Investigation of dimensionality in superconducting NbN thin film samples with different thicknesses and NbTiN meander nanowire samples by measuring the upper critical field*

Abstract

We study superconducting properties of NbN thin film samples with different thicknesses and an ultra-thin NbTiN meander nanowire sample. For the ultra-thin samples, we found that the temperature dependence of upper critical field (H c2) in parallel to surface orientation shows bending curvature close to critical temperature T c, suggesting a two-dimensional (2D) nature of the samples. The 2D behavior is further supported by the angular dependence measurements of H c2 for the thinnest samples. The temperature dependence of parallel upper critical field for the thick films could be described by a model based on the anisotropic Ginzburg–Landau theory. Interestingly, the results measured in the field perpendicular to the film surface orientation show a similar bending curvature but in a much narrow temperature region close to T c for the ultra-thin samples. We suggest that this feature could be due to suppression of pair-breaking caused by local in-homogeneity. We further propose the temperature dependence of perpendicular H c2 as a measure of uniformity of superconducting ultra-thin films. For the thick samples, we find that H c2 shows maxima for both parallel and perpendicular orientations. The H c2 peak for the perpendicular orientation is believed to be due to the columnar structure formed during the growth of the thick films. The presence of columnar structure is confirmed by transmission electron microscopy (TEM). In addition, we have measured the angular dependence of magneto-resistance, and the results are consistent with the H c2 data.

Anisotropic Superconducting Nb2CTx MXene Processed by Atomic Exchange at the Wafer Scale

“…The upper critical field is normalized by the B p and the temperature is normalized by the critical transition temperature T c(0) . According to the Ginzburg-Landau (GL) theory, the B c ⊥t (t = T c /T c(0) ) can be fitted using equation 32] The value of B c ∕∕ at the 0 K is deduced to be 22 T, about 2.8 times B p . The anisotropic parameter is 𝜁 = B c ∕∕ (0)∕B c ⊥ (0) = 2.2, implying the potential 2D nature of the superconductivity.…”

Analysis of Low-Temperature Magnetotransport Properties of NbN Thin Films Grown by Atomic Layer Deposition

“…However, previous investigations carried out at lower temperatures and inside a magnetically shielded setup still showed a complete transition for small film thicknesses [11]. The incomplete transition was most probably due to magnetic field stray fields that arose from the measurement setup (<50 Gauss) [14]. In general, in this work we defined the critical temperature as the temperature where the sheet resistivity ρ(T c ) dropped to 1 µΩcm.…”

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

“…Nevertheless, the PS features in the form of TAPS [23,[29][30][31] and QPS [24,25,[31][32][33] have been observed even for systems [18,[26][27][28][34][35][36] with physical dimensions higher than the coherence length. An interested reader may find that there are a number of reports, [18,[23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] in which the PS signatures in the form of TAPS, QPS in resistance-temperature transition below T C and intermediate resistive steps (IRS) in current-voltage characteristics (IVC) were reported for different nanostructures fabricated by FIB and other techniques. These PS features may evolve with respect to external parameters such as-magnetic field and temperature and can get suppress after a certain limit values.…”

“…Though the PS features are the manifestations of dimensional restrictions of the order of system coherence length, there are reports [21,[26][27][28] in which PS features are reported for type-II SCNWs of quasi-1D regime with diameter/width larger than the phase coherence length but lower than the magnetic penetration depth [21,26]. Also, the IRS features in IVC have been reported for 2D superconducting structures, [38][39][40][41][42] which are manifested through the interactions of vortex and anti-vortex pairs (V-Av) in the system [16,43]. It is reported that, with respect to temperature or magnetic field (selfgenerated field or an externally applied magnetic field), phase slip centers (PSCs) [32] and phase slip lines (PSLs) [44] emerge across the channel (for a system having channel width higher than the coherence length) which cause the occurrence of IRS states in IVC.…”