Abstract
The response of superconductors to controlled introduction of point-like disorder is an important tool to probe their microscopic electronic collective behavior. In the case of iron-based superconductors, magnetic fluctuations presumably play an important role in inducing high-temperature superconductivity. In some cases, these two seemingly incompatible orders coexist microscopically. Therefore, understanding how this unique coexistence state is affected by disorder can provide important information about the microscopic mechanisms involved. In one of the most studied pnictide family, hole-doped Ba1−xKxFe2As2 (BaK122), this coexistence occurs over a wide range of doping levels, 0.16 ≲ x ≲ 0.25. We used relativistic 2.5 MeV electrons to induce vacancy-interstitial (Frenkel) pairs that act as efficient point-like scattering centers. Upon increasing dose of irradiation, the superconducting transition temperature Tc decreases dramatically. In the absence of nodes in the order parameter this provides a strong support for a sign-changing s± pairing. Simultaneously, in the normal state, there is a strong violation of the Matthiessen’s rule and a decrease (surprisingly, at the same rate as Tc) of the magnetic transition temperature Tsm, which indicates the itinerant nature of the long-range magnetic order. Comparison of the hole-doped BaK122 with electron-doped Ba(FexCo1−x)2As2 (FeCo122) with similar Tsm ~ 110 K, x = 0.02, reveals significant differences in the normal states, with no apparent Matthiessen’s rule violation above Tsm on the electron-doped side. We interpret these results in terms of the distinct impact of impurity scattering on the competing itinerant antiferromagnetic and s± superconducting orders.
Highlights
In single-band high superconducting transition temperature cuprates, both magnetic and nonmagnetic impurities cause a rapid suppression of Tc, consistent with the nodal d−wave pairing.[14]
Matthiessen’s rule can be violated by Fermi surface reconstruction, In this paper, we focus on the effects of electron irradiation simultaneously on Tc, Tsm and normal state resistivity in an underdoped composition of (Ba1−xKx)Fe2As2, x = 0.2,44 in which long-range magnetic order (LRMO) coexists with superconductivity
We find which takes place below Tsm, or even above Tsm as a consequence of the anisotropic character of the magnetic fluctuations.[47]
Summary
The use of controlled disorder is a powerful phase-sensitive way to study the nature of the superconducting state without affecting the chemical composition.[1–10] According to Anderson’s theorem,[1] conventional isotropic s−wave superconductors are not affected by the scalar potential (i.e., non spin-flip) scattering, but are sensitive to spin-flip scattering due to magnetic impurities (for recent theoretical results on the impact of impurities on Tc, see for example refs. 11–13). The use of controlled disorder is a powerful phase-sensitive way to study the nature of the superconducting state without affecting the chemical composition.[1–10]. Its response to nonmagnetic scattering depends sensitively on the multi-band structure of the pairing interaction, on the chemical potential, and on the gap anisotropy, it is generally expected that intraband scattering is much less efficient in causing pair-breaking than interband scattering.[7,18,21–28]. (Here “sm” is used to indicate simultaneous structural and magnetic transitions in underdoped BaK122).[26] This is not a universal trend, as it depends on the relative ratio of the magnetic and superconducting state energies and on the relative strength of the intraband and interband scattering rates. Irradiation of relatively thin crystals (~20 μm in our case) with
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