Double-bowl State in photonic Dirac nodal line semimetal

TL;DR

This paper introduces a novel photonic Dirac nodal line semimetal with a unique double-bowl state feature, demonstrating nearly degenerate surface states and experimentally resolving the bulk and surface dispersions.

Contribution

It presents the first photonic Dirac nodal line semimetal with a new mechanism and characterizes the double-bowl surface states experimentally.

Findings

Discovery of double-bowl states in photonic DNLS

Experimental resolution of bulk and surface dispersions

Nearly degenerate surface states across spectrum

Abstract

The past decade has seen a proliferation of topological materials for both insulators and semimetals in electronic systems and classical waves. Topological semimetals exhibit topologically protected band degeneracies, such as nodal points and nodal lines. Dirac nodal line semimetals (DNLS), which own four-fold line degeneracy, have drawn particular attention. DNLSs have been studied in electronic systems but there is no photonic DNLS. Here in this work, we provide a new mechanism which is unique for photonic systems to investigate a stringent photonic DNLS. When truncated, the photonic DNLS exhibits double-bowl states (DBS), which comprises two sets of perpendicularly polarized surface states. In sharp contrast to nondegenerate surface states in other photonic systems, here the two sets of surface states are almost degenerate over the whole spectrum range. The DBS and the bulk Dirac nodal ring (DNR) dispersion along the relevant directions, are experimentally resolved.