Some 29 elements are superconductors under normal pressure conditions, and lithium brings to 23 the number that superconduct at higher pressures. In high-pressure experiments the sample is compressed between two diamond surfaces in a diamond anvil cell. However, lithium is highly reactive, which makes high-pressure experiments difficult.

Shimizu and co-workers have now managed to compress a ribbon of highly pure lithium in such a cell. They observe superconductivity as a drop in electrical resistance, and also find that the superconducting transition temperature rises to 20 Kelvin at 48 gigapascals. Although this is the highest observed transition temperature of any element, it is a factor of four less than theoretical predictions. The team also points out that it has failed to observe the Meissner effect – the expulsion of a magnetic field from the sample. Observation of the Meissner effect is often considered a more reliable indication of superconductivity than a dramatic reduction in resistance.

Meanwhile Russell Hemley and co-workers at the Carnegie Institution of Washington in the US have also observed evidence for superconductivity in lithium at extreme pressures. Hemley and co-workers have measured both the electrical conductivity and magnetic susceptibility of lithium to pressures above 80 gigapascals, and have observed transition temperatures between 9 and 16 Kelvin – again much lower than theoretical predictions. However, both sets of results appear to confirm that tentative claims of superconductivity in lithium at high pressures by a group at the University of California at Los Angeles in the mid-1980s were correct.