Compressibility of a 2D electron gas under microwave radiation

Microwave irradiation of a two-dimensional electron gas (2DEG) produces a non-equilibrium distribution of electrons, and leads to oscillations in the dissipative part of the conductivity. We show that the same non-equilibrium electron distribution induces strong oscillations in the 2DEG compressibility measured by local probes. Local measurements of the compressibility are expected to provide information about the domain structure of the zero resistance state of a 2DEG under microwave radiation.Comment: v2: analysis of the wave-vector dependence of the compressibility added; discussion of the Hall conductivity removed (shifted to cond-mat/0409590 in a revised form

Phonon-induced resistance oscillations of two-dimensional electron systems drifting with supersonic velocities

We present a theory of the phonon-assisted nonlinear dc transport of 2D electrons in high Landau levels. The nonlinear dissipative resistivity displays quantum magneto-oscillations governed by two parameters which are proportional to the Hall drift velocity $v_H$ of electrons in electric field and the speed of sound $s$. In the subsonic regime, $v_H<s$, the theory quantitatively reproduces the oscillation pattern observed in recent experiments. We also find the $\pi/2$ phase change of oscillations across the sound barrier $v_H=s$. In the supersonic regime, $v_H>s$, the amplitude of oscillations saturates with lowering temperature, while the subsonic region displays exponential suppression of the phonon-assisted oscillations with temperature.Comment: 4 pages, 3 figure