Influence of a Parallel Magnetic Field on Microwave-Induced Oscillatory and Zero-Resistance States

We have studied experimentally the influence of a parallel magnetic field on microwave-induced resistance oscillations and the subsequent zero-resistance states (ZRS) previously discovered in a high-quality two-dimensional electron gas. Our experiments were performed in a frequency range from 25 to 150 GHz and at temperatures from 0.5 to 8 K; samples were Hall bars of GaAs/Al$_{x}$Ga$_{1-x}$As heterojunctions and quantum wells having low temperature mobility as high as 2 x 10$^{7}$ cm$^{2}$/Vs. A two-axis superconducting magnet was employed to facilitate the experiment. We have observed pronounced suppression of oscillations/ZRS by a parallel magnetic field (B$_{//})$. In contrast, resistance peaks associated with magnetoplasmon resonance become stronger in B$_{//}$. We discuss possible explanations for the observations.