AC Response of the Edge States in a Two-Dimensional Topological Insulator Coupled to a Conducting Puddle

We calculate an AC response of the edge states of a two-dimensional topological insulator, which can exchange electrons with a conducting puddle in the bulk of the insulator. This exchange leads to finite corrections to the response of isolated edge states both at low and high frequencies. By comparing these corrections, one may determine the parameters of the puddle.