Superconductivity in nanocrystalline tungsten thin films growth by sputtering in a nitrogen-argon mixture

Abstract

We report on the structural and superconducting properties of nanocrystalline tungsten thin films growth by sputtering at room temperature with an N 2 :Ar mixture (N 2 from 3% to 50%). The crystalline phases were identified by comparing as-grown and thermal annealed thin films. For N 2 /(Ar+N 2 ) mixtures between 3 and 10 %, the films display nanocrystalline β-W phase.Coexistence of β-W and W 2 N phases are observed for gas mixtures with N 2 between 20 % and 40%. A detailed study of the superconducting properties as function of the thickness was performed for W films growth with 8 % N 2 mixtures. For this concentration, the nitrogen atoms increase the disorder at the nanoscale reducing the grain size and avoiding the crystallization of α-W. The superconducting critical temperature (T c = 4.7 K) is thickness independent for films thicker than ~ 17 nm. Below this thickness, the T c value decreases systematically being 3.1 K for 4 nm thick films. Our study provides a simple method for the fabrication of nanocrystalline β-W thin films with potential applications in superconducting devices.

Formation of tungsten carbide by focused ion beam process: A route to high magnetic field resilient patterned superconducting nanostructures

“…The limiting orbital field, H orb c2 may be calculated from experimental data as H orb c2 (T = 0) ≈ 0.7 T dH c2 dT Tc . The applicability of WHH theory to amorphous superconductors is well established [25][26][27]. Later on we shall show quantitatively, that the application of the WHH theory is well justified for this system.…”

Elucidating the role of disorder introduced by nitrogen in the superconducting properties of tungsten thin films

“…The electrical resistivity of β-W is much higher than the α-W 1 . Moreover, it displays high spin-orbit coupling (SOC) and type II superconductivity has been observed in disordered thin films 3,5,10 . The SOC converts the material into an exciting candidate for applications in spintronic 5,6,11 .…”

“…Tungsten is characterized by two different phases: alpha (a)-W (body-centered cubic structure) and beta (b)-W (A15 structure). 1 The latter is metastable, 2 and it is usually stabilized in sputtered films by modifying the deposition parameters 3 or adding nitrogen 4,5 or oxygen impurities in a reactive atmosphere. [6][7][8][9] The electrical resistivity of b-W is much higher than that of a-W. 1 Moreover, it displays high spin-orbit coupling (SOC) and type II superconductivity has been observed in disordered thin films.…”

“…[6][7][8][9] The electrical resistivity of b-W is much higher than that of a-W. 1 Moreover, it displays high spin-orbit coupling (SOC) and type II superconductivity has been observed in disordered thin films. 3,5,10 The SOC converts the material into an exciting candidate for applications in spintronics. 5,6,11 On the other hand, superconductivity with a critical temperature (T c ) ranging from 3 to 5 K may be relevant for fabricating devices such as superconducting nanowire single-photon detectors (SNSPDs).…”

“…3,5,10 The SOC converts the material into an exciting candidate for applications in spintronics. 5,6,11 On the other hand, superconductivity with a critical temperature (T c ) ranging from 3 to 5 K may be relevant for fabricating devices such as superconducting nanowire single-photon detectors (SNSPDs). 12 However, the origin of superconductivity in disordered W films is unclear.…”