Fig. 5.

Superconductivity dimensionality crossover in the Mo/Si superlattice. a The in-plane $H_{\mathrm{c2}}^{\mid \mid b}$ and out-of-plane $H_{\mathrm{c2}}^{\mid \mid c}$ upper critical fields versus temperature. Solid lines are fits ∝(T_c − T) in the 3D regime and ∝(T_c − T)^1/2 in the 2D regime. The 2D–3D crossover temperature T^* corresponding to ${\xi }_c\left(T^{*}\right)=s\mathrm{∕}\sqrt{2}$ is indicated. b Temperature dependence of the vortex core size ≃2ξ_c with the different regimes determined by the relation of ξ_c and the multilayer period s. Large circles indicate the temperature at which the emission spectra in Fig. 2 have been acquired