Hot electron lifetimes in metals probed by time-resolved two-photon photoemission

Ultrafast Multiphoton Thermionic Photoemission from Graphite

“…Moreover, strong modulation of the carrier density through ultrafast optical excitation and the ensuing hot carrier multiplication drives the electron and hole distributions to different chemical potentials, enabling applications in energy harvesting, ultrafast electronics, and coherent optics [1,3,[16][17][18][19][20]. These novel properties derive from graphene's Dirac fermion band structure, weak screening, and strong, moleculelike electron correlation [21][22][23][24][25][26][27][28][29][30][31], which distinguish it from conventional metals and semiconductors [22,32,33].…”

“…The conduction electrons undergoing multiple intraband e-e scattering interactions can thus gain several eV energy [66]. The screening and kinematic constraints thus make e-e scattering in graphitic materials much faster and more effective in reaching high temperatures than is possible in semiconductors or metals [33,67]. In other words, because of the ineffective screening and smaller heat capacity in graphitic materials, as compared with metals, thermalization happens on much shorter time scales before photoexcited electrons can dissipate a sizable amount of energy to the lattice.…”

Isolating lattice from electronic contributions in thermal transport measurements of metals and alloys above ambient temperature and an adiabatic model

“…Furthermore, these experiments show that a hot electron gas will equilibrate internally prior to equilibration with the lattice in diverse types of metals. [11][12][13][14] Although the consequences of the electron temperature exceeding the lattice temperature by hundreds of degrees during these transient excitation experiments 15,16 have received considerable attention, 14,17 ramifications of this discovery on heat transport in bulk metals at ordinary temperatures (above ∼100 K) have been overlooked. This paper quantifies the behavior of electrons and phonons in metals and alloys during timedependent heat transport, thereby providing important constraints for theoretical models and for technological applications.…”

Distinguishing attosecond electron–electron scattering and screening in transition metals

“…Using femtosecond lasers in combination with advanced spectroscopies, it is possible to measure the lifetime of excited charges and spins directly in the time domain (1). To date, such studies have been applied to a wide variety of materials, including noble metals and semiconductors (1)(2)(3)(4), ferromagnetic metals (5)(6)(7)(8), strongly correlated materials (9) and high-T c superconductors (10,11). These studies have significantly improved our understanding of the fastest coupled interactions and relaxation mechanisms in matter.…”

“…These studies have significantly improved our understanding of the fastest coupled interactions and relaxation mechanisms in matter. However, to date experimental investigations of electron dynamics have been limited to femtosecond timescale processes in materials with low charge densities (9)(10)(11)(12) or to Fermi-liquid metals with low excitation energies (<3.0 eV above E F , where E F is the Fermi energy) (3)(4)(5), due to the visible-to-UVwavelength photon energies used in these experiments. In this region, two fundamental electron interactions-electron-electron scattering and charge screening due to a rearrangement of adjacent charges-contribute to the signal, making it challenging to independently probe these dynamics.…”