Anomalously small magnetic relaxation rate of Ca₁₀(Pt₃As₈)(Fe_2−x Pt _x As₂)₅ superconductor

Abstract

Large critical current density and low magnetic relaxation are the main challenges for practical applications of high-temperature superconductors (HTSs). Magnetic relaxation refers to the decay of superconducting current density caused by thermal activation and/or quantum fluctuations. This process involves the motion of vortices, particularly vortex creep, which leads to energy dissipation. HTSs typically exhibit strong superconducting fluctuations and magnetic relaxation due to their short coherence length and large anisotropy. These characteristics are usually manifested by the large Ginzburg number Gi and high magnetic relaxation rate S. The correlation between the relaxation rate S and Gi is informative to understand the interplay between vortex dynamics and relevant parameters. Recently, Eley et al. (Nat. Mater. 16, 409 (2017)) proposed that almost all the HTSs follow a universal lower limit S ~ Gi1/2(T/Tc), providing new clues to design HTSs with small relaxation rate and evaluate their application potential. Here, we systematically studied the vortex dynamics in the Ca10(Pt3As8)(Fe2−xPtxAs2)5 superconductor with a large Gi ~ 0.16. Strikingly, this material exhibits a small relaxation rate (S ∼ 0.02 at Tc/4 under 1 T), approaching the proposed lower limit of S ~ Gi1/2(T/Tc). We propose that such a small value of S in Ca10(Pt3As8)(Fe2−xPtxAs2)5 may originate from its unique structure with metallic skutterudite blocking layers. Our results suggest a promising new avenue for the search and design of HTSs with low magnetic relaxation.