Enhanced vortex pinning with possible antiferromagnetic order in FeSe under pressure

The strong coupling between magnetic, structural, and electronic degrees of freedom is a prominent feature of Fe-based superconductors. However, the relationship between the degrees of freedom and vortex dynamics remains unclear. In this paper, we measure the vortex pinning energy U0/kB within the thermally activated flux-flow regime with respect to the pressure-induced phases in a FeSe single crystal. We show that the dependence of U0/kB on pressure, measured at a magnetic field higher than the crossover field Hcr, follows a trend like those of critical temperature Tc(p) and the average Fermi velocity v¯F(p). On the other hand, at magnetic fields lower than Hcr, U0/kB increases remarkably before reaching the pressure at which antiferromagnetic (AFM) long-range order occurs. Our results suggest the presence of additional pinning sites, possibly AFM domain boundaries, correlated with the enhanced U0/kB. In addition, in this paper, we provide a universal description of the vortex dynamics in FeSe.