Transport properties and charge density wave instabilities in the quasi-two-dimensional monophosphate tungsten bronzes (PO_2)_4(WO_3)_(2m) (m=5) and K_xP_4W_8O_(32)

摘要

The monophosphate tungsten bronzes (PO_2)_4(WO_3)_(2m) are quasi-two-dimensional conductors which show charge density wave (CDW) type electronic instabilities. These compounds can be viewed as model systems where the role of dimensionality, pressure and doping on the electronic instabilities can be investigated. Varying m lads to a change in the quasi-two-dimensional character while inserting an alkaline element in the tunnels of the crystal structure allows to study the role of band filling. On the other hand, the application of an hydrostatic pressure is a useful tool to study the role of intra- and inter-planes interactions. We report a study of classical and quantum transport properties of the recently synthesized m=5 compounds which exist under two structural varieties as well as transport properties of the doped compounds K_xP_4W_8O_(32). In undoped compounds, Shubnikov-de Haas and angular dependent magnetoresistance oscillations bring new information on the Fermi surface (FS) topology in the CDW state. In K_xP_4W_8O_(32), the transitions are not conventional Peierls instabilities in contrast with the parent undoped compound m=4. We discuss the origin of this anomaly.