Flux dynamics, anisotropy in Jc and vortex phase diagram of H+-intercalated FeSe single crystal

This paper investigates the superconductivity, pinning, and vortex dynamics of FeSe before and after protonation. The study shows that, after being protonated, FeSe's superconducting critical temperature T_c has been increased to more than 40 K and the critical current density J_c has also been increased from 2.1 × 10⁴ A/cm² to 1.2 × 10⁶ A/cm², with significantly larger magnetic relaxation rates (Q). Meanwhile, the critical current density anisotropy (γ) decreases substantially while the upper critical field H_c2 increases from 13 T to 91 T after protonation. In addition, the reasons for the absence of the second peak effect in H_x-FeSe were explored. This investigation also reveals the existence of the vortex phase transition associated with the pinning behavior in protonated FeSe, demonstrated by the foot-like characteristics of resistivity. Based on these results, the vortex phase diagrams of FeSe before and after protonation were established. These findings provide important insights for exploring new high-temperature superconductors and their magnetic flux dynamics through protonation.