Amplitude solitons in incommensurate Peierls systems: Implications for TTF-TCNQ

Abstract

Amplitude soliton excitations are described for both dimerized [i.e. commensurate with 2k f = ( π a ) ] and incommensurate charge-density- wave (CDW) ground states. For the dimerized case the soliton excitations can have charge + e, 0, − e with spin 0, ± 1 2 , 0 depending on the occupancy of the localized gap state. For the incommensurate case only the neutral spin- 1 2 soliton exists. Utilizing the results of Takayama, Lin-Liu and Maki, we show that E s = ( 2 π )Δ where 2Δ is gap for electron-hole excitations ( Δ i = W exp ( −1 λ ) for the incommensurate case and Δ c = W exp (− 1 2 λ) for the dimerized case where λ is the electron-phonon coupling constant and W is the bandwidth). We suggest that neutral soliton excitations may make significant contributions to the magnetic susceptibility of incommensurate CDW systems, and that this may be the origin of observed differences between the low-temperature magnetic and transport activation energies in TTF-TCNQ.