Quantized electromagnetic response of three-dimensional chiral topological insulators

TL;DR

This paper demonstrates that the magneto-electric polarization can reveal the integer topological invariant of 3D chiral topological insulators, with robustness against perturbations and potential realization in ultracold atom experiments.

Contribution

It shows how to identify the topological invariant via magneto-electric response without quantum Hall layers and proposes an experimental scheme using ultracold atoms.

Findings

Quantized magneto-electric response linked to topological invariant.

Robustness of the quantized response against weak perturbations.

Presence of gapless boundary states when coupling different topological phases.

Abstract

Protected by the chiral symmetry, three dimensional chiral topological insulators are characterized by an integer-valued topological invariant. How this invariant could emerge in physical observables is an important question. Here we show that the magneto-electric polarization can identify the integer-valued invariant if we gap the system without coating a quantum Hall layer on the surface. The quantized response is demonstrated to be robust against weak perturbations. We also study the topological properties by adiabatically coupling two nontrivial phases, and find that gapless states appear and are localized at the boundary region. Finally, an experimental scheme is proposed to realize the Hamiltonian and measure the quantized response with ultracold atoms in optical lattices.