Assessing the feasibility of near-ambient conditions superconductivity in the Lu-N-H system

Abstract

The report of near-ambient superconductivity in nitrogen-doped lutetium hydrides (Lu-N-H) has generated a great interest. However, conflicting results raised doubts regarding superconductivity. Here, we combine high-throughput crystal structure predictions with a fast predictor of superconducting critical temperature (Tc) based on electron localization function to shed light on the properties of Lu-N-H at 1 GPa. None of the predicted structures supports high-temperature superconductivity and the inclusion of nitrogen in the crystal structure predictions leads to more insulating structures than metallic ones in quantity. Despite the lack of near-ambient superconductivity, we consider alternative metastable templates and study their Tc and dynamical stability including quantum anharmonic effects. Lu4H11N exhibits a Tc of 100 K at only 20 GPa, a large increase compared to 30 K of its parent LuH3. Interestingly, it has a similar X-ray pattern to the experimental one. The LaH10-like LuH10 and CaH6-like LuH6 become high-temperature superconductors at 175 GPa and 100 GPa, with Tc of 286 K and 246 K, respectively. Our findings suggest that high-temperature superconductivity is not possible in stable phases at near-ambient pressure. However, at a slightly enhanced pressure of 20 GPa, high-Tc superconductivity emerges in Lu-H-N, and metastable room-temperature superconducting templates persist at high pressures.