Size-dependent anisotropic diamagnetic screening in superconducting Sn nanowires

We present orientation dependent magnetic measurements on ordered arrays of parallel Sn nanowires for diameters D approximate to 6-170 nm. For D >= 50 nm clear superconducting transitions could be detected below T-c=3.7 K attributed to superconductivity of the individual nanowires. Decreasing the wire diameters from bulk values to 50 nm strongly reduces the diamagnetism (by a factor of 10(4)) and enhances the critical field by a factor of 45. For magnetic fields parallel and perpendicular to the wire axis we detect an anisotropy in the diamagnetic screening that is enhanced with decreasing D far above the Ginzburg-Landau prediction. This behavior is attributed to size-dependent anisotropy in the electronic mean free path.