2014/07/31 by K. Cho, M. Konczykowski, M. Kończykowski +12
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paper · pdf · doi:10.1103/physrevb.90.104514
published as Phys. Rev. B 90, 104514 (2014)
arxiv created 2014/07/31 · openalex publication_date 2014/09/19 · arxiv updated 2014/11/10 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Irradiation with 2.5 MeV electrons at doses up to 5.2\ifmmode×\else\texttimes\fi1019 electrons/cm2 was used to introduce pointlike defects in single crystals of Ba_1\ensuremath-xKxFe2As2 with x=0.19 (Tc=14\phantom\rule0.16em0exK),0.26 (Tc=32\phantom\rule0.16em0exK), 0.32 (Tc=37\phantom\rule0.16em0exK), and 0.34 (Tc=39\phantom\rule0.16em0exK) to study the superconducting gap structure by probing the effect of nonmagnetic scattering on electrical resistivity \ensuremathρ(T) and London penetration depth \ensuremathλ(T). For all compositions, the irradiation suppressed the superconducting transition temperature Tc and increased resistivity. The low-temperature behavior of \ensuremathλ(T) is best described by the power-law function, \ensuremathΔ\ensuremathλ(T)=A(T/Tc)n. While substantial suppression of Tc supports s_\ifmmode±\else\textpm\fi pairing, in samples close to the optimal doping, x=0.26, 0.32, and 0.34, the exponent n remained high (n\ensuremath≥3), indicating almost exponential attenuation and thus a robust full superconducting gap. For the x=0.19 composition, which exhibits coexistence of superconductivity and long-range magnetism, the suppression of Tc was much more rapid, and the exponent n decreased toward the s_\ifmmode±\else\textpm\fi dirty limit of n=2. In this sample, the irradiation also suppressed the temperature of structural/magnetic transition Tsm from 103 to 98 K, consistent with the itinerant nature of the long-range magnetic order. Our results suggest that underdoped compositions, especially in the coexisting regime, are most susceptible to nonmagnetic scattering and imply that in multiband Ba_1\ensuremath-xKxFe2As2 superconductors, the ratio of the interband to intraband pairing strength, as well as the related gap anisotropy, increases upon the departure from the optimal doping.