disorder [21,22]. For these reasons it is more convenient to practically take into account the effects of Ni doping by modifying the coupling matrix instead.…”

“…Measurements of λ L (0) as a function of doping reveal a peak deep in the superconducting state due to the effective mass enhancement approaching a quantum phase transition [15][16][17][18]. Theoretically, London penetration depth can be computed on quite general grounds using the Eliashberg theory and, reproducing experimental data, one can discuss intrinsic quantities, such as the gap values and the coupling matrix coefficients [19][20][21][22].…”

Temperature-Dependent s± ↔ s++ Transitions in the Multiband Model for Fe-Based Superconductors with Impurities

“…Alas, superconducting gap structure has not been convincingly determined in experiments yet. Nevertheless, series of experimental observation such as the spin resonance peak in inelastic neutron scattering [17][18][19][20], a quasiparticle interference in tunneling experiments [21][22][23][24], the NMR spin-lattice relaxation rate [25,26], and the temperature dependence of the penetration-depth [27][28][29] are conveniently explained assuming the s ± state.Scattering on nonmagnetic impurities has different effect on superconductors with different gap symmetries and structures. The pure attractive interaction, both in the intraband and interband channels, results in the s ++ state.…”