Shubnikov–de Haas oscillations for two well-defined frequencies, corresponding, respectively, to areas of 0.8 and 1.36% of the first Brillouin zone, were observed in single crystals of ${\mathrm{Na}}_{0.3}{\mathrm{CoO}}_2$. The existence of Na superstructures in ${\mathrm{Na}}_{0.3}{\mathrm{CoO}}_2$, 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.

• Received 4 May 2006

DOI:https://doi.org/10.1103/PhysRevLett.97.126401