Impurity scattering and transport of fractional quantum Hall edge states

We study the effects of impurity scattering on the low-energy edge-state dynamics for a broad class of quantum Hall fluids at filling factor =n/ (np+1), for integer n and even integer p. When p is positive all n of the edge modes are expected to move in the same direction, whereas for negative p one mode moves in a direction opposite to the other n-1 modes. Using a chiral-Luttinger model to describe the edge channels, we show that for an ideal edge when p is negative, a nonquantized and nonuniversal Hall conductance is predicted. The nonquantized conductance is associated with an absence of equilibration between the n edge channels. To explain the robust experimental Hall quantization, it is thus necessary to incorporate impurity scattering into the model, to allow for edge equilibration. A perturbative analysis reveals that edge impurity scattering is relevant and will modify the low-energy edge dynamics. We describe a nonperturbative solution for the random n-chanel edge, which reveals the existence of a disorder-dominated phase, characterized by a stable zero-temperature renormalization-group fixed point. The phase consists of a single propagating charge mode, which gives a quantized Hall conductance, and n-1 neutral modes. The neutral modes all propagate at the same speed, and manifest an exact SU (n) symmetry. At finite temperatures the Su (n) symmetry is broken and the neutral modes decay with a finite rate which varies as T^2 at low temperatures. Various experimental predictions and implications which follow from the exact solution are described in detail, focusing on tunneling experiments through point contacts.