Twists and shifts make nonlinear metamaterials

Recent studies have demonstrated that it is possible to modify the properties of metamaterials by electromagnetic waves via inducing mechanical deformations of samples and therefore changing material properties. As an example, optical rotation of chiral particles was demonstrated [1], and a rich variety of nonlinear behaviour was achieved with magneto-elastic metamaterials [2]. The range of possible effects achievable in this way promises to be richer than in the prominent area of optomechanics, because the greater flexibility in metamaterial design overcomes the limits of available material functionalities, and offers wider possibilities for optimisation. At the same time, the implementation of magnetoelastic metamaterials [2] remains challenging and in some cases, such as the conformational nonlinearity in resonant spirals, remains inaccessible for optics. The reason for this is that the magnetic forces, employed in the initial designs, are relatively weak, so such materials require either high power or extremely small elastic restoring forces, which poses a considerable manufacturing challenge. We recall, however, that earlier research on structurally tunable metamaterials [3] indicated that near-field interaction may significantly improve the tunability range and leads to various effects associated with near-field coupling.