Interplay between magnetism and superconductivity probed by controlled disorder

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Interplay between magnetism and superconductivityprobed by controlled disorder
Strong violation of the Matthiessen's rule (additive resistivities) in hole-doped, but not in electron doped pnictide superconductors, demonstrates importance of interband pairing for hole-doped systems. Phase diagram (RHS) shows locations of the compositions. Inset shows significant suppression of both superconductivity and magnetism by disorder.

Understanding the interplay of superconductivity and magnetism and the role of magnetic fluctuations is crucial to unraveling the origins of unconventional superconductivity. One approach to untangling these effects is to disrupt the magnetic and electronic order parameters simultaneously, while keeping composition, magnetic field, temperature and pressure unchanged. This was achieved by using 2.5 MeV electron irradiation at various doses.Theory predicts a suppression of magnetism, if it is itinerant in nature, which is what was observed. However,depending on details of pairing and scattering in this multi-band system, disorder could enhance or suppress superconductivity. These experiments demonstrated strong suppression of both superconductivity and magnetism by adding disorder, thus setting stringent limits on the microscopic mechanisms. How these two phenomena interact is fundamentally important for understanding superconductivity in iron-based systems. Furthermore,comparing the changes in the resistivity of the irradiated hole-doped BaKFe2As2 to the electron-doped BaKCo2As2 with similar magnetic transition and long-range magnetism, revealed significant differences in their normal state electronic behavior. Altogether, our results imply a highly non-trivial influence of non-magnetic disorder on coupled superconductivity and magnetism in iron based superconductors.

R. Prozorov, M. Konczykowski, M. A. Tanatar, H. H. Wen, R. M. Fernandes, and P. C. Canfield, "Interplay between superconductivity and itinerant magnetism in underdoped Ba1-xKxFe2As2(x = 0.2) probed by the response to controlled point-like disorder", npj Quantum Materials (2019) 4:34;