# Optical conductivity of triple point fermions

## TL;DR

This paper investigates the optical conductivity of triple point fermions, revealing a strong dependence on an angular parameter and proposing optical signatures to distinguish them from Dirac/Weyl fermions.

## Contribution

It introduces a generic Hamiltonian for triple point fermions with a parameter-dependent analysis of optical absorption properties.

## Key findings

- Optical absorption varies significantly with the parameter λ.
- Deviations from Dirac/Weyl behavior can be identified via the Drude weight.
- Helicity reversal transitions are suppressed at λ=π/6 but emerge otherwise.

## Abstract

As a low-energy effective theory on non-symmorphic lattices, we consider a generic triple point fermion Hamiltonian which is parameterized by an angular parameter $\lambda$. We find strong $\lambda$ dependence in both Drude and interband optical absorption of these systems. The deviation of the $T^2$ coefficient of the Drude weight from Dirac/Weyl fermions can be used as a quick way to optically distinguish the triple point degeneracies from the Dirac/Weyl degeneracies. At the particular $\lambda=\pi/6$ point, we find that the "helicity" reversal optical transition matrix element is identically zero. But deviating from this point, the helicity reversal emerges as an absorption channel.