Distinguishing attosecond electron–electron scattering and screening in transition metals

Abstract

Electron-electron interactions are the fastest processes in materials, occurring on femtosecond to attosecond timescales, depending on the electronic band structure of the material and the excitation energy. Such interactions can play a dominant role in light-induced processes such as nano-enhanced plasmonics and catalysis, light harvesting, or phase transitions. However, to date it has not been possible to experimentally distinguish fundamental electron interactions such as scattering and screening. Here, we use sequences of attosecond pulses to directly measure electronelectron interactions in different bands of different materials with both simple and complex Fermi surfaces. By extracting the time delays associated with photoemission we show that the lifetime of photoelectrons from the d band of Cu are longer by ∼100 as compared with those from the same band of Ni. We attribute this to the enhanced electron-electron scattering in the unfilled d band of Ni. Using theoretical modeling, we can extract the contributions of electron-electron scattering and screening in different bands of different materials with both simple and complex Fermi surfaces. Our results also show that screening influences high-energy photoelectrons (≈20 eV) significantly less than low-energy photoelectrons. As a result, high-energy photoelectrons can serve as a direct probe of spin-dependent electron-electron scattering by neglecting screening. This can then be applied to quantifying the contribution of electron interactions and screening to low-energy excitations near the Fermi level. The information derived here provides valuable and unique information for a host of quantum materials.attosecond science | high harmonic generation | ARPES | electron-electron interactions E xcited-state electron dynamics in materials play a critical role in light-induced phase transitions in magnetic and charge density wave materials, in superdiffusive spin flow, in catalytic processes, and in many nano-enhanced processes. However, to date exploring such dynamics is challenging both experimentally and theoretically. 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 (1-4), ferromagnetic metals (5-8), 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. However, to date experimental investigations of electron dynamics have been limited to femtosecond timescale processes in materials with low charge densities (9-12) or to Fermi-liquid metals with low excitation energies (<3.0 eV above E F , where E F is the Fermi energy) (3-5), due to the visible-to-UVwavelength photon energies used in these experiments. In this region, two fundamental electron interactions-electron-electron sc...

Long lifetime polarized electron beam production from negative electron affinity GaAs activated with Sb-Cs-O: Trade-offs between efficiency, spin polarization, and lifetime

“…(5) is capable of capturing most of the features characterizing our experimental ESP data. The value of Γ ee is assumed to be constant and equal to 1.5 × 10 14 s −1 and is consistent with experimental measurements [36] indicating that photogenerated hot electrons in metals can thermalize with characteristic times even shorter than 10 fs through carrier-to-carrier or carrier-to-phonon scattering. Similar relaxation times have also been measured in the case of lead-iodide hybrid perovskite, a semiconductor having similar band gap energy to Cs 3 Sb for hot electrons with excess energies on the order of 0.5 eV [37].…”

Effective mass effect in attosecond electron transport

“…A recent study [12] could disentangle electron-electron scattering from screening effects in photoemission delays from solid state targets. In particular, the delay contribution of the screening effect was found to be negligible for electrons with a final state energy higher than 20 eV.…”

“…Attosecond metrology has provided the first results with this kind of electron transport in solids looking at the escape time of photoemitted electrons [9][10][11][12][13] and considering a simple ballistic transport model. The question about the correct escape velocity of the electrons and whether their dynamics are controlled by the periodic crystal potential on such small time and length scales has been debated [11,14,[15][16][17], and mainly free-electron-like propagation was observed or deduced.…”

Semiclassical approach for solving the time-dependent Schrödinger equation in spatially inhomogeneous electromagnetic pulses

“…This was demonstrated in proof-of-principle experiments for gaseous atomic [10][11][12][13][14][15][16] and molecular [17][18][19] targets. Attosecond time-resolved photoemission spectroscopy is currently being extended to complex targets [6,20], such as nanostructures and nanoparticles [21][22][23][24][25][26][27][28], and solid surfaces [9,[29][30][31][32][33][34][35][36], making it possible to examine, for example, the dynamics of photoemission from a surface on an absolute time scale [37] and suggesting, for example, the time-resolved observation of the collective motion of electrons (plasmons) in condensed-matter systems [38][39][40].…”