Hyperbolic metamaterials based on arrays of gold nanorods in the matrix of anodic alumina

Nanocomposites in which the transverse and longitudinal components of tensors of the dielectric (ε) and/or magnetic (μ) permeabilities have opposite signs are called hyperbolic metamaterials. The great interest for these materials is caused by the possibilities to achieve the negative refraction, as well as amplification of Raman scattering and transformation of the near field of the object into an image in the far field, which allows one to overcome the diffraction limit [1].

In our group, in collaboration with the staff of the group of Dr.Sci. T.V. Murzina (Physics Department of Moscow State University), nanocomposites with the properties of hyperbolic metamaterials were obtained and thoroughly studied. The samples were formed by means of templated electrodeposition of gold in a porous matrix of anodic aluminum oxide [2]. On the optical spectra of the obtained array of metallic nanorods in the dielectric matrix, two transmission minima, corresponding to the excitation of plasmons in transverse and longitudinal directions of the long axis of the rods, are observed. These features correspond to the ENP (Epsilon Near Pole, the dielectric constant pole) and ENZ (Epsilon Near Zero, change of the sign of ε) points that result from the hyperbolic dispersion law.

To control the optical properties of hyperbolic metamaterials using external fields, a thin nickel film was deposited on the surface of the nanocomposite [3]. It is shown that an increase in the density of states in the vicinity of the ENP point leads to a significant enhancement of the Faraday effect. In the case of magneto-plasmonic Ni/Au nanostructures, the position of the ENZ point can be tuned by an external magnetic field.

This work was supported by the Russian Foundation for Basic Research (grant number 18-03-01237) and the President’s grant (MK-5704.2018.2).

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[3] I.A. Kolmychek, A.R. Pomozov, A.P. Leontiev, K.S. Napolskii, T.V. Murzina. Magneto-optical effects in hyperbolic metamaterials // Optics Letters, 2018, v. 43(16), pp. 3917–3920. DOI: 10.1364/OL.43.003917.