Distinguishing the Roles of Atomic-Scale Surface Structure and Chemical Composition in Electron Phonon Coupling of the Nb(100) Surface Oxide Reconstruction

The (3 × 1)-O/Nb(100) surface λS was measured to be 0.20 ± 0.06, and its atomic-scale surface structure was confirmed. These results were supported by consistency between measured helium atom scattering Debye–Waller factors and ab initio density-functional theory predictions. The λS measured for the (3 × 1)-O surface reconstruction is further diminished from the metallic, unreconstructed Nb(100) value and the reported bulk Nb λ values. Furthermore, varying subsurface O has no significant effect on the λS of the (3 × 1)-O reconstruction. While the metallic, unreconstructed Nb(100) surface is significantly affected by accumulated subsurface C and O, the (3 × 1)-O reconstruction stabilizes its λS against the effects of subsurface O. Due to the low λS, a negligible critical temperature (TC) ≤ 6.2 × 10–3 K was estimated, indicating that at operational temperatures of ∼2 K, the (3 × 1)-O/Nb(100) reconstruction is not superconducting alone. However, the proximity effect indicates that a thin normal metal in contact with a superconductor exhibits some superconducting properties while the superconductor's properties are diminished. These results contain the first measurement of (3 × 1)-O/Nb(100) λS, distinguish the effects of surface structure and chemical composition on λS, and indicate that the (3 × 1)-O/Nb(100) surface has diminished superconducting properties relative to the unreconstructed, metallic Nb(100) and the Nb bulk.