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Energy Gap Induced by Friedel Oscillations Manifested as Transport Asymmetry at Monolayer-Bilayer Graphene Boundaries

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Physical Review X 2014年第1期4卷 011021-011021页

作者： Kendal W. Clark X.-G. Zhang Gong Gu Jewook Park Guowei He R. M. Feenstra An-Ping Li Center for Nanophase Materials Sciences Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Department of Electrical Engineering and Computer Science University of Tennessee Knoxville Tennessee 37996 USA Department of Physics Carnegie Mellon University Pittsburgh Pennsylvania 15213 USA

We show that Friedel charge oscillation near an interface opens a gap at the Fermi energy for electrons with wave vectors perpendicular to the interface. If the Friedel gaps on two sides of the interface are different, a nonequilibrium effect—shifting of these gaps under bias—leads to asymmetric transport upon reversing the bias polarity. The predicted transport asymmetry is revealed by scanning tunneling potentiometry at monolayer-bilayer interfaces in epitaxial graphene on SiC(0001). This intriguing interfacial transport behavior opens a new avenue toward novel quantum functions such as quantum switching.

关键词： Condensed matter physics Graphene

Strain-engineered high responsivity MoTe2 Photodetector for silicon photonic integrated circuits

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arXiv 2019年

作者： Maiti, R. Patil, C. Xie, T. Azadani, J.G. Saadi, M.A.S.R. Amin, R. Miscuglio, M. van Thourhout, D. Solares, S.D. Low, T. Agarwal, R. Bank, S. Sorger, V.J. Department of Electrical and Computer Engineering George Washington University WashingtonDC20052 United States Department of Electrical and Computer Engineering University of Minnesota MinneapolisMN55455 United States Department of Mechanical and Aerospace Engineering George Washington University WashingtonDC20052 United States Department of Information Technology Ghent University - IMEC Technologiepark Zwijnaarde 126 Gent9052 Belgium Department of Materials Science and Engineering University of Pennsylvania PhiladelphiaPA19104 United States Department of Electrical and Computer Engineering University of Texas AustinTX78758 United States

In integrated photonics, specific wavelengths are preferred such as 1550 nm due to low-loss transmission and the availability of optical gain in this spectral region. For chip-based photodetectors, layered two-dimensional (2D) materials bear scientific and technologically-relevant properties such as electrostatic tunability and strong light-matter interactions. However, no efficient photodetector in the telecommunication C-band has been realized with 2D transition metal dichalcogenide (TMDCs) materials due to their large optical bandgap. Here, we demonstrate a MoTe2-based photodetector featuring strong photoresponse (responsivity = 0.5 A/W) operating at 1550 nm on silicon micro ring resonator enabled by strain engineering of the transition-metal-dichalcogenide film. We show that an induced tensile strain of ~4% reduces the bandgap of MoTe2, resulting in large photo-response in the telecommunication wavelength, in otherwise photo-inactive medium when unstrained. Unlike Graphene-based photodetectors relying on a gapless band structure, this semiconductor-2D material detector shows a ~100X improved dark current enabling an efficient noise-equivalent power of just 90 pW/Hz0.5. Such strain-engineered integrated photodetector provides new opportunities for integrated optoelectronic systems. Copyright © 2019, The Authors. All rights reserved.

关键词： Photodetectors

3D In-Situ Characterization of Dislocation Density in Nickel-Titanium Shape Memory Alloys Using High-Energy Diffraction Microscopy

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SSRN

SSRN 2023年

作者： Li, Wenxi Lee, Sangwon Zhang, Tianchi Pagan, Darren Casalena, Lee Mills, Michael J. Bucsek, Ashley Department of Mechanical Engineering University of Michigan Ann ArborMI48109 United States Department of Materials Science and Engineering University of Michigan Ann ArborMI48109 United States Department of Electrical Engineering and Computer Science University of Michigan Ann ArborMI48109 United States Department of Materials Science and Engineering The Pennsylvania State University University Park PA16802 United States Thermo Fisher Scientific HillsboroOR97124 United States Department of Materials Science and Engineering The Ohio State University ColumbusOH43212 United States

Functional fatigue—changes to the material response during cyclic—is a major barrier to the cycle lifetime demands of shape memory alloy technologies. Functional fatigue is caused by permanent changes to the microstructure, such as the generation of dislocations during forward and reverse martensitic phase transformation. In this work, far-field and near-field high-energy diffraction microscopy (ff- and nf-HEDM) are used to characterize the local accumulation of geometrically necessary dislocation (GND) density in the austenite phase in situ and in 3D across a bulk Ni49.9Ti50.1 polycrystalline shape memory alloy during load-biased thermal cycling. A custom nf-HEDM data analysis procedure is used to reconstruct spatially resolved intragranular misorientation maps which are then converted to spatially resolved GND density maps. In this way, GND density is tracked in individual grains across cycles. We find that neither Schmid factor nor the maximum transformation work correlates strongly with GND density evolution during load-biased thermal cycling. The results show that the spatially resolved GND density is distributed heterogeneously, but GND density increases faster near grain boundaries, in grains at the sample surface, and in grains with large volumes, indicating that these regions/types of grains will undergo different functional fatigue behaviors. Finally, we also find that grain neighborhood play an important role in local defect evolution. GND density increases faster in "soft" grains with "hard" grain neighborhoods. This work demonstrates the utility of nf-HEDM for understanding the evolution of intragranular structural changes in polycrystalline materials, including those associated with martensitic phase transformation. © 2023, The Authors. All rights reserved.

关键词： Polycrystalline materials

Ferromagnetism triggered by band tripling in ruthenate Sr4Ru3O10

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Physical Review B 2024年第15期110卷 155134页

作者： N. Watanabe S. Souma K. Nakayama K. Yamauchi J. F. Ribeiro Y. Wang Miho Kitamura Koji Horiba Hiroshi Kumigashira T. Oguchi Z. Q. Mao Y. P. Chen T. Sato Department of Physics Graduate School of Science Advanced Institute for Materials Research (WPI-AIMR) Center for Science and Innovation in Spintronics (CSIS) Precursory Research for Embryonic Science and Technology (PRESTO) Center for Spintronics Research Network (CSRN) School of Electrical and Computer Engineering and Birck Nanotechnology Center Department of Physics Institute of Materials Structure Science (QST) Sendai 980-8579 Japan Institute of Multidisciplinary Research for Advanced Materials (IMRAM) Department of Physics and Astronomy and Purdue Quantum Science and Engineering Institute International Center for Synchrotron Radiation Innovation Smart (SRIS) Mathematical Science Center for Co-creative Society (MathCCS)

Itinerant ferromagnetism is understood in terms of a quasiparticle picture with renormalized many-body effects. While the ferromagnetic ground state is destabilized by thermal and quantum fluctuations leading to exotic states such as unconventional superconductivity, how the quasiparticles evolve across the ferromagnetic transition is a target of intensive debate. Here, we present a type of ferromagnetic transition that is accompanied by a drastic reconstruction of quasiparticle spectrum in a layered ferromagnetic ruthenate, Sr4Ru3O10. Angle-resolved photoemission spectroscopy uncovered that the three-dimensional coherent states below the ferromagnetic transition temperature (TC) turn into two-dimensional incoherent electronic states slightly above TC characterized by the disappearance of trilayer band splitting, ferromagnetic exchange splitting, and long-lived quasiparticles. Our findings suggest that the electronic coherence strongly modifies the fermiology and magnetic order, pointing to an intriguing coupling between quasiparticles and magnetic properties.

关键词： Electronic structure Fermi surface Ferromagnetism Quasiparticles & collective excitations van Hove singularity Ruddlesden-Popper compounds Angle-resolved photoemission spectroscopy Density functional theory First-principles calculations

Quantum photonics in triangular-cross-section nanodevices in silicon carbide

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arXiv 2020年

作者： Majety, Sridhar Norman, Victoria A. Li, Liang Bell, Miranda Saha, Pranta Radulaski, Marina Department of Electrical and Computer Engineering University of California DavisCA95616 United States Department of Physics University of California DavisCA95616 United States Department of Materials Science and Engineering University of California DavisCA95616 United States

Silicon carbide is evolving as a prominent solid-state platform for the realization of quantum information processing hardware. Angle-etched nanodevices are emerging as a solution to photonic integration in bulk substrates where color centers are best defined. We model triangular cross-section waveguides and photonic crystal cavities using Finite-Difference Time-Domain and Finite-Difference Eigensolver approaches. We analyze optimal color center positioning within the modes of these devices and provide estimates on achievable Purcell enhancement in nanocavities with applications in quantum communications. Using open quantum system modeling, we explore emitter-cavity interactions of multiple non-identical color centers coupled to both a single cavity and a photonic crystal molecule in SiC. We observe polariton and subradiant state formation in the cavity-protected regime of cavity quantum electrodynamics applicable in quantum simulation. © 2020, CC BY-SA.

关键词： Silicon carbide

Corner cutting connects chiral colorimetry to net electric flux in lossless all-dielectric metasurfaces

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arXiv 2024年

作者： Haddadin, Zaid Nguyen, Anna M.Y. Poulikakos, Lisa V. Department of Electrical & Computer Engineering UC San Diego La Jolla CA92093-0021 United States Department of Mechanical & Aerospace Engineering UC San Diego La Jolla CA92093-0021 United States Program of Materials Science & Engineering UC San Diego La Jolla CA92093-0021 United States

All-dielectric metasurfaces can produce structural colors, but the most advantageous design criteria are still being investigated. This work numerically studies how the two-dimensional shape of nanoparticles affects the colorimetric response under circularly polarized light (CPL) to develop a sensor distinguishing CPL orientations. Using lossless dielectric materials (silicon nitride on silicon dioxide), we achieve far-field dichroism by modifying oblong nanoparticles into L-shaped structures through corner cuts. This design suppresses one electric dipole under CPL illumination, leading to differential colorimetric responses. We link these responses to a decoupling effect in the near-field net electric flux. Our findings provide design guidelines for all-dielectric, lossless colorimetric sensors of chiral light. Copyright © 2024, The Authors. All rights reserved.

关键词： Silicon nitride

Effect of homogenization on precipitation behavior and strengthening of 17-4PH stainless steel fabricated using laser powder bed fusion

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arXiv 2021年

作者： Li, Kun Sridar, Soumya Tan, Susheng Xiong, Wei Physical Metallurgy and Materials Design Laboratory Department of Mechanical Engineering and Materials Science University of Pittsburgh PittsburghPA15261 United States Department of Electrical and Computer Engineering University of Pittsburgh PittsburghPA15260 United States Petersen Institute of Nanoscience and Engineering University of Pittsburgh PittsburghPA15260 United States

Effective post-heat treatment is critical to achieve desired microstructure for high-performance in additively manufactured (AM) components. In this work, the influence of homogenization on microstructure-property relationship in 17-4PH steels has been investigated. Precipitation of NbC, oxides, and Ε-Cu were observed in the as-built 17-4PH steels. To design an optimum post-heat treatment, homogenization was performed at 1050oC for different times followed by aging at 482oC for 1 hour. It was identified that homogenization for 1 hour followed by aging leads to the best combination of strength and ductility due to the refinement of martensite and prior austenite grains. Improved tensile properties were achieved for the post-heat-treated alloys that exceeded the traditionally fabricated 17-4PH steels. Through comprehensive microstructure characterization, it was deduced that the incoherent Ε-Cu precipitates in the as-built alloy were dissolved through homogenization, and subsequently, re-precipitated as coherent Cu-rich clusters during aging. This study demonstrates that altering the precipitation behavior using post-heat treatment is an effective pathway to significantly improve the mechanical properties of AM alloys. Copyright © 2021, The Authors. All rights reserved.

关键词： 3D printers

Hubbard Model Physics in Transition Metal Dichalcogenide Moiré Bands

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Physical Review Letters 2018年第2期121卷 026402-026402页

作者： Fengcheng Wu Timothy Lovorn Emanuel Tutuc A. H. MacDonald Materials Science Division Argonne National Laboratory Argonne Illinois 60439 USA Department of Physics University of Texas at Austin Austin Texas 78712 USA Department of Electrical and Computer Engineering Microelectronics Research Center The University of Texas at Austin Austin Texas 78758 USA

Flexible long period moiré superlattices form in two-dimensional van der Waals crystals containing layers that differ slightly in lattice constant or orientation. In this Letter we show theoretically that isolated flat moiré bands described by generalized triangular lattice Hubbard models are present in twisted transition metal dichalcogenide heterobilayers. The hopping and interaction strength parameters of the Hubbard model can be tuned by varying the twist angle and the three-dimensional dielectric environment. When the flat moiré bands are partially filled, candidate many-body ground states at some special filling factors include spin-liquid states, quantum anomalous Hall insulators, and chiral d-wave superconductors.

关键词： electrical properties 2-dimensional systems Bilayer films Transition metal dichalcogenides Band structure methods Hubbard model

Measurement of Water Diffusion Coefficient in Cross-Linked Gelatins Using the Terahertz Time-Domain Spectroscopy Technique

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Measurement of Water Diffusion Coefficient in Cross-Linked G...

CLEO: Applications and Technology in CLEO 2024, CLEO: A and T 2024 - Part of Conference on Lasers and Electro-Optics

关键词： Terahertz spectroscopy