Acoustic absorption by the electron-hole liquid in germanium

The absorption of ultrasonic acoustic waves by the electron-hole liquid that may be created in germanium at liquid helium temperatures by intense optical excitation is studied. This degenerate Compensated Fermi liquid exhibits the behavior of both classical dynamics in a force field, and quantum phenomena in a magnetic field. Results of theoretical and experimental studies of the interaction of the mobile liquid with a traveling acoustic wave force field, the attenuation of the wave due to energy-dissipative processes coupling the liquid to the crystal lattice, and the effect of a moderately strong magnetic field on the dynamic behavior of the system are presented. In unstrained germanium the electron-hole liquid is known to be condensed into small droplets of radius approximately 5 micron; the creation of an EHL energy well by the application of an inhomogeneous stress caused the liquid to be aggregated into a macroscopically large volume.