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

Abstract

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.