Tunable chirality and circular dichroism of a topological insulator with \( C_{2v} \) symmetry as a function of Rashba and Dresselhaus parameters

Abstract

Polarization-sensitive devices rely on meta-materials to exhibit varying degrees of absorption of light of a given handedness. The chiral surface states of a topological insulator(TI) selectively absorb right and left circularly polarized light in the vicinity of the Dirac cone reaching its maximum of unity at the \( \Gamma \) point. In this letter, we demonstrate that a band gap open TI with C\(_{2v}\) symmetry which is represented through a combination of Rashba and Dresselhaus Hamiltonians alters the preferential absorption of left and right circularly polarized light allowing a smooth variation of the circular dichroism(CD). This variation in CD, reflected in a range of positive and negative values is shown to be a function of the Rashba and Dresselhaus coupling parameters. Additionally, we draw a parallel between the varying CD and the emerging field of valley-electronics in transition metal dichalcogenides and note the possibility of the chiral states as a basis toward quantum information processing.