Abstract

The mineral tetradymite structures are interesting classes of materials. At their bandgap just near to the Fermi level they sustain time-reversal-invariant topological effects, which appears up in exceptional electronic surface states captured in the so-far investigated mass-less Dirac cones [1]. Another characteristic of tetradymites is caused by the huge uniaxial electric anisotropic behaviour of the material. It has been shown that tetradymites and in particular Bi₂Se₃ and Bi₂Te₃ belong to the naturally rare class of hyperbolic materials [2] in the visible frequency range, with a smooth transition from the elliptical to the hyperbolic dispersion, by marching over the frequency of excitation. Fig. 1 (a) shows the permittivity of Bi₂Se₃ obtained using the generalized spectroscopic ellipsometry technique reported in ref. [2].

© 2015 IEEE