Charge-density waves at intermediate coupling

Abstract

An electron–phonon theory for a quasi-one-dimensional band of electrons forming a moving incommensurate charge-density wave (CDW) state at zero temperature is presented. A useful analytic expression for the energy gap as a function of electron–phonon coupling is found. The gap is quite a bit larger than the well-known weak-coupling result, even for modest coupling, where the mean-field approximation should still be valid. It is also shown that the form of the Hamiltonian implies that there is no spread at all in the wavevector of the CDW in the vicinity of 2 k F . Comparisons of theoretical and experimental values of the energy gap and the lattice displacement amplitude are made for NbSe 3 .