Quantum phase slips in superconducting Nb nanowire networks deposited on self-assembled Si templates

Abstract

Robust porous silicon substrates were employed for generating interconnected networks of superconducting ultrathin Nb nanowires. Scanning electron microscopy analysis was performed to investigate the morphology of the samples, which constitute of polycrystalline single wires with grain size of about 10 nm. The samples exhibit nonzero resistance over a broad temperature range below the critical temperature, fingerprint of phase slippage processes. The transport data are satisfactory reproduced by models describing both thermal and quantum fluctuations of the superconducting order parameter in thin homogeneous superconducting wires

Nonlinear current-voltage characteristics due to quantum tunneling of phase slips in superconducting Nb nanowire networks

“…[19] The obtained value, L ≈ 70 nm, appears to be rather small if directly compared to the estimated length, around 10 µm, of a single continuous nanowire present in the network. This discrepancy could be explained considering that L is not a quantity which can be strictly defined for the network.…”

“…[19] As a consequence, also the zero temperature depairing current density [26] of the single wire j dp (0) = j dp (t)(1 − t) −1.5 ∼ [i dp (t)(1 − t) −1.5 ]/σ 2 ≃ 1.9 × 10 10 A/m 2 is comparable to the one reported in the case of the network with N = 250 and in the case of perforated Nb films. [19,27] This result indicates that the further reduction of N does not significantly depress the superconducting properties of the single wire and confirms, again, the good quality of the sample ruling out the presence of tunneling barriers at the grain boundaries. [16] In Fig.…”

“…For further information on both the normal-state and morphological properties of our samples the reader can refer to Ref. 19, where the central issue of their homogeneity, which can in principle be responsible of the observed excess of dissipation, [16,22] has been largely discussed. …”

“…[9,11,17] Several experiments have confirmed the presence of QPS phenomena in various superconducting materials and systems. [5,6,12,18,19] Recently, we developed a nanofabrication approach which can produce samples with physical properties resembling those of single nanowires. [19] The formation of interconnected networks consisting of ultrathin superconducting Nb nanowires was achieved by using porous silicon (PS) as a template.…”

“…[5,6,12,18,19] Recently, we developed a nanofabrication approach which can produce samples with physical properties resembling those of single nanowires. [19] The formation of interconnected networks consisting of ultrathin superconducting Nb nanowires was achieved by using porous silicon (PS) as a template. Due to the extremely reduced Nb thickness, d Nb ∼ 10 nm, the deposited material tends to occupy only the substrate pitch.…”