Mapping and Manipulation of Topological Singularities: From Photonic Graphene to T-Graphene

Abstract

Topological singularities (TSs) in momentum space give rise to intriguing fundamental phenomena as well as unusual material properties, attracting a great deal of interest in the past decade. Recently, we demonstrated universal momentum-to-realspace mapping of TSs and pseudospin angular momentum conversion using photonic honeycomb (graphene-like) and Lieb lattices. Such mapping arises from the nontrivial Berry phase winding and is thus of topological origin. In this paper, after a brief review of previous observations of pseudospin−orbital conversion, we present the first theoretical analysis and experimental demonstration of TS mapping in a new type of Dirac-like structure, namely, the T-graphene lattice. Unlike other lattices, there are two coexisting but distinct TSs located at different highsymmetry points in the first Brillouin zone of T-graphene, which enables controlled topological charge conversion in the same lattice. We show active manipulation of the TS mapping, turning the two TSs into vortices of different helicities, or one into a high-order vortex but the other eliminated and emerged as a quadrupole. Such mapping and manipulation of TSs may find applications in optical communications and quantum information, and may bring insight into the study of other Dirac-like structures with multiple TSs beyond the 2D photonic platform.

Ab Initio Discovery of Group IV–V Monolayers with Superlative Mechanical, Electronic, and Transport Properties

“…Since the successful synthesis of graphene, two-dimensional (2D) materials have gathered considerable attention in the past two decades, both theoretically and experimentally, because of their abundant physicochemical properties in comparison to bulk counterparts as well as various technological applications in next-generation high-performance advanced devices. To date, a plethora of 2D group IV-carbon allotropes have been theoretically proposed, and afterward quite a few of them have been experimentally fabricated. − Their applications in electronic devices overcome the impediments from silicon-based materials to abide by Moore’s Law. , As an extension of monoelemental 2D materials, the allotropes of phosphorus derived from the group V family, such as black phosphorene, blue phosphorene, and violet phosphorene, have sparked tremendous interest as well in chemistry, condensed matter physics, and materials science. The intrinsic semiconducting feature in these phosphorene allotropes with a broad range of bandgap from 0.3 to 2.7 eV conquers the gapless obstacle of both graphene and other group IV elemental 2D materials for digital electronics, promising great potential to surpass carbon allotropes and their derivatives for use in semiconductor technology. − As a consequence, significant fundamental and technological breakthroughs can be made by the discovery of novel 2D materials or their allotropes.…”