Ultrafast Laser-Induced Dynamics of Non-Equilibrium Electron Spill-Out in Nanoplasmonic Bilayers

TL;DR

This paper demonstrates ultrafast, non-thermal control of electron spill-out in nanoplasmonic bilayers using time-resolved spectroscopy, revealing dynamic changes in plasmonic properties on femtosecond scales.

Contribution

It introduces a method to manipulate surface plasmon dispersion via transient electron redistribution driven by ultrafast laser pulses in non-equilibrium conditions.

Findings

Transient electron spill-out increases by an order of magnitude.

Non-thermal superdiffusive hot electron transport observed.

Surface plasmon properties can be ultrafast controlled through electron dynamics.

Abstract

Contemporary quantum plasmonics capture subtle corrections to the properties of plasmonic nano-objects in equilibrium. Here, we demonstrate nonequilibrium spill-out redistribution of the electronic density at the ultrafast time scale. As revealed by time-resolved 2D spectroscopy of nanoplasmonic Fe/Au bilayers, an injection of the laser-excited non-thermal electrons induces transient electron spill-out thus changing the plasma frequency. The response of the local electronic density switches the electronic density behavior from spill-in to strong (an order of magnitude larger) spill-out at the femtosecond time scale. The superdiffusive transport of hot electrons and the lack of a direct laser heating indicate significantly non-thermal origin of the underlying physics. Our results demonstrate an ultrafast and non-thermal way to control surface plasmon dispersion through transient variations of the spatial electron distribution at the nanoscale. These findings expand quantum plasmonics into previously unexplored directions by introducing ultrashort time scales in the non-equilibrium electronic systems.