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9 pages, 1732 KiB

Open AccessArticle

Broadband Spin-Selective Wavefront Manipulations with Generalized Pancharatnam–Berry Phase Metasurface

by Shiming Gan, Tianci Zhao, Xiuzhuang Mei, Tingting Zhang, Zhiqi Wang, Hongyu Gao, Gensen Yang, Jixiang Cai and Fuzhong Bai

Photonics 2024, 11(8), 690; https://doi.org/10.3390/photonics11080690 - 24 Jul 2024

Viewed by 959

Abstract

Metasurfaces can flexibly manipulate electromagnetic waves by engineering subwavelength structures, which have attracted enormous attention in holography, cloaking, and functional multiplexing. For structures with n-fold (n > 2) rotational symmetry, they have been utilized to realize broadband and high-efficiency wavefront manipulation with generalized Pancharatnam–Berry phase, whereas spin-selective wavefront manipulation is still a challenge limited by their symmetrical spin–orbit interactions. Here, we demonstrate the spin-selective wavefront manipulations with generalized Pancharatnam–Berry phase in the range of 560–660 nm with a metal–insulator–metal metasurface consisting of the chiral C3 logarithmic spiral nanostructures. As a proof of concept, two deflectors and a bifocal metalens are designed. This configuration may provide a platform for various applications in polarimetry, polarization-selective images, and nonlinear optical responses. Full article

(This article belongs to the Special Issue Multifunctional Metasurfaces: Design Strategies and Applications)

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19 pages, 964 KiB

Open AccessArticle

Bifurcation Analysis in a Coffee Berry-Borer-and-Ants Prey–Predator Model

by Carlos Andrés Trujillo-Salazar, Gerard Olivar-Tost and Deissy Milena Sotelo-Castelblanco

Mathematics 2024, 12(11), 1670; https://doi.org/10.3390/math12111670 - 27 May 2024

Cited by 1 | Viewed by 1144

Abstract

One of the most important agricultural activities worldwide, coffee cultivation, is severely affected by the Coffee Berry Borer (CBB), Hypothenemus hampei, considered the primary coffee pest. The CBB is a tiny beetle that diminishes the quantity and quality of coffee beans by penetrating them to feed on the endosperm and deposit its eggs, continuing its life cycle. One strategy to combat CBBs is using biological control agents, such as certain species of ants. Here, a mathematical model (consisting of a system of nonlinear ordinary differential equations) is formulated to describe the prey–predator interaction between CBBs and an unspecified species of ants. From this mathematical perspective, the model allows us to determine conditions for the existence and stability of extinction, persistence or co-existence equilibria. Transitions among those equilibrium states are investigated through the maximum per capita consumption rate of the predator as a bifurcation parameter, allowing us to determine the existence of transcritical and saddle-node bifurcations. Phase portraits of the system are presented for different values of bifurcation parameter, to illustrate stability outcomes and the occurrence of bifurcations. It is concluded that an increase in bifurcation parameters significantly reduces the CBB population, suggesting that ant predation is an effective control strategy, at least theoretically. Full article

(This article belongs to the Special Issue Dynamics and Differential Equations in Mathematical Biology)

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13 pages, 6993 KiB

Open AccessArticle

On the Quantization of AB Phase in Nonlinear Systems

by Xi Liu, Qing-Hai Wang and Jiangbin Gong

Entropy 2022, 24(12), 1835; https://doi.org/10.3390/e24121835 - 16 Dec 2022

Viewed by 1910

Abstract

Self-intersecting energy band structures in momentum space can be induced by nonlinearity at the mean-field level, with the so-called nonlinear Dirac cones as one intriguing consequence. Using the Qi-Wu-Zhang model plus power law nonlinearity, we systematically study in this paper the Aharonov–Bohm (AB) phase associated with an adiabatic process in the momentum space, with two adiabatic paths circling around one nonlinear Dirac cone. Interestingly, for and only for Kerr nonlinearity, the AB phase experiences a jump of

π

at the critical nonlinearity at which the Dirac cone appears and disappears (thus yielding

π

-quantization of the AB phase so long as the nonlinear Dirac cone exists), whereas for all other powers of nonlinearity, the AB phase always changes continuously with the nonlinear strength. Our results may be useful for experimental measurement of power-law nonlinearity and shall motivate further fundamental interest in aspects of geometric phase and adiabatic following in nonlinear systems. Full article

(This article belongs to the Special Issue Quantum Chaos—Dedicated to Professor Giulio Casati on the Occasion of His 80th Birthday)

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18 pages, 12251 KiB

Open AccessArticle

High Harmonic Generation in Monolayer and Bilayer of Transition Metal Dichalcogenide

by Yeon Lee, Dasol Kim, Dong-Eon Kim and Alexis Chacón

Symmetry 2021, 13(12), 2403; https://doi.org/10.3390/sym13122403 - 12 Dec 2021

Cited by 4 | Viewed by 4018

Abstract

In transition metal dichalcogenides (TMDCs), charge carriers have spin, pseudospin, and valley degrees of freedom associated with magnetic moments. The monolayers and bilayers of the TMDCs, in particular, MoS

_{2}

, lead to strong couplings between the spin and pseudospin effects. This feature [...] Read more.

_{2}

, lead to strong couplings between the spin and pseudospin effects. This feature has drawn attention to TMDCs for their potential use in advanced tech devices. Meanwhile, high-order harmonic generation (HHG) has recently been applied to the characterization of the electronic structure of solids, such as energy dispersion, Berry-curvature, and topological properties. Here, we show theoretical results obtained with the ‘philosophy’ of using HHG to investigate the structural effects of the monolayer and bilayers of MoS

_{2}

on nonlinear optical emission. We use a simple model for MoS

_{2}

in the 3R AB staking. We find that the pseudospin and valley indexes (the Berry curvature and the dipole transition matrix element) in TMDC driven by a circularly polarized laser (CPL) can encode in the high-energy photon emissions. This theoretical investigation is expected to pave the way for the ultrafast manipulation of valleytronics and lead to new questions concerning the spin-obit-coupling (SOC) effects on TMDC materials, Weyl Semimetals, and topological phases and transitions in topological insulators. Full article

(This article belongs to the Section Physics)

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16 pages, 999 KiB

Open AccessArticle

Nonlinear Topological Effects in Optical Coupled Hexagonal Lattice

by Fude Li, Kang Xue and Xuexi Yi

Entropy 2021, 23(11), 1404; https://doi.org/10.3390/e23111404 - 26 Oct 2021

Cited by 1 | Viewed by 2575

Abstract

Topological physics in optical lattices have attracted much attention in recent years. The nonlinear effects on such optical systems remain well-explored and a large amount of progress has been achieved. In this paper, under the mean-field approximation for a nonlinearly optical coupled boson–hexagonal lattice system, we calculate the nonlinear Dirac cone and discuss its dependence on the parameters of the system. Due to the special structure of the cone, the Berry phase (two-dimensional Zak phase) acquired around these Dirac cones is quantized, and the critical value can be modulated by interactions between different lattices sites. We numerically calculate the overall Aharonov-Bohm (AB) phase and find that it is also quantized, which provides a possible topological number by which we can characterize the quantum phases. Furthermore, we find that topological phase transition occurs when the band gap closes at the nonlinear Dirac points. This is different from linear systems, in which the transition happens when the band gap closes and reopens at the Dirac points. Full article

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9 pages, 274 KiB

Open AccessFeature PaperArticle

Effect of Interactions on the Quantization of the Chiral Photocurrent for Double-Weyl Semimetals

by Ipsita Mandal

Symmetry 2020, 12(6), 919; https://doi.org/10.3390/sym12060919 - 2 Jun 2020

Cited by 28 | Viewed by 2677

Abstract

The circular photogalvanic effect (CPGE) is the photocurrent generated in an optically active material in response to an applied AC electric field, and it changes sign depending on the chirality of the incident circularly polarized light. It is a non-linear DC current as it is second order in the applied electric field, and for a certain range of low frequencies, takes on a quantized value proportional to the topological charge for a system which is a source of non-zero Berry flux. We show that for a non-interacting double-Weyl node, the CPGE is proportional to two quanta of Berry flux. On examining the effect of short-ranged Hubbard interactions up to first-order corrections, we find that this quantization is destroyed. This implies that unlike the quantum Hall effect in gapped phases or the chiral anomaly in field theories, the quantization of the CPGE in topological semimetals is not protected. Full article

(This article belongs to the Section Physics)

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