Surface Acoustic Wave Study in Microwave-Induced Non-Equilibrium Electron System

Microwave-induced resistance oscillations (MIRO) and zero-resistance states (ZRS) occur under microwave irradiation in the ultrahigh mobility two-dimensional electron gas (2DEG) in GaAs/AlGaAs quantum wells (QW). We employed the surface acoustic wave (SAW) to study the structure of MIRO and ZRS. We observe that the velocity shift (Δv/v) shows minima at the peak resistance regime (j ≡ ω/ω_C ~ 1, 2, 3, etc). And in the ZRS regime, an increase of the velocity shift appears at j = 5/4. The results conform to the theoretical and experimental studies of current domains at ZRS under high power microwave.