Superconducting properties of tungsten nanowires fabricated using focussed ion beam technique

We report superconducting properties of tungsten meander structures fabricated using the focussed ion beam (FIB) induced technique. Three meander structures with individual line widths of ∼70, ∼300 and ∼450 nm were fabricated for evaluation and comparison of the superconducting properties. The resistance-temperature characteristics of the meanders were measured and analysed down to a temperature of 100 mK. The superconducting properties such as critical temperature (T _C) and upper-critical field (H _C2) of these wires are in comparison to the reported values of FIB deposited tungsten available in literature. While the normal state resistance increases sharply as the width of the wire decreases, the superconducting transition temperature registered a slight decrease. Significant amount of residual resistance (3.8% of normal state value at 100 mK) was observed for the sample with the lowest width (70 nm). The residual resistance trails as function of temperature was analysed invoking theoretical models governing the phase slip induced dissipations in superconducting nanowires. The results indicated signature of phase slips as the width of the wire decreases: thermally activated phase slips dominant near to the T _C and quantum phase slip (QPS) near to T _C as well as much below to the T _C. The magneto-resistance isotherms indicated quantum phase transitions (QPT); typical of a superconductor-to-insulator transition (SIT) driven by magnetic field. The SIT transition which originates from the intrinsic disorder present in the sample can be tuned by an external parameter such as magnetic field, and can be modelled by standard theories of QPT for quasi 2D or (2 + 1) D XY models. The successful fabrication of meander structures of W using FIB and the demonstration of superconductivity suggest that FIB deposited W can be exploited for many of the technological applications of superconducting nanowires such as superconducting nanowire single photon detectors, bolometers, transition edge sensors and even for quantum current standard employing the QPS phenomenon.