Effect of damage by 2 MeV He ions on the normal and superconducting properties of magnesium diboride

We have studied the effect of damage induced by 2MeV alpha particles on the critical temperature, Tc, and resistivity, ρ, of MgB2 thin films. This technique allows defects to be controllably introduced into MgB2 in small successive steps. Tc decreases linearly as the intragrain resistivity at 40K increases, while the intergrain connectivity is not changed. Tc is ultimately reduced to less than 7K and we see no evidence for a saturation of Tc at about 20K, contrary to the predictions of the Tc of MgB2 in the dirty limit of interband scattering.