Evolution of hydrogen dissolution and superconductivity in Re-based solid solutions under pressure studied by ab initio calculations

The dissolving of hydrogen (H) into rhenium (Re) is non-negligible in high-pressure experiments involving dense hydrogen and hydrogenous materials, in which rhenium is often used as a gasket material in the high-pressure diamond-anvil cell devices. However, the evolution of hydrogen dissolution into Re and the pressure-induced effects of hydrogen coupling on the superconductivity of metal-based hydrides remain poorly understood experimentally, and theoretical investigations are currently lacking. The present work addresses these issues by applying ab initio calculations for systematically investigating the dissolution of H atoms in Re systems, as well as the electronic properties, lattice dynamics, and electron-phonon coupling (EPC) in the corresponding interstitial Re hydrides. A series of $\mathrm{Re}{\mathrm{H}}_{x}$ compounds with increasing $x$ in the range of 0 to 1 in increments of 0.125 are predicted to be stable at increasing pressures ranging from 1 to 50 GPa. It is found that H atoms generally play the role of impurities in the $\mathrm{Re}{\mathrm{H}}_{x}$ compounds except for $\mathrm{Re}{\mathrm{H}}_{0.5}$ and ReH, where H atoms are integrated into the crystal structure. Moreover, the atomic configuration of the Re host lattice is basically preserved with increasing $x$ and increasing pressure. Further analysis of the superconductive mechanism indicates that an increasing H concentration results in a decreased electronic density of states at the Fermi level and increasing phonon frequencies, which lead to a decrease of EPC \ensuremath{\lambda} and superconducting critical temperature. These findings quantitatively clarify the effects of hydrogen doping on superconductivity in metal-based hydrides, and thereby support the exploration of new types of superconductive hydrides.