Localization effects in the charge density wave state of the quasi-two-dimensional monophosphate tungsten bronzes (PO2)(4)(WO3)(2m) (m=7, 8, 9)

The monophosphate tungsten bronzes (PO2)(4)(WO3)(2m) are quasi-two-dimensio nal conductors which show charge density wave type electronic instabilities . We report electrical resistivity and magnetoresistance measurements down to 0.30 K and in magnetic fields up to 16 T for the m = 7, 8 and 9 members of this family. We show that these compounds exhibit at low temperature an upturn of resistivity and field dependences of the magnetoresistance charac teristic of localization effects. We discuss the dimensionality of the regi me of localization as m is varied. We show that for m = 7, the regime is qu asi-two-dimensional and three-dimensional for m = 8, 9.