Plasmon-assisted photoelectron emission in a model cluster using time-dependent density functional theory and the time-dependent surface-flux method

TL;DR

This work uses a 1D TDDFT model with the time-dependent surface-flux method to study plasmon-assisted photoelectron emission. It identifies two collective plasmon modes at frequencies $ \\omega_A$ and $ \\omega_B$ and shows that post-pulse emission produces sharp peaks at energies $E_{in} = \\varepsilon_i + n \\omega_{A,B}$, whose intensities scale with laser fluence in a way that reflects multi-photon and plasmon-driven processes. Time-frequency analysis resolves the emission timing, revealing ATI peaks during the pulse and plasmon-induced peaks afterward, with scaling exponents indicating plasmon-assisted mechanisms. The study highlights both the potential of TDDFT+t-SURFF to capture plasmonic dynamics and the limitations of ALDA, motivating improved functionals and cross-method benchmarking for quantitative accuracy.

Abstract

We investigate plasmon-assisted photoelectron emission using a one-dimensional time-dependent density-functional theory (TDDFT) model. Photoelectron spectra are computed with the time-dependent surface-flux (t-SURFF) method. In addition to the expected above-threshold ionization (ATI) comb, we observe peaks that arise from long-lived plasmon oscillations and the associated electron emission occurring after the laser pulse. We further analyze the positions of these peaks and their scaling behavior with the laser intensity.

Figures (10)

• Figure 1: Kohn-Sham potential $V_{\rm KS}(x)$ (solid black) of the 1D cluster and the 20 occupied KS orbitals (coloured) plotted as $|\varphi_i(x)|^2+\varepsilon_i$.
• Figure 2: Linear-response spectra. Black: full, dynamic response according to \ref{['eq:TDKS']}. Blue: response for frozen KS potential $V_\text{KS}[n](x,0)$. Vertical dashed lines indicate KS level differences. Two strong peaks at $\omega_A=0.106$ and $\omega_B=0.156$ appear in the fully dynamic ("unfrozen") response.
• Figure 3: Orbital-resolved spectra. A strong response of all KS orbitals at a given $\Omega$ indicates a collective mode. Instead, orbital-dependent responses are due to single-particle transitions.
• Figure 4: Oscillating current densities for the collective modes $\omega_A = 0.106$ (upper panel) and $\omega_B = 0.156$ (lower panel) as a function of time (in units of $2\pi/\omega_L$) and space. The modes were excited with laser pulses of frequencies $\omega_L=\omega_A/3$ and $\omega_L=\omega_B/3$, respectively. The oscillating current densities are shown for times after the laser pulses.
• Figure 5: Total photoelectron spectrum (red) and the individual contributions from the three highest initially populated KS orbitals for a pulse that dominantly excites $\omega_B = 0.156$ with three laser photons. Narrow spikes are equally spaced by $\omega_B$. Laser parameters are $a_0 = 0.004$, $\omega_L = 0.052=\omega_B/3$, $N_\text{cyc} =20$.