Electron-phonon or hole superconductivity in (MgB2) - art. no. 144523

The BCS electron-phonon mechanism and the unconventional "hole mechanism" h ave been proposed as explanations for the high-temperature superconductivit y observed in MgB2. It is proposed that a critical test of which theory is correct is the dependence of T-c on hole doping: the hole mechanism predict s that T-c will drop rapidly to zero as holes are added, while the electron -phonon mechanism appears to predict increasing T-c. for a substantial rang e of hole doping. Furthermore, the hole mechanism and electron-phonon mecha nism differ qualitatively in their predictions of the effect on T-c, of cha nge in the B-B distances. We discuss predictions of the hole mechanism for a variety of observables as a function of doping, emphasizing the expected differences and similarities with the electron-phonon explanation. The hole mechanism predicts coherence length and penetration depth to increase and decrease monotonically with hole doping, respectively.