Phonon-mediated superconductivity in the metal-bonded perovskite ${\mathrm{Al}}_4\mathrm{H}$ up to 54 K under ambient pressure

Multihydrogen lanthanum hydrides have shown the highest critical temperature $T_c$ at 250–260 K under pressures of 170–200 GPa. However, such high pressure is a great challenge for sample preparation and practical applications. To address this challenge, we propose a design strategy for ambient-pressure superconductors that involves constructing few-hydrogen metal-bonded perovskite hydrides, such as the Al-based superconductor ${\mathrm{Al}}_4\mathrm{H}$, with better ductility than the well-known multihydrogen, cuprate, and Fe-based superconductors. Based on the Migdal-Eliashberg theory, we predict that the structurally stable ${\mathrm{Al}}_4\mathrm{H}$ has a favorable $T_c$ of up to 54 K under ambient pressure.

Figure 1

The design idea for few-hydrogen metal-bonded perovskites, formed by combining a bcc metal lattice—with the body-centered atom (BCA) replaced by a small-mass atom (SMA) or small-radius atom—and a fcc metal lattice, with a much larger packing fraction than a fcc lattice. At top right, a ternary perovskite (see Table S3 for several examples) is depicted, derived from the bcc and fcc lattices by sharing bcc vertex atoms. If sharing fcc vertex atoms, a binary perovskite (shown at bottom right) can be obtained. The fcc body center, i.e., the octahedral interstice ${\mathrm{O}}_{\mathrm{h}}$, can be regarded as a normal lattice point from the viewpoint of perovskite. If the body center of a fcc metal, such as aluminum, is occupied by a H atom, which is the lightest element with the smallest radius, a typical binary Al-based metal-bonded perovskite, ${\mathrm{Al}}_4\mathrm{H}$, can be formed naturally.

Figure 2

Calculated electrostatic potential (a) and electron localization function (b) on the Al-H plane.

Figure 3

Energy bands and corresponding projected DOS (a) and lattice dynamic properties (b) of ${\mathrm{Al}}_4\mathrm{H}$. In (a), the size of the colored circles shows the orbital character, which is proportional to the weight for the orbital contribution. In (b), the left panel shows the phonon spectra decorated with the normalized phonon linewidth, while the right panel shows the projected phonon DOS (PHDOS), Eliashberg spectral function ${\alpha }^{2}F\left(\omega \right)$, and EPC constant $\lambda ={\lambda }_{\mathrm{Al}}+{\lambda }_{\mathrm{H}}$.

Figure 4

EPC constant and superconducting gap of ${\mathrm{Al}}_4\mathrm{H}$. [(a)–(c)] Fully $\mathbf{k}$-resolved EPC strength ${\lambda }_{\mathrm{n}\mathbf{k}}$ on the FS for the three crossing bands, bands 1, 2, and 3 [Fig. 3]. [(d)–(f)] Fully $\mathbf{k}$-resolved superconducting gap ${\mathrm{\Delta }}_{\mathrm{n}\mathbf{k}}$ on the three FS sheets at 10 K. (g) The anisotropic superconducting gap ${\mathrm{\Delta }}_{\mathrm{n}\mathbf{k}}$ as a function of temperature, where the red, blue, and purple lines represent the gaps defined by the maximum normalized quasiparticle DOS. (h) The normalized quasiparticle DOS from 10 to 50 K.