Common features in high Tc cuprates and diborides

The features of the normal state of cuprate superconductors, that drive up the Tc from the low temperature range Tc<TbH (where TbH=20.3 K is the boiling point of liquid hydrogen) to Tc>TbH, i.e., the “smoking gun” for the “high-Tc” has not been found even after 18 years from the discovery of the superconductivity in these complex doped Mott insulators. Magnesium diboride provides a superconductor with Tc>TbH that has a normal phase well described by the standard solid state theory. Therefore it provides the simplest system for the “high Tc superconductivity” as the atomic hydrogen was the simplest system for the “quantum mechanics”. Here we show that the normal state of the magnesium diboride shows key features, that are in common with cuprates, and shed light on the pairing mechanism for Tc amplification in the high-Tc superconductors.