Thickness-induced crossover from strong to weak collective pinning in exfoliated FeTe$_{0.6}$Se$_{0.4}$ thin films at 1 T

Abstract

We studied flux pinning in exfoliated FeTe0.6Se0.4 thin-film devices with a thickness d from 30 to 150 nm by measuring the critical current density Jc. In bulk FeTe0.6Se0.4, the flux pinning has been discussed in the framework of weak collective pinning, while there is little knowledge on the pinning mechanism in the thin-film region. From the thickness d dependence of Jc at a fixed magnetic field of 1 T, we found that the strong pinning is dominant below d ≈ 70 nm, while the weak collective pinning becomes more important above d ≈ 100 nm. This crossover thickness can be explained by the theoretical model proposed by van der Beek et al [Phys. Rev. B. 66, 024523 (2002)].