Effective Hamiltonian approach to optical activity in Weyl spin-orbit system

TL;DR

This paper develops an effective Hamiltonian framework to understand optical activity in Weyl spin-orbit systems, revealing how chirality influences optical responses in time-reversal invariant materials.

Contribution

It introduces a novel effective Hamiltonian derived from path-integral formalism that incorporates optical chirality in Weyl spin-orbit systems, advancing theoretical understanding.

Findings

Optical chirality is represented by an effective Hamiltonian.

The Hamiltonian explains natural optical activity in Weyl systems.

Chirality induces measurable optical responses in time-reversal invariant materials.

Abstract

Chirality or handedness in condensed matter induces anomalous optical responses such as natural optical activity, rotation of the plane of light polarization, as a result of breaking of spatial-inversion symmetry. In this study, optical properties of a Weyl spin-orbit system with quadratic dispersion, a typical chiral system invariant under time-reversal, are investigated theoretically by deriving an effective Hamiltonian based on an imaginary-time path-integral formalism. We show that the effective Hamiltonian can be indeed written in terms of an optical chirality order parameter suggested by Lipkin. The natural optical activity is discussed based on the Hamiltonian.