COLLECTIVE RESPONSE IN THE MICROWAVE PHOTOCONDUCTIVITY OF HALL BAR STRUCTURES

We have investigated the microwave photoconductivity of 100-mum- and 5 0-mum-wide Hall bars fabricated from GaAs/AlxGa1-xAs heterostructures. We found resonant responses at frequencies f(res) with f(res)2(B) = f (res)2(B = 0) + f(c)2, where f(c) is the cyclotron frequency of the tw o-dimensional electron gas in the perpendicularly applied magnetic fie ld B. This shows that the photoresponse is dominated by collective pla smon excitations confined within the width of the Hall structure.