Two-band model works well for Hall effect in topological insulators. It turns out to be non-Hermitian when the system is subjected to environments, and its topology characterized by Chern numbers has received extensiv...Two-band model works well for Hall effect in topological insulators. It turns out to be non-Hermitian when the system is subjected to environments, and its topology characterized by Chern numbers has received extensive studies in the past decades. However, how a non-Hermitian system responses to an electric field and what is the connection of the response to the Chern number defined via the non-Hermitian Hamiltonian remains barely explored. In this paper, focusing on a k-dependent decay rate, we address this issue by studying the response of such a non-Hermitian Chern insulator to an external electric field. To this aim, we first derive an effective non-Hermitian Hamiltonian to describe the system and give a specific form of k-dependent decay rate. Then we calculate the response of the non-Hermitian system to a constant electric field.We observe that the environment leads the Hall conductance to be a weighted integration of curvature of the ground band and hence the conductance is no longer quantized in general. And the environment induces a delay in the response of the system to the electric field. A discussion on the validity of the non-Hermitian model compared with the master equation description is also presented.展开更多
The development of electronic devices that possess the functionality of biological synapses is a crucial step towards neuromorphic computing.In this work,we present a WOx-based memristive device that can emulate volta...The development of electronic devices that possess the functionality of biological synapses is a crucial step towards neuromorphic computing.In this work,we present a WOx-based memristive device that can emulate voltage-dependent synaptic plasticity.By adjusting the amplitude of the applied voltage,we were able to reproduce short-term plasticity(STP)and the transition from STP to long-term potentiation.The stimulation with high intensity induced long-term enhancement of conductance without any decay process,thus representing a permanent memory behavior.Moreover,the image Boolean operations(including intersection,subtraction,and union)were also demonstrated in the memristive synapse array based on the above voltage-dependent plasticity.The experimental achievements of this study provide a new insight into the successful mimicry of essential characteristics of synaptic behaviors.展开更多
Single-phased,high-color-rendering index(CRI)white-light phosphors are emerging as potential phosphor-converted white-light-emitting diodes(WLEDs)and as an alternative to blends of tricolor phosphors.However,it is a c...Single-phased,high-color-rendering index(CRI)white-light phosphors are emerging as potential phosphor-converted white-light-emitting diodes(WLEDs)and as an alternative to blends of tricolor phosphors.However,it is a challenge to create a high CRI white light from a single-doped activator.Here,we present a high CRI(Ra 591)white-light phosphor,Sr_(5)(PO_(4))_(3-x)(BO_(3))_(x)Cl:Eu^(2+),composed of Sr5(PO4)3Cl as the beginning member and Sr_(5)(BO_(3))_(3)Cl as the end member.This work utilized the solid-solution method,and tunable Eu^(2+) emission was achieved.Color-tunable Eu^(2+) emissions in response to structural variation were observed in Sr_(5)(PO_(4))_(3-x)(BO_(3))_(x)Cl solid solutions.This was further confirmed using X-ray Rietveld refinement,electron paramagnetic resonance spectroscopy,and in the photoluminescence spectra.The color-tunable emissions included the white light that originated from the combination of the blue emission of Sr_(5)(PO_(4))_(3)Cl:Eu^(2+) and an induced Eu^(2+) yellow emission at approximately 550 nm in the solid solution.Importantly,the white-light phosphors showed a greater R9590.2 under excitation at 365 nm.This result has rarely been reported in the literature and is greater than that of(R9514.3)commercial Y_(3)A_(l5)O_(12):Ce^(3+)-based WLEDs.These findings demonstrate the great potential of Sr_(5)(PO_(4))_(3-x)(BO_(3))_(x)Cl:0.04Eu^(2+) as a white-light phosphor for near-UV phosphor-converted WLEDs.These results also provide a shortcut for developing a high CRI white-light phosphor from a single Eu^(2+)-doped compound.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 12175033 and 12147206)。
文摘Two-band model works well for Hall effect in topological insulators. It turns out to be non-Hermitian when the system is subjected to environments, and its topology characterized by Chern numbers has received extensive studies in the past decades. However, how a non-Hermitian system responses to an electric field and what is the connection of the response to the Chern number defined via the non-Hermitian Hamiltonian remains barely explored. In this paper, focusing on a k-dependent decay rate, we address this issue by studying the response of such a non-Hermitian Chern insulator to an external electric field. To this aim, we first derive an effective non-Hermitian Hamiltonian to describe the system and give a specific form of k-dependent decay rate. Then we calculate the response of the non-Hermitian system to a constant electric field.We observe that the environment leads the Hall conductance to be a weighted integration of curvature of the ground band and hence the conductance is no longer quantized in general. And the environment induces a delay in the response of the system to the electric field. A discussion on the validity of the non-Hermitian model compared with the master equation description is also presented.
基金the fund from Ministry of Science and Technology of China(Nos.2018YFE0118300 and 2019YFB2205100)the NSFC Program(Nos.11974072,51701037,51732003,51872043,51902048,61774031,61574031 and U19A2091)+4 种基金the“111”Project(No.B13013)the fund from Ministry of Education of China(No.6141A02033414)The fund from China Postdoctoral Science Foundation(No.2019M661185)The Fundamental Research Funds for the Central Universities(No.2412019QD015)the Fund from Jilin Province(JJKH20201163KJ).
文摘The development of electronic devices that possess the functionality of biological synapses is a crucial step towards neuromorphic computing.In this work,we present a WOx-based memristive device that can emulate voltage-dependent synaptic plasticity.By adjusting the amplitude of the applied voltage,we were able to reproduce short-term plasticity(STP)and the transition from STP to long-term potentiation.The stimulation with high intensity induced long-term enhancement of conductance without any decay process,thus representing a permanent memory behavior.Moreover,the image Boolean operations(including intersection,subtraction,and union)were also demonstrated in the memristive synapse array based on the above voltage-dependent plasticity.The experimental achievements of this study provide a new insight into the successful mimicry of essential characteristics of synaptic behaviors.
基金supported by theNational Natural Science Foundations of China(Grant No.51302034,11304035,51372036,31271442,and 91233204)the National Basic Research Program(2012CB933703)+2 种基金the Fundamental Research Funds for the Central Universities(Grant No.12QNJJ007,12SSXM001)the International Science&Technology Cooperation Program of China(2013DFG50150)111 project(No.B13013).
文摘Single-phased,high-color-rendering index(CRI)white-light phosphors are emerging as potential phosphor-converted white-light-emitting diodes(WLEDs)and as an alternative to blends of tricolor phosphors.However,it is a challenge to create a high CRI white light from a single-doped activator.Here,we present a high CRI(Ra 591)white-light phosphor,Sr_(5)(PO_(4))_(3-x)(BO_(3))_(x)Cl:Eu^(2+),composed of Sr5(PO4)3Cl as the beginning member and Sr_(5)(BO_(3))_(3)Cl as the end member.This work utilized the solid-solution method,and tunable Eu^(2+) emission was achieved.Color-tunable Eu^(2+) emissions in response to structural variation were observed in Sr_(5)(PO_(4))_(3-x)(BO_(3))_(x)Cl solid solutions.This was further confirmed using X-ray Rietveld refinement,electron paramagnetic resonance spectroscopy,and in the photoluminescence spectra.The color-tunable emissions included the white light that originated from the combination of the blue emission of Sr_(5)(PO_(4))_(3)Cl:Eu^(2+) and an induced Eu^(2+) yellow emission at approximately 550 nm in the solid solution.Importantly,the white-light phosphors showed a greater R9590.2 under excitation at 365 nm.This result has rarely been reported in the literature and is greater than that of(R9514.3)commercial Y_(3)A_(l5)O_(12):Ce^(3+)-based WLEDs.These findings demonstrate the great potential of Sr_(5)(PO_(4))_(3-x)(BO_(3))_(x)Cl:0.04Eu^(2+) as a white-light phosphor for near-UV phosphor-converted WLEDs.These results also provide a shortcut for developing a high CRI white-light phosphor from a single Eu^(2+)-doped compound.