Raising the diboride superconductor transition temperature using quantum interference effects

The model of two (sigma and pi) channel superconductivity known to be necessary to explain the superconductivity in MgB2 has been applied to the Al1-xMgxB2 diborides by tuning x from MgB2 to AlMgB4. The interband coupling parameter (probing the strength of the interchannel pairing due to quantum interference effects) and the two gaps in the sigma and pi channel have been calculated as a function of x by using experimental data for the two phonon mode energies which are most relevant for the pairing interaction. It is found that the two gaps reverse in leading order around x=0.6 and that in comparison with the dominant intra-sigma-band single channel pairing an increase in T-c of 1.5 occurs for MgB2 while in AlMgB4 the dominant pi band single channel pairing leads to enhancement of T-c of 100.