Quantum Stabilization and Flat Hydrogen-based Bands of Nitrogen-doped Lutetium Hydride

A plausible candidate for near-ambient superconductivity in the Lu-H-N system, Fm3m Lu_8H_23N, is found to be harmonically unstable up to 20 GPa, but is anharmonically stabilized at near-ambient pressures when including quantum corrections. The presence of flat bands near E_F is understood to come from quantum interference caused by the nitrogen, creating a nearly flat hydrogen band at E_F with huge effective mass, meaning non-adiabatic corrections are expected to be anomalously large. The superconducting T_c of Fm3m Lu_8H_23N is estimated to be high by comparison to related compounds and flat band models. The resiliency to defects and pressure dependence of the flat bands is examined. The results here imply this structure is metastable yet flexible enough to synthesize and has electronic properties that can explain the reported near-ambient superconductivity in Lu-H-N.