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 T_c 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 ξ_q) 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 ξ_q. 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.