Visualizing hot carrier dynamics by nonlinear optical microscopy at the atomic length scale

TL;DR

This paper demonstrates real-time visualization of hot carrier dynamics at the atomic scale using nonlinear optical microscopy combined with femtosecond spectroscopy, enabling new insights into nanoscale light-matter interactions.

Contribution

It introduces a novel experimental approach combining pump-probe spectroscopy with STM to track hot carriers and generate nonlinear signals at the atomic length scale.

Findings

Hot carrier dynamics can be tracked in real-time at the atomic scale.

ERRS and FWM signals are more efficiently generated along graphene nanoribbon edges.

The method enables ultrafast control of nonlinear optical signals at the atomic level.

Abstract

Probing and manipulating the spatiotemporal dynamics of hot carriers in nanoscale metals is crucial to a plethora of applications ranging from nonlinear nanophotonics to single molecule photochemistry. The direct investigation of these highly non-equilibrium carriers requires the experimental capability of high energy resolution (~ meV) broadband femtosecond spectroscopy. When considering the ultimate limits of atomic scale structures, this capability has remained out of reach until date. Using a two color femtosecond pump-probe spectroscopy, we present here the real-time tracking of hot carrier dynamics in a well-defined plasmonic picocavity, formed in the tunnel junction of a scanning tunneling microscope (STM). The excitation of hot carriers in the picocavity enables ultrafast all optical control over the broadband (~ eV) anti Stokes electronic resonance Raman scattering (ERRS) and the four-wave mixing (FWM) signals generated at the atomic length scale. By mapping the ERRS and FWM signals from a single graphene nanoribbon (GNR), we demonstrate that both signals are more efficiently generated along the edges of the GNR: a manifestation of atomic-scale nonlinear optical microscopy. This demonstration paves the way to the development of novel ultrafast nonlinear picophotonic platforms, affording unique opportunities in a variety of contexts, from the direct investigation of non equilibrium light matter interactions in complex quantum materials, to the development of robust strategies for hot carriers harvesting in single molecules and the next generation of active metasurfaces with deep-sub-wavelength meta-atoms.