Optical nonlocality in multilayered hyperbolic metamaterials based on   Thue-Morse superlattices
  We show that hyperbolic electromagnetic metamaterials implemented as multilayers based on two material constituents arranged according to Thue-Morse (ThM) aperiodic sequence may exhibit strong nonlocal effects, manifested as the appearance of additional extraordinary waves which are not predicted by standard effective-medium-theory (local) models. From the mathematical viewpoint, these effects can be associated with stationary points of the transfer-matrix trace, and can be effectively parameterized via the trace-map formalism. We show that their onset is accompanied by a strong wavevector dependence in the effective constitutive parameters. In spite of the inherent periodicity enforced by the unavoidable (Bloch-type) supercell terminations, we show that such strong nonlocality is retained at any arbitrarily high-order iterations, i.e., approaching the actual aperiodic regime. Moreover, for certain parameter configurations, at a given wavelength and for two given material layers, these effects may be significantly less prominent when the same layers are arranged in a standard periodic fashion. Our findings indicate that the (aperiodic) positional order of the layers constitutes an effective and technologically inexpensive additional degree of freedom in the engineering of optical nonlocality. 
Silvio Savoia, Giuseppe Castaldi, and Vincenzo Galdi
physics.optics cond-mat.mes-hall