  We develop a theory of the helicity driven nolinear dc response of gated
two-dimensional electron gas to the terahertz radiation. We demonstrate that
the helicity-sensitive part of the response dramatically increases in the
vicinity of the plasmonic resonances and oscillates with the phase shift
between excitation signals on the source and drain. The resonance line shape is
an asymmetric function of the frequency deviation from the resonance. In
contrast, the helicity-insensitive part of the response is symmetrical. These
properties yield significant advantage for using plasmonic detectors as
terahertz and far infrared spectrometers and interferometers.
