Circular-Polarization-Dependent Study of the Microwave Photoconductivity in a Two-Dimensional Electron System

The polarization dependence of the low field microwave photoconductivity and absorption of a two-dimensional electron system has been investigated in a quasioptical setup in which linear and any circular polarization can be produced in situ. The microwave induced resistance oscillations and the zero resistance regions are notably immune to the sense of circular polarization. This observation is discrepant with a number of proposed theories. Deviations between different polarizations occur only near the cyclotron resonance where an unprecedented large resistance response is observed.

Figure 1

Top panel: Quasioptical setup. Bottom panel: Transmission data for 200 GHz linear, left or right hand circular polarized radiation. The inset highlights optical components controlling or affecting the polarization state.

Figure 2

Comparison of the magnetoresistivity $R_{\mathrm{xx}}$ under microwave radiation for both senses of circular polarization and at three frequencies. The transmitted power $P_{\mathrm{trans}}$ (arbitrary units) at 200 GHz is plotted at the top for comparison with the 200 GHz transport data. The blue dotted curve in the bottom panel displays $R_{\mathrm{xx}}$ in the absence of microwaves.

Figure 3

$R_{\mathrm{xx}}$ for 243 and 254 GHz radiation for various polarizations. Curves are offset for clarity. The dashed line represents the transmitted microwave power (no ordinate shown). The bottom panel is a blown up version of the 254 GHz data (no offset). The top inset illustrates the influence of standing waves within the substrate on the line shape of the cyclotron resonance line. The bottom inset plots the resistance maximum marked by a blue triangle as a function of microwave power. The maximum incident power and the corresponding peak height are denoted as $P_{\max }$ and $R_{\max }$.