Energy and Momentum Distribution of Surface Plasmon-Induced Hot Carriers Isolated via Spatiotemporal Separation

Abstract

Understanding the differences between photoninduced and plasmon-induced hot electrons is essential for the construction of devices for plasmonic energy conversion. The mechanism of the plasmonic enhancement in photochemistry, photocatalysis, and light-harvesting and especially the role of hot carriers is still heavily discussed. The question remains, if plasmon-induced and photon-induced hot carriers are fundamentally different or if plasmonic enhancement is only an effect of field concentration producing these carriers in greater numbers. For the bulk plasmon resonance, a fundamental difference is known, yet for the technologically important surface plasmons, this is far from being settled. The direct imaging of surface plasmon-induced hot carriers could provide essential insight, but the separation of the influence of driving laser, field-enhancement, and fundamental plasmon decay has proven to be difficult. Here, we present an approach using a two-color femtosecond pump−probe scheme in time-resolved 2-photonphotoemission (tr-2PPE), supported by a theoretical analysis of the light and plasmon energy flow. We separate the energy and momentum distribution of the plasmon-induced hot electrons from that of photoexcited electrons by following the spatial evolution of photoemitted electrons with energy-resolved photoemission electron microscopy (PEEM) and momentum microscopy during the propagation of a surface plasmon polariton (SPP) pulse along a gold surface. With this scheme, we realize a direct experimental access to plasmon-induced hot electrons. We find a plasmonic enhancement toward high excitation energies and small in-plane momenta, which suggests a fundamentally different mechanism of hot electron generation, as previously unknown for surface plasmons.

Optical Properties of Gold After Intense Short-Pulse Excitations

“…The interaction of short laser pulses with matter has drawn broad attention over the last few decades due to its importance for fundamental science as well as for a plentitude of applications in diverse fields [1][2][3][4][5][6][7][8][9]. Advances in laser technology have opened new possibilities and new research areas [10][11][12] and allowed for remarkable qualitative improvements of temporal, spatial and energy resolution of experiments [13][14][15][16][17][18]. Accordingly, the capabilities to probe and control materials properties even at extreme conditions and ultrashort time scales have been enhanced considerably in the last decade.…”

Influence of Electronic Non-Equilibrium on Energy Distribution and Dissipation in Aluminum Studied with an Extended Two-Temperature Model

“…For many experiments, the energy-resolved occupation is of interest. With the time-resolved two-photon photoemission, it is possible to observe the dynamics of high-energetic electrons [ 18 , 57 , 58 , 59 ]. For instance, photo-electron spectroscopy is a widely used tool to investigate ultrafast processes in microscopic solid state physics [ 13 , 22 , 24 , 60 ].…”

Electron emission from plasmonically induced Floquet bands at metal surfaces

“…Replacement of A(r, t) by the above A(r, t) in ( 9) and corresponding removal of H pl 0 therefrom results in the Hamiltonian describing electron dynamics governed by the static scalar potential (14) and the sum of time dependent effective vector fields ( 18) and (19). In what follows we shall ignore the dissipative environment because it is not expected to be of significance on the energy scale of Floquet dynamics [19] discussed below.…”

“…On low index surfaces of metals which exhibit surface projected band gaps the potential V scal (r) defined in (14) can support the set of Q2D surface state (SS) and image potential state (IP) bands. Localization of SS and IP electrons in the direction perpendicular to the surface is only few atomic radii over the image potential well whereas their Q2D Bloch state dynamics in the lateral direction parallel to the surface is well described in the effective mass approximation.…”

“…In the present work we investigate a complementary mechanism of non-Einsteinian electron yield via the surface plasmon-assisted emission channels [11][12][13][14] building on the plasmonically induced surface Floquet bands. [15][16][17][18][19] We shall demonstrate the formation of such bands in electron systems subject to pumping of coherent plasmonic states by strong external perturbations.…”