Theoretical investigation of superconductivity in quaternary double perovskite hydrides at moderate pressure

Recently, perovskite hydrides have received great attention due to their excellent superconductivity at moderate pressures. Based on perovskite structure $Pm\overline{3}m\text{\ensuremath{-}}{\mathrm{KInH}}_{3}$, a series of quaternary double perovskite hydrides ${A}_{2}{\mathrm{In}Z\mathrm{H}}_{6}$ $(A=\mathrm{Li}, \mathrm{Na}, \mathrm{K}, \mathrm{Rb}, \mathrm{Cs}, Z=\mathrm{Cu}, \mathrm{Ag} \mathrm{Au}, \mathrm{Zn}, \mathrm{Cd}, \mathrm{Hg}, \mathrm{Ga}, \mathrm{Tl}, \mathrm{Ge}, \mathrm{Sn}, \mathrm{Pb}, \mathrm{As}, \mathrm{Sb}, \mathrm{Bi})$ were designed. High-throughput screening show that 27 compounds are dynamically stable below 50 GPa. Double perovskite hydrides ${A}_{2}{\mathrm{In}Z\mathrm{H}}_{6}$ which are dynamically stable at moderate pressures are all superconductors. Four hydrides exhibit high-temperature superconductivity, including ${\mathrm{K}}_{2}{\mathrm{InCuH}}_{6}$ (92 K at 0 GPa), ${\mathrm{K}}_{2}{\mathrm{InAuH}}_{6}$ (108 K at 6 GPa), ${\mathrm{Cs}}_{2}{\mathrm{InGeH}}_{6}$ (82 K at 20 GPa), and ${\mathrm{Cs}}_{2}{\mathrm{InAuH}}_{6}$ (104 K at 20 GPa). Additionally, ${\mathrm{K}}_{2}{\mathrm{InAgH}}_{6}$ has a superconducting ${T}_{c}$ of 75 K, which is approaching liquid nitrogen temperature. The flat band of ${\mathrm{K}}_{2}{\mathrm{InCuH}}_{6}$ at \ensuremath{\Gamma} point is governed by $\mathrm{H}\text{\ensuremath{-}}s$ and $\mathrm{Cu}\text{\ensuremath{-}}{e}_{1g}$ orbitals hybridization. Further analysis indicates that there is strong coupling between electrons and hydrogen-dominated optical phonons. This strong electron-phonon coupling (EPC) plays a critical role in high-temperature superconductivity for ${\mathrm{K}}_{2}{\mathrm{InCuH}}_{6}$. Our results enhance confidence in the exploration of high-temperature superconducting perovskite hydrides at moderate pressure, and stimulates further exploration of quaternary superconducting hydrides.