Synthetic Weyl points in generalized parameter space and their topological properties

TL;DR

This paper introduces the concept of generalized Weyl points in parameter space, reports their first experimental observation in 1D photonic crystals, and explores their topological properties and associated interface states.

Contribution

It demonstrates the existence of generalized Weyl points in parameter space and provides the first experimental observation in optical photonic crystals, revealing their topological characteristics.

Findings

Weyl points can exist in parameter space, not just momentum space.

Reflection phase vortices indicate the presence of Weyl points.

Interface states emerge as Fermi arc analogs from Weyl nodes.

Abstract

Weyl fermions1 do not appear in nature as elementary particles, but they are now found to exist as nodal points in the band structure of electronic and classical wave crystals. Novel phenomena such as Fermi arcs and chiral anomaly have fueled the interest of these topological points which are frequently perceived as monopoles in momentum space. Here, we demonstrate that generalized Weyl points can exist in a parameter space and we report the first observation of such nodal points in one-dimensional photonic crystals in the optical range. The reflection phase inside the band gap of a truncated photonic crystal exhibits vortexes in the parameter space where the Weyl points are defined and they share the same topological charges as the Weyl points. These vortexes guarantee the existence of interface states, the trajectory of which can be understood as "Fermi arcs" emerging from the Weyl nodes.