Linear Optical Conductivity of Chiral Multifold Fermions: $$k\cdot p$$ and Tight-Binding Models

Abstract

In this chapter we will derive the general expressions for the optical conductivity in the length gauge. The formalism presented here constitutes the building block for computing the linear and nonlinear responses throughout the following chapters. Using the expressions derived here, we will compute the linear optical conductivity of the low-energy $$k\cdot p$$ models for all chiral multifold fermions and identify fingerprints for each type of multifold fermion. To obtain a more realistic optical conductivity of real materials, we will use the tight-binding models for SG198 and SG199 described in Sect. 2.3 . We will compare our theoretical calculations with experimental data for materials crystallizing in SG198 in the next chapter.