Four-Dimensional Topological Insulators with Nodal-Line Boundary States

TL;DR

This paper introduces a new four-dimensional topological insulator featuring boundary states with nodal lines, protected by symmetry, and proposes a cold-atom system to realize it experimentally.

Contribution

It presents a novel four-dimensional topological insulator with unique boundary nodal-line states and proposes an experimental cold-atom setup for realization.

Findings

Boundary band has a single PT-symmetric nodal line with double topological charges

Proposes a cold-atom system to realize the four-dimensional topological insulator

Connects to recent experimental realization of four-dimensional quantum Hall effect

Abstract

Conventional topological insulators and superconductors have topologically protected nodal points on their boundaries, and the recent interests in nodal-line semimetals only concerned bulk band structures. Here, we present a novel four-dimensional topological insulator protected by an anti-unitary reflection symmetry, whose boundary band has a single $PT$-symmetric nodal line with double topological charges. Inspired by the recent experimental realization of the four-dimensional quantum Hall effect, we also propose a cold-atom system which realizes the novel topological insulator with tunable parameters as extra dimensions.