MAGNETOTRANSPORT PROPERTIES IN THE CHARGE-DENSITY-WAVE STATE OF THE QUASI-2-DIMENSIONAL COMPOUNDS (PO2)4(WO3)(2M)

Magnetotransport has been studied on the quasi-two-dimensional monopho sphate tungsten bronzes (PO2)4(WO3)2m for m = 4, 6 and 7. These series provide a model system where the low-dimensional character and the el ectron density can be changed with m. In P4W8O3 (m = 4) and P4W12O44 ( m = 6), both Hall effect and magnetoresistance data corroborate the ex istence of two successive charge density wave transitions. Large aniso tropic magneto-resistance in the low-temperature state is well account ed for by the presence of small electron and hole pockets with large m obilities. In P4W14O50 (m = 7), the high-temperature transition, close to first order, may be associated with strong electron-phonon couplin g or strong electron-electron interactions. The low-temperature transi tion is mainly structural.