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Two-dimensional charge order stabilized in clean polytype heterostructures

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arXiv 2021年

作者： Sung, Suk Hyun Schnitzer, Noah Novakov, Steve El Baggari, Ismail Luo, Xiangpeng Gim, Jiseok Vu, Nguyen M. Li, Zidong Brintlinger, Todd H. Liu, Yu Lu, Wenjian Sun, Yuping Deotare, Parag B. Sun, Kai Zhao, Liuyan Kourkoutis, Lena F. Heron, John T. Hovden, Robert Department of Materials Science and Engineering University of Michigan Ann ArborMI48109 United States Department of Materials Science and Engineering Cornell University IthacaNY14853 United States Kavli Institute at Cornell for Nanoscale Science IthacaNY14853 United States Department of Physics University of Michigan Ann ArborMI48109 United States Department of Physics Cornell University IthacaNY14853 United States Rowland Institute at Harvard CambridgeMA02142 United States Electrical and Computer Engineering Department University of Michigan Ann ArborMI48109 United States Materials Science and Technology Division U.S. Naval Research Laboratory WashingtonDC20375 United States Key Laboratory of Materials Physics Institute of Solid State Physics Chinese Academy of Sciences Hefei230031 China High Magnetic Field Laboratory Chinese Academy of Sciences Hefei230031 China Collaborative Innovation Centre of Advanced Microstructures Nanjing University Nanjing210093 China Applied Physics Program University of Michigan Ann ArborMI48109 United States School of Applied and Engineering Physics Cornell University IthacaNY14853 United States

Compelling evidence suggests distinct correlated electron behavior may exist only in clean 2D materials such as 1T-TaS2. Unfortunately, experiment and theory suggest that extrinsic disorder in free standing 2D layers disrupts correlation-driven quantum behavior. Here we demonstrate a route to realizing fragile 2D quantum states through endotaxial polytype engineering of van der Waals materials. The true isolation of 2D charge density waves (CDWs) between metallic layers stabilizes commensurate long-range order and lifts the coupling between neighboring CDW layers to restore mirror symmetries via interlayer CDW twinning. The twinned-commensurate charge density wave (tC-CDW) reported herein has a single metal–insulator phase transition at ~350 K as measured structurally and electronically. Fast in-situ transmission electron microscopy and scanned nanobeam diffraction map the formation of tC-CDWs. This work introduces endotaxial polytype engineering of van der Waals materials to access latent 2D ground states distinct from conventional 2D fabrication. © 2021, CC BY.

关键词： Charge density waves

Validating first-principles molecular dynamics calculations of oxide/water interfaces with x-ray reflectivity data

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Physical Review Materials 2020年第11期4卷 113805-113805页

作者： Katherine J. Harmon Kendra Letchworth-Weaver Alex P. Gaiduk Federico Giberti Francois Gygi Maria K. Y. Chan Paul Fenter Giulia Galli Applied Physics Graduate Program Northwestern University Evanston Illinois 60208 USA Center for Nanoscale Materials Argonne National Laboratory Lemont Illinois 60439 USA Pritzker School of Molecular Engineering University of Chicago Chicago Illinois 60637 USA Department of Physics and Astronomy James Madison University Harrisonburg Virginia 22807 USA Department of Computer Science University of California Davis California 95616 USA Chemical Sciences and Engineering Division Argonne National Laboratory Lemont Illinois 60439 USA Materials Science Division Argonne National Laboratory Lemont Illinois 60439 USA Department of Chemistry University of Chicago Chicago Illinois 60637 USA

Metal oxide/water interfaces play a crucial role in many electrochemical and photocatalytic processes, such as photoelectrochemical water splitting, the creation of fuel from sunlight, and electrochemical CO2 reduction. First-principles electronic structure calculations can reveal unique insights into these processes, such as the role of the alignment of the oxide electronic energy levels with those of liquid water. An essential prerequisite for the success of such calculations is the ability to predict accurate structural models of these interfaces, which in turn requires careful experimental validation. Here we report a general, quantitative validation protocol for first-principles molecular dynamics simulations of oxide/aqueous interfaces. The approach makes direct comparisons of interfacial x-ray reflectivity (XR) signals from experimental measurements and those obtained from ab initio simulations with semilocal and van der Waals functionals. The protocol is demonstrated here for the case of the Al2O3(001)/water interface, one of the simplest oxide/water interfaces. We discuss the technical requirements needed for validation, including the choice of the density functional, the simulation cell size, and the optimal choice of the thermodynamic ensemble. Our results establish a general paradigm for the validation of structural models and interactions at solid/water interfaces derived from first-principles simulations. While there is qualitative agreement between the simulated structures and the experimental best-fit structure, direct comparisons of simulated and measured XR intensities show quantitative discrepancies that derive from both bulk regions (i.e., alumina and water) as well as the interfacial region, highlighting the need for accurate density functionals to properly describe interfacial interactions. Our results show that XR data are sensitive not only to the atomic structure (i.e., the atom locations) but also to the electron-density distributions in bo

关键词： First-principles calculations Surface & interfacial phenomena Liquid-solid interfaces Electronic structure X-ray reflectivity

Experience sharing between cooperative reinforcement learning agents

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arXiv 2019年

作者： Souza, Lucas Oliveira de Oliveira Ramos, Gabriel Ralha, Celia Ghedini Numenta Redwood City United States Graduate Program in Applied Computing Universidade do Vale do Rio dos Sinos São Leopoldo Brazil Computer Science Department University of Brasilia Brasilia Brazil

The idea of experience sharing between cooperative agents naturally emerges from our understanding of how humans learn. Our evolution as a species is tightly linked to the ability to exchange learned knowledge with one another. It follows that experience sharing (ES) between autonomous and independent agents could become the key to accelerate learning in cooperative multiagent settings. We investigate if randomly selecting experiences to share can increase the performance of deep reinforcement learning agents, and propose three new methods for selecting experiences to accelerate the learning process. Firstly, we introduce Focused ES, which prioritizes unexplored regions of the state space. Secondly, we present Prioritized ES, in which temporal-difference error is used as a measure of priority. Finally, we devise Focused Prioritized ES, which combines both previous approaches. The methods are empirically validated in a control problem. While sharing randomly selected experiences between two Deep Q-Network agents shows no improvement over a single agent baseline, we show that the proposed ES methods can successfully outperform the baseline. In particular, the Focused ES accelerates learning by a factor of 2, reducing by 51% the number of episodes required to complete the task. Copyright © 2019, The Authors. All rights reserved.

关键词： Deep learning

Radio-pathomic estimates of cellular growth kinetics predict survival in recurrent glioblastoma

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CNS Oncology 2024年第1期13卷 2415285页

作者： Oshima, Sonoko Yao, Jingwen Bobholz, Samuel Nagaraj, Raksha Raymond, Catalina Teraishi, Ashley Guenther, Anna-Marie Kim, Asher Sanvito, Francesco Cho, Nicholas S C Eldred, Blaine S Connelly, Jennifer M Nghiemphu, Phioanh L Lai, Albert Salamon, Noriko Cloughesy, Timothy F LaViolette, Peter S Ellingson, Benjamin M UCLA Brain Tumor Imaging Laboratory (BTIL) Center for Computer Vision & Imaging Biomarkers University of California Los Angeles Los Angeles 90024 CA United States Department of Radiological Sciences David Geffen School of Medicine University of California Los Angeles Los Angeles 90024 CA United States Department of Bioengineering Henry Samueli School of Engineering & Applied Science University of California Los Angeles Los Angeles 90024 CA United States Department of Radiology Medical College of Wisconsin Milwaukee 53226 WI United States Medical Scientist Training Program David Geffen School of Medicine University of California Los Angeles Los Angeles 90024 CA United States UCLA Neuro-Oncology Program David Geffen School of Medicine University of California Los Angeles Los Angeles 90024 CA United States Department of Neurology Medical College of Wisconsin Milwaukee 53226 WI United States Department of Neurology David Geffen School of Medicine University of California Los Angeles Los Angeles 90024 CA United States Department of Biophysics Medical College of Wisconsin Milwaukee 53226 WI United States Department of Biomedical Engineering Medical College of Wisconsin Milwaukee 53226 WI United States Department of Psychiatry & Biobehavioral Sciences David Geffen School of Medicine University of California Los Angeles Los Angeles 90024 CA United States Department of Neurosurgery David Geffen School of Medicine University of California Los Angeles Los Angeles 90024 CA United States

Aim: A radio-pathomic machine learning (ML) model has been developed to estimate tumor cell density, cytoplasm density (Cyt) and extracellular fluid density (ECF) from multimodal MR images and autopsy pathology. In this multicenter study, we implemented this model to test its ability to predict survival in patients with recurrent glioblastoma (rGBM) treated with chemotherapy. Methods: Pre- and post-contrast T₁-weighted, FLAIR and ADC images were used to generate radio-pathomic maps for 51 patients with longitudinal pre- and post-treatment scans. Univariate and multivariate Cox regression analyses were used to test the influence of contrast-enhancing tumor volume, total cellularity, mean Cyt and mean ECF at baseline, immediately post-treatment and the pre- and post-treatment rate of change in volume and cellularity on overall survival (OS). Results: Smaller Cyt and larger ECF after treatment were significant predictors of OS, independent of tumor volume and other clinical prognostic factors (HR = 3.23 × 10^-6, p < 0.001 and HR = 2.39 × 10⁵, p < 0.001, respectively). Both post-treatment volumetric growth rate and the rate of change in cellularity were significantly correlated with OS (HR = 1.17, p = 0.003 and HR = 1.14, p = 0.01, respectively). Conclusion: Changes in histological characteristics estimated from a radio-pathomic ML model are a promising tool for evaluating treatment response and predicting outcome in rGBM. © 2024 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.

关键词： MRI rad-path radiopathomic mapping recurrent glioblastoma survival tumor growth rate

Nanoscale probing of image-potential states and electron transfer doping in borophene polymorphs

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arXiv 2020年

作者： Liu, Xiaolong Wang, Luqing Yakobson, Boris I. Hersam, Mark C. Applied Physics Graduate Program Northwestern University EvanstonIL60208 United States Department of Materials Science and NanoEngineering Rice University HoustonTX77005 United States Department of Chemistry Rice University HoustonTX77005 United States Department of Materials Science and Engineering Northwestern University EvanstonIL60208 United States Department of Chemistry Northwestern University EvanstonIL60208 United States Department of Electrical and Computer Engineering Northwestern University EvanstonIL60208 United States

Using field-emission resonance spectroscopy with an ultrahigh vacuum scanning tunneling microscope, we reveal Stark-shifted image-potential states of the v1/6 and v1/5 borophene polymorphs on Ag(111) with long lifetimes, suggesting high borophene lattice and interface quality. These image-potential states allow the local work function and interfacial charge transfer of borophene to be probed at the nanoscale and test the widely employed self-doping model of borophene. Supported by apparent barrier height measurements and density functional theory calculations, electron transfer doping occurs for both borophene phases from the Ag(111) substrate. In contradiction with the self-doping model, a higher electron transfer doping level occurs for denser v1/6 borophene compared to v1/5 borophene, thus revealing the importance of substrate effects on borophene electron transfer. Copyright © 2020, The Authors. All rights reserved.

关键词： Electron transitions

Exciton transport under periodic potential in MoSe2/WSe2 heterostructures

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arXiv 2020年

作者： Li, Zidong Lu, Xiaobo Cordovilla Leon, Darwin F. Hou, Jize Lu, Yanzhao Kaczmarek, Austin Lyu, Zhengyang Taniguchi, Takashi Watanabe, Kenji Zhao, Liuyan Yang, Li Deotare, Parag B. Department of Electrical Engineering and Computer Science University of Michigan Ann ArborMI48109 United States Department of Physics Washington University in St. Louis St. LouisMO63130 United States Applied Physics Program University of Michigan Ann ArborMI48109 United States Department of Physics University of Michigan Ann ArborMI48109 United States National Institute for Materials Science Tsukuba Japan Institute of Materials Science and Engineering Washington University in St. Louis St. LouisMO63130 United States

The predicted formation of moiré superlattices leading to confined excitonic states in heterostructures formed by stacking two lattice mismatched transition metal dichalcogenide (TMD) monolayers was recently experimentally confirmed. Such periodic potential in TMD heterostructure functions as a diffusion barrier that affects the energy transport and dynamics of interlayer excitons (electron and hole spatially concentrated in different monolayers). Understanding the transport of excitons under such condition is essential to establish the material system as a next generation device platform. In this work, we experimentally quantify the diffusion barrier experienced by the interlayer excitons in a hexagonal boron nitride (h-BN) – encapsulated, molybdenum diselenide/tungsten diselenide (MoSe2/WSe2) heterostructure by studying the exciton transport at various temperatures. Copyright © 2020, The Authors. All rights reserved.

关键词： Selenium compounds

Roadmap on Nonlocality in Photonic Materials and Metamaterials

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arXiv 2025年

作者： Monticone, Francesco Mortensen, N. Asger Fernández-Domínguez, Antonio I. Luo, Yu Tserkezis, Christos Khurgin, Jacob B. Shahbazyan, Tigran V. Chaves, André J. Peres, Nuno M.R. Wegner, Gino Busch, Kurt Hu, Huatian della Sala, Fabio Zhang, Pu Ciracì, Cristian Aizpurua, Javier Babaze, Antton Borisov, Andrei G. Chen, Xue-Wen Christensen, Thomas Yan, Wei Yang, Yi Hohenester, Ulrich Huber, Lorenz Wubs, Martijn de Liberato, Simone Gonçalves, P.A.D. de Abajo, F. Javier García Hess, Ortwin Tarasenko, Illya Cox, Joel D. Jelver, Line Dias, Eduardo J.C. Sánchez, Miguel Sánchez Margetis, Dionisios Gómez-Santos, Guillermo Stauber, Tobias Tretyakov, Sergei Simovski, Constantin Pakniyat, Samaneh Gómez-Díaz, J. Sebastián Bondarev, Igor V. Biehs, Svend-Age Boltasseva, Alexandra Shalaev, Vladimir M. Krasavin, Alexey V. Zayats, Anatoly V. Alù, Andrea Song, Jung-Hwan Brongersma, Mark L. Levy, Uriel Long, Olivia Y. Guo, Cheng Fan, Shanhui Bozhevolnyi, Sergey I. Overvig, Adam Prudêncio, Filipa R. Silveirinha, Mário G. Gangaraj, S. Ali Hassani Argyropoulos, Christos Huidobro, Paloma A. Galiffi, Emanuele Yang, Fan Pendry, John B. Miller, David A.B. School of Electrical and Computer Engineering Cornell University IthacaNY14853 United States POLIMA Center for Polariton-driven Light–Matter Interactions University of Southern Denmark Campusvej 55 Odense MDK-5230 Denmark D-IAS—Danish Institute for Advanced Study University of Southern Denmark Campusvej 55 Odense MDK-5230 Denmark Departamento de Física Teórica de la Materia Condensada Universidad Autónoma de Madrid MadridE-28049 Spain Universidad Autónoma de Madrid MadridE-28049 Spain School of Electrical and Electronic Engineering Nanyang Technological University Singapore639798 Singapore Key Laboratory of Radar Imaging and Microwave Photonics Ministry of Education College of Electronic and Information Engineering Nanjing University of Aeronautics and Astronautics Nanjing211106 China Department of Electrical and Computer Engineering Johns Hopkins University BaltimoreMD21218 United States Department of Physics Jackson State University JacksonMS39217 United States Department of Physics Aeronautics Institute of Technology SP So Jos dos Campos12228-900 Brazil Departamento de Física Universidade do Minho BragaP-4710-057 Portugal Av Mestre José Veiga Braga4715-330 Portugal Max-Born-Institut Berlin12489 Germany Humboldt-Universität zu Berlin Institut für Physik AG Theoretische Optik and Photonik Berlin12489 Germany Center for Biomolecular Nanotechnologies Istituto Italiano di Tecnologia Via Barsanti 14 Arnesano73010 Italy Via Monteroni Campus Unisalento Lecce73100 Italy School of physics Huazhong University of Science and Technology Luoyu Road 1037 Wuhan430074 China Donostia International Physics Center DIPC Donostia-San Sebastián20018 Spain Ikerbasque Basque Foundation for Science Bilbao48009 Spain Department of Electricity and Electronics University of the Basque Country Leioa48940 Spain Department of Applied Physics University of the Basque Country Donostia20018 Spain Université Paris-Saclay CNRS Institut des Scienc

Photonic technologies continue to drive the quest for new optical materials with unprecedented responses. A major frontier in this field is the exploration of nonlocal (spatially dispersive) materials, going beyond the local, wavevector-independent assumption traditionally made in optical material modeling. On one end, the growing interest in plasmonic, polaritonic and quantum materials has revealed naturally occurring nonlocalities, emphasizing the need for more accurate models to predict and design their optical responses. This has major implications also for topological, nonreciprocal, and time-varying systems based on these material platforms. Beyond natural materials, artificially structured materials—metamaterials and metasurfaces–can provide even stronger and engineered nonlocal effects, emerging from long-range interactions or multipolar effects. This is a rapidly expanding area in the field of photonic metamaterials, with open frontiers yet to be explored. In the case of metasurfaces, in particular, nonlocality engineering has become a powerful tool for designing strongly wavevector-dependent responses, enabling enhanced wavefront control, spatial compression, multifunctional devices, and wave-based computing. Furthermore, nonlocality and related concepts play a critical role in defining the ultimate limits of what is possible in optics, photonics, and wave physics. This Roadmap aims to survey the most exciting developments in nonlocal photonic materials, highlight new opportunities and open challenges, and chart new pathways that will drive this emerging field forward–toward new scientific discoveries and technological advancements. Copyright © 2025, The Authors. All rights reserved.

关键词： Nanocrystals

Crouzeix’s Conjecture and Related Problems

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arXiv 2020年

作者： Bickel, Kelly Gorkin, Pamela Greenbaum, Anne Ransford, Thomas Schwenninger, Felix Wegert, Elias Department of Mathematics Bucknell University LewisburgPA17837 United States Department of Mathematics Bucknell University LewisburgPA17837 United States Department of Applied Mathematics University of Washington Département de mathématiques et de statistique Université Laval QuébecQCG1V 0A6 Canada Department of Mathematics Universität Hamburg Department of Applied Mathematics University of Twente Netherlands Department of Mathematics and Computer Science Technische Universität Bergakademie Freiberg Division of Mathematical Sciences National Science Foundation United States NSERC and the Canada Research Chairs program

In this paper, we establish several results related to Crouzeixs conjecture. We show that the conjecture holds for contractions with eigenvalues that are sufficiently well-separated. This separation is measured by the so-called separation constant, which is defined in terms of the pseudohyperbolic metric. Moreover, we study general properties of related extremal functions and associated vectors. Throughout, compressions of the shift serve as illustrating examples which also allow for refined *** Codes 47A25, 47A12, 15A60, 47A20, 30J10 Copyright © 2020, The Authors. All rights reserved.

关键词： Eigenvalues and eigenfunctions

Interplay of Purcell Effect, Stimulated Emission, and Leaky Modes in the Photoluminescence Spectra of Microsphere Cavities

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Physical Review applied 2019年第5期11卷 051001-051001页

作者： Ching-Hang Chien Shang-Hsuan Wu Trong Huynh-Buu Ngo Yia-Chung Chang Research Center for Applied Sciences Academia Sinica Taipei 115 Taiwan Nano Science and Technology Program TIGP Academia Sinica Taipei 115 Taiwan Department of Engineering and System Science National Tsing Hua University Hsinchu 300 Taiwan Department of Electrical and Computer Engineering University of Texas at Austin USA Department of Electrical and Computer Engineering University of Alberta Edmonton Alberta T6G 2V4 Canada

A theoretical model for describing the emission spectra of microsphere cavities is presented and its predictions of detailed line shapes of emission spectra associated with whispering gallery modes (WGMs) of various orders in ZnO microspheres (MSs) are verified experimentally by photoluminescence (PL) spectroscopy. The interplay of the Purcell effect, quality factor, and leaky modes in spontaneous and stimulated emission spectra related to WGMs of all orders is revealed. The key success of the theory is based on the expansion of the full Green’s function of the MS in terms of all possible resonance modes in complex frequency space, which allows incorporation of contributions from leaky modes, stimulated emission processes, and the Purcell effect. We show that the spontaneous emission spectrum calculated according to Mie theory (without the Purcell effect) is dominated by the contribution of leaky modes, while the spontaneous and stimulated emission enhanced by the Purcell effect is responsible for the main WGM resonance peaks observed experimentally. It is found that the stimulated emission peaks are doubly enhanced by their respective mode quality factor Q: one factor from the Purcell effect and the other factor from the photon number derived from the rate equation. After combining all these effects, the theory can provide a quantitative description of fine features of both TE and TM modes (including higher-order modes) observed in the PL spectra of ZnO MSs. Surprisingly, it is found that for ZnO MS with a diameter larger than 5 μm, the PL emission spectrum is dominated by higher-order modes. The quantitative understanding of the interplay of these emission mechanisms should prove useful for optimizing the performance of light-emitting devices based on microresonators.

关键词： Cavity quantum electrodynamics Lasers Light-matter interaction Optical pumping Photonics Semiconductor quantum optics Spontaneous emission Whispering gallery mode resonators