Surface induced superconductivity of Bi nanowires?

Owing to its large Fermi wavelength and very long mean free paths, Bi is a fascinating metal for studies of transport phenomena in samples of reduced dimensions. Previous experiments explored the influence of the wire diameter on the resistance and the magnetoresistance in a wide temperature range above 1 K. Here, we present to our knowledge for the first time transport measurements below 1 K of crystalline Bi wires with diameters in the 100 nm range. At temperatures below about 0.3 K we find a remarkable decrease of the sample resistances and related effects of an external magnetic field. At first glance, some of our measurements are reminiscent of weak localization. By considering the observed conductance variations of up to 600 e2/h this can be ruled out after all. Although the measurements suggest that the band structure of our wires are close to that of bulk crystalline Bi, which is not superconducting, one might speculate whether surface states can change the electronic structure in favor of superconductivity.