Plasmonically assisted channels of photoemission from metals

TL;DR

This paper investigates nonlinear photoemission from silver surfaces, revealing resonances linked to bulk plasmons, and proposes a plasmon-assisted mechanism for enhanced photoemission channels.

Contribution

It introduces a new theoretical framework combining response formalism and first-principles calculations to explain plasmon-assisted photoemission phenomena.

Findings

Resonances pinned to multiples of bulk plasmon energy observed in spectra.

Plasmons generated by electronic polarization influence photoemission.

Proposed scenario of plasmons acting as a pump field for photoemission.

Abstract

We analyse recently measured nonlinear photoemission spectra from Ag surfaces that reveal resonances whose energies do not scale with the applied photon energy but stay pinned to multiples of bulk plasmon energy $\hbar\omega_p$ above the Fermi level. To elucidate these unexpected and peculiar features we investigate the spectra of plasmons generated in a solid by the optically pumped electronic polarization and their effect on photoemission. By combining quadratic response formalism for calculations of photoemission yield, a nonperturbative approach to inelastic electron scattering, and first-principles calculations for the electronic structure, we demonstrate the dependence of probability amplitude for single- and multiplasmon excitations on the basic parameters characterizing the photon pulse and the system. The resulting multiexcitation spectrum evolves towards a truncated plasmonic coherent state. Analogous concept is extrapolated to interpret plasmon generation by multiphoton excited electronic polarization. Based on this we elaborate a scenario that the thus created real plasmons act as supplementary frequency-locked pump field for non-Einsteinian plasmonically assisted channels of photoemission from metals. The established paradigm enables assignment and assessment of the observed linear $\hbar\omega_p$- and nonlinear $2\hbar\omega_p$-electron yields from Ag. Such effects may be exploited for selective filtering of optical energy conversion in electronic systems.