A calculation of the electronic response function in 2H-NbSe2including electron-phonon matrix element effects

The electronic response including electron-phonon matrix elements in a simple tight-binding model is calculated for the 'd z2 ' sub-band in 2H-NbSe 2 . This function, in contrast to the bare response, shows a peak in the region of the charge density wave (CDW) wavevector. It is therefore concluded that the CDW is driven not simply by Fermi surface nesting but rather by a combination of matrix element effects and weak nesting.