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, Fm3̄m Lu₈H₂₃N, 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 EF is understood to come from quantum interference caused by the nitrogen, creating a nearly flat hydrogen band at EF with huge effective mass, meaning non-adiabatic corrections are expected to be anomalously large. The superconducting Tc of Fm3̄m Lu₈H₂₃N 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.