Interfacial Engineering of YBa₂Cu₃O₇/Bi₂Se₃ Heterostructures via Ultrathin Cu Buffer Layers for Mitigating...

The integration of high-temperature superconductor/topological insulator (HTS/TI) heterostructures is essential for next-generation hybrid electronic systems, yet severe interfacial reactions typically lead to the catastrophic degradation of superconductivity in cuprates. In this work, we report a nanoscale interface-engineering approach that utilizes an ultrathin Cu buffer layer to bridge the chemical gap between YBa₂Cu₃O₇ (YBCO) and Bi₂Se₃. By systematically modulating the Cu buffer thickness from 0.5 to 2.0 nm, we identify an optimal regime (0.5 nm) that effectively suppresses detrimental Ba diffusion and stabilizes the Bi-Se framework, as confirmed by depth-resolved X-ray photoelectron spectroscopy and electron microscopy. Notably, this subnanometer buffering enables partial retention of a resistive superconducting-like transition at ∼55 K, while the transport behavior indicates spatially nonuniform superconducting pathways. These results suggest that the ultrathin Cu buffer layer mitigates interfacial degradation rather than fully preserving bulk superconductivity. The present work provides insight into interfacial control in complex oxide/chalcogenide heterostructures and establishes a platform for future investigations of proximity effects in HTS/TI systems.