Competing length scales and 2D versus 3D dimensionality in relatively thick superconducting NbN films.

Magneto-transport characteristics of 2D and 3D superconducting layers, in particular, temperature and angular dependences of the upper critical field H, are usually considered to be fundamentally different. In the work, using non-local resistance measurements at temperatures near the normal-to-superconducting transition, we probed an effective dimensionality of nm-thick NbN films. It was found that in relatively thick NbN layers, the thicknesses of which varied from 50 to 100 nm, the temperature effect on H certainly pointed to the three-dimensionality of the samples, while the angular dependence of H revealed behavior typical for 2D samples.

Intermediate-spin state of a 3d ion in the octahedral environment and generalization of the Tanabe-Sugano diagrams.

Electronic spectra of 3d(n) transition ions in an octahedral ligand surrounding have been studied using the modified crystal field approach (MCFA), which includes a relativistic spin-orbital interaction. A new variable parameter, the effective nuclear charge Z(eff) of a metal ion that allows accounting implicitly the covalence degree of a metal-ligand bond, has been introduced. Energy diagrams similar to the Tanabe-Sugano ones have been calculated.