Influence of disorder strength on the superconducting mechanism of MgB2

Abstract

Abstract We investigate the effect of disorder on the superconducting mechanism of MgB2 thin films using low-energy ion irradiation. The c-axis lattice constant and T c of MgB2 thin films change systematically as the magnitude of disorder, which corresponds to the value of average displacements per atom (dpa avg), increases. Here, dpa avg is controlled by the amount of irradiated ions. The dpa avg dependence of the electron–phonon coupling constants (λ) is estimated using the McMillan equation. For dpa avg ⩽ 0.049, λ is linearly proportional to dpa avg. On the other hand, for dpa avg > 0.049, the T c of the disordered MgB2 deviates from the linear fitting curve, and insulating behavior is observed in the normal state resistivity. These results indicate that the superconducting mechanism of MgB2 can be changed by the electronic system caused by disorder strength affecting the electron–phonon coupling constant λ.