Effect of disorder in neutron irradiated MgB$_{2}$ thin films investigated by transport measurements in high magnetic field

We analyse a series of MgB$_{2}$ thin films grown by Hybrid Physical Chemical Vapor Deposition (HPCVD), where disorder is introduced by neutron irradiation. Increasing progressively the neutron fluence, T$_{c}$ monotonously decreases down to 2K and $\rho _{0}$ increases by one order of magnitude. A complete characterization of this series of samples is presented. In particular, we propose high field magnetoresistivity and critical field as a method to study the effect of disorder in the two bands. Differently from polycrystalline samples, H$_{c2}$, after a first increase at the lowest neutrons fluences, only weakly depends on the irradiation level. This suggests that in thin films H$_{c2}$ and resistivity are affected by different mechanisms induced by irradiation. From a quantitative analysis of the magnetoresistivity curves as a function of the angle between the field and the crystalline axes, we extract the scattering times in $\pi $- and $\sigma $-bands. We find that the unirradiated films have less mobile $\pi -$bands than $\sigma -$ones; upon irradiation, the scattering rates of both bands progressively increase, allowing to estimate resistivity values consistent with the measured ones.