new paper published: Electron-phonon Coupling and Energy Flow in a Simple Metal beyond the Two-Temperature Approximation

Teaser: Interactions between atomic ions and valence electrons are fundamental to superconductivity and the properties of materials. Now, researchers have demonstrated electron-lattice interactions in aluminum heated by an infrared laser pulse.

Short summary: All condensed matter is composed of atomic ions and valence electrons moving swiftly through the material that act as glue for the otherwise-repellent ions. The ions and electrons are never at rest but continuously affect one another. These interactions between the electrons and vibrations of the atomic ions are a central subject in solid-state physics; they dictate fundamental effects such as the electron and thermal conductivity of materials, energy dissipation in electronic devices, and the emergence of quantum phenomena like superconductivity. Theoretical descriptions of these phenomena rely on knowledge of the coupling strength between electrons and the lattice, which cannot be directly measured. Here, we present an experimental and theoretical investigation of electron-lattice interactions in nanometer-thick films of aluminum, a prototypical metal.

We study how energy is transferred from electrons to phonons by visualizing the aluminum’s internal response to a sudden external disturbance. The disturbance is imposed by a very short (50 femtosecond) infrared laser pulse, which instantly heats up the electrons. The excited electrons then—because of their mutual interactions—start to equilibrate with the atomic vibrations. By taking snapshots of the atomic vibrations at various times after excitation, we obtain a “movie” of the relaxation pathway. Combining our experimental findings with state-of-the-art numerical calculations of atomic mean squared displacements, we are able to revise the existing model of these interactions.

Our work highlights that the standard model for describing the energy exchange between the moving electrons and the vibrating ions needs to be refined. We expect that our findings will improve our understanding of the inner workings of solids and motivate future studies of phonon distributions.

Original Publication: Physical Review X vol. 6, 021003