Negative effective permeability and left-handed materials at optical frequencies

A Alù,A Salandrino,N Engheta

doi:10.1364/oe.14.001557

Abstract

We present here the design of nano-inclusions made of properly arranged collections of plasmonic metallic nano-particles that may exhibit a resonant magnetic dipole collective response in the visible domain. When such inclusions are embedded in a host medium, they may provide metamaterials with negative effective permeability at optical frequencies. We also show how the same inclusions may provide resonant electric dipole response and, when combining the two effects at the same frequencies, left-handed materials with both negative effective permittivity and permeability may be synthesized in the optical domain with potential applications for imaging and nano-optics applications.

Highlights

The interest in materials with negative effective magnetic, as well as electric, properties has grown considerably in the past several years, mainly due to the recent interest in unconventional characteristics of composite metamaterials with both negative permittivity and permeability, known as left-handed (LH) or double negative (DNG) materials [1]
In the microwave regime, such complex materials have been constructed by embedding arrays of metallic split-ring resonators (SRR) and wires in a host medium and some of their anomalous properties have been experimentally demonstrated [2]
In addition to challenges in nanofabrication of ring or loop resonators and small gaps, it should be mentioned that the electric conductivity of metals, on which the resonance of SRR at microwave frequencies depends, behaves differently as the frequency is increased into the IR and visible domains

Summary

Introduction

The interest in materials with negative effective magnetic, as well as electric, properties has grown considerably in the past several years, mainly due to the recent interest in unconventional characteristics of composite metamaterials with both negative permittivity and permeability, known as left-handed (LH) or double negative (DNG) materials [1]. In addition to challenges in nanofabrication of ring or loop resonators and small gaps, it should be mentioned that the electric conductivity of metals, on which the resonance of SRR at microwave frequencies depends, behaves differently as the frequency is increased into the IR and visible domains Following these issues, several novel ideas have been put forward by other researchers to achieve LH materials in the IR and visible regimes. Several novel ideas have been put forward by other researchers to achieve LH materials in the IR and visible regimes They include the possibility of using coupled plasmonic parallel nano-wires and nano-plates [4]-[8], coupled nano-cones [9], anisotropic waveguides [10], modified SRR in the near-IR region [11]-[12], closely-packed inclusions with negative permittivity and their electrostatic resonances [13], and defects in regular photonic band gap structures [14]. In the following we justify theoretically our findings and validate the results with numerical simulations and some physical insights

Geometry of the nano-ring and its electromagnetic response

Magnetic dipole moment and effective magnetic permeability

Electric dipole moment and effective electric permittivity

Left-handed metamaterials at optical frequencies

Conclusion