Universal influence of disorder on MgB2 wires
The influence of disorder on the superconducting properties of MgB2 wires was investigated. Disorder was introduced in three different ways: by the addition of SiC, by neutron irradiation or by a low processing temperature. We find a nearly identical influence of these three methods on the normal state resistivity, on the upper critical field and on the critical currents in all three cases. The residual resistivity turns out to be a useful parameter for disorder, if normalized appropriately. We extract the mean free path of the charge carriers in the band from the Gor'kov-Goodman relation. The wires investigated in this study fall in the range from the moderately clean to the dirty limit. The most important change in view of possible applications is the increase of the upper critical field, leading to higher critical currents in high magnetic fields.