New metallic superconductor makes an immediate impact

The recent chance discovery that magnesium diboride becomes superconducting at 40 K - almost twice the temperature of other simple intermetallic compounds - has sparked a race to uncover its basic properties and to process the material for applications. Hot on the heels of the discovery of charge-induced superconductivity at 50 K on the surface of carbon-60 molecules late last year comes the discovery of bulk superconductivity at temperatures approaching 40 K in magnesium diboride. This almost doubles the previous record transition temperature, Tc, of simple intermetallic compounds - previously held by niobium germanium at 23.2 K. This record had not been challenged since the early 1970s, although in 1994 a much more complicated compound - yttrium palladium borocarbide - was found to have a Tc of about 23 K. In bulk materials the transition temperature of magnesium diboride (MgB2) is only exceeded by the much more complicated perovskite cuprate structures. The new discovery provides a salutary reminder of the richness of the solid state and the way that interesting physics can emerge from quite unexpected areas. (U.K.)