Theory of Helimagnons in Itinerant Quantum Systems IV: Transport in the Weak-Disorder Regime

We apply a recent quasiparticle model for the electronic properties of metallic helimagnets to calculate the transport properties of three-dimensional systems in the helically ordered phase. We focus on the ballistic regime tau^2 T epsilon_F >> 1 at weak disorder (large elastic mean-free time tau) or intermediate temperature. In this regime, we find a leading temperature dependence of the electrical conductivity proportional to T. This is much stronger than either the Fermi-liquid contribution (T^2) or the contribution from helimagnon scattering in the clean limit (T^{5/2}). It is reminiscent of the behavior of non-magnetic two-dimensional metals, but the sign of the effect is opposite to that in the non-magnetic case. Experimental consequences of this result are discussed.