NONOHMIC CONDUCTIVITY IN THE FLUCTUATION REGIME OF CHARGE-DENSITY-WAVE AND SPIN-DENSITY-WAVE SYSTEMS

We extend an earlier analysis of the fluctuation contribution to the electric conductivity in quasi-one-dimensional (quasi-1D) charge- (CDW) and spin-density-wave (SDW) systems to the non-Ohmic regime and to nonvanishing frequencies. We find that the electric conductivity increases quadratically with E, when E is sufficiently small, and this increase is given by sigma-(E) - sigma-(0) = ALPHA-sigma-(a)(0)[7-zeta-(3)e-upsilon-E/8(pi-T)2-tau]2, where sigma-(a)(0), upsilon, and T are the anomalous contribution in the absence of E, the Fermi velocity in the chain direction, and the temperature, respectively, and tau = ln(T/T(c)) and zeta-(3) = 1.202.... Here ALPHA takes on values of 3/8, 3/16, 1, and 1/2 for a 3D CDW, 3D SDW, 2D CDW, and 2D SDW, respectively. The effect of the nonvanishing frequency scales exactly with the effect of E in the case of 2D fluctuation, while this scaling is approximate for 3D fluctuation. For 2D fluctuation the scaling is expressed by E = omega-(GAMMA + approximately-GAMMA)/e-upsilon, where GAMMA and approximately-GAMMA are the inverse of the pair-breaking lifetime and the quasiparticle lifetime, respectively.