A dynamical response of a two-dimensional electron system to an in-plane ac electric field has been observed in a strong magnetic field at frequencies f which are smaller than known characteristic frequencies. The effect is shown to be caused by the dynamical accumulation of charge and the formation of a dynamical potential near the edge of the sample. Its spatial distribution is characterized by a length ${\mathit{l}}_{\mathit{E}}$ which depends on f and the conductivity ${\mathrm{\sigma }}_{\mathit{x}\mathit{x}}$ but not on ${\mathrm{\sigma }}_{\mathit{x}\mathit{y}}$. This response offers a contactless method to measure very small values of ${\mathrm{\sigma }}_{\mathit{x}\mathit{x}}$ in the quantum Hall regime.

• Received 27 March 1991

DOI:https://doi.org/10.1103/PhysRevB.44.1946