The electronic susceptibility and charge density waves in 2H layer compounds

Abstract

The authors have calculated the susceptibility chi (q) for 2H- NbSe2 and NbS2 from a tight binding fit to the layer method band structure. It is found to have a broad peak centred about qc the wavevector of the observed charge density wave (CDW). The peak is not caused by saddle points but rather by weak nesting near the Fermi surface. The dependence of chi (q) on electron concentration is investigated, the peak is found to become much sharper with increased occupancy of the band. It is shown that chi (qc) is large enough to be compatible with the criterion for CDW formation which is more easily fulfilled for NbSe2 than NbS2.