Common features in high Tc cuprates and diborides

The normal state of magnesium diboride, the simplest metallic system showing the macroscopic quantum coherence at high temperature (high Tc superconductivity--HTcS) shows some features that are common with the cuprates, shedding light on the pairing mechanism for Tc amplification in HTcS: (1) two or more electronic components associated with multiple Fermi surface portions; (2) crossing of electronic topological transitions (ETT) where the Fermi surface changes its topology and (3) phonon softening in extended Kohn anomalies (EKA) over a large wave-vector range.