Magnesium diboride (MgB2) is an inexpensive and simple superconductor that is also quite common. It was announced in the journal Nature in March 2001. Its critical temperature (39 K) is the highest amongst conventional superconductors (phonon-mediated superconductors). This material was first synthesized in 1953 but its superconducting properties were not discovered until half a century later.
Though a conventional superconductor, it is a rather unusual one. Its electronic structure is such that there exist two types of electrons at the Fermi level with widely differing behaviours, one of them being much more strongly superconducting than the other. This is at odds with usual theories of phonon-mediated superconductivity which assume that all electrons behave in the same manner. For this reason, theoretical understanding of the properties of MgB2 is not yet achieved, particularly so in the presence of magnetic field.
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