S. Liu, W. Chen, J. Du, Z. Lin, S. T. Chui and C. T. Chan, Manipulating negative refracting behavior with a magnetic field, Phys. Rev. Lett. 101, 157407 (2008). [PDF] S. T. Chui and Z. Lin, Long-wavelength behavior of two-dimensional photonic crystals, Phys. Rev. E 78, 065601 (2008). [PDF] S. T. Chui, C. T. Chan, and Z. F. Lin, Multilayer structures as negative refractive and left-handed materials, J. Phys.: Condens. Matter 18, L89 (2006). [URL]
Metamaterials are a new class of ordered composites that exhibit exceptional properties not readily observed in nature. These properties arise from qualitatively new response functions that are not observed in the constituent materials and which result from the inclusion of artificially fabricated, extrinsic, low dimensional inhomogeneities. While the original metamaterials definition encompassed many more material properties, most of recent scientific activity has centered on the electromagnetic properties or tailored magnetism of metamaterials.
Electromagnetic waves interact with the atoms and molecules that compose naturally occurring materials. Materials can therefore be used to guide or manipulate electromagnetic waves in the way a glass lens can focus light. But the available electromagnetic response from naturally occurring materials is limited; for example, there are no known materials with a negative index of refraction. Artificialy constructed metamaterials are not subject to the same limitations as real materials, and can be used to extend material response where negative index metamaterials bend beam of light in opposite direction to natural materials and lead to opposite direction of phase and energy velocities of the wave.
Since the refractive index is one of the most fundamental characteristics of light propagation in materials, metamaterials with negative index are envisaged to make possible superlenses capable of imaging objects and fine structures that are much smaller than the wavelength of light. Other exciting applications of metamaterials include antennas with superior properties, optical nanolithography and nanocircuits, and "metacoatings" that can make objects invisible.
Early experiments have been carried out on a medium consisting of arrays of metallic rings and wrires. An example of a different class of anisotropic left-handed materials are metallic magnetic granular composites. Delaware researchers have suggested that by incorporating metallic magnetic nanoparticles into an appropriate insulating matrix, it may be possible to prepare a composite medium of low eddy current loss which is left-handed for electromagnetic waves propagating in some special direction and polarization in a frequency region near the ferromagnetic resonance frequency. This composite may be easier to make on an industrial scale. In addition, its physical properties may be easily tuned by rotating the magnetization locally.
- new classes of negative index metamaterials based on magnetic granular composites (Xiao and Chui)
- photonic crystals and plasmonics (Chui)
- mixtures of hard and soft magnets (Hadjipanayis and Chui)
- creep of fiber reinforced magnetic materials (Chui).