Strong magnetism at visible wavelengths via coupled silver nano- hoops C. García-Meca, R. Ortuño, F.J. Rodríguez-Fortuño, J. Martí, and A. Martínez Nanophotonics Technology Center, Universidad Politécnica de Valencia C.P. 46022, Camino de Vera, s/n, Valencia, Spain. Fax: + 34 963877827; email: cargarm2@ntc.upv.es Abstract We study the optical properties of a metamaterial made up of close silver nanohoops. Under normal inci- dence, this metamaterial exhibits a strong magnetic response. A highly negative real part of the permeability is achieved in the visible spectrum, even at blue light. We also show that the strength of the magnetic resonance and consequently the metamaterial’s permeability are easily tuneable through the inner radius of the nanohoops. 1. Introduction In the quest for low loss negative refraction, two main properties are needed: negative permittivity and negative permeability [1]. The last one is often harder to obtain, proving itself specially challenging in the visible spectrum. There exist several proposals with the purpose of achieving negative permeabil- ity in this frequency range [2-5]. In this work, we study the optical properties of silver nanohoops as an alternative way to obtain comparatively strong magnetic responses in the visible regime. 2. Magnetic properties of coupled nanohoops. Let us consider a metamaterial whose unit cell is a silver planar hoop with inner radius r i , outer radius r o and thickness t, as shown in Fig. 1. Fig. 1: Array of silver nanohoops. Silver is known to have lower losses than other metals in this region, being that the reason for choos- ing this element to build the nanohoops. In order to obtain the electromagnetic response of this struc- ture, we have performed a series of numerical simulations using CST Microwave Studio. In the simu- lations, silver has been described through the Drude model with a plasma frequency ω p = 1.37x10 16 s -1 and a collision frequency ω c = 6x10 13 s -1 . This last value is somewhat higher than that in bulk because the losses increase when the metal is nanostructured [6]. Nevertheless, the exact value of ω c can only 3rd International Congress on Advanced Electromagnetic Materials in Microwaves and Optics ISBN 978-0-9551179-6-1 ©2009 Metamorphose-VI ISBN 978-0-9551179-6-1 ISBN 978-0-9551179-6-1 ©2009 Metamorphose-VI 767