SPIN-DENSITY-WAVE AND CHARGE-DENSITY-WAVE FLUCTUATION AND ELECTRIC-CONDUCTIVITY

Making use of a microscopic model, we study theoretically the fluctuation contribution to the electric conductivity in the vicinity of the spin-density-wave (SDW) or the charge-density-wave (CDW) transition. We find that the vertex corrections associated with the SDW (or the CDW) fluctuation, which are neglected in earlier works, are of ′ importance. For example, we find the excess resistance in the vicinity of the SDW (or the CDW) transition diverges like ±, with ±=1/2(4-D) and =ln(T/Tc), where D is the dimension of the fluctuation in the clean system. This exponent is larger by unity from the value obtained by Horn and Guiddoti [Phys. Rev. B 16, 491 (1977)]. In dirtier samples in which the vertex renormalization is not so important, we recover the result of Horn and Guiddoti. Further, we find a non-Ohmic term in the fluctuation regime. The non-Ohmic conductivity increases with an external electric field E. Moreover, the effect of E is equivalent to the shift in the temperature T by T=-7(3)(ev-E)(4Tc)-1, with (3)=1.202 and v the Fermi velocity in the chain direction. These results account nicely for recent experimental results by Richard et al., which found no explanation until now. © 1990 The American Physical Society.