Azbel'-Kaner-like cyclotron resonance in a two-dimensional electron system

Resonant microwave absorption of a two-dimensional electron system in an AlGaAs/GaAs heterostructure excited by a near-field technique was investigated. Along with collective magnetoplasmon modes, we observed resonance that precisely follows the cyclotron resonance (CR) position and revealed no signs of a collective plasma depolarization shift. We show that the discovered CR mode is absent in the Faraday geometry, and it is localized at the edge of the exciting metal electrode. Such behavior points in favor of the single-particle Azbel'-Kaner nature of the discovered resonance.

Figure 1

Dependence of microwave absorption vs magnetic field for different sample geometries and excitation techniques. Sample schematics are drawn next to the corresponding curves. The excitation frequency is $f=16$ GHz for all curves. Fundamental magnetoplasmon (MP), screened magnetoplasmon (SMP), and cyclotron resonance (CR) magnetic-field positions at $f=16$ GHz are marked by labels and vertical dashed lines. MP and SMP modes are excited in both Faraday and near-field geometries, whereas CR is excited only in near-field geometry. The inset plots magnetodispersions of MP (red circles) and SMP (blue circles) modes for a disk sample of $D=1$ mm outer diameter and $d=0.1$ mm concentric central gate. Solid curves correspond to the theoretical dependencies. CR magnetodispersion is also indicated. The insets show a schematic view of the device with excitation geometry.

Figure 2

(a) Microwave absorption as a function of the magnetic field measured for a series of microwave frequencies ($f=9.5$, 15, and $20.5\mathrm{GHz}$). The sample had a quasi-Corbino geometry with microwave radiation guided directly to the central top gate. Curves are offset vertically for clarity. (b) The magnetic-field position of the dark axisymmetric MP, SMP, and CR vs excitation frequency.

Figure 3

Microwave absorption vs magnetic field measured at different values of gate bias ($f=16\mathrm{GHz}$). The CR position $B_c=\omega m^{*}/e=38$ mT is marked by an arrow. Inset: plots of the normalized resonance amplitude vs gate bias for dark axisymmetric MP, SMP, and CR modes.