Figure 2From: Topological insulator metamaterials with tunable negative refractive index in the optical regionDielectric constant of the Bi 2 Se 3 . (a) Real part of dielectric function ϵ1(ω) for trigonal and orthorhombic phases of Bi2Se3. (b) Imaginary part of dielectric function ϵ2(ω) for trigonal and orthorhombic phases of Bi2Se3.Back to article page