Realization of Photonic Charge-2 Dirac Point by Engineering Super-modes in Topological Superlattices

TL;DR

This paper demonstrates the experimental realization of charge-2 Dirac points in a 1-D optical superlattice, revealing new topological states and enabling control over topological end modes for potential applications in field engineering.

Contribution

It introduces the first experimental creation of synthetic charge-2 Dirac points using super-modes in a 1-D optical superlattice with synthetic dimensions.

Findings

Observation of super-modes linked to charge-2 Dirac points in the visible spectrum

Manipulation of Weyl points with identical charges in synthetic space

Control over topological end modes in truncated superlattice samples

Abstract

Quite recently a novel variety of unconventional fourfold linear band degeneracy points has been discovered in certain condensed-matter systems. Contrary to the standard 3-D Dirac monopoles, these quadruple points referred to as the charge-2 Dirac points are characterized by nonzero net topological charges, which can be exploited to delve into hitherto unknown realms of topological physics. Here, we report on the experimental realization of the charge-2 Dirac point by deliberately engineering hybrid topological states called super-modes in a 1-D optical superlattice system with two additional synthetic dimensions. Utilizing direct reflection and transmission measurements, we exhibit the existence of super-modes attributed to the synthetic charge-2 Dirac point, which has been achieved in the visible region for the first time. We also show the experimental approach to manipulating two spawned Weyl points that are identically charged in synthetic space. Moreover, topological end modes uniquely resulting from the charge-2 Dirac point can be delicately controlled within truncated superlattice samples, opening a pathway for us to rationally engineer local fields with intense enhancement.