Thickness uniformity is regarded as an important parameter in designing thin film devices. However, some applications based on films with nonuniform thickness have recently emerged, such as gas sensors and optimized materials based on the gradual change of film composition. This work deals with superconducting Pb thin films with a thickness gradient prepared with the aid of a diffuse stencil mask. Atomic force microscopy and energydispersive x-ray spectroscopy show variations in the range 90 nm-154 nm. Quantitative magneto-optical images reveal interesting features during both the abrupt and the smooth penetration regimes of magnetic flux, as well as the thickness-dependent critical current density (J c ). In addition, we observe a gradual superconducting transition as the upper critical field is progressively reached for certain thicknesses. Furthermore, the hysteresis observed for triggering flux avalanches when increasing and decreasing magnetic fields is also accounted for by the J c profile evolution along the thickness gradient. Numerical simulations based on the thermomagnetic model are in fair agreement with the experimental data. These findings demonstrate that wedge-shaped films are a viable approach to investigate, in a continuous fashion, thickness-dependent properties of superconducting materials.
In this paper, we investigate QCD-like running coupling αsAdS (Q2) and its associated β-function β(Q2) in the spirit of tachyonic AdS/QCD. We distort the bulk AdS5 space using color dielectric function G(ϕ(z)) associated with tachyons, with ϕ(z) the tachyon field. The function presents different properties of αsAdS (Q2) at small and large values of the fifth-dimensional holographic variable z. The function distorts the AdS space, giving αsAdS (Q2) and its β-function β(Q2) at any Q2 scale, with Q2 the space-like momentum. The result obtained for a large value of z is expected to show characteristics similar to nonperturbative QCD. On the other hand, the result obtained for a small value of z is expected to show characteristics similar to perturbative QCQ. The presence of free tachyons leads to distortion of the AdS space at a small z, that notwithstanding, condensed tachyon states also lead to large z distortion. This provides a unified background for determining αsAdS (Q2) and its β(Q2) in both the ultraviolet (UV) and infrared (IR) regions using a single function in the framework of tachyonic AdS/QCD.
In this paper we investigate the QCD running coupling α AdS s (Q 2 ) and the associated β-function β(Q 2 ) in the spirit of tachyonic AdS/QCD. We distort the AdS5 conformal symmetry using color dielectric function G(φ(z)) associated with free tachyons. Results obtained in this region are expected to present characteristics similar to the perturbative QCD. We further study the distortion of the conformal symmetry with condensed tachyon color dielectric function G(η(z)) which leads to color confinement in the IR region similar to low energy nonperturbative QCD. Results obtained in this region are compared with AdS/QCD with positive dilaton profile, e κ 2 z 2 . The color dielectric function is carefully defined to generate the needed characteristics in both regions with dependence only on fifth dimensional coordinate z.
We investigate the targeted and localized material modifications produced by electropulsing on Al capped Nb microbridges with multiterminal configuration. The affected regions on the Nb/Al bilayer terminals are revealed by an in-lens secondary electrons detector in a scanning electron microscope as well as by Kelvin-probe force microscopy, both suggesting a decrease of the work function in the modified areas. In contrast to that, the affected areas are neither apparent through an Everhart-Thornley secondary electrons detector nor through atomic force microscopy, which indicates little morphological changes on the microstructure. In addition, we demonstrate that the extension of the electroannealed regions is strongly influenced by the terminal geometry. These results are captured by complementary finite element modelling which permits us to estimate a threshold temperature of 435 ± 35 K needed to induce material modifications. These findings provide further insights on the subtle modifications produced by gentle electroannealing of Nb/Al microstructures and represent a step forward towards mastering this emerging nanofabrication technique.
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