Collective response in the microwave photoconductivity of Hall bar structures

Abstract

We have investigated the microwave photoconductivity of 100-\ensuremath{\mu}m- and 50-\ensuremath{\mu}m-wide Hall bars fabricated from GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As heterostructures. We found resonant responses at frequencies ${\mathit{f}}_{\mathrm{res}}$ with ${\mathit{f}}_{\mathrm{res}}^{2}$(B)=${\mathit{f}}_{\mathrm{res}}^{2}$(B=0)+${\mathit{f}}_{\mathit{c}}^{2}$, where ${\mathit{f}}_{\mathit{c}}$ is the cyclotron frequency of the two-dimensional electron gas in the perpendicularly applied magnetic field B. This shows that the photoresponse is dominated by collective plasmon excitations confined within the width of the Hall structure.