In V986, an 'earthquake' hit the field of high-temperature superconductivity: layered copper oxides with complicated crystal structures were discovered to super-conduct at amazingly high temperatures, 90-100 K and above (in fact, the superconductivity record is now closer to room temperature than to absolute zero). Then came the aftershock, with the announcement by Jun Akimitsu last year that a simple intermetallic compound superconducts at almost double the temperature of previously studied intermetallic compounds. Although not competing with the copper oxides, magnesium diboride (MgB_2) has atransition temperature of 39 K, and good prospects that uses may be found for it. Our understanding of why this compound should superconduct at such a relatively high temperature has progressed rapidly in the past 18 months. Now Choi et al. (.page 758 of this issue) have calculated the superconducting structure of MgB_2 from basic atomic data and physical laws, and find that it is intrinsically a 'two-band' superconductor of a kind not previously seen. They have used computational techniques not only to obtain the correct value for the transition temperature of MgB_2, but also to map its two-band structure in detail.
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