Structure and pressure dependence of the Fermi surface of lithium

Abstract

We report studies of the Fermi surface (FS) of isotopically pure polycrystalline $^{7}\mathrm{Li}$ from ambient pressure to 4.7 GPa. Shubnikov--de Haas (SdH) oscillations at 300 mK in external magnetic fields up to 35 T are measured to map the spherical parts of the FS of lithium. Our ambient pressure data show that the principal SdH frequencies consist of three distinct peaks at $41.25\ifmmode\pm\else\textpm\fi{}0.05, 41.65\ifmmode\pm\else\textpm\fi{}0.05$, and $42.05\ifmmode\pm\else\textpm\fi{}0.05\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.16em}{0ex}}\mathrm{kT}$, which are theoretically consistent with the presence of two crystal structure domains exhibiting nearly spherical FS. The size of the spherical parts of the FS is compatible with bcc and fcc crystal structures. The measured frequencies at 41.25 and 42.65 kT present direct quantitative evidence for the spherical deformation of the FS in fcc Li. Our high-pressure data show that while the FS of Li deforms under compression, it remains mostly spherical up to 4.7 GPa and the pressure dependence of the SdH frequency is consistent with the theoretically calculated pressure dependence in the fcc structure. Finally, we find that the electron effective mass does not deviate under pressure significantly from its ambient pressure value.