Nonreciprocal Vortex Pinning and Re-entrant Superconductivity through Niobium Interface Design

Abrikosov vortex motion in type-II superconductors generates finite resistance under applied current, limiting practical use. Traditional suppression via defect engineering is complex and hard to reproduce. Here, we show that interfacial engineering-specifically, tuning the penetration depth (λ) mismatch between an Nb superconducting channel and its capping layer-offers an alternative control of vortex dynamics and re-entrant behavior. Nb microstrips capped with Ta, V, or Cu reveal that force balance-induced vortex pinning yields a re-entrant, dissipationless state in Nb/Ta under magnetic fields of 1.64 T and currents above 0.5 mA, whereas Nb/V and Nb/Cu lack this effect. The phenomenon is strongly anisotropic, appearing only for a magnetic field along the in-plane y-axis and becoming asymmetric under field reversal above 0.8 mA, leading to nonreciprocal behavior. Force analysis shows a ∼0.56 meV/nm pinning energy per vortex, indicating an interface-controlled mechanism that is far weaker yet highly tunable compared to defect-based pinning.