Superconductivity in compressed lithium at 20 K

Superconductivity at high temperatures is expected in elements with low atomic numbers, based in part on conventional BCS (Bardeen-Cooper-Schrieffer) theory(1). For example, it has been predicted that when hydrogen is compressed to its dense metallic phase (at pressures exceeding 400 GPa), it will become superconducting with a transition temperature above room temperature(2). Such pressures are difficult to produce in a laboratory setting, so the predictions are not easily confirmed. Under normal conditions lithium is the lightest metal of all the elements, and may become superconducting at lower pressures(3,4); a tentative observation of a superconducting transition in Li has been previously reported(5). Here we show that Li becomes superconducting at pressures greater than 30 GPa, with a pressure-dependent transition temperature (T-c) of 20 K at 48 GPa. This is the highest observed Tc of any element; it confirms the expectation that elements with low atomic numbers will have high transition temperatures, and suggests that metallic hydrogen will have a very high T-c. Our results confirm that the earlier tentative claim(5) of superconductivity in Li was correct.