"Giant" enhancement of the upper critical field and fluctuations above the bulk T_c in superconducting ultrathin lead nanowire arrays

We have produced ultrathin lead (Pb) nanowires in the 6 nm pores of SBA-15 mesoporous silica substrates by chemical vapor deposition. The nanowires form regular and dense arrays. We demonstrate that bulk Pb (a type-I superconductor below T_c = 7.2 K with a critical field of 800 Oe) can be tailored by nanostructuring to become a type-II superconductor with an upper critical field (H_c2) exceeding 15 T and signs of Cooper pairing 3-4 K above the bulk T_c. The material undergoes a crossover from a one-dimensional fluctuating superconducting state at high temperatures to three-dimensional long-range-ordered superconductivity in the low-temperature regime. We show with our data in an impressive way that superconductivity in elemental metals can be greatly enhanced by nanostructuring.