The plasma resonance of electron-hole drops in uniaxially stressed germanium

The far infrared absorption spectrum of electron-hole drops in Ge under uniaxial stress S ≤ 20 kg/mm2 is studied. Large variations in positions and lineshape are observed for different stress values and direction of polarization of the infrared electric field with respect to the stress direction. A sharp decrease in the plasma frequency occurs at S ~ 3 kg/mm2, reflecting the change in occupancy of the conduction band valleys. The density of the fluid, n, as a function of [111] stress is obtained from the fit of the experimental results to a theory with the band structure modified by stress.