Optical properties of superconducting EuFe₂ (As_1‐xP_x)₂

Abstract

We present a broadband optical-conductivity study of superconducting single-crystalline EuFe2(As1-xPx)2 with three different substitutional levels. We analyze the normal-state electrodynamics by decomposing the conductivity spectra using a Drude-Lorentz model with two Drude terms representing two groups of carriers with different scattering rates. The analysis reveals that the scattering rate of at least one of the Drude components develops linearly with temperature for each doping level. This points towards strong electron-electron correlations and a non-Fermi-liquid behavior in the P-substituted superconducting Eu-122 pnictides. We also detect a transfer of the spectral weight from mid-infrared to higher frequencies and assign it to the Hund's-rule coupling between itinerant and localized carriers. The conductivity spectra below the superconducting transition show no sharp features to be associated with the dirty-limit superconducting BCS gaps. We interpret these results in terms of clean-limit superconductivity in EuFe2(As1-xPx)2. The best parametrization fit can be achieved using a two-gap model. We find that the larger gap at the hole pockets of the Fermi surface is likely to be isotropic, while the smaller gap at the electron pockets is anisotropic or even nodal.Comment: to be published in Physica Status Solidi B - Special Issue on Iron Pnictide

Microwave analysis of the interplay between magnetism and superconductivity in EuFe2(As1−xPx)2Ghigo1, Torsello2, Gozzelino3 et al. 2019Phys. Rev. Research241290View full textAdd to dashboardCite

“…Within this range, the same procedure leads to results for λ L and σ n qualitatively similar to those for the Ba122 sample, see the right part of Fig. 2(d), and quantitatively consistent with previous optical investigations [21,22]. Below T on , an additional signal due to a bulk susceptibility contribution emerges.…”

Unique interplay between superconducting and ferromagnetic orders in EuRbFe4As4

“…The decomposition of the itinerant carriers into a narrow and a broad Drude term accounts for the multiband scenario of ironpnictides [19,20]. Similar to the observations in Eu-based 122-compounds [7,24,25], the mid-IR band and higherenergy interband transitions are also visible. Fig.…”

“…For CaKFe 4 As 4 with T c = 31-36 K, for instance, indications of two gaps, at 1-4 meV and at 6-9 meV have been reported [33]. The narrow Drude component of EuRbFe 4 As 4 , however, suggests that here we fall in the clean limit since 1/τ nD ≈ 0.15∆; while the broad Drude term allows a small gap: 1/τ bD = 22∆ [24,34]. It is remarkable that the gap ∆(T ) in the IR spectra does not open gradually, as expected for a second-order transition, but rises sharply at T c , as depicted in Fig.…”

Reentrant phases in electron-dopedEuFe2As2: Spin glass and superconductivity

“…[2,36]. It is interesting to compare our findings with one on Psubstituted EuFe 2 As 2 compounds where no gap was recognized in the optical response, because the samples are clean-limit superconductors [37].…”