Zhaoju Yang

Zhejiang University

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Baile Zhang

Nanyang Technological University

Fei Gao

Zhejiang University

Xihang Shi

Technion – Israel Institute of Technology

Xiao Lin

Zhejiang University

Eran Lustig

Stanford University

Mordechai Segev

Technion – Israel Institute of Technology

Z. Gao

Guangdong Academy of Medical Sciences

Yonatan Plotnik

Technion – Israel Institute of Technology

Hongsheng Chen

Zhejiang University

Y. D. Chong

Nanyang Technological University

Cooperative Institutions

Zhejiang University

State Key Laboratory of Modern Optical Instruments

Zhejiang University of Technology

Nanyang Technological University

Technion – Israel Institute of Technology

Jinhua Academy of Agricultural Sciences

Shaoxing University

Chinese Academy of Sciences

Zhejiang University of Science and Technology

University of Chinese Academy of Sciences

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Fractal photonic topological insulators

Conference on Lasers and Electro-Optics (2022)

Matthias Heinrich Tobias Biesenthal Lukas J. Maczewsky Zhaoju Yang Mark Kremer

We present the first experimental observation of a fractal topological insulator and demonstrate how the self-similar properties of the Sierpinski gasket systematically enhance the transport of light in its topologically protected edge states.

Topological insulator

10.1364/cleo_qels.2022.ftu5j.1

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Citations (1)

Weyl points in a magnetic tetrahedral photonic crystal

Optics Express (2017)

Zhaoju Yang Meng Xiao Fei Gao Ling Lü Y. D. Chong

Weyl points have recently been predicted and experimentally observed in double-gyroid photonic crystals, as well as in other complex photonic structures such as stacked hexagonal-lattice slabs and helical waveguide arrays. In all above structures, the Weyl points are located between high frequency bands, and are difficult to probe experimentally. In this work, we show that a photonic crystal with a simple tetrahedral structure can host frequency-isolated Weyl points between the second and third bands. The minimal number of two Weyl points emerges from a threefold quadratic degeneracy at the Brillouin zone corner when time-reversal symmetry is broken. We verify theoretically that the Weyl points carry opposite topological charges, and are associated with Fermi arc-like surface states. This photonic crystal can be realized using ferromagnetic rods in the microwave frequency regime, providing a simple platform for studying the physics of Weyl points.

Brillouin zone

Tetrahedron

Gyroid

Weyl semimetal

10.1364/oe.25.015772

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Citations (35)

Probing topological protection using a designer surface plasmon structure

Nature Communications (2016)

Fei Gao Z. Gao Xihang Shi Zhaoju Yang Xiao Lin

Abstract Topological photonic states, inspired by robust chiral edge states in topological insulators, have recently been demonstrated in a few photonic systems, including an array of coupled on-chip ring resonators at communication wavelengths. However, the intrinsic difference between electrons and photons determines that the ‘topological protection’ in time-reversal-invariant photonic systems does not share the same robustness as its counterpart in electronic topological insulators. Here in a designer surface plasmon platform consisting of tunable metallic sub-wavelength structures, we construct photonic topological edge states and probe their robustness against a variety of defect classes, including some common time-reversal-invariant photonic defects that can break the topological protection, but do not exist in electronic topological insulators. This is also an experimental realization of anomalous Floquet topological edge states, whose topological phase cannot be predicted by the usual Chern number topological invariants.

Topological insulator

Floquet theory

Surface States

Topological degeneracy

10.1038/ncomms11619

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Citations (251)

Acoustic Type-II Weyl Nodes from Stacking Dimerized Chains

Physical Review Letters (2016)

Zhaoju Yang Baile Zhang

Lorentz-violating type-II Weyl fermions, which were missed in Weyl's prediction of nowadays classified type-I Weyl fermions in quantum field theory, have recently been proposed in condensed matter systems. The semimetals hosting type-II Weyl fermions offer a rare platform for realizing many exotic physical phenomena that are different from type-I Weyl systems. Here we construct the acoustic version of type-II Weyl Hamiltonian by stacking one-dimensional dimerized chains of acoustic resonators. This acoustic type-II Weyl system exhibits distinct features in finite density of states and unique transport properties of Fermi-arc-like surface states. In a certain momentum space direction, the velocity of these surface states are determined by the tilting direction of the type-II Weyl nodes, rather than the chirality dictated by the Chern number. Our study also provides an approach of constructing acoustic topological phases at different dimensions with the same building blocks.

Weyl semimetal

Weyl transformation

Hamiltonian (control theory)

10.1103/physrevlett.117.224301

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Citations (135)

Dispersion-tunable designer-plasmonic resonator with enhanced high-order resonances

Optics Express (2015)

Fei Gao Zhen Gao Xihang Shi Zhaoju Yang Xiao Lin

We propose and experimentally demonstrate an approach to efficiently tune the dispersion of a designer-plasmonic resonator, or a plasmonic 'meta-atom', by incorporating an extra ground plane underneath. We demonstrate that this ground plane is able to enhance resonances, and the enhancing effect can render those higher-order azimuthal modes, being absent in previously reported designer-plasmonic resonators, experimentally observable. After incorporating the ground plane, all resonance modes are red shifted with their Q factors enhanced. By increasing the separation from the planar resonator to the underneath ground plane, all enhanced modes are blue shifted with Q factors decreased slightly, whose trend is opposite to increasing the thickness of a dielectric substrate of a common meta-atom without a ground. These results may find potential applications in tunable designer-plasmonic sensors and plasmonic metamaterial designs.

Ground plane

10.1364/oe.23.006896

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Citations (45)

The Superlight Inverse Doppler Effect

Conference on Lasers and Electro-Optics (2018)

Xihang Shi Xiao Lin Ido Kaminer Fei Gao Zhaoju Yang

An inverse Doppler frequency shift of light, i.e., superlight inverse Doppler effect, is shown possible even in homogeneous media with positive-refractive index, contrary to the status quo ante. We show an example with graphene plasmons.

10.1364/cleo_qels.2018.fm4j.8

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Citations (2)

Observation of squeezed Chern insulator in an acoustic fractal lattice

arXiv (Cornell University) (2022)

Junkai Li Yeyang Sun Qingyang Mo Zhichao Ruan Zhaoju Yang

Topological insulators are a new phase of matter with the distinctive characteristics of an insulating bulk and conducting edge states. Recent theories indicate there even exist topological edge states in the fractal-dimensional lattices, which are fundamentally different from the current studies that rely on the integer dimensions. Here, we propose and experimentally demonstrate the squeezed Chern insulator in a fractal-dimensional acoustic lattice. First, through calculating the topological invariant of our topological fractal system, we find the topological phase diagram is squeezed by about 0.54 times, compared with that of the original Haldane model. Then by introducing synthetic gauge flux into an acoustic fractal lattice, we experimentally observe the one-way edge states that are protected by a robust mobility gap within the squeezed topological regimes. Our work demonstrates the first example of acoustic topological fractal insulators and provides new directions for the advanced control of sound waves.

Topological insulator

Lattice (music)

10.48550/arxiv.2205.05297

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3D Parity Time symmetry in 2D photonic lattices utilizing artificial gauge fields in synthetic dimensions

Conference on Lasers and Electro-Optics (2019)

Eran Lustig Yonatan Plotnik Zhaoju Yang Mordechay Segev

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text E. Lustig, Y. Plotnik, Z. Yang, and M. Segev, "3D Parity Time symmetry in 2D photonic lattices utilizing artificial gauge fields in synthetic dimensions," in Conference on Lasers and Electro-Optics, OSA Technical Digest (Optica Publishing Group, 2019), paper FTu4B.1. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Parity (physics)

10.1364/cleo_qels.2019.ftu4b.1

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Citations (1)

Higher-order topological phase in an acoustic fractal lattice

arXiv (Cornell University) (2022)

Junkai Li Qingyang Mo Jianhua Jiang Zhaoju Yang

Higher-order topological insulators, which support lower-dimensional topological boundary states than the first-order topological insulators, have been intensely investigated in the integer dimensional systems. Here, we provide a new paradigm by presenting experimentally a higher-order topological phase in a fractal-dimensional system. Through applying the Benalcazar, Bernevig, and Hughes model into a Sierpinski carpet fractal lattice, we uncover a squeezed higher-order phase diagram featuring the abundant corner states, which consist of zero-dimensional outer corner states and 1.89-dimensional inner corner states. As a result, the codimension is now 1.89 and our model can be classified into the fractional-order topological insulators. The non-zero fractional charges at the outer/inner corners indicate that all corner states in the fractal system are indeed topologically nontrivial. Finally, in a fabricated acoustic fractal lattice, we experimentally observe the outer/inner corner states with local acoustic measurements. Our work demonstrates a higher-order topological phase in an acoustic fractal lattice and may pave the way to the fractional-order topological insulators.

Topological insulator

Lattice (music)

Sierpinski carpet

10.48550/arxiv.2205.05298

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Citations (2)

Fractality-induced topological phase squeezing and devil's staircase

Physical Review Research (2023)

Junkai Li Yeyang Sun Qingyang Mo Zhichao Ruan Zhaoju Yang

We propose and experimentally demonstrate the first example of Chern fractal insulators in an acoustic Sierpinski lattice. Through introducing fractality into the well-known Haldane model, we find that the topological phase diagram is significantly squeezed by about 0.5 times, compared with that of the original Haldane model. The energy spectra for different generations of a fractal lattice exhibits a hierarchy of self-similar energy bands in the form of a devil's staircase. With local acoustic measurements, we fabricate the sonic sample based on the theoretical model and experimentally confirm the fractality-induced squeezing and observe the one-way edge states that are protected by a robust mobility gap. Our work demonstrates the fundamental interplay between the fractality and topological Haldane insulator, and may provide new directions for the advanced control of sound waves.

Topological insulator

Lattice (music)

Acoustic Metamaterials

10.1103/physrevresearch.5.023189

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Citations (10)