Quantum spill-out in nanometer-thin gold slabs: Effect on plasmon mode index and plasmonic absorption

TL;DR

This paper investigates how quantum spill-out affects plasmon modes and absorption in nanometer-thin gold slabs, revealing significant increases in absorption and mode index imaginary parts even in relatively wide slabs.

Contribution

It introduces a quantum mechanical approach to analyze plasmon behavior in thin gold slabs, highlighting the impact of spill-out on absorption and mode properties.

Findings

Quantum spill-out increases mode index imaginary parts by 20%.

Enhanced plasmonic absorption occurs near the slab surface.

Significant effects persist even in slabs approaching bulk width.

Abstract

A quantum mechanical approach and local response theory are applied to study plasmons propagating in nanometer-thin gold slabs sandwiched between different dielectrics. The metal slab supports two different kinds of modes, classified as long-range and short-range plasmons. Quantum spill-out is found to significantly increase the imaginary part of their mode indices, and, surprisingly, even for slabs wide enough to approach bulk the increase is 20%. This is explained in terms of enhanced plasmonic absorption, which mainly takes place at narrow peaks located near the slab surface.