Transport properties of superconducting and non superconducting sputtered thin films of Nb-N

We have prepared and studied various kinds of sputered Nb-N samples. By changing the preparation conditions we can indeed obtain superconducting samples or on the opposite very resistive samples. In the first case we have studied the behaviour of the slope of the critical field versus temperature curves near T
c
and we have shown that
(\frac{dH_{c2}}{dT})_{T_{c}}
is a regular increasing function of the Ginzburg-Landau parameter κ. On the other hand have measured the perature dependent resistivity
\rho(T)
, of the nonsuperconducting samples. The results can be interpreted in terms of hopping conduction in disordered materials, the resistivity indeed fit well Mott's relation,
\rho=\rho_{0}\exp(\frac{T}{T_{o}})^{-1/4}
.