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

TL;DR

This study investigates how 2-MeV He ion damage affects the superconducting transition temperature and resistivity of MgB2 thin films, revealing a linear decrease in Tc with increased resistivity without saturation.

Contribution

It demonstrates controllable defect introduction in MgB2 and challenges existing theories predicting Tc saturation in the dirty limit.

Findings

Tc decreases linearly with resistivity

Intergrain connectivity remains unchanged

No Tc saturation observed at high damage levels

Abstract

We have studied the effect of damage induced by 2-MeV alpha particles on the critical temperature, Tc, and resistivity 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 40 K increases, while the intergrain connectivity is not changed. Tc is ultimately reduced to less than 7 K and we see no evidence for a saturation of Tc at about 20 K, contrary to the predictions of the Tc of MgB2 in the dirty limit of interband scattering.