Electron-phonon interaction and superconductivity in the high-pressure cI16 phase of lithium from first principles.

Abstract

Superconductivity in different phases of lithium (Li) under high pressure has been widely studied both experimentally and theoretically, whereas detailed first-principles investigation of the microscopic mechanism has been limited to the fcc and bcc phases below 40 GPa. Here, we study the electron-phonon interaction and superconductivity in one interesting high-pressure phase of Li (cI16) between 45 GPa and 76 GPa using first-principles calculations and the Wannier interpolation technique. The nature of superconductivity in the cI16 phase is examined by solving the Eliashberg equations, and the superconducting transition temperature Tc of the Li-cI16 in the range of 45-76 GPa is calculated. We analyze the electron-phonon coupling (EPC) effect on the electronic bands, phonon dispersions, the Fermi surface topology (nesting ξq) and the Eliashberg spectral function α2F(ω) at different pressures. In particular, α2F(ω) shows an anomalous trend in spectral weight at a low-frequency region with increasing pressure, which originates from the reduction of the nesting function ξq. The trend of the EPC strength from each phonon branch with pressure is also presented in detail. Another interesting phenomenon from our calculation is the tendency of a metal-to-semiconductor transition with structural optimization at different pressures, which have been reported by previous experiments. Our theoretical studies demonstrate clearly the mechanism behind the anomalous superconducting properties of the high-pressure Li-cI16 phase.