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Observation of Photonic Chiral Flatbands

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Physical Review Letters 2025年第10期134卷 103801-103801页

作者： Minho Choi Andrea Alù Arka Majumdar Department of Electrical and Computer Engineering University of Washington Seattle Washington 98195 USA Photonics Initiative Advanced Science Research Center City University of New York New York New York 10031 USA and Physics Program Graduate Center City University of New York New York New York 10031 USA Department of Electrical and Computer Engineering University of Washington Seattle Washington 98195 USA and Department of Physics University of Washington Seattle Washington 98195 USA

Distinct selectivity to the spin angular momenta of photons has garnered significant attention in recent years, for its relevance in basic science and for imaging and sensing applications. While nonlocal metasurfaces with strong chiral responses to the incident light have been reported, these responses are typically limited to a narrow range of incident angles. In this study, we demonstrate a nonlocal metasurface that showcases strong chirality, characterized by circular dichroism (∼0.6), over a wide range of incident angles ±5°. Its quality factor, circular dichroism and resonant frequency can be optimized by design. These findings pave the way to further advance the development of valley-selective optical cavities and augmented reality applications.

关键词： Natural frequencies

Loss Compensation and Super-Resolution with Excitations at Complex Frequencies

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arXiv 2023年

作者： Kim, Seunghwi Peng, Yu-Gui Yves, Simon Alù, Andrea Photonics Initiative Advanced Science Research Center City University of New York New YorkNY10031 United States School of Physics Huazhong University of Science and Technology Wuhan430074 China Physics Program Graduate Center City University of New York New YorkNY10016 United States

Abbe diffraction limit fundamentally bounds the resolution of conventional optical imaging and spectroscopic systems. Along the years, several schemes have been introduced to overcome this limit, each offering opportunities and trade-offs. Metamaterials have been proposed as a promising platform in this context, in principle enabling superlenses capable of drastic resolution enhancements. However, their performance is severely hindered by material loss and nonlocal phenomena, which become increasingly more detrimental as we attempt to image more subwavelength details. Active metamaterials have been explored to overcome these challenges, however material gain introduces other obstacles, e.g., instabilities, nonlinearities and noise. Here, we demonstrate that the temporal excitation of passive superlenses using signals oscillating at complex frequencies compensates material loss, leading to resolution enhancement. Our results demonstrate that virtual gain stemming from tailored forms of excitation can tackle the impact of loss in superlenses. More broadly, our work opens promising avenues for loss compensation in metamaterials, with a broad range of applications extendable to optics and nanophotonic systems. © 2023, CC BY-NC-ND.

关键词： Metamaterials

Nanophotonics Beyond Passivity Limitations Using Complex Frequency Excitations

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Nanophotonics Beyond Passivity Limitations Using Complex Fre...

Conference on Lasers and Electro-Optics (CLEO)

作者： Seunghwi Kim Andrea Alù Photonics Initiative Advanced Science Research Center City University of New York New York New York USA Physics Program Graduate Center City University of New York New York NY USA

Non-monochromatic excitations oscillating at complex frequencies can overcome the limits imposed by passivity. We discuss a few examples in which this approach can be successfully implemented in nanophotonic platforms.

ISBN: (纸本)9781957171258

关键词： Amplified spontaneous emission Forward scattering Nanophotonics Negative refractive index Point spread function Ring resonators

Engineering Topological States in Arrays of Two-mode Nanostructured Dielectric Waveguides

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Engineering Topological States in Arrays of Two-mode Nanostr...

Progress in Electromagnetic Research Symposium (PIERS)

作者： A. O. Mikhin V. Rutckaia R. S. Savelev I. S. Sinev A. Alù M. A. Gorlach School of Physics and Engineering ITMO University Saint Petersburg Russia Photonics Initiative Advanced Science Research Center The City University of New York New York USA Centre for Innovation Competence SiLi-Nano Martin-Luther-University Germany Physics Program Graduate Center The City University of New York New York USA

ISBN: (数字)9798350375909

ISBN: (纸本)9798350375916

Designs of the optical structures that support topologically nontrivial states typically rely on the combining of simple single-mode meta-atoms in a lattice with a symmetry that guarantees the occurrence of the topological states. Here, we explore an alternative approach that does not require the use of complex lattice geometries, but instead relies on the tailoring of the spatial distribution of the near fields in the individual meta-atoms operating in the multi-mode regime. To this end we consider specially designed subwavelength grating dielectric waveguides with two quasi-degenerate modes that interfere in the near-field zone leading to highly asymmetric field patterns of the propagating waves. We show that a one-dimensional array of such waveguides exhibits non-trivial topological properties and supports topological edge states even with one waveguide in the unit cell. Theoretical predictions are confirmed experimentally by visualizing the excited states of the array by measuring the intensity of the radiation at the frequency of the third harmonic.

关键词： Visualization Lattices Electromagnetic waveguides Waveguide lasers Optical waveguide theory Frequency measurement Dielectrics

B(s) → D((s∗))M decays in the presence of final-state interaction

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arXiv 2024年

作者： Panuluh, Albertus Hariwangsa Tanaka, Satoshi Umeeda, Hiroyuki Physics Program Graduate School of Advanced Science and Engineering Hiroshima University 1-3-1 Kagamiyama Higashi-Hiroshima739-8526 Japan Department of Physics Education Faculty of Teacher Training and Education Sanata Dharma University Paingan Maguwohardjo Sleman Yogyakarta55282 Indonesia Ibaraki prefecture Japan Center for Theoretical Physics College of Physics Jilin University Changchun130012 China China Center of Advanced Science and Technology Beijing100190 China Institute of High Energy Physics Chinese Academy of Sciences Beijing100049 China

In light of the recent data for B¯(s) → D((s∗))P and B¯(s) → D(s)V decays, we perform a model-independent phenomenological analysis in the presence of quasi-elastic rescattering. With the Wilson coefficients including contributions beyond the standard model, lifetimes of B meson as well as the Bd0 −B¯d0 mixing are investigated for clarifying correlations among the observables. We show that parameter regions for quasi-elastic rescattering, the size of color-suppressed tree amplitudes and new physics are constrained due to the lifetime data. As a consequence, it is revealed that this scenario can be testable by the future LHCb measurement of width difference in Bd0 − B¯d0 mixing and semi-leptonic CP asymmetry. © 2024, CC BY.

关键词： Bosons

Surface Second Harmonic Generation from Topological Dirac Semimetal PdTe2

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arXiv 2023年

作者： Faizanuddin, Syed Mohammed Chien, Ching-Hang Chan, Yao-Jui Kuo, Chia-Nung Lue, Chin Shuan Wen, Yu-Chieh Institute of Physics Academia Sinica Taipei11529 Taiwan Nano Science and Technology Program Taiwan International Graduate Program Academia Sinica Taipei11529 Taiwan Department of Engineering and System Science National Tsing Hua University Hsinchu300044 Taiwan Department of Physics National Cheng Kung University Tainan701401 Taiwan Research Center for Applied Sciences Academia Sinica Taipei11529 Taiwan

Three-dimensional topological semimetals were shown to host anomalously strong optical nonlinearity, but yet whether such enhancement can occur at their surfaces via topological boundary states remains an open question. Here we tackle this question by examining polarization-dependent rotational-anisotropy optical second harmonic generation (SHG) from transition metal dichalcogenide Dirac semimetal PdTe2. We find its reflected SHG to follow C3v surface symmetry with a time-varying intensity dictated by oxidation kinetics of the material after its surface cleavage, confirming the surface-derived origin of SHG. The complex surface nonlinear optical susceptibility tensor is fully characterized by heterodyne interferometry, unveiling a hidden giant out-of-plane response χzzz (2) (> 10.6 nm2/V or, equivalently, an effective bulk nonlinear susceptibility > 10.3 nm/V). Our results highlight the topological surfaces/interfaces as a new route toward nonlinear optical applications with released symmetry constraints, and demonstrate SHG as a viable means for in situ probing of surface chemistry of topological systems. Copyright © 2023, The Authors. All rights reserved.

关键词： Nonlinear optics

Calibration of nuclear charge density distribution by back-propagation neural networks

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Physical Review C 2023年第3期108卷 034315-034315页

作者： Zu-Xing Yang (杨祖星) Xiao-Hua Fan (范小华) Tomoya Naito (内藤智也) Zhong-Ming Niu (牛中明) Zhi-Pan Li (李志攀) Haozhao Liang (梁豪兆) RIKEN Nishina Center Wako 351-0198 Japan School of Physical Science and Technology Southwest University Chongqing 400715 China RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program Wako 351-0198 Japan Department of Physics Graduate School of Science The University of Tokyo Tokyo 113-0033 Japan School of Physics and Optoelectronic Engineering Anhui University Hefei 230601 China

Based on the back-propagation neural networks and density functional theory, a supervised learning is performed firstly to generate the nuclear charge density distributions. The charge density is further calibrated to the experimental charge radii by a composite loss function. It is found that, when the parity, pairing, and shell effects are taken into account, about 96% of the nuclei in the validation set fall within 2 standard deviations of the predicted charge radii. Moreover, the kink in charge radii on Hg isotopes has been successfully reproduced. The calibrated charge density is then mapped to the matter density and further mapped to the binding energies according to the Hohenberg-Kohn theorem. It provides an improved description of some nuclei in both binding energies and charge radii. Moreover, the anomalous overbinding in Ca48 implies that the segmental calibrations by neural networks for beyond-mean-field effects deserve further discussion.

关键词： Binding energy & masses Nuclear charge radii Artificial neural networks Density functional theory Machine learning

Helicity-tunable spin Hall and spin Nernst effects in unconventional chiral fermion semimetals XY (X=Co, Rh;Y=Si, Ge)

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arXiv 2022年

作者： Hsieh, Ting-Yun Prasad, Babu Baijnath Guo, Guang-Yu Department of Physics National Taiwan University Taipei10617 Taiwan Nano Science and Technology Program Taiwan International Graduate Program Academia Sinica Taipei11529 Taiwan Physics Division National Center for Theoretical Sciences Taipei10617 Taiwan

Transition metal monosilicides CoSi, CoGe, RhSi and RhGe in the chiral cubic B20 structure (the CoSi family) have recently been found to host unconventional chiral fermions beyond spin-1/2 Weyl fermions, and also to exhibit exotic physical phenomena such as long Fermi arc surface states, gyrotropic magnetic effect and quantized circular photogalvanic effect. Thus, exploring novel spin-related transports in these unconventional chiral fermion semimetals may open a new door for spintronics and spin caloritronics. In this paper, we study the intrinsic spin Hall effect (SHE) and spin Nernst effect (SNE) in the CoSi family based on ab initio relativistic band structure calculations. First, we find that unlike nonchiral cubic metals, the CoSi family have two independent nonzero spin Hall (Nernst) conductivity tensor elements, namely, σxyz and σxzy (αzxy and αyxz) instead of one element. Furthermore, the SHC (σxyz and σxzy ) and helicity of the chiral structure are found to be correlated, thus enabling SHE detection of structural helicity and also chiral fermion chirality. Second, the intrinsic SHE and SNE in some of the CoSi family are large. In particular, the calculated spin Hall conductivity (SHC) of RhGe is as large as -140 (~/e)(S/cm). The calculated spin Nernst conductivity (SNC) of CoGe is also large, being -1.3 (~/e)(A/m K) at room temperature. Due to their semimetallic nature with low electrical conductivity, these topological semimetals may have large spin Hall and spin Nernst angles, being comparable to that of platinum metal. The SHC and SNC of these compounds can also be increased by raising or lowering chemical potential to, e.g., the topological nodes, via either chemical doping or electrical gating. Our findings thus indicate that transition metal monosilicides of the CoSi family not only would provide a material platform for exploring novel spin-transports and exotic phenomena in unconventional chiral fermion semimetals but also could be promising materia

关键词： Calculations

Terahertz phonon polariton concentrator based on perovskite oxides

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Terahertz phonon polariton concentrator based on perovskite ...

Conference on Lasers and Electro-Optics (CLEO)

作者： Rui Xu Tong Lin Jiaming Luo Xiaotong Chen Elizabeth R. Blackert Alyssa R. Moon Khalil M. JeBailey Hanyu Zhu Department of Materials Science and Nano Engineering Rice University Houston U.S.A. Applied Physics Graduate Program Rice University Houston U.S.A. Nanotechnology Research Experience for Undergraduates (Nano REU) Program Rice University Houston U.S.A.

We report the experimental demonstration of surface phonon-polaritonic devices in a broad spectral range of 7-13 THz based on SrTiO 3 . We designed planar ultrafast concentrators that amplifies transient electric fiel... 详细信息

ISBN: (纸本)9781957171258

关键词： Concentrators Electric fields Fast Fourier transforms Field enhancement Fused silica Second harmonic generation