The origin of charge density waves in the 2H-polytypes of the group-V layer compounds

Abstract

The group-V metallic layer compounds exhibit superconductivity at low temperatures and all (except NbS2) undergo phase changes due to the formation of CDW at certain temperatures. In order to understand this theoretically, the electronic susceptibility is calculated and the electron-phonon interaction estimated. The susceptibility is computed directly from the band structure, for the example, of NbSe2. A broad maximum, centred onq c , the wave vector of the observed distotion, is obtained indicating an absence of strong nesting. The electron-photon interaction is estimated by using the theory of Barisic and the mass enhancement λ is deduced from experimental data. It is shown that the condition for CDW formation can be fulfilled from our calculations.