Attosecond momentum-resolved resonant inelastic x-ray scattering for imaging coupled electron-hole dynamics

Abstract

Improving our understanding of electron dynamics is essential for advancing energy transfer, optoelectronics, light harvesting systems and quantum computing. Recent developments in attosecond x-ray sources provide the fundamental possibility of observing these dynamics with atomic-scale resolution. However, connecting a time-resolved signal to dynamics is challenging due to the broad bandwidth of an attosecond probe pulse. This makes exploring the capabilities of different attosecond imaging techniques crucial. Here, we propose attosecond momentum-resolved resonant inelastic x-ray scattering as a prominent technique for tracking ultrafast dynamics. We demonstrate that the scattering signal contains an information about the instantaneous distribution of charge density across the scattering atoms. To illustrate this, we consider scattering from an $α$-sexithiophene molecule, in which coupled electron-hole dynamics are excited.

Figures (2)

• Figure 1: (a) Illustration of attosecond pump-probe experiment. (b) Sexithiophene molecule. (c) Sulfur K-edge spectra of an excited sexithiophene molecule at different time delays ($\mathbf{k}_{\text{in}}||y$, $\boldsymbol{\epsilon}_\text{in}||x$). (d) Illustration of states involved in the dynamics and transitions.
• Figure 2: (a) - (b) Exciton density, hole and electron contributions to the exciton density at (a) $t_p=1.3$ fs and (b) $t_p=2.7$ fs visualized with the VESTA package Momma2011. Yellow and cyan isosurfaces correspond to the negatively- and positively-charged regions. (c)--(d) The even part of the momentum maps at $Q_z = 0$, $\left[P(Q_x, Q_y, 0)+P(-Q_x, -Q_y, 0)\right]/(2\theta(\mathbf n_Q))$, with the final state being the ground state at (c) $t_p=1.3$ fs and (d) $t_p=2.7$ fs and (e) illustration of the involved transitions. (f)--(i) The same as (c)--(d), but with the final state being a valence-excited state at (f) $\omega_\text{s}-\omega_\text{in}=\Delta\omega_{\text{s}2}$ and $t_p=1.3$ fs; (g) $\omega_\text{s}-\omega_\text{in}=\Delta\omega_{\text{s}2}$ and $t_p=2.7$ fs; (h) $\omega_\text{s}-\omega_\text{in}=\Delta\omega_{\text{s}1}$ and $t_p=1.3$ fs; and (i) $\omega_\text{s}-\omega_\text{in}=\Delta\omega_{\text{s}1}$ and $t_p=2.7$ fs. (j) Illustration of the scattering process with a final state being a valence-excited state.