For exploring the superconductivity mechanisms and seeking potential high-temperature superconductors in hydrogen-rich compounds, we perform a systematical investigation of the phase diagram, crystal structures, electronic properties, and electron-phonon coupling (EPC) of titanium hydrides under high pressures. Strikingly, the low $T_{\mathrm{c}}$ in $\mathrm{Ti}{\mathrm{H}}_3$ (∼4 K) contrast sharply with the high $T_{\mathrm{c}}$ (above 200 K) in $\mathrm{S}{\mathrm{H}}_3$, though they both possess the same stoichiometry and both crystallize in high-symmetrical cubic crystal. The large difference of $T_{\mathrm{c}}$ motivates us to discover the superconductive mechanism by probing the electron-phonon coupling interaction in the cubic crystal of $\mathrm{S}{\mathrm{H}}_3, \mathrm{Ti}{\mathrm{H}}_3, \mathrm{V}{\mathrm{H}}_3$, and $\mathrm{Se}{\mathrm{H}}_3$. The analyses of phonon linewidths and Fermi surface nesting functions reveal that the contrasting $T_{\mathrm{c}}$ is mainly attributed to the disparate intensity of electrons interacting with optic phonons, rather than the contributions from global electronic structures. Furthermore, it is found that the strong dependency of optic phonon frequencies on the wave vector is an essential ingredient for strong EPC λ.

• Received 17 May 2018
• Revised 25 June 2018

DOI:https://doi.org/10.1103/PhysRevB.98.024514