Negative effective refractive index in superconductor-ferromagnet superlattice

Abstract

Tensors of the effective material parameters in a long-wavelength approximation are constructed and dispersion relations for the intrinsic TE and TM modes are obtained for a superlattice that comprises alternating layers of a high temperature superconductor and a ferromagnet. The control magnetic field is perpendicular to the direction of wave propagation and to the axis of periodicity of the superlattice. Based on the results of a numerical analysis performed for YBaCuO/U₃Fe₅O₁₂ superlattices, intervals of the frequency and field strength are found in which the effective refractive index for the intrinsic waves becomes negative. It is shown that high selective reflection or transmission of TE modes in a superlattice can be achieved by properly selecting the working frequency, external magnetic field, and relative thicknesses of layers in the system.