Ultrafast Surface Plasmonic Switch in Non-Plasmonic Metals

TL;DR

This paper shows that ultrafast laser excitation can temporarily induce surface plasmonic properties in non-plasmonic metals like tungsten, enabling dynamic optical control for nanostructuring.

Contribution

It introduces a first-principles method to demonstrate ultrafast plasmonic switching in non-plasmonic metals through carrier excitation and optical property modulation.

Findings

Carrier heating mobilizes d electrons, inducing plasmonic response.

Sign flip in optical conductivity activates plasmonic properties.

Time-resolved ellipsometry confirms optical index evolution.

Abstract

We demonstrate that ultrafast carrier excitation can drastically affect electronic structures and induce brief surface plasmonic response in non-plasmonic metals, potentially creating a plasmonic switch. Using first-principles molecular dynamics and Kubo-Greenwood formalism for laser-excited tungsten we show that carrier heating mobilizes d electrons into collective inter and intraband transitions leading to a sign flip in the imaginary optical conductivity, activating plasmonic properties for the initial non-plasmonic phase. The drive for the optical evolution can be visualized as an increasingly damped quasi-resonance at visible frequencies for pumping carriers across a chemical potential located in a d-band pseudo-gap with energy-dependent degree of occupation. The subsequent evolution of optical indices for the excited material is confirmed by time-resolved ultrafast ellipsometry. The large optical tunability extends the existence spectral domain of surface plasmons in ranges typically claimed in laser self-organized nanostructuring. Non-equilibrium heating is thus a strong factor for engineering optical control of evanescent excitation waves, particularly important in laser nanostructuring strategies.