EFFECTS OF LATTICE FLUCTUATION ON AN ELECTRON BAND IN QUASI-ONE-DIMENSIONAL ELECTRON-PHONON SYSTEM

We investigate the effects of lattice vibrations on an electron gap in the Peierls-Frolich state using the Hartree-Fock approximation with r espect to the electron-phonon coupling, considering both amplitude mod e and phase mode with anisotropic dispersion. In the one-dimensional e lectron-phonon system, the electron gap is induced by the Umklapp scat tering intermediated by the amplitude-mode phonon with momentum transf er of 2k(F). However, the phase-mode phonon gives the large fluctuatio n to the electron band and reduces the band gap. The band gap is deter mined by the competetion between the amplitude mode and the phase mode . We find that the band gap becomes narrower as the velocity of the ph ase-mode phonon u is increased. The band gap tail appears from the ele ctron-phonon scattering. The electron scattering rate due to phonon is estimated to be piuDELTA0/2upsilon(F), where DELTA0 is the electron b and gap and upsilon(F) is the Fermi velocity.