Photo-induced non-radiative energy dissipation pathways in nanoscale materials are ubiquitous. They are the dominant loss channels in most opto-electronic devices, and offer new opportunities for optical control of quantum materials. We combine femtosecond electron diffuse scattering experiments and first-principles calculations of the coupled electron–phonon dynamics to provide a detailed momentum-resolved picture of lattice thermalization in black phosphorus. The measurements reveal the emergence of highly anisotropic nonthermal phonon populations persisting for several picoseconds after exciting the electrons with a light pulse. Ultrafast dynamics simulations based on the time-dependent Boltzmann formalism are supplemented by calculations of the structure factor, defining an approach to reproduce the experimental signatures of nonequilibrium structural dynamics. The combination of experiments and theory enables us to identify highly anisotropic electron–phonon scattering processes as the primary driving force of the nonequilibrium lattice dynamics in black phosphorus.

Full publication: Seiler et al. Nano Letters. Article ASAP