Large Perpendicular Critical Field of Superconductivity at EuO/KTaO ₃ (111) Interface

Abstract The recent discovery of superconducting interfaces in KTaO ₃ heterostructures has provided a fertile platform for realizing exciting superconducting properties, while the pairing mechanism remains elusive. Here, an extremely large perpendicular critical field ( B _C2 ) observed at the superconducting EuO/KTaO ₃ (111) interface is reported, strongly suggesting an unusual superconducting pairing mechanism. For comparison, a much smaller B _C2 is observed at the MgO/KTaO ₃ (111) superconducting interface, indicating the significant contributions of EuO to the pairing mechanism at the EuO/KTaO ₃ interface. Furthermore, different from conventional Ginzburg–Landau theory, an abnormal large up‐turn feature is also observed in the B _C2 vs superconducting critical temperature ( T _C ) relationship only at the EuO/KTaO ₃ interface, while absent in all other KTaO ₃ heterostructures. These results strongly suggest an additional pairing mechanism exists at the interface, which may arise from an additional spin‐fluctuation‐enhanced pairing potential due to ferromagnetic EuO.