Assessing the possible superconductivity in doped perovskite hydride KMgH$_3$: Effects of lattice anharmonicity and spin fluctuations

Abstract: The superconducting properties of uniformly hole-doped perovskite hydride KMgH$3$ with varying doping concentration and lattice parameter corresponding to different pressures were investigated from first principles. The superconducting transition temperature ($T{\mathrm{c}}$) was predicted from the density functional theory for superconductors (SCDFT), where the effects of lattice anharmonicity and spin-fluctuation were considered and examined. Although lattice anharmonicity tends to suppress superconductivity around the edge of dynamical stability, where the phase is stabilized due to anharmonic effects, $T_{\mathrm{c}}$ is enhanced. In the hole-doped \ce{KMgH3}, substantial spin-fluctuation (SF) effects were discovered, which counters the phonon-mediated pairing and decreases $T_{\mathrm{c}}$. Such anomalously strong SF is evaluated for similar hydrides, where the hydrogen 1-$s$ bands are isolated at the Fermi level, and its correlation with the electronics density of states was explored.