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Nonvolatile Multilevel States in Multiferroic Tunnel Junctions

Physical Review Applied 2019年第4期12卷 044049-044049页

作者： Mei Fang Sangjian Zhang Wenchao Zhang Lu Jiang Eric Vetter Ho Nyung Lee Xiaoshan Xu Dali Sun Jian Shen Hunan Key Laboratory of Super Microstructure and Ultrafast Process School of Physics and Electronics Central South University Changsha Hunan 410083 China State Key Laboratory of Surface Physics and Department of Physics and Collaborative Innovation Center of Advanced Microstructure Fudan University Shanghai 200433 China Materials Science and Technology Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Department of Physics North Carolina State University Raleigh North Carolina 27695 USA Department of Physics and Astronomy Nebraska Center for Materials and Nanoscience University of Nebraska Lincoln Nebraska 68588 USA

Manipulation of tunneling spin-polarized electrons via a ferroelectric interlayer sandwiched between two ferromagnetic electrodes, dubbed multiferroic tunnel junctions (MFTJs), can be achieved not only by the magnetic alignment of two ferromagnets, but also by the electric polarization of the ferroelectric interlayer; this provides great opportunities for next-generation multistate memory devices. Here, we show that a La0.67Sr0.33MnO3(LSMO)/PbZr0.2Ti0.8O3(PZT)/Co structured MFTJ device can exhibit multilevel resistance states in the presence of gradually reversed ferroelectric domains via tunneling electroresistance and tunneling magnetoresistance, respectively. Nonvolatile ferroelectric control in the MFTJ can be attributed to separate contributions that arise from two independent ferroelectric channels in the PZT interlayer with opposite polarization. Our study shows the dominant role of “mixed” ferroelectric states on achieving accumulative electrical modulation of multilevel resistance states in MFTJs; thus paving the way for multifunctional device applications.

关键词： Electrical conductivity Ferroelectricity Ferromagnetism Magnetoresistance Spintronics Artificial neural networks Magnetic tunnel junctions Multiferroics

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All-optical generation of quantum entangled states with strictly constrained ultrafast laser pulses

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Physical Review A 2019年第2期100卷 023409-023409页

作者： Yu Guo Xiaobing Luo Shan Ma Chuan-Cun Shu Hunan Key Laboratory of Super-Microstructure and Ultrafast Process School of Physics and Electronics Central South University Changsha 410083 China Hunan Provincial Key Laboratory of Flexible Electronic Materials Genome Engineering School of Physics and Electronic Science Changsha University of Science and Technology Changsha 410114 China Institute of Atomic Molecular Physics & Functional Materials Department of Physics Jinggangshan University Ji'an 343009 China School of Automation Central South University Changsha 410083 China

We present a quantum optimal control theory study combined with theoretical analysis to determine a pulsed laser field, capable of generating a maximally entangled state in two trapped two-level atoms. By expanding the time-dependent unitary operator to the first leading term of Magnus expansion, we reexamine the pulse area theorem for the trapped atoms driven by an arbitrarily temporary field. Due to the dipole-dipole interaction blockade, we find that the two trapped atoms described by a three-level ladder system can be reduced into an equivalent two-level model by using narrow-bandwidth pulses, leading to an analytical solution for generating the maximally entangled state. We also solve a highly constrained optimization problem to search for optimal laser pulses with broad bandwidths. A zero pulse-area constraint is employed to remove the dc offset of the optimized laser pulses, and a fixed fluence limitation combined with a constant pulse-area constraint at the resonant frequency of the equivalent two-level system are utilized to restrict the unitary evolution of quantum systems by the first leading term of Magnus expansion. This work provides a potentially useful approach to find all-optical control schemes for generating the maximally entangled state by using ultrafast laser pulses while satisfying multiple strict limitations.

关键词： Coherent control Quantum control Quantum entanglement Quantum state engineering

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Unveiling the Electric-Current-Limiting and Photodetection Effect in Two-Dimensional Hydrogenated Borophene

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Physical Review Applied 2019年第6期11卷 064031-064031页

作者： Yipeng An Yusheng Hou Hui Wang Jie Li Ruqian Wu Tianxing Wang Haixia Da Jutao Jiao College of Physics and Materials Science & International United Henan Key Laboratory of Boron Chemistry and Advanced Energy Materials Henan Normal University Xinxiang Henan 453007 China Department of Physics and Astronomy University of California Irvine California 92697 USA Hunan Key Laboratory of Super Microstructure and Ultrafast Process School of Physics and Electronic Central South University Changsha Hunan 410083 China College of Electronic and Optical Engineering & College of Microelectronics Nanjing University of Posts and Telecommunications Nanjing Jiangsu 210046 China

The electronic transport and photoelectric properties of hydrogenated borophene B4H4, which were realized in a recent experiment by Nishino, et al. [J. Am. Chem. Soc. 139, 13761 (2017)] are systematically investigated using the density functional theory and nonequilibrium Green's function methods. We find that B4H4 exhibits a perfect current-limiting effect and has high (along the zigzag direction) and low (along the armchair one) optional levels due to its strong electrical anisotropy. Moreover, B4H4 can generate sizable photocurrents under illumination, with strong photoelectronic response to blue or green light along the zigzag or armchair direction. Our work demonstrates that B4H4 is promising for the applications of current limiter and photodetectors.

关键词： Electrical conductivity Optoelectronics Quantum transport 2-dimensional systems Elemental metals Monolayer films Density functional calculations Nonequilibrium Green's function

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Anomalous Anisotropy in superconducting Nanodiamond Films Induced by Crystallite Geometry

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Physical Review Applied 2019年第6期12卷 064042-064042页

作者： Gufei Zhang Jozef Kačmarčík Zelin Wang Ramiz Zulkharnay Miroslav Marcin Xiaoxing Ke Serguei Chiriaev Vadzim Adashkevich Pavol Szabó Yejun Li Peter Samuely Victor V. Moshchalkov Paul W. May Horst-Günter Rubahn NanoSYD Mads Clausen Institute and DIAS Danish Institute for Advanced Study University of Southern Denmark Alsion 2 DK-6400 Sonderborg Denmark Centre of Low Temperature Physics Institute of Experimental Physics Slovak Academy of Sciences & Faculty of Science P. J. Safarik University Kosice Slovakia Institute of Microstructure and Properties of Advanced Materials Beijing University of Technology 100124 Beijing China School of Chemistry University of Bristol Bristol BS8 1TS United Kingdom Centre of Industrial Electronics Mads Clausen Institute University of Southern Denmark Alsion 2 DK-6400 Sonderborg Denmark Hunan Key Laboratory of Super Microstructure and Ultrafast Process School of Physics and Electronics Central South University 410083 Changsha China Institute for Nanoscale Physics and Chemistry KU Leuven B-3001 Heverlee Belgium

Tunable electronic properties upon doping make laboratory-grown nanodiamond films a promising and intriguing platform for not only refining conventional electronics, but also developing superconducting quantum devices. In a variety of superconducting systems, mostly in layered materials and heterointerfaces, superconductivity exhibits a two-dimensional (2D) character as evidenced by the anisotropy factor ε=μ0Hc2∥/μ0Hc2⊥≫1, where μ0Hc2∥ and μ0Hc2⊥ are the in-plane and out-of-plane upper critical fields, respectively. Here, we report on the observation of an anomalous anisotropy of superconductivity in heavily boron-doped nanodiamond films, which had been considered a purely three-dimensional (3D) material owing to the minute value of its coherence length in contrast to the film thickness. We investigate the resistive superconducting transition as a function of the angle of the applied magnetic field. The angular dependence of the resistive superconducting transition reveals ɛ

关键词： Grain boundaries Nanocrystals Quantum transport superconductivity Diamond Doped semiconductors superconducting devices Thin films

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Surface-Tension-Controlled Crystallization for High-Quality 2D Perovskite Single Crystals for Ultrahigh Photodetection

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Matter 2019年第2期1卷 465-480页

作者： Yucheng Liu Haochen Ye Yunxia Zhang Kui Zhao Zhou Yang Yongbo Yuan Haodi Wu Guangtao Zhao Zupei Yang Jiang Tang Zhuo Xu Shengzhong (Frank) Liu Key Laboratory of Applied Surface and Colloid Chemistry Ministry of Education Shaanxi Key Laboratory for Advanced Energy Devices Shaanxi Engineering Lab for Advanced Energy Technology Institute for Advanced Energy Materials School of Materials Science and Engineering Shaanxi Normal University 710119 Xi'an China Hunan Key Laboratory of Super-microstructure and Ultrafast Process School of Physics and Electronics Central South University 410083 Hunan China Wuhan National Laboratory for Optoelectronics (WNLO) and School of Optical and Electronic Information Huazhong University of Science and Technology (HUST) 430074 Wuhan China iChEM Dalian National Laboratory for Clean Energy Dalian Institute of Chemical Physics Chinese Academy of Sciences 116023 Dalian China

The two-dimensional (2D) layered organic-inorganic hybrid perovskites have demonstrated better performance in applications than their 3D counterparts due to their promising stability and excellent optoelectronic properties. In particular, the 2D perovskites show even better performance for certain optoelectronic devices, especially the ones fabricated on (001) plane. Unfortunately, these advantageous characteristics cannot be easily extracted from the randomly oriented microcrystalline films. Herein, we developed a surface-tension-controlled crystallization method to prepare large 2D (C 6 H 5 C 2 H 4 NH 3 ) 2 PbI 4 ((PEA) 2 PbI 4 ) perovskite single crystals (PSCs). Using this technique, we have harvested some inch-sized 2D (PEA) 2 PbI 4 PSCs, with the largest one reaching 36 mm in length, resulting in extraordinary device performance. More specifically, the photodetectors fabricated on the (001) plane exhibit responsivity as high as 139.6 A W −1 , external quantum efficiency 37,719.6%, detectivity 1.89 × 10 15 cm Hz 1/2 W −1 , and response speed as fast as τ rise = 21 μs and τ decay = 37 μs.

关键词： MAP 2: Benchmark perovskite 2D single crystal surface-tension-controlled crystallization anisotropy photodetector ultrahigh photodetection

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Substrate-dependent Growth of CH3NH3PbI3 Films Deposited by Vacuum Evaporation

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Journal of Physics: Conference Series 2020年第1期1637卷

作者： Ying Lu Qiang Han Yuan Zhao Chenggang Yang Youzhen Li Xiaoliang Liu Institute of Super-Microstructure and Ultrafast Process in Advanced Materials School of Physics and Electronics Central South University Changsha 410083 P. R. China

CH3NH3PbI3 (MAPbI3) films were prepared by dual-source vacuum evaporation on Au, poly(3,4-ethylenedioxythiophene) (PEDOT), and indium-tin-oxide(ITO) with the similar deposition parameters. The films were characterized with X-ray diffraction (XRD), steady-state photoluminescence (PL) and Raman spectroscopy. The interface electronic structures of co-evaporated MAPbI3 films on different substrates were studied with ultraviolet photoemission spectroscopy (UPS) and X-ray photoemission spectroscopy (XPS). The research indicates that Au is more suitable for the film growth than the other substrates, especially when the film is very thin. The poor adsorption of the precursors may make it difficult to form MAPbI3 thin film on ITO. Furthermore, it is found that the charge transfer efficiency at the interface between PEDOT and MAPbI3 is relatively high, which indicates that PEDOT can act as an effective hole transport layer for MAPbI3-based devices.

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Manipulating Giant Rashba Valley Splitting and Quantum Hall States in Few-Layer Black Arsenic by Electrostatic Gating

arXiv

引用

arXiv 2020年

作者： Sheng, Feng Hua, Chenqiang Sun, Xikang Hu, Jie Tao, Qian Lu, Hengzhe Lu, Yunhao Zhong, Mianzeng Watanabe, Kenji Taniguchi, Takashi Xia, Qinling Xu, Zhu-An Zheng, Yi Zhejiang Province Key Laboratory of Quantum Technology and Device Department of Physics Zhejiang University Hangzhou310027 China School of Physics and Electronics Hunan Key Laboratory for Super-microstructure and Ultrafast Process Central South University Changsha410083 China National Institute for Materials Science 1-1 Namiki Tsukuba305-0044 Japan Collaborative Innovation Centre of Advanced Microstructures Nanjing University Nanjing210093 China

Exciting phenomena may emerge in non-centrosymmetric two-dimensional (2D) electronic systems when spin-orbit coupling (SOC) interplays dynamically with Coulomb interactions, band topology, and external modulating forces, etc [1–5]. Here, we report illuminating synergetic effects between SOC and Stark in centrosymmetric few-layer black arsenic (BAs), manifested as giant Rashba valley splitting and exotic quantum Hall states (QHS) reversibly controlled by electrostatic gating. The unusual finding is rooted in the puckering square lattice of BAs, in which heavy 4p orbitals form highly asymmetric Γ valley with the pz symmetry and D valleys of the px origin, located at the Brillouin zone (BZ) center and near the time reversal invariant momenta of X, respectively. When the structure inversion symmetry is broken by perpendicular electric field, giant Rashba SOC is activated for the px bands to produce strong spin-polarized D+ and D− valleys related by time-reversal symmetry, coexisting with weak Γ Rashba bands constrained by the pz symmetry. Intriguingly, strong Stark effect shows the same px-orbital selectiveness for D, collectively shifting the valence band maximum of D± valleys to exceed the Γ pockets. Such an orchestrating effect between SOC and Stark allows us to realize gate-tunable spin valley manipulations for 2D hole gas, as revealed by unconventional magnetic field triggered even-to-odd transitions in QHS. For electron doping, the quantization of the Γ Rashba bands is characterized by peculiar density-dependent transitions in band topology from two parabolic valleys to a unique inner-outer helical structure when charge carrier concentrations increase. Copyright © 2020, The Authors. All rights reserved.

关键词： Landforms

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Structural and mechanical properties of monolayer amorphous carbon and boron nitride

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Physical Review B 2024年第17期109卷 174106-174106页

作者： Xi Zhang Yu-Tian Zhang Yun-Peng Wang Shiyu Li Shixuan Du Yu-Yang Zhang Sokrates T. Pantelides University of Chinese Academy of Sciences and Institute of Physics Chinese Academy of Sciences Beijing 100049 China CAS Key Laboratory of Theoretical Physics Institute of Theoretical Physics Chinese Academy of Sciences Beijing 100190 China Hunan Key Laboratory for Super Microstructure and Ultrafast Process School of Physics and Electronics Central South University Changsha 410083 China Songshan Lake Materials Laboratory Dongguan Guangdong 523808 China Department of Physics and Astronomy and Department of Electrical and Computer Engineering Vanderbilt University Nashville Tennessee 37235 USA

Amorphous materials exhibit various characteristics that are not featured by crystals and can sometimes be tuned by their degree of disorder (DOD). Here, we report results on the mechanical properties of monolayer amorphous carbon (MAC) and monolayer amorphous boron nitride (maBN) with different DOD. The pertinent structures are obtained by kinetic Monte Carlo (kMC) simulations using machine-learning potentials with density-functional theory-level accuracy. An intuitive order parameter, namely, the areal fraction Fx occupied by crystallites within the continuous random network, is proposed to describe the DOD. We find that Fx captures the essence of the DOD: Samples with the same Fx but different sizes and arrangements of crystallites, obtained using two distinct kMC procedures, have virtually identical radial distribution functions as well as bond-length and bond-angle distributions. Furthermore, by simulating the fracture process with molecular dynamics, we found that the mechanical responses of MAC and maBN before fracture are mainly determined by Fx and are insensitive to the sizes and specific arrangements and to some extent the numbers and area distributions of the crystallites. The behavior of cracks in the two materials is analyzed and found to mainly propagate in meandering paths in the continuous random network region and to be influenced by crystallites in distinct ways that toughen the material. The present results reveal the relation between structure and mechanical properties in amorphous monolayers and may provide a universal toughening strategy for two-dimensional materials.

关键词： Cracking Defects Fracture Material failure Mechanical deformation microstructure Plasticity Stress 2-dimensional systems Amorphous materials Boron nitride Graphene Artificial neural networks Density functional calculations First-principles calculations High-throughput calculations Machine learning materials modeling Molecular dynamics Monte Carlo methods

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Effect of nitrogen pressure on the fabrication of AlCrFeCoNiCu0.5 high entropy nitride thin films via cathodic arc deposition

Effect of nitrogen pressure on the fabrication of AlCrFeCoNi...

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作者： Jiang, Tenghao Zhao, Hong Tsoutas, Kostadinos Sun, Lixian Liu, Hongwei Liu, Yanping Xu, Fanjun Zheng, Zhong Bilek, Marcela M. Liu, Zongwen School of Chemical and Biomolecular Engineering The University of Sydney SydneyNSW2006 Australia School of Physics The University of Sydney SydneyNSW2006 Australia School of Biomedical Engineering The University of Sydney SydneyNSW2006 Australia Guangxi Key Laboratory of Information Materials Guangxi Collaborative Innovation Center of Structure and Property for New Energy and Materials School of Material Science & Engineering Guilin University of Electronic Technology Guilin541004 China The University of Sydney SydneyNSW2006 Australia Hunan Key Laboratory for Super-microstructure and Ultrafast Process School of Physics and Electronics Central South University Hunan410083 China The University of Sydney Nano Institute The University of Sydney SydneyNSW2006 Australia

In the past two decades, high entropy alloy (HEA) coatings have attracted great attention due to their superior mechanical properties, outstanding corrosion and oxidation resistance, and exceptionally high thermal stability. In comparison to HEA thin films, high entropy nitrides (HENs) exhibit higher mechanical strength and chemical inertness. In this work, AlCrFeCoNiCu0.5 HEA and HEN thin films were fabricated using a filtered cathodic arc. By regulating the deposition pressure from 0.0005 Pa (HEA thin film) to 0.05 Pa, the nitrogen concentration in each thin film was precisely controlled to tune the mechanical properties. Scanning transmission electron microscopy-energy dispersive spectroscopy revealed that the nitrogen concentration of the films was up to 21.2 at. % at the pressure of 0.05 Pa. The reduced effect of preferential sputtering increased aluminum concentration from 8.3 ± 1.5 to 12.9 ± 2.2 at. % as pressure increased up to 0.05 Pa. X-ray photoelectron spectroscopy further confirmed the formation of AlN and CrN at pressures of 0.01-0.05 Pa. The highest hardness and elastic modulus of the HEN film were 12.4 ± 0.6 and 347.3 ± 17.7 GPa, respectively, which were 84.8% and 131.4% higher than those of the HEA thin film. © 2023 Author(s).

关键词： Entropy

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Nonvolatile multilevel states in multiferroic tunnel junctions

arXiv

引用

arXiv 2019年

作者： Fang, Mei Zhang, Sangjian Zhang, Wenchao Jiang, Lu Vetter, Eric Lee, Ho Nyung Xu, Xiaoshan Sun, Dali Shen, Jian Hunan Key Laboratory of Super Microstructure and Ultrafast Process School of Physics and Electronics Central South University Changsha Hunan410083 State Key Laboratory of Surface Physics Department of Physics Collaborative Innovation Center of Advanced Microstructure Fudan University Shanghai200433 Materials Science and Technology Division Oak Ridge National Laboratory Oak RidgeTN37831 United States Department of Physics North Carolina State University RaleighNC27695 United States Department of Physics and Astronomy University of Nebraska LincolnNE68588 United States

Manipulation of tunneling spin-polarized electrons via a ferroelectric interlayer sandwiched between two ferromagnetic electrodes, dubbed Multiferroic Tunnel Junctions (MFTJs), can be achieved not only by the magnetic alignments of two ferromagnets but also by the electric polarization of the ferroelectric interlayer, providing great opportunities for next-generation multi-state memory devices. Here we show that a La0.67Sr0.33MnO3(LSMO)/PbZr0.2Ti0.8O3(PZT)/Co structured MFTJ device can exhibit multilevel resistance states in the presence of gradually reversed ferroelectric domains via tunneling electro-resistance and tunneling magnetoresistance, respectively. The nonvolatile ferroelectric control in the MFTJ can be attributed to separate contributions arising from two independent ferroelectric channels in the PZT interlayer with opposite polarization. Our study shows the dominant role of 'mixed' ferroelectric states on achieving accumulative electrical modulation of multilevel resistance states in MFTJs, paving the way for multifunctional device applications. Copyright © 2019, The Authors. All rights reserved.

关键词： Tunnel junctions

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