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 2 MeV alpha particles on the critical temperature, T-c, and resistivity, rho, of MgB2 thin films. This technique allows defects to be controllably introduced into MgB2 in small successive steps. T-c decreases linearly as the intragrain resistivity at 40 K increases, while the intergrain connectivity is not changed. T-c is ultimately reduced to less than 7 K and we see no evidence for a saturation of T-c at about 20 K, contrary to the predictions of the T-c of MgB2 in the dirty limit of interband scattering. (C) 2005 American Institute of Physics.