Experimental observation of photonic nodal line degeneracies in metacrystals

Wenlong Gao,Alastair P Hibbins,Shuang Zhang,Ben Tremain,Lingbo Xia,Hongchao Liu,Biao Yang,Qinghua Guo

doi:10.1038/s41467-018-03407-5

Abstract

Nodal line semimetals (NLS) are three-dimensional (3D) crystals that support band crossings in the form of one-dimensional rings in the Brillouin zone. In the presence of spin–orbit coupling or lowered crystal symmetry, NLS may transform into Dirac semimetals, Weyl semimetals, or 3D topological insulators. In the photonics context, despite the realization of topological phases, such as Chern insulators, topological insulators, Weyl, and Dirac degeneracies, no experimental demonstration of photonic nodal lines (NLs) has been reported so far. Here, we experimentally demonstrate NL degeneracies in microwave cut-wire metacrystals with engineered negative bulk plasma dispersion. Both the bulk and surface states of the NL metamaterial are observed through spatial Fourier transformations of the scanned near-field distributions. Furthermore, we theoretically show that the NL degeneracy can transform into two Weyl points when gyroelectric materials are incorporated into the metacrystal design. Our findings may inspire further advances in topological photonics.

Highlights

Nodal line semimetals (NLS) are three-dimensional (3D) crystals that support band crossings in the form of one-dimensional rings in the Brillouin zone
The concept of nontrivial topological physics in solid-state systems has been extended to photonic systems, with particular interests focusing on achieving one-way disorderimmune surface states (SSs)
We report the experimental realization of a clean nodal lines (NLs) in a cut-wire metacrystal, which may provide a fertile ground for investigating the interesting topological features such as drumhead SSs and topological phase transitions between NL and Weyl degeneracies, and a number of other interesting optical properties, for instance, resonance scattering[41] and negative refraction

Summary

Introduction

Nodal line semimetals (NLS) are three-dimensional (3D) crystals that support band crossings in the form of one-dimensional rings in the Brillouin zone. We report the experimental realization of a clean NL in a cut-wire metacrystal, which may provide a fertile ground for investigating the interesting topological features such as drumhead SSs and topological phase transitions between NL and Weyl degeneracies, and a number of other interesting optical properties, for instance, resonance scattering[41] and negative refraction.

Results

Conclusion