Novel homogeneous negative refractive index materials

Abstract

We introduce a family of materials which are homogeneous and which posses a negative index of refraction at optical frequencies. The desirable negative effect is not based on the chirality of the molecules, but rather on two other ideas (A.-G. Kussow and A. Akyurtlu, Phys. Rev. B, 78, 205202 (2008)): Firstly, there are known materials such as magnetic semiconductors (e.g. <i>In_2-xCr_xO₃</i>,), and 3 d <i>transition metals</i> (Fe, Ni), in which the high-frequency spin wave modes coexist with the plasmonic modes. The spin wave (magnon) mode is coupled with the e.m. field of the light close to the boundary of the Brillouin zone. Consequently, the spin wave mode, along with the plasmonic mode, are activated by the e.m. field of the light, with simultaneous negative permittivity and permeability responses. As a result, the material exhibits the negative refractive index effect within the frequency band close to the ferromagnetic resonance. Secondly, based on methods of <i>Quantum Optics</i>, we discuss the possibility of achieving the negative index of refraction in an <i>n-type doped semiconductor</i>. The quantum states of hydrogen-like donor atom and states of an electron in conduction band constitute a discrete-level atomic medium within the optical range. The coherent coupling of an electric dipole transition with a magnetic dipole transition leads to negative permeability and permittivity responses and ensures the negative refractive index effect. The implementation of this scheme is carried out in tin-doped indium oxide, <i>In_2-xSn_xO₃</i> (ITO), and calculations show feasibility of this effect with FOM &gt; 10.