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

TL;DR

This study investigates how flux pinning mechanisms in exfoliated FeTe$_{0.6}$Se$_{0.4}$ thin films transition from strong to weak collective pinning as film thickness increases from 30 to 150 nm at 1 T.

Contribution

It reveals a thickness-induced crossover in flux pinning regimes in FeTe$_{0.6}$Se$_{0.4}$ thin films, supported by experimental data and theoretical modeling.

Findings

Strong pinning dominates below ~70 nm thickness.

Weak collective pinning becomes dominant above ~100 nm.

The crossover aligns with a theoretical model by van der Beek et al.

Abstract

We studied flux pinning in exfoliated FeTe$_{0.6}$Se$_{0.4}$ thin-film devices with a thickness $d$ from 30 to 150 nm by measuring the critical current density $J_{\mathrm{c}}$. In bulk FeTe$_{0.6}$Se$_{0.4}$, 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 $J_{\mathrm{c}}$ at a fixed magnetic field of 1 T, we found that the strong pinning is dominant below $d \approx 70$ nm, while the weak collective pinning becomes more important above $d \approx 100$ nm. This crossover thickness can be explained by the theoretical model proposed by van der Beek $\textit{et al}$ [Phys. Rev. B. ${\bf 66}$, 024523 (2002)].