?
Proximity-effect engineering in aluminum-based planar Josephson junctions with intrinsic superconductivity
We present a comprehensive study of planar Nb-Al-Nb Josephson junctions with submicrometer dimen sions (L ≈ 100 nm, active area of approximately 5 × 104 nm2), where the intrinsic superconductivity of the aluminum weak link plays a crucial role in enhancing device performance. Through a combi nation of theoretical modeling and experimental characterization, we demonstrate that the aluminum interlayer significantly boosts the critical current Ic ≈ 50 µA and the characteristic voltage Vc ≈ 1mVat T =4 K, while maintaining the nonhysteretic current-voltage characteristics essential for digital appli cations. Our microscopic model, based on self-consistent solutions of the Usadel equations, reveals that this enhancement originates from the coexistence of proximity-induced superconductivity and intrinsic pairing in aluminum, which is particularly pronounced at an optimal boundary resistance. Structural anal ysis confirms epitaxial Nb-Al interfaces with minimal interdiffusion, enabling reproducible fabrication of these compact junctions. These results establish Nb-Al-Nb bridges as promising building blocks for high-density superconducting electronics operating at helium temperatures.