Impact of Gd Doping on Morphology and Superconductivity of NbN Sputtered Thin Films

Abstract

We report effect of Gd inclusion in the NbN superconductor thin films. The films are deposited on single crystalline Silicon (100) by DC reactive sputtering technique i.e., deposition of Nb and Gd in presence of reactive N 2 gas. The fabricated relatively thick films (400 nm) are crystallized in cubic structure. These films are characterized for their morphology, elemental analysis and roughness by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDAX) and Atomic Force Microscopy (AFM) respectively. The optimized film (maximum T c ) is achieved with gas ratio of Ar:N 2 (80:20) for both pristine and Gd doped films.The optimized NbN film possesses T c (R=0) in zero and 140kOe fields are at 14.8K and 8.8Krespectively. The Gd doped NbN film showed T c (R=0) in zero and 130kOe fields at 11.2K and 6.8 K respectively. The upper critical field Hc 2 (0) of the studied superconducting films is calculated from the magneto-transport [R(T)H] measurements using GL equations. It is found that Gd doping deteriorated the superconducting performance of NbN.

Spin Seebeck effect mediated reversal of vortex-Nernst effect in superconductor-ferromagnet bilayers

“…where the resistivity becomes 50% of its normal state value) and (ii) the derivative of the resistivity, at different applied magnetic fields to plot it with error bars. This H c2 (T) approximation agrees well with the Ginzburg-Landau (GL) model 38 , which can be described as:…”

Gap fluctuations, Cooper pairs with finite center-of-mass momentum, and suppression of superconductivity in inhomogeneous systems with dopant superpuddles agglomerates

“…In the case of strong disorder and high concentration of impurity centers the superconducting correlation length is comparable to the disorder correlation length and the meanfield equations can lead to self-organized granularity where fluctuations of the local order parameter are present [32]. This is likely to be the case for overdoped cuprate superconductors with high concentration of interstitial oxygens that can lead to the formation of nanosized oxygen puddles, regions with agglomeration of Oi, that support superconductivity [17,18,[33][34][35], but it is also relevant for other systems where granularity and the division between superconducting and metallic domains is important, for instance Mg 1−x Al x B 2 [36], thin films of NbN doped with magnetic impurities [37,38] and in disordered InO x films [39]. Remarkably, disorder also induces reduction of T c in molybdenum nitride (Mo 2 N x ) thin films by increasing the amount of amorphous MoN regions [40] and the loss of superconductivity is associated with the increase of dopant Al atoms near a structural instability in Al−doped MgB 2 [41].…”