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Proposal for valleytronic materials:Ferrovalley metal and valley gapless semiconductor

Frontiers of physics 2024年第2期19卷 131-139页

作者： San-Dong Guo Yu-Ling Tao Guangzhao Wang Shaobo Chen Dong Huang yee sin ang School of Electronic Engineering Xi’an University of Posts and TelecommunicationsXi’an 710121China Key Laboratory of Extraordinary Bond Engineering and Advanced Materials Technology of Chongqing School of Electronic Information EngineeringYangtze Normal UniversityChongqing 408100China College of Electronic and Information Engineering Anshun UniversityAnshun 561000China Science Mathematics and Technology(SMT)Singapore University of Technology and Design(SUTD)8 Somapah RoadSingapore 487372Singapore

Valleytronic materials can provide new degrees of freedom to future electronic *** this work,the concepts of the ferrovalley metal(FVM)and valley gapless semiconductor(VGS)are proposed,which can be achieved in valleytronic bilayer systems by electric field *** valleytronic bilayer systems,the interaction between out-of-plane ferroelectricity and A-type antiferromagnetism can induce layer-polarized anomalous valley Hall(LP-AVH)*** K and−K valleys of FVM are both metallic,and electron and hole carriers simultaneously *** the extreme case,the FVM can become VGS by analogizing spin gapless semiconductor(SGS).Moreover,it is proposed that the valley splitting enhancement and valley polarization reversal can be achieved by electric field engineering in valleytronic bilayer *** the bilayer RuBr_(2)as an example,our proposal is confirmed by the first-principle *** FVM and VGS can be achieved in bilayer RuBr_(2)by applying electric *** appropriate electric field range,increasing electric field can enhance valley splitting,and the valley polarization can be reversed by flipping electric field *** effectively tune valley properties by electric field in bilayer systems,the parent monolayer should possess out-of-plane magnetization,and have large valley *** results shed light on the possible role of electric field in tuning valleytronic bilayer systems,and provide a way to design the ferrovalley-related material by electric field.

关键词： valleytronics electric field bilayer

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经典电路网络中奇异束缚态的实验观察

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Science Bulletin 2024年第14期69卷 2194-2204页

作者：邹德源陈天孟海瑜 yee sin ang 张向东李庆华 Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurements of Ministry of Education Beijing Key Laboratory of Nanophotonics and Ultrafine Optoelectronic SystemsSchool of PhysicsBeijing Institute of TechnologyBeijing 100081China School of Physics and Optoelectronics Xiangtan UniversityXiangtan 411105China Department of Physics National University of SingaporeSingapore 117542Singapore Science Mathematics and Technology ClusterSingapore University of Technology and DesignSingapore 487372Singapore Joint School of National University of singapore and Tianjin University International Campus of Tianjin UniversityFuzhou 350207China

Exceptional bound(EB)states represent a unique new class of robust bound states protected by the defectiveness of non-Hermitian exceptional *** distinct from the more well-known topological states and non-Hermitian skin states,they were recently discovered as a novel source of negative entanglement entropy in the quantum entanglement ***,EB states have been physically elusive,being originally interpreted as negative probability eigenstates of the propagator of nonHermitian Fermi *** this work,we show that EB states are in fact far more ubiquitous,also arising robustly in broad classes of systems whether classical or *** hinges crucially on a newlydiscovered spectral flow that rigorously justifies the EB nature of small candidate lattice *** a highlight,we present their first experimental realization through an electrical circuit,where they manifest as prominent stable resonant voltage *** work brings a hitherto elusive but fundamentally distinctive quantum phenomenon into the realm of classical metamaterials,and provides a novel pathway for the engineering of robust modes in otherwise sensitive systems..

关键词： Exceptional bound states Classical circuit network Non-Hermitian Robustness Exceptional point

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Physics of electron emission and injection in two-dimensional materials: Theory and simulation

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InfoMat 2021年第5期3卷 502-535页

作者： yee sin ang Liemao Cao Lay Kee ang Science Mathematics and Technology(SMT)Singapore University of Technology and Design(SUTD)SingaporeSingapore College of Physics and Electronic Engineering Hengyang Normal UniversityHengyangChina

Electrically contacting two-dimensional(2D)materials is an inevitable process in the fabrication of devices for both the study of fundamental nanoscale charge transport physics and the design of high-performance novel electronic and optoelectronic *** physics of electrical contact formation and interfacial charge injection critically underlies the performance,energyefficiency and the functionality of 2D-material-based devices,thus representing one of the key factors in determining whether 2D materials can be successfully implemented as a new material basis for the development of nextgeneration beyond-silicon solid-state device *** this review,the recent developments in the theory and the computational simulation of electron emission,interfacial charge injection and electrical contact formation in 2D material interfaces,heterostructures,and devices are *** on thermionic charge injection phenomena which are omnipresent in 2Dmaterials-based metal/semiconductor Schottky contacts,we summarize various transport models and scaling laws recently developed for 2D *** progress on the first-principle density functional theory simulation of 2D-material-based electrical contacts are also *** review aims to provide a crystalized summary on the physics of charge injection in the 2D Flatlands for bridging the theoretical and the experimental research communities of 2D material device physics and technology.

关键词： 2D material interfaces charge injection contact engineering heterostructures theory and simulations

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Nonlinear optical response of graphene in terahertz and near-infrared frequency regime

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Frontiers of Optoelectronics 2015年第1期8卷 3-26页

作者： yee sin ang Qinjun CHEN Chao ZHang School of Physics University of Wollongong New South Wales 2522 Australia Institute of Superconducting and Electronic Materials University of Wollongong New South Wales 2522 Australia

In this review, we discuss our recent theoretical work on the nonlinear optical response of graphene and its sister structure in terahertz （THz） and near-infrared frequency regime. Due to Dirac-like linear energymomentum dispersion, the third-order nonlinear current in graphene is much stronger than that in conventional semiconductors. The nonlinear current grows rapidly with increasing temperature and decreasing frequency. The third-order nonlinear current can be as strong as the linear current under moderate electric field strength of 104 V/cm. In bilayer graphene （BLG） with low energy trigonal warping effect, not only the optical response is strongly nonlinear, the optical nonlinearity is well-preserved at elevated temperature. In the presence ofa bandgap （such as semihydrogenated graphene （SHG））, there exists two well separated linear response and nonlinear response peaks. This suggests that SHG can have a unique potential as a two-color nonlinear material in the THz frequency regime where the relative intensity of the two colors can be tuned with the electric field. In a graphene superlattice structure of Kronig-Penney type periodic potential, the Dirac cone is elliptically deformed. We found that not only the optical nonlinearity is preserved in such a system, the total optical response is further enhanced by a factor proportional to the band anisotropy. This suggests that graphene superlattice is another potential candidate in THz device application.

关键词： graphene terahertz (THz) response nonlinear effect photomixing

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Broadband strong optical dichroism in topological Dirac semimetals with Fermi velocity anisotropy

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Chinese Physics B 2020年第7期29卷 128-134页

作者： J Lim K J A Ooi C Zhang L K ang yee sin ang Science Math and TechnologySingapore University of Technology and DesignSingapore School of Energy and Chemical Engineering Xiamen University MalaysiaSelangor Darul Ehsan 43900Malaysia College of Chemistry and Chemical Engineering Xiamen UniversityXiamen 361005China School of Physics University of WollongongNorthfields AvenueNew South Wales 2522Australia

Prototypical three-dimensional(3D)topological Dirac semimetals(DSMs),such as Cd3As2 and Na3Bi,contain electrons that obey a linear momentum-energy dispersion with different Fermi velocities along the three orthogonal momentum *** being extensively studied in recent years,the inherent Fermi velocity anisotropy has often been neglected in the theoretical and numerical studies of 3D *** this omission does not qualitatively alter the physics of light-driven massless quasiparticles in 3D DSMs,it does quantitatively change the optical coefficients which can lead to nontrivial implications in terms of nanophotonics and plasmonics *** we study the linear optical response of 3D DSMs for general Fermi velocity values along each *** the signature conductivity-frequency scaling,σ(ω)∝ω,of 3D Dirac fermion is well-protected from the Fermi velocity anisotropy,the linear optical response exhibits strong linear dichroism as captured by the universal extinction ratio scaling law,Λi j=(vi/v j)^2(where i=j denotes the three spatial coordinates x,y,z,and vi is the i-direction Fermi velocity),which is independent of frequency,temperature,doping,and carrier scattering *** Cd3As2 and Na3Bi3,an exceptionally strong extinction ratio larger than 15 and covering a broad terahertz window is *** findings shed new light on the role of Fermi velocity anisotropy in the optical response of Dirac semimetals and open up novel polarization-sensitive functionalities,such as photodetection and light modulation.

关键词： topological Dirac semimetal optical anisotropy linear dichroismn linear response theory

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Symmetry-driven half-integer conductance quantization in Cobalt–fulvalene sandwich nanowire

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npj Computational Materials 2023年第1期9卷 314-321页

作者： Zhuoling Jiang Kah-Meng Yam yee sin ang Na Guo Yongjie Zhang Hao Wang Chun Zhang Department of Physics and Centre for Advanced 2D Materials National University of SingaporeSingapore 117551Singapore Science Mathematics and Technology(SMT)ClusterSingapore University of Technology and DesignSingapore 487372Singapore Department of Chemistry National University of SingaporeSingapore 117543Singapore National University of singapore Chongqing Research Institute 401123 ChongqingChina

Precise manipulation and monitoring spin transport in one-dimensional (1D) systems is a long-sought goal in the field of nano-spintronics. Based on first-principles calculations, we report the observation of half-integer conductance quantization in the Cobalt-fulvalene sandwich nanowire. Compared with a pure monatomic Cobalt wire, the introduction of fulvalene molecules leads to threeimportant features: Firstly, the strong coupling between the fulvalene and the Cobalt prevents the contamination of the ambientair, ensuring both chemical and physical stabilities;Secondly, the fulvalene symmetry-selectively filters out most of the d-typeorbitals of the Cobalt while leaving a single d-type orbital to form an open spin channel around the Fermi level, which offers amechanism to achieve the observed half-integer conductance;Thirdly, it maintains a superexchange coupling between adjacent Coatoms to achieve a high Curie temperature. Spin transport calculations show that this half-metallic nanowire can serve as a perfectspin filter or a spin valve device, thus revealing the potential of Cobalt-fulvalene sandwich nanowire as a promising building blockof high-performance spintronics technology.

关键词： sandwich coupling transport

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Challenges and Opportunities in the Practice of Chinese Medicine in singapore

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Chinese Journal of Integrative Medicine 2024年第6期30卷 483-488页

作者： CHEW sin yee National University Hospital Singapore119074Singapore

According to the World Health Oranization(WHO)Traditional Medicine Strategy 2014-2023,traditional medicine is defined as"the sum total of the knowledge,skill and practices based on the theories,beliefs,and experiences indigenous to different cultures,whether explicable or not,used in the maintenance of health as well as in the prevention,diagnosis,improvement or treatment of physical and mental illness.

关键词： theories prevention diagnosis

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Design of an all-day electrical power generator based on thermoradiative devices

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Science China(Technological Sciences) 2021年第10期64卷 2166-2173页

作者： ZHang Xin Yang GuoFeng YAN MengQi ang Lay Kee ang yee sin CHEN JinCan School of Science Jiangnan UniversityWuxi 214122China Science Mathematics and TechnologySingapore University of Technology and DesignSingapore 487372Singapore Department of Physics Xiamen UniversityXiamen 361005China

Energy harvesting from sun and outer space using thermoradiative devices(TRDs),despite being promising renewable energy sources,is limited only to daytime and nighttime period,*** a system with 24-hour continuous electric power generation remains an open question thus ***,a TRD-based power generator that harvests solar energy via concentrated solar irradiation during daytime and via thermal infrared emission towards the outer space at nighttime is proposed,thus achieving the much sought-after 24-hour electrical power ***,a rigorous thermodynamical model is developed to investigate the all-day performance characteristics,parametric optimum design,and the role of various energy loss *** calculated results predict that the daytime TRD-based system yields a peak efficiency of 12.6%under 10 suns,thus sig-nificantly outperforming the state-of-art record-setting solar thermoelectric *** work reveals the potential of TRD towards 24-hour electricity generation and future renewable energy technology.

关键词： sustainable energy HgCdTe solar energy thermoradiative optimum design

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Age of onset of diabetes and all-cause mortality

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World Journal of Diabetes 2020年第4期11卷 95-99页

作者： Gary yee ang Health Services and Outcomes Research National Healthcare GroupSingapore 138543Singapore

Diabetes mellitus continues to present a large social,financial and health system burden across the *** relationship between age of onset of the different types of diabetes and all-cause mortality is *** this review paper,the relationship between age of onset of the different types of diabetes and all-cause mortality will be reviewed and an update of the current evidence will be *** is strong evidence of the relationship between age of onset of type 2 diabetes mellitus(T2 DM) and all-cause mortality,good evidence of the relationship between age of onset of T1 DM and all-cause mortality and no evidence of the relationship between age of onset of gestational diabetes or prediabetes and all-cause *** research is needed to look at whether aggressive management of earlier onset of T2 DM can help to reduce premature mortality.

关键词： Diabetes mellitus Age of onset Mortality Type 1 diabetes Type 2 diabetes Gestational diabetes Prediabetes

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Reversibility of diabetes mellitus: Narrative review of the evidence

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World Journal of Diabetes 2018年第7期9卷 127-131页

作者： Gary yee ang Health Services and Outcomes Research National Healthcare Group

The global disease burden of diabetes mellitus is high. It is well-established that prediabetes is reversible but it is unclear whether diabetes is reversible once it has been diagnosed. The objective of this narrative review is to review the evidence of reversibility of diabetes me-llitus and stimulate interest in prolonged remission as a treatment target. The current evidence for bariatric surgery is stronger than intensive medical management and the evidence is stronger for type 2 diabetes pa-tients compared with type 1 diabetes patients. It is also unclear whether non obese diabetes patients would benefit from such interventions and the duration of diabetes before diabetes become irreversible. Further research is needed in this area especially with regards to the subgroup of diabetes patient who will benefit from these interventions and the long term safety and efficacy remains unknown especially with intensive me-dical management.

关键词： Diabetes Reversibility Remission Bariatric surgery Obesity

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