Collapse of electron-phonon coupling due to nonthermal phonon populations

Electron-phonon coupling governs the energy transfer rate between electrons and the crystal lattice. It is of crucial importance to the relaxation dynamics of laser-excited solids, as only the electron system can be directly excited by optical lasers. For numerous materials, it has been found that the electrons preferentially couple to high-wavenumber phonons. In this work, we demonstrate how hot phonons emerge at the edge of the Brillouin zone from such wavenumber-dependent coupling. We show that these hot phonons lead to a collapse of the energy transfer rate and considerably delay the equilibration between electrons and phonons.