Four-probe measurements of individual metallic and superconducting nanowires

We have performed 4-probe measurements for a number of individual Au, Ag, Sn and Zn nanowires. The resistivity of these nanowires is always larger than their bulk values, and varies with the crystallinity of the nanowires. Single crystalline Sn nanowires have a resistivity similar to that of bulk Sn, while polycrystalline Au nanowires shows a resistivity twenty to thirty times higher than that of bulk Au. For Sn nanowires with diameter from 280 nm to 70 nm, the superconducting transition temperature $T_{c}$ remains the same as, or slightly lower than the $T_{c}$ of bulk Sn, 3.7 K. The critical current density of these Sn nanowires is measured to be in the order of 105 A/cm2 at low temperature. The critical fields of the nanowires, as expected, are much higher than that of Sn films. A finite resistance, which increases with increasing excitation current, is observed in all the samples. The origins of this finite resistance will be discussed. We have also obtained evidence that the four metallic leads assembled on each single nanowire may have remarkable effects on the transport properties of the nanowire.