Microwave-Induced Resistance Oscillations in Non-Faraday Configurations

The microwave-induced resistance oscillations (MIRO) are commonly observed in high-mobility GaAs 2D electron systems (2DES), typically using a Faraday configuration. In a Faraday configuration, the electromagnetic components (E$_{\omega }$ and H$_{\omega })$ coincide with the 2DES plane. We explore MIRO in a microstrip line geometry, in which the dominant excitation component in the 2DES plane is H$_{\omega }$. Our samples were 100 or 200 $\mu $m wide Hall bars of very-high mobility ($\mu \quad >$ 8 $\times $ 10$^{6}$ cm$^{2}$/Vs) GaAs/Al$_{x}$Ga$_{1-x}$As heterojunctions or quantum wells with electron density ranging from 2.1 - 7.0 $\times $ 10$^{11}$/cm$^{2}$. Microwaves from a tunable source (2 GHz - 40 GHz) were fed via a semi-rigid coax cable to the microstrip line over the length of the Hall bar. In a temperature range of 0.3 K -- 2.0 K, we observed strong MIRO in all the samples measured. We have studied the fractional MIRO using both the microstrip line and dipole antenna geometries. By increasing the MW power, MIRO features associated with $\varepsilon $ = 1/2, 1/3, and 1/4 emerged, where $\varepsilon =\omega $/$\omega _{c}$, and $\omega _{c}$ is the cyclotron frequency. Experimental data as well as a brief discussion will be presented. The work at Rice was funded by NSF DMR-0706634.