Design Principles for High Temperature Superconductors with Hydrogen-based Alloy Backbone at Moderate Pressure

Abstract

Hydrogen-based superconductors provide a route to the long-sought goal of room-temperature superconductivity, but the high pressures required to metallize these materials limit their immediate application. For example, carbonaceous sulfur hydride, the first room-temperature superconductor made in a laboratory, can reach a critical temperature (Tc) of 288 K only at the extreme pressure of 267 GPa. The next recognized challenge is the realization of room-temperature superconductivity at significantly lower pressures. Here, we propose a strategy for the rational design of high-temperature superconductors at low pressures by alloying small-radius elements and hydrogen to form ternary H- based superconductors with alloy backbones. We identify a ‘fluorite-type’ backbone in compositions of the form AXH8, which exhibit high temperature superconductivity at moderate pressures compared with other reported hydrogen-based superconductors. The Fm3m phase of LaBeH8, with a ‘fluorite- type’ H-Be alloy backbone, is predicted to be thermodynamically stable above 98 GPa, and dynamically stable down to 20 GPa with a high Tc ~ 185 K. This is substantially lower than the synthesis pressure required by the geometrically similar clathrate hydride LaH10 (170 GPa). Our approach paves the way for finding high-Tc ternary H-based superconductors at conditions close to ambient pressures.