Hydrodynamic charge transport in ultrahigh-mobility two-dimensional electron gas

Viscous fluid in an ultrahigh-mobility (between 2 to 3*10^7 cm^2/Vs) two-dimensional electron gas (2DEG) in GaAs/AlGaAs quantum wells was systematically studied through measurements of negative magnetoresistance (NMR) and photoresistance under microwave radiation, and the data were analyzed according to recent theoretical works by e.g., Alekseev, Physical Review Letters 117,166601 (2016). Size-dependent and temperature dependent NMR were found to conform to the theoretical predictions. The size dependence of microwave induced resistance oscillations (MIRO) and that of the ‘2nd harmonic’ peak indicate that 2DEG in a moderate magnetic field should be regarded as viscous fluid as well. Our results suggest that the hydrodynamic effects must be considered in order to understand semiclassical electronic transport in a clean 2DEG.