High T c Superconductivity in Heavy Rare Earth Hydrides

Sulfur and lanthanum hydrides under compression display superconducting states with high observed critical temperatures. It has been recently demonstrated that carbonaceous sulfur hydride displays room temperature superconductivity. However, this phenomenon has been observed only at very high pressure. Here, we theoretically search for superconductors with very high critical temperatures, but at much lower pressures. We describe two of such sodalite-type clathrate hydrides, YbH6 and LuH6. These hydrides are metastable and are predicted to superconduct with T (c) similar to 145 K at 70 GPa and T (c) similar to 273 K at 100 GPa, respectively. This striking result is a consequence of the strong interrelationship between the f states present at the Fermi level, structural stability, and the final T (c) value. For example, TmH6, with unfilled 4f orbitals, is stable at 50 GPa, but has a relatively low value of T (c) of 25 K. The YbH6 and LuH6 compounds, with their filled f-shells, exhibit prominent phonon softening, which leads to a strong electron-phonon coupling, and as a result, an increase in T (c).

Automated summary

Recently, carbonaceous sulfur hydride was found to exhibit room temperature superconductivity under high pressure. The authors theoretically identified two sodalite-type clathrate hydrides, YbH6 and LuH6, which may have high superconducting critical temperatures at lower pressures. This is attributed to the electron-phonon coupling enhancement due to the presence of filled f-shells in the YbH6 and LuH6 compounds.