Theory

Phonons are vibration waves that propagate in solids. Their study and quantification is fundamental for understanding many material properties, from superconductivity to thermoelectricity. Numerous techniques have been developed for studying phonons, such as high-resolution electron-energy-loss spectroscopy (HREELS), in which electrons are sent toward an object of interest, and the energy of the phonons is deduced from that lost by the electrons. Recently, HREELS has been pushed to the nanometer scale. With the success of these experiments, researchers now want to determine what types of phonons are being measured and how to rationalize some of the observations. A similar problem once arose in HREELS experiments on electronic waves known as plasmons, experiments that were interpreted at the time using analogies with phonons. In a recent paper published in PRX, we show that, in a reversal of traditional analogies, current phonon experiments can now be interpreted using modern concepts for plasmons. Read more »