The surprising superconductor

It was last year, around this time, that physicists were stunned by the announcement that magnesium diboride, MgB2, a material known since the 1950s, superconducts1 at a critical temperature, Tc, of 39 K. Since this surprising discovery we have witnessed an explosion of research on MgB2 and other related compounds to answer the following questions: is MgB2 unique or are there other similar compounds with higher Tc; what is the mechanism of superconductivity; and what are the potential technical applications of this discovery? This brief report of the progress made in the first year of the MgB2 era gives an insight into the answers to these questions.The serendipitous discovery by Akimitsu’s group1 of the superconductivity of MgB2 at Tc=39 K, almost twice the temperature of other simple intermetallic compounds, has sparked a race to uncover its basic properties and to find other related diborides with even higher Tcs. After the first announcement, the number of preprints appearing on the Los Alamos preprint server (Fig. 1) grew almost exponentially, reaching a maximum of about 60 studies in March (two papers a day), then decreasing linearly down to a paper every other day in August, and staying steady at about this rate until now. During the first year of the MgB2 era, more than 300 studies were published, exploring both fundamental and practical issues, such as the mechanism of the superconductivity; synthesis of MgB2 in the form of powder, thin films, wires, and tapes; the effect on Tc of substitution with various elements and on critical current and fields.