Anisotropic conductivity tensor on a half-filled high Landau level

We study two-dimensional interacting electrons in a weak perpendicular magnetic field with the filling factor $\nu \gg 1$ and in the presence of a quenched disorder. As it is known, the unidirectional charge density wave state can exist near a half-filled high Landau level at low temperatures if disorder is weak enough. We show that the existence of the unidirectional charge density wave state at temperature $T<T_c$ where $T_c$ is the transition temperature leads to the anisotropic conductivity tensor. We find that the anisotropic part of conductivity tensor is proportional to $(T_c-T)/T_c$ below the transition in accordance with the experimental findings. The order parameter fluctuations wash out the mean-field cusp at $T=T_c$ and the conductivity tensor becomes anisotropic even above the mean-field transition temperature $T_c$.