Increase of critical current density in FeSe superconductors due to the strain effect

Abstract Conventional J c -enhancement methods like doping and irradiation often introduce extrinsic elements or defects, altering the intrinsic properties. Here, we report a significant J c enhancement in FeSe single crystals through compressive strain applied using a glass-fiber-reinforced plastic substrate with anisotropic thermal contraction during cooling. Under zero field at 2 K, J c increases by a factor of ∼4 from ∼ 2.3 × 10 4 to ∼ 8.7 × 10 4 A cm −2 ; at 5 T, it achieves an order-of-magnitude enhancement, rising from ∼ 1.0 × 10 3 to ∼ 1.0 × 10 4 A cm −2 . Analysis based on the Dew-Hughes model of the f p ( h ) relationship shows that strain strengthens vortex pinning, and shifts the pinning mechanism from point-like pinning to combined point and surface pinnings. This work offers an effective method to enhance FeSe’s current-carrying limitation, deepens our understanding of iron-based superconductors’ pinning mechanisms, and highlights strain engineering’s potential for optimizing superconducting performance.