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Understanding the flat band in 1T−TaS2 using a rotated basis

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Physical Review B 2021年第24期104卷 L241114-L241114页

作者： Li Cheng Xuanyu Long Xiaobin Chen Xiaolong Zou Zheng Liu Shenzhen Geim Graphene Center (SGC) Tsinghua-Berkeley Shenzhen Institute (TBSI) and Tsinghua Shenzhen International Graduate School Tsinghua University Shenzhen 518055 China Institute for Advanced Study Tsinghua University Beijing 100084 China School of Science State Key Laboratory on Tunable Laser Technology and Ministry of Industry and Information Technology Key Lab of Micro-Nano Optoelectronic Information System Harbin Institute of Technology Shenzhen Shenzhen 518055 China

Electronic flat bands serve as a unique platform to achieve strongly correlated phases. The emergence of a flat band around the Fermi level in 1T−TaS2 accompanied by the development of a 13×13 charge density wave (CDW) superlattice has long been noticed experimentally, but a transparent theoretical understanding remains elusive. We show that without the CDW order, the primary feature of the 1×1 bands can be fitted by a simple trigonometric function, and physically understood by choosing a rotated t2g basis with the principal axes aligning to the tilted TaS6 octahedron. Using this basis, we trace the band evolution in the 13×13 superlattice by progressively including different CDW effects. We point out that the CDW order strongly rehybridizes the three t̃2g orbitals, which leads to the formation of a well-localized molecular orbital and the flat band.

关键词： Charge density waves Electronic structure Strongly correlated systems Transition metal dichalcogenides

Field-free superconducting diode effect and magnetochiral anisotropy in FeTe0.7Se0.3 junctions with the inherent asymmetric barrier

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arXiv 2024年

作者： Li, Shengyao Deng, Ya Hu, Dianyi Zhu, Chao Yang, Zherui Tian, Wanghao Wang, Xueyan Yue, Ming Wu, Qiong Liu, Zheng Wang, Xiao Renshaw Division of Physics and Applied Physics School of Physical and Mathematical Sciences Nanyang Technological University Singapore637371 Singapore School of Materials Science and Engineering Nanyang Technological University Singapore639798 Singapore SEU-FEI Nano-Pico Center Key Laboratory of MEMS of Ministry of Education Collaborative Innovation Center for Micro/Nano Fabrication Device and System Southeast University Nanjing210096 China School of Electrical and Electronic Engineering Nanyang Technological University Singapore639798 Singapore Faculty of Materials and Manufacturing Key Laboratory of Advanced Functional Materials Ministry of Education of China Beijing University of Technology Beijing100124 China CINTRA CNRS NTU/THALES UMI 3288 Research Techno Plaza Singapore637553 Singapore

Nonreciprocal electrical transport, characterized by an asymmetric relationship between current and voltage, plays a crucial role in modern electronic industries. Recent studies have extended this phenomenon to superconductors, introducing the concept of the superconducting diode effect (SDE). The SDE is characterized by unequal critical supercurrents along opposite directions. Due to the requirement on broken inversion symmetry, the SDE is commonly accompanied by electrical magnetochiral anisotropy (eMCA) in the resistive state. Achieving a magnetic field-free SDE with field tunability is pivotal for advancements in superconductor devices. Conventionally, the field-free SDE has been achieved in Josephson junctions by intentionally intercalating an asymmetric barrier layer. Alternatively, internal magnetism was employed. Both approaches pose challenges in the selection of superconductors and fabrication processes, thereby impeding the development of SDE. Here, we present a field-free SDE in FeTe0.7Se0.3 (FTS) junction with eMCA, a phenomenon absent in FTS single nanosheets. The field-free property is associated with the presence of a gradient oxide layer on the upper surface of each FTS nanosheet, while the eMCA is linked to spin-splitting arising from the absence of inversion symmetry. Both the SDE and eMCA respond to magnetic fields with distinct temperature dependencies. This work presents a versatile and straightforward strategy for advancing superconducting electronics. Copyright © 2024, The Authors. All rights reserved.

关键词： Nanosheets

Thermal Strain-Induced Self-Rolling Mesh Cuff Electrodes for Non-Linear Peripheral Nerve

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Thermal Strain-Induced Self-Rolling Mesh Cuff Electrodes for...

IEEE International Conference on micro Electro Mechanical systems

作者： Bowen Ji Lin Chen Minghao Wang Zhejun Guo Yuhao Zhou Shuaiqi Huangfu Kai Zhang Huicheng Feng Honglong Chang Jingquan Liu Unmanned System Research Institute Northwestern Polytechnical University Xi’an China Ministry of Education Key Laboratory of Micro/Nano Systems for Aerospace School of Mechanical Engineering Northwestern Polytechnical University Xi’an China State Key Laboratory for Mechanical Behavior of Materials School of Materials Science and Engineering Xi’an Jiaotong University Xi’an China College of Electronics and Information Hangzhou Dianzi University Hangzhou China National Key Laboratory of Science and Technology on Micro/Nano Fabrication Shanghai Jiao Tong University China

ISBN: (数字)9781665419123

ISBN: (纸本)9781665430241

Cuff electrodes have been widely utilized on peripheral nerve for neural stimulation and recording applications. In this paper, we have proposed a self-rolling meshed cuff electrode induced by the thermal strain. The final cuff diameter is about 1.4 mm, which can match well with the peripheral nerve of rat (diameter of 1.54 mm at ischial tuberosity of sciatic nerve). The mechanical simulation of the mesh cuff illustrates the oblivious change from the plane cuff when bending with the nerve model. The mesh cuff not only facilities the flow of interstitial fluid in and out, but also shows the potential to combine with microfluidics or optogenetics technology.

关键词： Electrodes micromechanical devices Electric potential Fluids Rats microfluidics Strain

A Superhydrophobic Chip Integrated with an Array of Medium Reservoirs for Long-Term Hanging Drop Spheroid Culture

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SSRN

SSRN 2021年

作者： Sun, Bangyong Zhao, Yi Wu, Weimin Zhao, Qiang Li, Gang Key Laboratory of Optoelectronic Technology and Systems Ministry of Education Defence Key Disciplines Lab of Novel Micro-Nano Devices and System Technology Chongqing University Chongqing400044 China Chongqing Key Laboratory of Translational Research for Cancer Metastasis and Individualized Treatment Chongqing University Cancer Hospital Chongqing400030 China School of Mechanical and Power Engineering Chongqing University of Science and Technology Chongqing401331 China

Hanging drop (HD) is one of the most popular methods used for forming three-dimensional (3D) cell spheroids. However, conventional hanging drop systems are only applicable for short-term spheroid culture due to their inconvenience in exchanging cell culture media. Here we present a medium-reservoir-integrated superhydrophobic (MRI-SH) chip for long-term HD spheroid cultures. The device consists of two main components: i) a patterned superhydrophobic (SH) surface containing an array of wettable spots which anchor arrays of droplets of cell suspension, and ii) an array of chambers that serve as medium reservoirs, both interconnected via an array of thru-holes. This configuration provides two distinct advantages over conventional HD configurations: i) the high wettability contrast of the SH pattern on the chip leads to the formation and adhesion of nearly spherical hanging droplets on its surface, which minimizes interactions between the liquid and the substrate;ii) the integrated chambers provide large volumes of medium to maintain longer culture durations. Using this device, spheroids of MHCC97H cells were successfully formed, and the cultured spheroids could maintain high viability for up to 30 days and exhibited enhanced spheroid morphology compared to those cultured in the conventional HD systems. © 2021, The Authors. All rights reserved.

关键词： Drops

Towards ultrafast cooling through transient phonon currents: A closed-form solution

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Physical Review B 2021年第7期103卷 075427-075427页

作者： Xiaobin Chen Jiangtao Yuan Jian Wang School of Science State Key Laboratory on Tunable laser Technology and Ministry of Industry and Information Technology Key Lab of Micro-Nano Optoelectronic Information System Harbin Institute of Technology Shenzhen Shenzhen 518055 China Collaborative Innovation Center of Extreme Optics Shanxi University Taiyuan 030006 China Department of Physics and the Center of Theoretical and Computational Physics The University of Hong Kong Hong Kong China College of Physics and Optoelectronic Engineering Shenzhen University Shenzhen 518060 China

We develop a closed-form formula to calculate the transient thermal currents flowing through an arbitrary nanoscale phonon device in response to a sudden thermal switch. Our theory provides a solution to the problem in the far-from-equilibrium nonlinear response regime beyond the wide-band-like approximation and Drude regularization. We present calculations in a one-dimensional monatomic chain with Lorentzian-like thermal baths and show that the transient phonon currents are significantly larger than the long-time-limit steady-state phonon current. From the formula's clear mathematical structure, we also show that the transient oscillation periodicity and relaxation time are determined by the poles of the retarded phonon Green's function. In addition, higher temperatures of the thermal baths and stronger coupling between the baths and the central monatomic chain result in higher transient thermal currents. Our results suggest that ultrafast cooling of nanodevices through transient phonon currents is a promising route.

关键词： Ballistic transport Phonons Quantum transport Nonequilibrium Green's function

Probing quasi-long-range ordering by magnetostriction in monolayer CoPS3

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arXiv 2021年

作者： Liu, Qiye Wang, Le Fu, Ying Zhang, Xi Huang, Lianglong Su, Huimin Lin, Junhao Chen, Xiaobin Yu, Dapeng Cui, Xiaodong Mei, Jia-Wei Dai, Jun-Feng Shenzhen Institute for Quantum Science and Engineering Department of Physics Southern University of Science and Technology Shenzhen518055 China Department of Physics The University of Hong Kong Pokfulam999077 Hong Kong Shenzhen Key Laboratory of Quantum Science and Engineering Shenzhen518055 China Shenzhen Key Laboratory of Advanced Quantum Functional Materials and Devices Southern University of Science and Technology Shenzhen518055 China Shannxi Institute of Flexible Electronics Northwestern Polytechnical University Xi’an710072 China School of Science State Key Laboratory on Tunable Laser Technology Ministry of Industry and Information Technology Key Lab of Micro-Nano Optoelectronic Information System Harbin Institute of Technology Shenzhen518055 China

Mermin-Wagner-Coleman theorem predicts no long-range magnetic order at finite temperature in the two-dimensional (2D) isotropic systems, but a quasi-long-range order with a divergent correlation length at the Kosterlitz–Thouless (KT) transition for planar magnets. As a representative of two-dimensional planar antiferromagnets, single-layer CoPS3 carries the promise of monolayer antiferromagnetic platforms for the ultimately thin spintronics. Here, with the aid of magnetostriction which is sensitive to the local magnetic order, we observe the signatured phonon mode splitting of below TKT in monolayer CoPS3, revealing the presence of quasi-long-range ordering in XY-type antiferromagnet. Moreover, the ratio (J’/J) between the interlayer and intralayer interactions, which characterizes the 2D behaviors, is evaluated to be around 0.03 for the first time. Our results provide an efficient method to detect the quasi-long-range antiferromagnetic ordering in the two-dimensional magnets down to monolayer limit. Copyright © 2021, The Authors. All rights reserved.

关键词： Monolayers

Graphene-based all-optical modulators

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Frontiers of Optoelectronics 2020年第2期13卷 114-128,F0004页

作者： Chuyu ZHONG Junying LI Hongtao LIN Key Laboratory of Micro-Nano Electronics and Smart System of Zhejiang Province College of Information Science and Electronic EngineeringZhejiang UniversityHangzhou 310027China School of Microelectronics Zhejiang UniversityHangzhou 310027China College of Optical-Electrical and Computer Engineering University of Shanghai for Science and TechnologyShanghai 200093China

All-optical devices,which are utilized to process optical signals without electro-optical conversion,play an essential role in the next generation ultrafast,ultralow power-consumption optical information processing *** satisfy the performance requirement,nonlinear optical materials that are associated with fast response,high nonlinearity,broad wavelength operation,low optical loss,low fabrication cost,and integration compatibility with optical components are *** is a promising candidate,particularly considering its electrically or optically tunable optical properties,ultrafast large nonlinearity,and high integration compatibility with various *** far,three all-optical modulation systems utilize graphene,namely free-space modulators,fiber-based modulators,and on-chip *** paper aims to provide a broad view of state-of-the-art researches on the graphene-based all-optical modulation *** performances of different devices are reviewed and compared to present a comprehensive analysis and perspective of graphene-based all-optical modulation devices.

关键词： graphene saturable absorption low power consumption all-optical modulation

Strong Neel ordering and luminescence correlation in a two-dimensional antiferromagnet

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arXiv 2022年

作者： Zhou, Yongheng He, Kaiyue Hu, Huamin Ouyang, Gang Zhu, Chao Wang, Wei Qin, Sichen Tao, Ye Chen, Runfeng Zhang, Le Shi, Run Cheng, Chun Wang, Han Liu, Yanjun Liu, Zheng Wang, Taihong Huang, Wei Wang, Lin Chen, Xiaolong Department of Electrical and Electronic Engineering Southern University of Science and Technology Shenzhen518055 China 30 South Puzhu Road Nanjing211816 China Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education Key Laboratory for Matter Microstructure and Function of Hunan Province Hunan Normal University Changsha410081 China SEU-FEI Nano-Pico Center Key Laboratory of MEMS of Ministry of Education Collaborative Innovation Center for Micro/Nano Fabrication Device and System Southeast University Nanjing210096 China School of Materials Science and Engineering Nanyang Technological University Singapore639798 Singapore 127 West Youyi Road Xi'An710072 China Nanjing University of Posts & Telecommunications 9 Wenyuan Road Nanjing210023 China Department of Materials Science and Engineering Southern University of Science and Technology Shenzhen518055 China

Magneto-optical effect has been widely used in light modulation, optical sensing and information storage. Recently discovered two-dimensional (2D) van der Waals layered magnets are considered as promising platforms for investigating novel magneto-optical phenomena and devices, due to the long-range magnetic ordering down to atomically-thin thickness, rich species and tunable properties. However, majority 2D antiferromagnets suffer from low luminescence efficiency which hinders their magneto-optical investigations and applications. Here, we uncover strong light-magnetic ordering interactions in 2D antiferromagnetic MnPS3 utilizing a newly-emerged near-infrared photoluminescence (PL) mode far below its intrinsic bandgap. This ingap PL mode shows strong correlation with the Neel ordering and persists down to monolayer thickness. Combining the DFT, STEM and XPS, we illustrate the origin of the PL mode and its correlation with Neel ordering, which can be attributed to the oxygen ion-mediated states. Moreover, the PL strength can be further tuned and enhanced using ultraviolet-ozone treatment. Our studies offer an effective approach to investigate light-magnetic ordering interactions in 2D antiferromagnetic semiconductors. © 2022, CC BY-NC-SA.

关键词： Manganese compounds

Understanding the flat band in 1T-TaS2 using a rotated basis

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arXiv 2021年

作者： Cheng, Li Long, Xuanyu Chen, Xiaobin Zou, Xiaolong Liu, Zheng Tsinghua Shenzhen International Graduate School Tsinghua University Shenzhen518055 China Institute for Advanced Study Tsinghua University Beijing100084 China School of Science State Key Laboratory on Tunable Laser Technology Ministry of Industry and Information Technology Key Lab of Micro-Nano Optoelectronic Information System Harbin Institute of Technology Shenzhen Shenzhen518055 China

Electronic flat bands serve as a unique platform to achieve strongly-correlated phases. The emergence of a flat band around the Fermi level in 1T-TaS2 in accompany with the development of a √13 × √13 charge density wave (CDW) superlattice has long been noticed experimentally, but a transparent theoretical understanding remains elusive. We show that without CDW, the primary feature of the 1×1 bands can be fitted by a simple trigonometric function, and physically understood by choosing a rotated (Equation presented)2g basis with the principle axes aligning to the tilted TaS6 octahedron. Using this basis, we trace the band evolution in the √13 × √13 superlattice by progressively including different CDW effects. We point out that CDW strongly rehybridizes the three (Equation presented)2g orbitals, which leads to the formation of a well-localized molecular orbital and spawns the flat band. Copyright © 2021, The Authors. All rights reserved.

关键词： Charge density waves