Superconductivity of Regular and Fibonacci Mo/V Superlattices
Regular and Fibonacci Mo/V superlattices were epitaxially grown by magnetic sputtering under ultra high vacuum conditions on (1120) Al2O3 substrates held at ≈1000 K during deposition [1,2]. The upper critical field determined from magnetic torque as well as resistivity measurements are investigated as a function of temperature and magnetic field orientation and for various modulations of the proximity-coupled superconducting multilayer. For small modulation lengths Λ (Λ = 19.1 and 16.3 nm for the regular and Fibonacci sequence, respectively) a three-dimensional behavior of the superconducting multilayer is observed with a zero-temperature coherence length ξ∥ ≈ 21 nm and an anisotropy Hc2∥/Hc2⊥ ≈ 2. For multilayers with large modulation lengths (Λ ≈ 64.4 nm) a peculiar temperature dependence is revealed in Hc2∥, which is attributed to dimensional crossovers similar to those described theoretically by Takahashi and Tachiki . Due to the complexity of our multilayer structure dimensionality features occur at different temperatures. If ξ⊥ equals the thinnest V layer thickness, a commensurability between the vortex lattice and the multilayer exists.