Superconductivity of ultra-fine tungsten nanowires grown by focused-ion-beam direct-writing

The electrical properties of lateral ultra-fine tungsten nanowires, which were grown by focused-ion-beam-induced deposition with 1pA ion-beam current, were investigated. Temperature-dependent electrical measurements show that the wires are conducting and have a superconducting transition with a transition temperature (Tc) about 5.1K. Resistance vs. temperature measurements reveal that, with decreasing cross-sectional area, the wires display an increasingly broad superconducting transition. A residual resistive tail extending down to the low-temperature region is found only for the thinnest tungsten nanowire, which is 10nm thick and 19nm wide. The logarithm of the residual resistance of this wire appears as two linear sections as a function of temperature, one within 300mK below Tc and the other extending down to the lowest measuring temperature of 4.26K. Such features have previously been identified with phase slip processes. Our results are suggestive that the focused-ion-beam technique might be a potential approach to fabricate ultra-thin and ultra-narrow nanowires for the study of superconducting suppression in nanoscale materials and for maskless superconducting device fabrication.