Monochromatic Phonon Propagation in Ge:Sb Using Superconducting Tunnel Junctions

The frequency spectrum of the phonons generated by a superconducting SnO-Sn tunnel junction has been determined through the observation of resonance absorption by Sb donor levels in Ge. These measurements show that one can use such junctions to generate and detect milliwatts of phonon power at energies of $2\Delta$ (1.2 meV).