A new method of probing the phonon mechanism in superconductors, including MgB2

Weak localization has a strong influence on both the normal and superconducting properties of metals. In particular, since weak localization leads to the decoupling of electrons and phonons, the temperature dependence of resistance (i.e. lambda (tr)) decreases with increasing disorder, as manifested by Mooij's empirical rule. In addition, Testardi's universal correlation of T-c (i.e. lambda) and the resistance ratio (i.e. lambda (tr)) follows. This understanding provides a new means to probe the phonon mechanism in superconductors, including MgB2. The merits of this method are its applicability to any superconductor and its reliability because the McMillan's electron-phonon coupling constant lambda and lambda (tr) change in a broad range, from finite values to zero, due to weak localization. Karkin et al's preliminary data of irradiated MgB2 show the Testardi correlation, indicating that the dominant pairing mechanism in MgB2 is a phonon-mediated interaction.