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 2k F . Comparisons of theoretical and experimental values of the energy gap and the lattice displacement amplitude are made for NbSe 3 .

Charge-density waves arising from two electron bands

“…Similarly, the electron energy E el2 corresponding to pairs |3 , |4 is the same expression as E el1 , except that the energy cutoff is now E c 2 . Just as for the single-band case (see Buker 2009), the phonon energy is…”

“…The total energy is then minimized with respect to this parameter, which yields a fairly simple analytic expression for the gap in terms of an effective electron-phonon (el-phon) coupling l eff . *donbuker@telus.net In a previous treatment (Buker 2009), the CDW-PLD system was solved in the simple context of a single electron band. The present work extends the theory to the common case where the CDW arises from two bands.…”

“…Just as for the single-band case (see Buker 2009), the phonon energy is 10) where the effective coupling l eff is given by 11) and where the dimensionless el-phon coupling l is given by…”

“…In a previous treatment (Buker 2009), the CDW-PLD system was solved in the simple context of a single electron band. The present work extends the theory to the common case where the CDW arises from two bands.…”