Upper critical magnetic field and vortex-free state in very thin epitaxial δ-MoN films grown by polymer-assisted deposition

We measured the thickness dependence of the superconducting properties in epitaxial δ-MoN thin films grown on α-Al₂O₃ (001) substrates by polymer-assisted deposition. Our results indicate that the superconducting properties such as the upper critical field (μ ₀H_c2 ≈ 10 T) and the superconducting critical temperature (T_c = 12.5 K) are thickness independent for films thicker than ∼36 nm. By measuring the critical current density (J_c) in the vortex-free state, which coincides with the depairing current density (J₀), we estimate that films thicker than ∼36 nm have a coherence length ξ(0) = 5.8 ± 0.2 nm and penetration depth λ(0) = 420 ± 50 nm. We found that it is possible to enhance the H_c2 (0) values to close to 10 T without any appreciable reduction in T_c.