Ultrafast momentum-resolved visualization of the interplay between phonon-mediated scattering and plasmons in graphite

• Main Authors: Barantani, Francesco, Claude, Rémi, Iyikanat, Fadil, Madan, Ivan, Sapozhnik, Alexey A, Puppin, Michele, Weaver, Bruce, LaGrange, Thomas, de Abajo, F. Javier Garcia, Carbone, Fabrizio
• Format: Journal Article
• Language: English
• Published: 09-10-2024
• Subjects: Physics - Materials Science; Physics - Mesoscale and Nanoscale Physics
• DOI: 10.48550/arxiv.2410.06810

Scattering between individual charges and collective modes in materials
governs fundamental phenomena such as electrical resistance, energy
dissipation, switching between different phases, and ordering. The study of
such scattering requires a simultaneous access to the ultrafast
momentum-resolved dynamics of single-particle and collective excitations, which
remains as an experimental challenge. Here, we demonstrate time- and
momentum-resolved electron energy-loss spectroscopy, and apply it to graphite
showing that large ($\Delta q\simeq$1.2~{\AA}$^{-1}$) photoexcited
electron-hole (e-h) pockets in the band structure induce a renormalization of
the collective in-plane and bulk plasmons that can be described quantitatively
by invoking intra- and inter-valley scattering processes mediated by $E_{2g}$
and $A_{1}'$ phonon modes, which we directly observe by ultrafast electron
diffraction and identify via ab initio calculations. Conversely, the
photoexcitation of smaller e-h pockets ($\Delta q\simeq$0.7~{\AA}$^{-1}$) close
to the K point of graphite results in the renormalization of in-plane plasmons,
which can only be partially explained by phonon-mediated scattering and thermal
expansion. Our results show the importance of combining momentum- and
time-resolved information to elucidate microscopic details associated with
electronic scattering processes.