Ultrafast Electron Dynamics in Metals

Abstract

During the last decade, significant progress has been achieved in the rapidly growing field of the dynamics of hot carriers in metals. Here we present an overview of the recent achievements in the theoretical understanding of electron dynamics in metals, and focus on the theoretical description of the inelastic lifetime of excited hot electrons. We outline theoretical formulations of the hot-electron lifetime that is originated in the inelastic scattering of the excited quasiparticle with occupied states below the Fermi level of the solid. First-principles many-body calculations are reviewed. Related work and future directions are also addressed.Keywords: ab initio calculations, electron lifetimes, femtochemistry, time-resolved spectroscopy, many-body INTRODUCTIONRecent advances in femtosecond laser technology have made possible the investigation of electron transfer processes at solid surfaces, which are known to be the basis for many fundamental steps in surface photochemistry and ultrafast chemical reactions. [1,2,3] These are typically atomic and molecular adsorption processes and catalytic reactions between different chemical species, which transfer energy from the reaction complex into the nuclear and electronic degrees of freedom of the solid substrate. These reactions may induce elementary excitations, such as quantized lattice vibrations (phonons), collective electronic excitations (plasmons), and electronhole (e-h) pairs. In metals, the excitation of e-h pairs leads to an excited or hot electron with energy above the Fermi level ε F and to an excited or hot hole with energy below ε F . It is precisely the coupling of these hot carriers with the underlying substrate which governs the cross sections and branching ratios of electronically induced adsorbate reactions at metal surfaces.It is the intent of this Review to discuss the current status of the rapidly growing field of the dynamics of hot carriers in metals. The energy relaxation of these hot electrons and holes is almost exclusively attributed to the inelastic scattering with cold electrons below the Fermi level (e-e scattering) and with phonons (e-ph scattering), since radiative recombination of e-h pairs may be neglected. Assuming that the excess energy of the hot carrier is much larger than the thermal energy k B T , the e-e scattering rate does not depend on temperature. Furthermore, for excitation energies larger than ∼ 1 eV inelastic lifetimes are dominated by e-e scattering, e-ph interactions being in general of minor importance. Only at energies closer to the Fermi level, where the e-e inelastic lifetime increases rapidly, does e-ph scattering become important. [4,5] Different techniques have recently become available for measuring hot-carrier lifetimes. Inverse photoemission (IPE) [6] and high resolution angle resolved photoemission (ARPE) [7] provide an indirect access to the lifetime of hot electrons and holes, respectively, by measuring the energetic broadening of transition lines after impigning an electron (IPE) or a photon (ARPE) in...

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

“…In the Green functions method, the effect of interactions on the single-(quasi)particle properties are completely contained in the self-energy R. Most calculations of this quantity have been performed within the Hedin GW approximation [42,71] by taking the band structure of the material into account [19,51,72] instead of considering plane wave states as in the case of the homogeneous electron gas. In the many-body perturbation theory, the imaginary part of the self-energy R is expanded in terms of the single particle Green function G and the screened Coulomb interaction W(r, r 0 , x).…”

“…There are also a number of reviews on different theoretical approaches to this problem, see e.g. [18][19][20][21]. A very general review on current developments within this field can furthermore be found in [22].…”

GW+Ttheory of excited electron lifetimes in metals

“…A number of theoretical methods have also been developed for the evaluation of lifetimes, such as semiempirical methods based on the scattering theory 10,14-16 and firstprinciple approaches 17 based on the self-energy formalism of many-body perturbation theory ͑MBPT͒. 18 First-principle evaluations of lifetimes have been performed for a variety of metallic systems including simple metals, [19][20][21][22][23] noble, 19,20,[22][23][24][25][26] and transition metals.…”

Hole-Phonon Relaxation and Photocatalytic Properties of Titanium Dioxide and Zinc Oxide: First-Principles Approach

“…Hence, despite the important role of the hole-phonon relaxation, the available data on the timing of these processes are scanty and insufficiently accurate. The number of theoretical works on this subject is limited and incomparable to the numerous studies of relaxation time in metals [17][18][19]. The formerly developed methods and computer codes for the solid state theory [20] facilitate firstprinciple calculations for the temporal characteristics of the relaxation processes.…”