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arXiv 2018年

作者： Liu, Wenjing Wang, Yuhui Zheng, Biyuan Hwang, Minsoo Ji, Zhurun Liu, Gerui Li, Ziwei Sorger, Volker J. Pan, Anlian Agarwal, Ritesh Department of Materials Science and Engineering University of Pennsylvania PhiladelphiaPA19104 United States Key Laboratory for Micro-Nano Physics and Technology of Hunan Province School of Physics and Electronic Science Hunan University Changsha Hunan410082 China Department of Electrical and Computer Engineering George Washington University Science & Engineering Hall 800 22nd St. WashingtonDC20052 United States

Two-dimensional semiconductors host excitons with very large oscillator strengths and binding energies due to significantly reduced carrier screening. Two-dimensional semiconductors integrated with optical cavities are emerging as a promising platform for studying strong light-matter interactions as a route to explore a variety of exotic many-body effects. Here, in few-layered WS2 coupled with plasmonic nanoparticle lattices, we observe the formation of a collective polaritonic mode near the exciton energy and the formation of a complete polariton band gap with energy scale comparable to the exciton-plasmon coupling strength. A coupled oscillator model reveals that the collective mode arises from the cooperative coupling of the excitons to the plasmonic lattice diffraction orders via exciton-exciton interactions. The emergence of the collective mode is accompanied by a superlinear increase of the polariton mode splitting as a function of the square root of the exciton oscillator strength. The presence of these many body effects, which are enhanced in systems which lack bulk polarization, not only allows the formation of a collective mode with periodically varying field profiles, but also further enhances the exciton-plasmon coupling. By integrating the hybrid WS2-plasmonic lattice device with a field-effect transistor, we demonstrate active tuning of the collective mode and the polariton band gap. These systems provide new opportunities for obtaining a deeper and systematic understanding of many body cooperative phenomena in periodic photonic systems and for designing more complex and actively controllable polaritonic devices including switchable polariton lasers, waveguides, and optical logical elements. Copyright © 2018, The Authors. All rights reserved.

关键词： Excitons

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Limiting optical diodes enabled by the phase transition of vanadium dioxide

arXiv

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arXiv 2018年

作者： Wan, Chenghao Horak, Erik King, Jonathan Salman, Jad Zhang, Zhen Zhou, You Roney, Patrick Gundlach, Bradley Ramanathan, Shriram Goldsmith, Randall Kats, Mikhail A. Department of Electrical and Computer Engineering University of Wisconsin-Madison MadisonWI53706 United States Department of Materials Science & Engineering University of Wisconsin-Madison MadisonWI53706 United States Department of Chemistry University of Wisconsin-Madison MadisonWI53706 United States School of Materials Engineering Purdue University West LafayetteIN47907 United States Harvard John A. Paulson School of Engineering and Applied Sciences Harvard University CambridgeMA02138 United States

A limiting optical diode is an asymmetric nonlinear device that is bidirectionally transparent at low power, but becomes opaque when illuminated by sufficiently intense light incident from a particular direction. We explore the use of a phase-transition material, vanadium dioxide (VO2), as an active element of limiting optical diodes. The VO2 phase transition can be triggered by optical absorption, resulting in a change in refractive index orders of magnitude larger than what can be achieved with conventional nonlinearities. As a result, a limiting optical diode based on incident-direction-dependent absorption in a VO2 layer can be very thin, and can function at low powers without field enhancement, resulting in broadband operation. We demonstrate a simple thin-film limiting optical diode comprising a transparent substrate, a VO2 film, and a semi-transparent metallic layer. For sufficiently high incident intensity, our proof-of-concept device realizes broadband asymmetric transmission across the near infrared, and is approximately ten times thinner than the free-space wavelength. Copyright © 2018, The Authors. All rights reserved.

关键词： Vanadium dioxide

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Growth, electrical, structural, and magnetic properties of half-Heusler CoTi1−xFexSb

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Physical Review materials 2018年第1期2卷 014406-014406页

作者： S. D. Harrington A. D. Rice T. L. Brown-Heft B. Bonef A. Sharan A. P. McFadden J. A. Logan M. Pendharkar M. M. Feldman O. Mercan A. G. Petukhov A. Janotti L. Colakerol Arslan C. J. Palmstrøm Materials Department University of California Santa Barbara California 93106 USA Department of Physics and Astronomy University of Delaware Newark Delaware 19716 USA Department of Electrical and Computer Engineering University of California Santa Barbara California 93106 USA Physics Department University of California Santa Barbara California 93106 USA Physics Department Gebze Technical University Kocaeli 41400 Turkey Physics Department South Dakota School of Mines and Technology Rapid City South Dakota 57701 USA Department of Materials Science & Engineering University of Delaware Newark Delawere 19716 USA

Epitaxial thin films of the substitutionally alloyed half-Heusler series CoTi1−xFexSb were grown by molecular beam epitaxy on InAlAs/InP(001) substrates for concentrations 0.0≤x≤1.0. The influence of Fe on the structural, electronic, and magnetic properties was studied and compared to that expected from density functional theory. The films are epitaxial and single crystalline, as measured by reflection high-energy electron diffraction and x-ray diffraction. Using in situ x-ray photoelectron spectroscopy, only small changes in the valence band are detected for x≤0.5. For films with x≥0.05, ferromagnetism is observed in SQUID magnetometry with a saturation magnetization that scales linearly with Fe content. A dramatic decrease in the magnetic moment per formula unit occurs when the Fe is substitutionally alloyed on the Co site indicating a strong dependence on the magnetic moment with site occupancy. A crossover from both in-plane and out-of-plane magnetic moments to only in-plane moment occurs for higher concentrations of Fe. Ferromagnetic resonance indicates a transition from weak to strong interaction with a reduction in inhomogeneous broadening as Fe content is increased. Temperature-dependent transport reveals a semiconductor to metal transition with thermally activated behavior for x≤0.5. Anomalous Hall effect and large negative magnetoresistance (up to -18.5% at 100 kOe for x=0.3) are observed for higher Fe content films. Evidence of superparamagnetism for x=0.3 and 0.2 suggests, for moderate levels of Fe, that demixing of the CoTi1−xFexSb films into Fe-rich and Fe-deficient regions may be present. Atom probe tomography is used to examine the Fe distribution in an x=0.3 film. Statistical analysis reveals a nonhomogeneous distribution of Fe atoms throughout the film, which is used to explain the observed magnetic and electrical behavior.

关键词： Anomalous Hall effect Ferromagnetism Growth Magnetoresistance Magnetotransport Superparamagnetism Half-Heusler alloy Heusler alloy Density functional theory Ferromagnetic resonance Hall bar Magnetization measurements Molecular beam epitaxy Time-of-flight mass spectrometry

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Vectorial Holograms: Full‐Color Complex‐Amplitude Vectorial Holograms Based on Multi‐Freedom Metasurfaces (Adv. Funct. Mater. 21/2020)

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Advanced Functional materials 2020年第21期30卷 2070131-2070131页

作者： Zi‐Lan Deng Mingke Jin Xuan Ye Shuai Wang Tan Shi Junhong Deng Ningbin Mao Yaoyu Cao Bai‐Ou Guan Andrea Alù Guixin Li Xiangping Li Guangdong Provincial Key Laboratory of Optical Fiber Sensing and Communications Institute of Photonics Technology Jinan University Guangzhou 510632 P. R. China Department of Materials Science and Engineering Shenzhen Institute for Quantum Science and Engineering Southern University of Science and Technology Shenzhen 518055 P. R. China Photonics Initiative Advanced Science Research Center City University of New York 85 St. Nicholas Terrace New York NY 10031 USA Physics Program The Graduate Center City University of New York 365 Fifth Avenue New York NY 10016 USA Department of Electrical Engineering City College of New York New York NY 10031 USA

In article number 1910610, Zi‐Lan Deng, Guixin Li, Xiangping Li, and co‐workers show how multi‐dimensional wavefront shaping of light in amplitude, polarization, phase, and frequency can be realized simultaneously through a single layer multi‐freedom metasurface. Consequently, full‐color complex‐amplitude vectorial holographic image can be vividly reconstructed.

关键词： full‐color vectorial holograms metasurfaces multi‐dimensional manipulation

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Atomic-resolution visualization and doping effects of complex structures in intercalated bilayer graphene

arXiv

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arXiv 2019年

作者： Bonacum, Jason P. O'Hara, Andrew Bao, De-Liang Ovchinnikov, Oleg S. Zhang, Yan-Fang Gordeev, Georgy Arora, Sonakshi Reich, Stephanie Idrobo, Juan-Carlos Haglund, Richard F. Pantelides, Sokrates T. Bolotin, Kirill Department of Physics and Astronomy Vanderbilt University NashvilleTN United States Institute of Physics University of Chinese Academy of Sciences Chinese Academy of Sciences Beijing100190 China Institute for Functional Imaging of Materials Oak Ridge National Laboratory Oak RidgeTN United States Freie Universität Berlin Fachbereich Physik Institut für Experimentalphysik Arnimallee 14 Berlin14195 Germany Center for Nanophase Materials Sciences Oak Ridge National Laboratory Oak RidgeTN United States Department of Electrical Engineering and Computer Science Vanderbilt University NashvilleTN37235 United States

Molecules intercalating two-dimensional (2D) materials form complex structures that have been mostly characterized by spatially averaged techniques. Here we use aberration-corrected scanning transmission electron microscopy and densityfunctional-theory (DFT) calculations to study the atomic structure of bilayer graphene (BLG) and few-layer graphene (FLG) intercalated with FeCl3. In BLG we discover two distinct intercalated structures that we identify as monolayer-FeCl3 and monolayer-FeCl2. The two structures are separated by atomically sharp boundaries and induce large but different free-carrier densities in the graphene layers, 7.1 × 10-13cm-2and 7.8 × 1013cm-2respectively. In FLG, we observe multiple FeCl3layers stacked in a variety of possible configurations with respect to one another. Finally, we find that the microscope's electron beam can convert the FeCl3monolayer into FeOCl monolayers in a rectangular lattice. These results reveal the need for a combination of atomically-resolved microscopy, spectroscopy, and DFT calculations to identify intercalated structures and study their properties. Copyright © 2019, The Authors. All rights reserved.

关键词： Iron compounds

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Performance of resource allocation in device-to-device communication systems based on particle swarm optimization

Performance of resource allocation in device-to-device commu...

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2017 IEEE International Conference on Systems, Man, and Cybernetics, SMC 2017

作者： Huang, Yung-Fa Tan, Tan-Hsu Liu, Shing-Hong Chen, Yung-Fu Department of Information and Communication Engineering Chaoyang University of Technology Taichung Taiwan Bor-An Chen Department of Electrical Engineering National Taipei University of Technology Taipei Taiwan Department of Computer Science and Information Engineering Chaoyang University of Technology Taichung Taiwan Department of Dental Technology and Materials Science Central Taiwan University of Science and Technology Taichung Taiwan

ISBN: (纸本)9781538616451

In this study, the resource blocks (RB) are allocated to user equipment (UE) according to the evolutional algorithms for long term evolution (LTE) systems. Particle Swarm Optimization (PSO) algorithm is one of the evolutionary algorithms, based on the imitation of a flock of birds foraging behavior through learning and grouping the best experience. Therefore, we propose a Simple Particle Swarm Optimization (SPSO) algorithm for RB allocation to enhance the throughput of Device-to-Device (D2D) communications and improve the system capacity performance. The simulation results show that with less population size of M=10, the SPSO can perform quickly convergence to sub-optimal solution in the 100th generation. Therefore, as compared to the random allocation (Rand) method, the proposed SPSO can obtain sub-optimum performance with more 2 UEs than the Rand method. © 2017 IEEE.

关键词： Resource allocation

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Extreme broadband transparent optical phase change materials for high-performance nonvolatile photonics

arXiv

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arXiv 2018年

作者： Zhang, Yifei Chou, Jeffrey B. Li, Junying Li, Huashan Du, Qingyang Yadav, Anupama Zhou, Si Shalaginov, Mikhail Y. Fang, Zhuoran Zhong, Huikai Roberts, Christopher Robinson, Paul Bohlin, Bridget Ríos, Carlos Lin, Hongtao Kang, Myungkoo Gu, Tian Warner, Jamie Liberman, Vladimir Richardson, Kathleen Hu, Juejun Department of Materials Science & Engineering Massachusetts Institute of Technology CambridgeMA United States Lincoln Laboratory Massachusetts Institute of Technology LexingtonMA United States Shanghai Key Laboratory of Modern Optical Systems College of Optical-Electrical and Computer Engineering University of Shanghai for Science and Technology Shanghai China Sino-French Institute for Nuclear Energy and Technology Sun Yat-sen University Guangzhou China College of Optics & Photonics Department of Materials Science and Engineering University of Central Florida Orlando United States Department of Materials University of Oxford Oxford United Kingdom College of Information Science & Electronic Engineering Zhejiang University Hangzhou China

Optical phase change materials (O-PCMs), a unique group of materials featuring drastic optical property contrast upon solid-state phase transition, have found widespread adoption in photonic switches and routers, reconfigurable meta-optics, reflective display, and optical neuromorphic computers. Current phase change materials, such as Ge-Sb-Te (GST), exhibit large contrast of both refractive index (∆n) and optical loss (∆k), simultaneously. The coupling of both optical properties fundamentally limits the function and performance of many potential applications. In this article, we introduce a new class of O-PCMs, Ge-Sb-Se-Te (GSST) which breaks this traditional coupling, as demonstrated with an optical figure of merit improvement of more than two orders of magnitude. The first-principle computationally optimized alloy, Ge2Sb2Se4Te1, combines broadband low loss (1 – 18.5 μm), large optical contrast (∆n = 2.0), and significantly improved glass forming ability, enabling an entirely new field of infrared and thermal photonic devices. We further leverage the material to demonstrate nonvolatile integrated optical switches with record low loss and large contrast ratio, as well as an electrically addressed, microsecond switched pixel level spatial light modulator, thereby validating its promise as a platform material for scalable nonvolatile photonics. Copyright © 2018, The Authors. All rights reserved.

关键词： Phase change materials

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The use of strain to tailor electronic thermoelectric transport properties: A first principles study of 2H-‐phase CuAlO2

arXiv

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arXiv 2018年

作者： Witkoske, Evan Guzman, David Feng, Yining Strachan, Alejandro Lundstrom, Mark Lu, Na School of Electrical and Computer Engineering Purdue University West Lafayette IN47907 United States School of Materials Engineering Birck Nanotechnology Center Purdue University West Lafayette IN47907 United States Lyles School of Civil Engineering Purdue University West Lafayette IN47907 United States Condensed Matter Physics and Materials Science Department Brookhaven National Laboratory UptonNY11973

Using first principles calculations, the use of strain to adjust electronic transport and the resultant thermoelectric (TE) properties is discussed using 2H phase CuAlO2 as a test case. Transparent oxide materials, such as CuAlO2, a p-‐type transparent conducting oxide (TCO), have recently been studied for high temperature thermoelectric power generators and coolers for waste heat. Given TCO materials with relative ease of fabrication, low cost of materials, and non-toxicity, the ability to tailor them to specific temperature ranges, power needs, and size requirements, through the use of strain opens an interesting avenue. We find that strain can have a significant effect on these properties, in some cases detrimental and in others beneficial, including the potential for n-‐type power factors larger than the highest p-‐type case. The physical reasons for this behavior are explained in the terms of the thermoelectric transport distribution and the Landauer distribution of modes. Copyright © 2018, The Authors. All rights reserved.

关键词： Transparent conducting oxides

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Exciton behavior under the influence of metal nanoparticle near fields: Significance of nonlocal effects

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Physical Review B 2018年第11期98卷 115430-115430页

作者： Harini Hapuarachchi Sarath D. Gunapala Qiaoliang Bao Mark I. Stockman Malin Premaratne Advanced Computing and Simulation Laboratory (AχL) Department of Electrical and Computer Systems Engineering Monash University Clayton Victoria 3800 Australia Jet Propulsion Laboratory California Institute of Technology Pasadena California 91109 USA Department of Materials Science and Engineering Monash University Clayton Victoria 3800 Australia Department of Physics and Astronomy Georgia State University Atlanta Georgia 30303 USA

We analytically characterize the influence of a neighboring metal nanoparticle (MNP) on the behavioral trends of a quantum dot (QD) using a generalized nonlocal optical response (GNOR) method based approach, taking the MNP distance dependent modifications to the QD population relaxation and dephasing rates into account. The GNOR model is a recent generalization and an extension of the hydrodynamic Drude model (HDM), which goes beyond HDM by taking into account both the convection current and electron diffusion in the MNPs. It allows unified theoretical explanation of some experimentally observed plasmonic phenomena which otherwise would require ab initio analysis as the conventional local response approximation (LRA) fails to account for them. For example, it has been demonstrated in literature that the GNOR model captures size dependent resonance shifts of small MNPs which are unrevealed by the conventional LRA based methods, and it has proven to yield results displaying better agreement with the experimental observations for plasmonic experiments. Attempts to incorporate MNP nonlocal effects in the analytical characterization of vicinal excitons found in literature utilize the phenomenological hydrodynamic model and assume the absence of MNP interband effects. Moreover, they are only applicable to narrow parameter regions. In this paper we present a complete analytical characterization which overcomes these drawbacks and lends to the perusal of the system over wide continua of various parameters, enabling us to get an elevated view at a much lesser level of complexity compared to the conventional LRA based numerical methods or the conventional ab initio methods of accounting for the nonlocal effects. Our proposed GNOR based model predicts strong modifications to various QD properties such as population difference, absorption, MNP induced shifts to excitonic energy and Förster enhanced broadening, coherent plasmonic field enhancement, and quantum state purity, comp

关键词： Excitons Near-field optics Plasmonics Nanoparticles Quantum dots

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Binding a hopfion in chiral magnet nanodisk

arXiv

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arXiv 2018年

作者： Liu, Yizhou Lake, Roger K. Zang, Jiadong Department of Electrical and Computer Engineering University of California RiversideCA92521 United States Department of Physics and Materials Science Program University of New Hampshire DurhamNH03824 United States Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sci-ences Beijing100190 China

Hopfions are three-dimensional (3D) topological textures characterized by the integer Hopf invariant QH. Here, we present the realization of a zero-field, stable hopfion spin texture in a magnetic system consisting of a chiral magnet nanodisk sandwiched by two films with perpendicular magnetic anisotropy. The preimages of the spin texture and numerical calculations of QH show that the hop-fion has QH = 1. Furthermore, another non-trivial state that includes a monopole{antimonopole pair (MAP) is also stabilized in this system. By applying an external magnetic field, hopfion and MAP states with the same polarization can be switched between each other. The topological transition between the hopfion and the MAP state involves a creation (annihilation) of the MAP and twist of the preimages. Our work paves the way to study non-trivial 3D topological spin textures and stimulates more investigations in the field of 3D spintronics. Copyright © 2018, The Authors. All rights reserved.

关键词： Textures

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