Shubnikov—de Haas measurements in alkali-metal—graphite intercalation compounds

Abstract

Shubnikov\char22{}de Haas (SdH) oscillations are reported for well-characterized (single stage) encapsulated potassium (stages $n=4,5,8$) and rubidium ($n=2,3,5,8$) graphite intercalation compounds. Shapes of the Fermi surface (FS) are deduced from the dependence of the FS cross sections on the angle between the $c$-axis of the sample and $\stackrel{\ensuremath{\rightarrow}}{H}$. The temperature dependence ($1.4lT\ensuremath{\le}25$ K) of the amplitudes of the SdH oscillations has been studied to find cyclotron effective masses for specific FS cross sections. A simple phenomenological energy-band model, based on the $\ensuremath{\pi}$ bands of pristine graphite and $c$-axis zone folding, is used to calculate SdH frequencies as a function of Fermi energy and is applied to interpret the stage- and intercalant-dependent experimental SdH frequencies and effective masses. The good agreement between the observed and predicted effective masses and the FS cross sections confirms the general validity of this model.