Observation of Quadratic (Charge‐2) Weyl Point Splitting in Near‐Infrared Photonic Crystals

Abstract

Weyl points are point degeneracies that occur in momentum space of 3D periodic materials and are associated with a quantized topological charge. Here, the splitting of a quadratic (charge‐2) Weyl point into two linear (charge‐1) Weyl points in a 3D micro‐printed photonic crystal is observed experimentally via Fourier‐transform infrared spectroscopy. Using a theoretical analysis rooted in symmetry arguments, it is shown that this splitting occurs along high‐symmetry directions in the Brillouin zone. This micro‐scale observation and control of Weyl points is important for realizing robust topological devices in the near‐infrared.

A brief review of topological photonics in one, two, and three dimensions

“…Charge 2 Weyl points have been proposed in woodpile photonic crystals [294,295] and been observed experimentally in the mid-infrared regime in a low-index chiral woodpile photonic crystal fabricated by two-photon polymerization [296]. The splitting of the charge 2 Weyl point into two charge 1 Weyl points was further experimentally observed in [297] under careful symmetry breaking. However, due to the low index contrast in [296], there is only an incomplete bandgap surrounding the Weyl point, making it challenging to study the Weyl point in isolation.…”

Automated Discovery and Optimization of 3D Topological Photonic Crystals

“…Exemplifying this, the first experimental realization of a Chern insulator without Landau levels, the quantum anomalous Hall effect, , was achieved in a gyromagnetic 2D PhC . Similarly, the first experimental observation of a Weyl point was achieved in a 3D high-index PhC, simultaneously with its observation in TaAs. , Gapless photonic topology has since grown to encompass a wide variety of phases, including unconventional Weyl points, − Dirac points, − and nodal lines. − …”

Topological Photonic Crystals: Physics, Designs, and Applications

“…Therefore, there are various intriguing properties of Weyl points, which attract tremendous attention. [38,39,[236][237][238][239][240][241][242][243][244][245][246][247][248] The effective Hamiltonian of Weyl points has the general form of…”

“…Therefore, there are various intriguing properties of Weyl points, which attract tremendous attention. [ 38,39,236–248 ] The effective Hamiltonian of Weyl points has the general form of $$\begin{equation} \delta H\left( {\delta {{\bf k}}} \right) = \sum_{i,j} {{\nu _{ij}}{{\hat{\sigma }}_i}\delta {k_j}} \end{equation}$$where i, j = x, y, z . The topological property of Weyl point is characterized by its chirality χ = sgn[det( v ij )].…”