Topological Optical Chirality Dichroism

Abstract

We report on a universal topological dichroism of chiral three-dimensional systems in response to the chirality of light. We show that chiral topological invariants result in integer-quantized dichroic excitation rate differences. Moreover, we demonstrate that such topological effects arise more generally from coupling optical chirality to higher tensor Berry curvatures and Dixmier-Douady invariants of quantum states, including Hopf indices. We finally propose an experimental setup that leverages superchiral light as a smoking-gun probe of chiral band topologies in three-dimensional materials. Our findings establish an optical route for probing to date unobserved chiral electronic band topologies.

Figures (2)

• Figure 1: Topological optical chirality dichroism (TOCD). (a) Chiral topological insulator ($\mathcal{DD} \neq 0$) exhibiting dichroism between light beams ($\gamma$) with optical chiralities $\pm Z_0$, absorbing zilch $-Z_0$ (blue), transmitting zilch $Z_0$ (white). The effect arises from gyrotropic birefringence of chiral bulk electric currents supported by topologically nontrivial electrons. (b) Experimentally measurable absorptive chiral topological response to superchiral light with enhanced zilch $Z_0$. We establish TOCD of superchiral light as a smoking-gun signature of chiral bulk topologies.
• Figure 2: (a)-- (d) TOCD of chiral topological insulators responding to light with frequency $\omega$ and zilch $Z_0$. The panels display the total gyrotropic birefringent responses (dashed) and the topological (TOCD) contribution (bold). The corresponding integrated responses evaluated over $(0,\omega)$ range are shown with additional markers ($+$), with quantizations converging under the excitations of full bands, in the $\omega \rightarrow \infty$ limit. (e)-- (h) TOCD of chiral topological insulators responding to zilch $Z_0$ at different chemical potentials $\mu$. TOCD remains quantized in integers when $\mu$ lies in band gap. We show TOCD for a range of chiral topological insulator realizations: (a,e) Three-band chiral topological insulator Neupert2012Palumbo2019. (b,f) Four-band chiral topological insulator Liu2023. (c,g) Two-band Hopf insulator Moore2008Kennedy2016. (d,h) Three-band real Hopf insulator Jankowski2024PRB.