Isotropic Optical Magnetism in Visible Light in a Self-Assembled Bulk Metamaterial

The magnetic susceptibility of natural materials is known to be negligible in visible light, so that the generation of optical magnetism has been intensively searched in artificial nanocomposites, generally designed so as to... [ view full abstract ]

The magnetic susceptibility of natural materials is known to be negligible in visible light, so that the generation of optical magnetism has been intensively searched in artificial nanocomposites, generally designed so as to develop loops of intense induced currents upon illumination by a light wave. Such artificial magnetism is a non local phenomenon, formally equivalent to the spatial dispersion of the dielectric permittivity. It is in general not reducible to a rank 2 tensor mu(i,j) so that the familiar notion of a bulk magnetic permeability loses a large part of its meaning, hence precluding the achievement in visible light of the extraordinary properties expected from metamaterials. Here we report on the first experimental realization of a three-dimensional isotropic metamaterial exhibiting strong artificial magnetism that satisfies the principle of effective locality across a wide range of visible wavelengths. We have used colloidal self-assembly to create artificial "nanomolecules" that generate the desired magnetic response and microfluidic self-assembly to produce a bulk metastructure. The magnetic response of the "nanomolecules" and of the bulk material are unambiguously measured by polarized light scattering and spectroscopic ellipsometry respectively. Numerical simulations confirm the experimental data. A large-scale fabrication of such magnetic metamaterials of arbitrary size and shape is made possible by our bottom-up approach that restores the hope of extending the physics of metamaterials to visible light frequencies.