Mapping momentum-dependent electron-phonon coupling and nonequilibrium phonon dynamics with ultrafast electron diffuse scattering

Despite their fundamental role in determining material properties, detailed momentum-dependent information on the strength of electron-phonon and phonon-phonon coupling (EPC and PPC, respectively) across the entire Brillouin zone has remained elusive. Here we demonstrate that ultrafast electron diff...

Full description

Saved in:
Bibliographic Details
Published in:Physical review. B 2018-04, Vol.97 (16), Article 165416
Main Authors: Stern, Mark J., René de Cotret, Laurent P., Otto, Martin R., Chatelain, Robert P., Boisvert, Jean-Philippe, Sutton, Mark, Siwick, Bradley J.
Format: Article
Language:English
Subjects:
Brillouin zones
Coupling
Electrons
Energy resolution
Material properties
Momentum
Phonons
Populations
Scattering
Symmetry
Thermalization (energy absorption)
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Despite their fundamental role in determining material properties, detailed momentum-dependent information on the strength of electron-phonon and phonon-phonon coupling (EPC and PPC, respectively) across the entire Brillouin zone has remained elusive. Here we demonstrate that ultrafast electron diffuse scattering (UEDS) directly provides such information. By exploiting symmetry-based selection rules and time resolution, scattering from different phonon branches can be distinguished even without energy resolution. Using graphite as a model system, we show that UEDS patterns map the relative EPC and PPC strength through their profound sensitivity to photoinduced changes in phonon populations. We measure strong EPC to the K−point TO phonon of A1′ symmetry (K−A1′) and along the entire TO branch between Γ−K, not only to the Γ−E2g phonon. We also determine that the subsequent phonon relaxation of these strongly coupled optical phonons involve three stages: decay via several identifiable channels to TA and LA phonons (1−2 ps), intraband thermalization of the non-equilibrium TA/LA phonon populations (30–40 ps) and interband relaxation of the TA/LA modes (115 ps). Combining UEDS with ultrafast angle-resolved photoelectron spectroscopy will yield a complete picture of the dynamics within and between electron and phonon subsystems, helping to unravel complex phases in which the intertwined nature of these systems has a strong influence on emergent properties.
ISSN:2469-9950
2469-9969
DOI:10.1103/PhysRevB.97.165416