Topological Proximity Coupling in Pb/Sb Thin-Film Heterostructures

Proximity coupling between topological thin films and ordinary metals can result in the propagation of spin-polarized topological surface states over extended distances. This effect may be utilized to realize the sought-after topological superconductors essential for quantum computing applications. However, suitable candidate systems are rare. Herein, we report a case study of topological proximity coupling in the thin-film heterostructures of Pb, a conventional s-wave superconductor, and Sb, a topological semimetal. By band mappings with angle-resolved photoemission spectroscopy, we show evidence of coherent coupling of Pb and Sb that results in composite quantum well states and emergent surface states at the Pb/vacuum interface consistent with the surface state propagation scenario. The spin texture and spatial charge distribution of the emergent states are investigated by first-principles theoretical calculations. Our results demonstrate the rich possibilities of emergent physics in metal/topological thin film heterostructures and establish Pb/Sb as a topological superconductor candidate.