Phonon-mediated high-temperature superconductivity in ternary borohydride KB$_2$H$_8$ around 12 GPa

TL;DR

This study predicts that the ternary borohydride KB$_2$H$_8$ becomes a high-temperature superconductor around 12 GPa, with a transition temperature exceeding 130 K, based on first-principles calculations of its electronic and phonon properties.

Contribution

The paper introduces a new hydrogen-rich compound, KB$_2$H$_8$, predicted to be a high-temperature superconductor at relatively low pressure, expanding the search for practical superconducting materials.

Findings

Superconducting transition temperature of 134-146 K at ~12 GPa.

KB$_2$H$_8$ is dynamically stable under moderate high pressure.

Strong coupling between metallized bands and phonons drives superconductivity.

Abstract

Discovery of high-temperature superconductivity in hydrogen-rich compounds has fuelled the enthusiasm for finding materials with more promising superconducting properties among hydrides. However, the ultrahigh pressure needed to synthesize and maintain high-temperature hydrogen-rich superconductors hinders the experimental investigation of these materials. For practical applications, it is also highly desired to find more hydrogen-rich materials that superconduct at high temperatures but under relatively lower pressures. Based on first-principles density functional theory, we calculate the electronic and phonon band structures for a ternary borohydride formed by intercalating BH$_4$ tetrahedrons into a face-centered-cubic potassium lattice, KB$_2$H$_8$. Remarkably, we find that this material is dynamically stable and one of its $sp^3$-hybridized $\sigma$-bonding bands is metallized (i.e. partially filled) above a moderate high pressure. This metallized $\sigma$-bonding band couples strongly with phonons, giving rise to a strong superconducting pairing potential. By solving the anisotropic Eliashberg equations, we predict that the superconducting transition temperature of this compound is 134-146 K around 12 GPa.