Frequency and amplitude responses of ac susceptibility in high temperature superconductors

From δl- to δT c-pinning in CaKFe4As4 single crystals obtained by adjusting their defect structures

“…where q can be taken as 3/2 like in most high T c superconductors and iron based superconductors, α can be taken as a constant at given dc fields (H dc ≫ h ac ) and ac frequency, µ is glassy exponent of the collective pinning model [32]. The values µ are about 1/5 for No.1 and 1/8 for No.2 samples determined according to equation (1), which are close to the theoretic value of 1/7 for single vortex pinning but far from the µ values of 3/2 for small bundles (SB) and 7/9 for large bundles (LB) pinning [33,34].…”