Quantum oscillations and magnetic field induced Fermi surface reconstruction in the charge density wave state of A0.9Mo6 O17 (A=Na, K)

We present a detailed study of the magnetotransport properties of the charge density wave state in quasi-two-dimensional purple bronze Na0.9Mo6O17 under pulsed fields up to 62 T. Pronounced Shubnikov-de Haas (SdH) oscillations of three frequencies have been observed in the field induced charge density/spin density wave state of the present compound. The two slow oscillations are attributed to the reconstructed electron and hole pockets near the M′ point of the Brillouin zone (BZ). The highest-frequency oscillations correspond to an orbit occupying 18.1% of the BZ, which is consistent with the hexagonal electron Fermi surface in the normal state. The appearance of the highest-frequency oscillations can be explained by the magnetic breakdown between the electron pockets at the M′ point. This magnetic breakdown behavior has also been observed in K0.9Mo6O17 under very high field range up to 80 T. Based on analyses of the high field SdH oscillations, we propose a possible Fermi surface structure of Na0.9Mo6O17.