MAGNETOTRANSPORT AND CHARGE-DENSITY-WAVE INSTABILITIES IN THE QUASI-2-DIMENSIONAL PHOSPHATE TUNGSTEN BRONZES (PO2)4(WO3)2M (M = 4,6,7)

Electrical resistivity has been measured between 4.2 K and 300 K in fields up to 6 Tesla on the monophosphate tungsten bronzes P4W8O32, P4W12O44 and P4W14O50. These compounds are anisotropic quasi-two-dimensional metals showing several charge density wave instabilities. For m = 4 and m = 6, a large anisotropic magnetoresistance is found in die lowest temperature charge density wave state, as expected, with small carrier pockets left on die Fermi surface by gap openings. For m = 7, several instabilities are found by the transport properties together with a small magnetoresistance. These results are partly consistent with X-ray diffuse scattering studies.