Shubnikov de Haas effect in the metallic state of Na$_{0.3}$CoO$_2$
  Shubnikov de Haas oscillations for two well defined frequencies, corresponding respectively to areas of 0.8 and 1.36% of the first Brillouin zone (FBZ), were observed in single crystals of Na$_{0.3}$CoO$_2$. The existence of Na superstructures in Na$_{0.3}$CoO$_2$, coupled with this observation, suggests the possibility that the periods are due to the reconstruction of the large Fermi surface around the $\Gamma$ point. An alternative interpretation in terms of the long sought-after $\epsilon_g^\prime$ pockets is also considered but found to be incompatible with existing specific heat data. 
L. Balicas, J. G. Analytis, Y. J. Jo, K. Storr, H. Zandbergen, Y. Xin,   N. E. Hussey, F. C. Chou, and P. A. Lee