Current–voltage characteristics of focused ion beam fabricated superconducting tungsten meanders

Abstract

We report on the superconducting properties and intermediate resistive steps (IRS) observed in the current-voltage characteristics (IVC) of tungsten meander (MW) structures fabricated using focused ion beam (FIB) technique. Three numbers of MWs were studied with individual wire widths of 240 nm, 640 nm and 850 nm with superconducting transition temperatures (TC) of 4.5 K, 4.55 K and 4.60 K respectively. The measured normal state resistance values at 8 K for these wires are of ~182 kΩ, ~49 kΩ and ~32 kΩ, respectively as a function of increasing wire widths; are higher than the quantum of resistance (h/4e2 = 6.45 kΩ) indicating extreme disorder nature of the fabricated samples. The variation of resistance with respect to temperature (for T < TC) follows the theoretical frame work related to weak-link induced thermally activated phase slip (WL-TAPS) for the MW wire of width ~240 nm, while for other samples the convergence between WL-TAPS and the experimental data are not satisfactory. Though the IRS features are present in all the samples with varying degree of prominence, an external magnetic field causes its evolution demarcating different boundary lines with respect to temperature for all the samples. Finally, we believe that the occurrence of IRS is due to phase slip mechanism which further proliferates through PSCs or PSLs in IVC either with respect to temperature or magnetic field. We also believe that the formation of PSCs or PSLs are due to interaction of vortex-anti vortex pairs present along the channel width due to the disorder in the samples. As per our knowledge, such IRS features are not being reported for W-meander wires fabricated using FIB technique. The observation IRS features is promising for the use of FIB fabricated W nanowires for various quantum applications including single photon detection.