High-pressure band structure and superconductivity of bcc and fcc lithium

Abstract

The electronic band structure, density of states, Fermi surface cross sections and superconductivity of bcc and fcc lithium (Li) as a function of pressure are investigated. The high-pressure band structure exhibits significant deviations from the normal-pressure band structure due to $s\ensuremath{\rightarrow}p$ transition. At normal pressure, the superconducting transition of bcc-Li occurs at $0.12\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$. On further increase of pressure, ${T}_{c}$ increases considerably and its maximum value may exceed $40\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ (at $1.65\phantom{\rule{0.3em}{0ex}}\mathrm{Mbar}$) both in bcc and fcc lithium. At $0.48\phantom{\rule{0.3em}{0ex}}\mathrm{Mbar}$ pressure, the calculated value of ${T}_{c}$ is very close to the experimental value of $20\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The high-pressure bcc and fcc lithium Fermi surfaces are distorted spheres with necks along the $\ensuremath{\Gamma}N$ and $\ensuremath{\Gamma}L$ directions, respectively. The nonlinear increase of ${T}_{c}(P)$ is connected with the non-linear variation of the radius $[{k}_{F}(P)]$ of the Fermi surface neck at high pressure. Our results indicate that, Li is a one-band rather than a one-electron metal. The electron-phonon interaction parameter $(\ensuremath{\lambda})$ and its variation under pressure are structure independent in lithium, and Li is an electron-phonon mediated superconductor.