Resonant Magnetophonon Emission by Supersonic Electrons in Ultrahigh-Mobility Two-Dimensional Systems

Area of Science:

• Condensed Matter Physics
• Quantum Phenomena
• Materials Science

Background:

• Two-dimensional electron gas (2DEG) systems exhibit unique electronic properties.
• Acoustic phonon scattering significantly influences electron transport in 2DEGs.
• Understanding electron-phonon interactions is crucial for novel electronic devices.

Purpose of the Study:

• Investigate resonant acoustic phonon scattering in 2DEG magnetoresistivity.
• Analyze the impact of carrier drift velocity relative to the speed of sound.
• Characterize electron-phonon coupling in a nonlinear transport regime.

Main Methods:

• Measurements of magnetoresistivity in an ultrahigh-mobility 2DEG.
• Application of DC current to induce carrier drift velocity.
• Systematic temperature variation from 10 mK to 3.9 K.

Main Results:

• Observed strong resonant features (phonon-induced resistance oscillations) above the "sound barrier" (drift velocity > speed of sound).
• Demonstrated weak temperature dependence of these oscillations in the supersonic regime.
• Found strong suppression of scattering in the subsonic regime unless amplified by inter-Landau-level scattering.

Conclusions:

• Electron-phonon coupling constant (g^2 = 0.0016) extracted for the nonlinear transport regime.
• Evidence for a predicted oscillation phase change upon crossing the "sound barrier".
• Magnetic field induces sharp resonant phonon emission due to Landau quantization above the sound barrier.