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Giant microwave absorption in fine powders of superconductors

TitleGiant microwave absorption in fine powders of superconductors
Publication TypeJournal Article
Year of Publication2018
AuthorsCsosz, G, Markus, BG, Janossy, A, Nemes, NM, Muranyi, F, Klupp, G, Kamaras, K, Kogan, VG, Bud'ko, SL, Canfield, PC, Simon, F
JournalScientific Reports
Date Published07
Type of ArticleArticle
ISBN Number2045-2322
Accession NumberWOS:000440288600014
Keywordsflux-creep, ii superconductors, mixed-state, muon-spin-relaxation, rf magnetic-permeability, sum-rule, surface impedance, Technology - Other Topics, temperature-dependence, thin-films, vortex dynamics

Enhanced microwave absorption, larger than that in the normal state, is observed in fine grains of type-II superconductors (MgB2 and K3C60) for magnetic fields as small as a few %of the upper critical field. The effect is predicted by the theory of vortex motion in type-II superconductors, however its direct observation has been elusive due to skin-depth limitations; conventional microwave absorption studies employ larger samples where the microwave magnetic field exclusion significantly lowers the absorption. We show that the enhancement is observable in grains smaller than the penetration depth. A quantitative analysis on K3C60 in the framework of the Coffey-Clem (CC) theory explains well the temperature dependence of the microwave absorption and also allows to determine the vortex pinning force constant.

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