Replacing Noble Metals with Alternative Materials in Plasmonics and Metamaterials: how good an idea?

TL;DR

Replacing noble metals with alternative plasmonic materials like doped oxides and nitrides does not necessarily reduce modal loss unless their plasma frequency is significantly higher than the operational frequency, especially in the mid-infrared spectrum.

Contribution

This work provides a rigorous analytical assessment showing that low material loss alone does not guarantee reduced modal loss in plasmonic structures.

Findings

Low material loss is not sufficient for reduced modal loss.

High plasma frequency relative to operational frequency is essential.

Metals still outperform alternative materials in the mid-infrared range.

Abstract

Noble metals that currently dominate the fields of plasmonics and metamaterials suffer from large ohmic losses. New plasmonic materials, such as doped oxides and nitrides, have smaller material loss, and, using them in place of metals carries promise of reduced-loss plasmonic and metamaterial structures, with sharper resonances and higher field concentration. This promise is put to a rigorous analytical test in this work which reveals that having low material loss is not sufficient to have a reduced modal loss in plasmonic structures. To reduce the modal loss it is absolutely necessary for the plasma frequency to be significantly higher than the operational frequency. Using examples of nanoparticle plasmons and gap plasmons one comes to the conclusion that even in the mid-infrared spectrum metals continue to hold advantage over the alternative media. The new materials may still find application niche where the high absorption loss is beneficial, e.g. in medicine and thermal photovoltaics.