Anomalous behavior of the superconducting critical temperature of Mo-V superlattices

We calculate the superconducting critical temperatures of Mo-V superlattices using an extension of Werthamer’s proximity-effect theory. We find a strong discrepancy with experiment for short modulation wavelength Λ, Λ<70 Å, for which the calculated values do not reproduce the anomalous sharp drop observed experimentally. Using a structural model coupled with an analysis of low- and high-angle x-ray diffractograms allows us to determine the strains throughout the multilayers and the density of the misfit dislocations at the interfaces. This structural information is strongly correlated to the anomaly observed both in the superconducting critical temperature and in the residual resistivity ratio. The $T_c$ anomaly reflects a transition from incoherent to partially coherent growth as Λ decreases below 70 Å. In this region where experimental and calculated $T_c$ values diverge, we show that the multilayers are strained, thus providing evidence for the crucial role played by epitaxial growth on the electronic properties.