Abstract
The critical current of a superconducting nanostructure can be suppressed by applying an electric field in its vicinity. This phenomenon is investigated throughout the fabrication and electrical characterization of superconducting tungsten-carbon (W-C) nanostructures grown by Ga^+ focused ion beam induced deposition (FIBID). In a 45 nm-wide, 2.7 upmu m-long W-C nanowire, an increasing side-gate voltage is found to progressively reduce the critical current of the device, down to a full suppression of the superconducting state below its critical temperature. This modulation is accounted for by the squeezing of the superconducting current by the electric field within a theoretical model based on the Ginzburg–Landau theory, in agreement with experimental data. Compared to electron beam lithography or sputtering, the single-step FIBID approach provides with enhanced patterning flexibility and yields nanodevices with figures of merit comparable to those retrieved in other superconducting materials, including Ti, Nb, and Al. Exhibiting a higher critical temperature than most of other superconductors, in which this phenomenon has been observed, as well as a reduced critical value of the gate voltage required to fully suppress superconductivity, W-C deposits are strong candidates for the fabrication of nanodevices based on the electric field-induced superconductivity modulation.
Highlights
The critical current of a superconducting nanostructure can be suppressed by applying an electric field in its vicinity
The modulation of the critical current induced by the electric field was assessed by measuring current–resistance curves of the nanowire below the critical temperature while sequentially increasing the voltage difference between the gate electrodes, obtaining the resistance as a function of the driving current (Fig. 2)
The obtained values of critical current density are comparable to those obtained in different devices of W-C grown via focused ion beam induced deposition (FIBID), with both 2 D35 and 3 D42 Ga+ and He+ W-C FIBID nanostructures, respectively
Summary
The critical current of a superconducting nanostructure can be suppressed by applying an electric field in its vicinity. The term field effect is used to define the modulation of the charge carrier density that takes place in the active channel of a semiconductor when an electric field is externally applied[1] This electric field-induced resistivity control is at the core of the operation of field-effect transistors (FETs). Recent calculations indicate that such a field is able to extend within a superconducting material over at least the value of its coherence length[4], and the study of the phenomenon in superconducting materials has gained interest in recent years due to its potential application in superconducting e lectronics[5] Central to this interest is the fact that an increasing electric field applied in close proximity to a superconducting bridge has been recently found to progressively suppress the critical current of superconducting channels. Contrarily to other works, an enhancement of the critical current with increasing gate voltage has been observed in niobium nitride thin micro- and nano-bridges, being ascribed to changes in the superconducting vortex surface b arrier[12]
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