The use of high pressure to realize superconductivity in the vicinity of room temperature has a long history, much of it focused on achieving this in hydrogen-rich materials. Theoretical calculations using density-functional based structure-search methods combined with BCS-type models predicted a new class of dense, hydrogen-rich materials – superhydrides (MHx, with x > 6 and M selected rare earth elements) – with superconducting critical temperatures (Tc) in the vicinity of room temperature up to and above 200 GPa. The existence of a series of these phases in the La-H system was subsequently confirmed experimentally, and techniques were developed for their syntheses and characterization at megabar pressures. A variety of x-ray diffraction and transport measurements have identified a cubic phase of LaH10 with Tc’s above 260 K near 200 GPa. The measured critical temperatures are in excellent agreement with the original BCS-based calculations assuming conventional superconductivity, and the overall results subsequently confirmed by another experimental group. Our experiments reveal additional superconducting phases with Tc‘s between 150 K and above 260 K in the La-H system, and new hydrogen-rich superconductors with other chemical compositions have been explored. Further understanding the mechanism of superconductivity in these systems requires a more detailed theoretical treatment of the quantum character of these hydrogen-rich materials. These efforts highlight the novel physics in hydrogen-rich materials at high densities, the success of ‘materials by design’ in the discovery and creation of new materials, and the possibility of new classes of superconductors with critical temperatures at and above room temperature.
*Collaborators: M. Somayazulu, M. Ahart, Z. M. Geballe, H. Liu, A. K. Mishra, M. Baldini, Y. Meng, V. V. Struzhkin, I. I. Naumov, R. Hoffmann, and N. W. Ashcroft.