Charge Density Waves in Layered Compounds
The Transition Metal Dichalcogenide compounds (eg. TaS2) have a layered structure where each layer consists of a hexagonally packed plane of metal atoms sandwiched between two of chalcogen atoms . In the metallic compounds, the Fermi surface consists of cylindrical electron or hole pockets with axes perpendicular to the layer . This “two-dimensional” electronic character leads in most cases to a Periodic Lattice Distortion (PLD) below some temperature Td . The distortion is screened by the electron gas, giving rise to an associated Charge Density Wave (CDW).