Image of the Fermi Surface and Screening Effects in Phonon Attenuation

Heat pulses transmitted into $n$-type InSb were detected by using superconducting diodes. By change of InSb doping, and by magnetic tuning of the superconducting gap, a singularity in phonon attenuation was observed at twice the Fermi radius. The long waves, whose absorption is screened by the conduction electrons, are resolved by time-of-flight spectroscopy.