Charge-density-wave instabilities and quantum transport in the monophosphate tungsten bronzes (PO2)(4)(WO3)(2m) with m=5 alternate structure

Resistivity, thermoelectric power and magnetotransport measurements have be en performed on single crystals of the quasi two-dimensional monophosphate tungsten bronzes (PO2)(4)(WO3)(2m) for m = 5 with alternate structure. betw een 0.4 K and 500 K, in magnetic fields of up to 36 T. These compounds show one charge density instability (CDW) at approximate to 160 K and a possibl e second one at approximate to 30 K. Large positive magnetoresistance in th e CDW state is observed. The anisotropic Shubnikov-de Haas and de Haas-van Alphen oscillations detected at low temperatures are attributed to the exis tence of small electron and hole Dockets left by the CDW gap openings. Angu lar dependent magnetoresistance oscillations (AMRC) have been found at temp eratures below approximate to 30 K. The results are discussed in terms: of a weakly corrugated cylindrical Fermi surface. They are shown to be consist ent with a change of the Fermi surface below approximate to 30 K.