Interaction of Non-Equilibrium, Ballistic Phonons in a Keat Pulse with the Electron-Hole Liquid in Ge: The Phonon Wind

Abstract

The discovery of the electron-hole (e-h) drop in Ge and subsequent investigation of its unique properties1 have stimulated exciting new directions in phonon research. One remarkable property of the e-h drop is its mobility. In the past several years a number of experiments2–4 have demonstrated that mobile e-h drops can be propelled by a flux of non-equilibrium phonons; this novel concept,5 dubbed the “phonon wind”, has been instrumental in explaining how the e-h droplet cloud, typically a mm in size, is produced. The mechanism underlying the phonon wind entails interesting phonon physics: (1) absorption of non-equilibrium phonons by the metallic e-h liquid; (2) the characteristics of ballistic phonon propagation in the Ge lattice, i.e. phonon focusing and low temperature phonon scattering. We have made a comprehensive investigation4,6 of all aspects of the problem by means of a phonon transmission technique utilizing sharply collimated beams of ballistic phonons in a heat pulse. The following is a short synopsis.