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DOI	10.1073/pnas.2019578118
	Evolution and global charge conservation for polarization singularities emerging from non-Hermitian degeneracies
	Chen W.; Yang Q.; Chen Y.; Liu W.
发表日期	2021
ISSN	00278424
卷号	118 期号:12
英文摘要	Core concepts in singular optics, especially the polarization singularities, have rapidly penetrated the surging fields of topological and non-Hermitian photonics. For open photonic structures with non-Hermitian degeneracies in particular, polarization singularities would inevitably encounter another sweeping concept of Berry phase. Several investigations have discussed, in an inexplicit way, connections between both concepts, hinting at that nonzero topological charges for far-field polarizations on a loop are inextricably linked to its nontrivial Berry phase when degeneracies are enclosed. In this work, we reexamine the seminal photonic crystal slab that supports the fundamental two-level non-Hermitian degeneracies. Regardless of the invariance of nontrivial Berry phase (concerning near-field Bloch modes defined on the momentum torus) for different loops enclosing both degeneracies, we demonstrate that the associated far polarization fields (defined on the momentum sphere) exhibit topologically inequivalent patterns that are characterized by variant topological charges, including even the trivial scenario of zero charge. Moreover, the charge carried by the Fermi arc actually is not well defined, which could be different on opposite bands. It is further revealed that for both bands, the seemingly complex evolutions of polarizations are bounded by the global charge conservation, with extra points of circular polarizations playing indispensable roles. This indicates that although not directly associated with any local charges, the invariant Berry phase is directly linked to the globally conserved charge, physical principles underlying which have all been further clarified by a two-level Hamiltonian with an extra chirality term. Our work can potentially trigger extra explorations beyond photonics connecting Berry phase and singularities. © 2021 National Academy of Sciences. All rights reserved.
英文关键词	Berry phase; Non-Hermiticity; Photonic crystal slabs; Polarization singularities; Singular optics
语种	英语
scopus关键词	article; berry; chirality; crystal; male; optics; polarization
来源期刊	Proceedings of the National Academy of Sciences of the United States of America
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/180183
作者单位	School of Optical and Electronic Information, Huazhong University of Science and Technology, Hubei, 430074, China; WuhanNational Laboratory for Optoelectronics, Huazhong University of Science and Technology, Hubei, 430074, China; College forAdvanced Interdisciplinary Studies, National University of Defense Technology, Hunan, 410073, China
推荐引用方式 GB/T 7714	Chen W.,Yang Q.,Chen Y.,et al. Evolution and global charge conservation for polarization singularities emerging from non-Hermitian degeneracies[J],2021,118(12).
APA	Chen W.,Yang Q.,Chen Y.,&Liu W..(2021).Evolution and global charge conservation for polarization singularities emerging from non-Hermitian degeneracies.Proceedings of the National Academy of Sciences of the United States of America,118(12).
MLA	Chen W.,et al."Evolution and global charge conservation for polarization singularities emerging from non-Hermitian degeneracies".Proceedings of the National Academy of Sciences of the United States of America 118.12(2021).