Magnetoresistance properties of quasi-two-dimensional charge-density wave compounds AMo6O17 (A = Na, K, and Tl)

Temperature dependence of resistivity in quasi-two-dimensional purple bronzes AMo(6)O(17) (A=Na, K, and Tl) has been comparatively studied between 2 and 300 K at different magnetic fields. Huge positive magnetoresistance (MR) behavior below the Peierls transition temperature T(P)similar to 110 K was found in both K/Tl purple bronzes for H parallel toc, but only a weak one in the Na purple bronze. At lower temperature T(M)similar to 16 K, a second anomaly of the resistivity, which moved to higher temperatures under a magnetic field, was also observed in both K/Tl compounds, with no corresponding anomaly in the Na purple bronze. For H perpendicular toc, the MR effect becomes much weaker in all three compounds. These results suggest that the second anomaly is possibly related to the second Peierls instability, and the huge MR effect results from the large modification of the third FS along the [100] direction induced by the magnetic field, in which the third FS is imperfectly nested in K/Tl purple bronzes and absent in the Na purple bronze. (C) 2001 American Institute of Physics.