Anisotropy of quasiparticle lifetimes and the role of disorder in
graphite from ultrafast time-resolved photoemission spectroscopy
PHYSICAL REVIEW LETTERS, (December 2001)DOI: {10.1103/PhysRevLett.87.267402}
Abstract
Femtosecond time-resolved photoemission of photoexcited electrons in
highly oriented pyrolytic graphite (HOPG) provides strong evidence for
anisotropies of quasiparticle (QP) lifetimes. Indicative of such
anisotropies is a pronounced anomaly in the energy dependence of QP
lifetimes between 1.1 and 1.5 eV-the vicinity of a saddle point in the
graphite band structure. This is supported by recent ab initio
calculations and a comparison with experiments on defect-enriched HOPG
which reveal that disorder, e.g., defects or phonons, increases electron
energy relaxation rates.