Gate-field control of valley polarization in valleytronics

Valleytronics materials are a kind of special semiconductors which can host multiple symmetry-connected and wellseparated electron or hole pockets in the Brillouin zone when the system is slightly n or p doped. Since the low-energy particles residing in these pockets generally are not easily scattered to each other by small perturbations, they are endowed with an additional valley degree of freedom. Analogous to spin, the valley freedom can be used to process information,leading to the concept of valleytronics. The prerequisite for valleytronics is the generation of valley polarization. Thus,a focus in this field is achieving the electric generation of valley polarization, especially the static generation by the gate electric field alone. In this work, we briefly review the latest progress in this research direction, focusing on the concepts of the couplings between valley and layer, i.e., the valley–layer coupling which permits the gate-field control of the valley polarization, the couplings between valley, layer, and spin in magnetic systems, the physical properties, the novel designing schemes for electronic devices, and the material realizations of the gate-controlled valleytronics materials.

Technologies and applications of silicon-based micro-optical electromechanical systems:A brief review

Micro-optical electromechanical systems(MOEMS)combine the merits of micro-electromechanical systems(MEMS)and micro-optics to enable unique optical functions for a wide range of advanced applications.Using simple external electromechanical control methods,such as electrostatic,magnetic or thermal effects,Si-based MOEMS can achieve precise dynamic optical modulation.In this paper,we will briefly review the technologies and applications of Si-based MOEMS.Their basic working principles,advantages,general materials and micromachining fabrication technologies are introduced concisely,followed by research progress of advanced Si-based MOEMS devices,including micromirrors/micromirror arrays,micro-spectrometers,and optical/photonic switches.Owing to the unique advantages of Si-based MOEMS in spatial light modulation and high-speed signal processing,they have several promising applications in optical communications,digital light processing,and optical sensing.Finally,future research and development prospects of Si-based MOEMS are discussed.

Quantum search of many vertices on the joined complete graph

The quantum search on the graph is a very important topic.In this work,we develop a theoretic method on searching of single vertex on the graph[Phys.Rev.Lett.114110503(2015)],and systematically study the search of many vertices on one low-connectivity graph,the joined complete graph.Our results reveal that,with the optimal jumping rate obtained from the theoretical method,we can find such target vertices at the time O(√N),where N is the number of total vertices.Therefore,the search of many vertices on the joined complete graph possessing quantum advantage has been achieved.

Optimization of Light Field for Generation of Vortex Knot

The theory of knots and links focuses on the embedding mode of one or several closed curves in three-dimensional Euclidean space.In an electromagnetic field system,all-optical knots or links composed of phase or polarization singularities have been verified theoretically and experimentally.Recent studies have shown that robust topological all-optical coding can be achieved by using optical knots and links.However,in the current design of optical knots and links based on phase or polarization singularities,the amplitude of light between adjacent singularities is relatively weak.This brings great pressure to detection of optical knots and links and limits their applications.Here,we propose a new optimization method in theory.Compared with the existing design methods,our design method improves the relative intensity distribution of light between adjacent singularities.We verify the feasibility of our design results in experiments.Our study reduces the detection difficulty of optical knots and links,and has a positive significance for promotion of applications of optical knots and links.

Asymmetric Fraunhofer pattern in Josephson junctions from heterodimensional superlattice V_(5)S_(8)

Introduction of spin-orbit coupling(SOC)in a Josephson junction(JJ)gives rise to unusual Josephson effects.We investigate JJs based on a newly discovered heterodimensional superlattice V_(5)S_(8) with a special form of SOC.The unique homointerface of our JJs enables elimination of extrinsic effects due to interfaces and disorder.We observe asymmetric Fraunhofer patterns with respect to both the perpendicular magnetic field and the current.The asymmetry is influenced by an in-plane magnetic field.Analysis of the pattern points to a nontrivial spatial distribution of the Josephson current that is intrinsic to the SOC in V_(5)S_(8).

A general methodology to measure the light-to-heat conversion efficiency of solid materials

Light-to-heat conversion has been intensively investigated due to the potential applications including photothermal therapy and solar energy harvesting.As a fundamental property of materials,accurate measurement of light-to-heat conversion efficiency(LHCE)is of vital importance in developing advanced materials for photothermal applications.Herein,we report a photothermal and electrothermal equivalence(PEE)method to measure the LHCE of solid materials by simulating the laser heating process with electric heating process.The temperature evolution of samples during electric heating process was firstly measured,enabling us to derive the heat dissipation coefficient by performing a linear fitting at thermal equilibrium.The LHCE of samples can be calculated under laser heating with the consideration of heat dissipation coefficient.We further discussed the effectiveness of assumptions by combining the theoretical analysis and experimental measurements,supporting the obtained small error within 5%and excellent reproducibility.This method is versatile to measure the LHCE of inorganic nanocrystals,carbon-based materials and organic materials,indicating the applicability of a variety of materials.

Superchiral fields generated by nanostructures and their applications for chiral sensing

Chirality is ubiquitous in natural world.Although with similar physical and chemical properties,chiral enantiomers could play different roles in biochemical processes.Discrimination of chiral enantiomers is extremely important in biochemical,analytical chemistry,and pharmaceutical industries.Conventional chiroptical spectroscopic methods are disadvantageous at a limited detection sensitivity because of the weak signals of natural chiral molecules.Recently,superchiral fields were proposed to effectively enhance the interaction between light and molecules,allowing for ultrasensitive chiral detection.Intensive theoretical and experimental works have been devoted to generation of superchiral fields based on artificial nanostructures and their application in ultrasensitive chiral sensing.In this review,we present a survey on these works.We begin with the introduction of chiral properties of electromagnetic fields.Then,the optical chirality enhancement and ultrasensitive chiral detection based on chiral and achiral nanostructures are discussed respectively.Finally,we give a short summary and a perspective for the future ultrasensitive chiral sensing.

Correlated optical convolutional neural network with“quantum speedup”

Compared with electrical neural networks,optical neural networks(ONNs)have the potentials to break the limit of the bandwidth and reduce the consumption of energy,and therefore draw much attention in recent years.By far,several types of ONNs have been implemented.However,the current ONNs cannot realize the acceleration as powerful as that indicated by the models like quantum neural networks.How to construct and realize an ONN with the quantum speedup is a huge challenge.Here,we propose theoretically and demonstrate experimentally a new type of optical convolutional neural network by introducing the optical correlation.It is called the correlated optical convolutional neural network(COCNN).We show that the COCNN can exhibit“quantum speedup”in the training process.The character is verified from the two aspects.One is the direct illustration of the faster convergence by comparing the loss function curves of the COCNN with that of the traditional convolutional neural network(CNN).Such a result is compatible with the training performance of the recently proposed quantum convolutional neural network(QCNN).The other is the demonstration of the COCNN’s capability to perform the QCNN phase recognition circuit,validating the connection between the COCNN and the QCNN.Furthermore,we take the COCNN analog to the 3-qubit QCNN phase recognition circuit as an example and perform an experiment to show the soundness and the feasibility of it.The results perfectly match the theoretical calculations.Our proposal opens up a new avenue for realizing the ONNs with the quantum speedup,which will benefit the information processing in the era of big data.

Refractive index sensing based on a twisted nano-kirigami metasurface

Plasmonic sensing technology has attracted considerable attention for high sensitivity due to the ability to effectively localize and manipulate light.In this study,we demonstrate a refractive index(RI)sensing scheme based on open-loop twisted meta-molecule arrays using the versatile nano-kirigami principle.RI sensing has the features of a small footprint,flexible control,and simple preparation.By engineering the morphology of meta-molecules or the RI of the ambient medium,the chiral surface lattice resonances can be significantly enhanced,and the wavelength,intensity,and sign of circular dichroism(CD)can be flexibly tailored.Utilizing the relation between the wavelength of the CD peak and the RI of the superstrate,the RI sensor achieves a sensitivity of 1133 nm/RIU.Additionally,we analyze these chiroptical responses by performing electromagnetic multipolar decomposition and electric field distributions.Our study may serve as an ideal platform for applications of RI measurement and provide new insights into the manipulation of chiral light–matter interactions.

Electric-Circuit Realization of Fast Quantum Search

Quantum search algorithm,which can search an unsorted database quadratically faster than any known classical algorithms,has become one of the most impressive showcases of quantum computation.It has been implemented using various quantum schemes.Here,we demonstrate both theoretically and experimentally that such a fast search algorithm can also be realized using classical electric circuits.The classical circuit networks to perform such a fast search have been designed.It has been shown that the evolution of electric signals in the circuit networks is analogies of quantum particles randomly walking on graphs described by quantum theory.The searching efficiencies in our designed classical circuits are the same to the quantum schemes.Because classical circuit networks possess good scalability and stability,the present scheme is expected to avoid some problems faced by the quantum schemes.Thus,our findings are advantageous for information processing in the era of big data.

Cascaded multilayer nano-kirigami for extensible 3D nanofabrication and visible light manipulation

Nano-kirigami enables direct and versatile shape transformations from two-dimensional predesigns to threedimensional(3 D)architectures in microscale/nanoscale.Here a new and extensible strategy for cascaded multilayer nano-kirigami is demonstrated in a gold/silicon nitride(Au/SiN)bilayer nanofilm for 3 D nanofabrication and visible light manipulation.By employing a focused ion-beam-based Boolean irradiation,rich 3 D shape transformation and nested multilayer nanostructures are precisely manufactured,which are well reproduced by developing a modified mechanical model.Based on the multilayer and deformable features of the nano-kirigami structures,potentials in manipulating the phase and intensity of visible light are explored.The developed new nano-kirigami strategies,as well as the novel exotic 3 D nanostructures,could be helpful to build a novel platform for 3 D nanofabrication and find potential applications in microelectromechanical/nanoelectromechanical systems,holographic display,plasmonics,nanophotonics,biophotonics,etc.

量子自旋霍尔绝缘体Bi_(4)Br_(4)体与边缘的可区分的光学性质研究

量子自旋霍尔绝缘体拥有具有带隙的体态和无能隙的一维拓扑边缘态.然而,由于拓扑边缘态局域在纳米尺度,所以很难用光学手段直接观测并区分体态和边缘态,这就限制了对拓扑边缘态独特的光学特性和光电响应等方面的研究和应用.Bi_(4)Br_(4)体材料的台阶存在一维非平庸的边缘态,多个台阶累加的效应使得通过较为宏观的光学和光电分析手段来研究一维边缘态成为可能.该工作利用中远红外显微吸收光谱和泵浦探测光谱,对比研究了Bi_(4)Br_(4)体和边缘的光学响应行为.研究发现Bi_(4)Br_(4)的边缘在小于带隙(约0.22 eV)的波段存在明显的强于体内的红外吸收,且该吸收呈现较强的各向异性.室温下的红外泵浦探测首次观察到边缘处载流子激发态超长的弛豫时间(1.5 ns),该激发态载流子寿命要比体内载流子寿命长两个量级.该工作证实体态和拓扑边缘态具有明显不同的光学和光电响应行为,为未来设计新型红外探测器提供了材料和物理基础.

Low-threshold topological nanolasers based on the second-order corner state

Topological lasers are immune to imperfections and disorder.They have been recently demonstrated based on many kinds of robust edge states,which are mostly at the microscale.The realization of 2D on-chip topological nanolasers with a small footprint,a low threshold and high energy efficiency has yet to be explored.Here,we report the first experimental demonstration of a topological nanolaser with high performance in a 2D photonic crystal slab.A topological nanocavity is formed utilizing the Wannier-type 0D corner state.Lasing behaviour with a low threshold of approximately 1μW and a high spontaneous emission coupling factor of 0.25 is observed with quantum dots as the active material.Such performance is much better than that of topological edge lasers and comparable to that of conventional photonic crystal nanolasers.Our experimental demonstration of a low-threshold topological nanolaser will be of great significance to the development of topological nanophotonic circuitry for the manipulation of photons in classical and quantum regimes.

(C_(16)H_(28)N)_(2)SbCl_(5):一种具有亮橙色发射的新型无铅零维金属卤化物杂化物

零维金属卤化物因其迷人的光电特性而处于蓬勃发展的状态.本文报道了一种(C_(16)H_(28)N)_(2)SbCl_(5)(C_(16)H_(28)N+=苄基三丙基铵阳离子)的锑基金属卤化物,其中孤立的[SbCl_(5)]2−团簇被C_(16)H_(28)N+包围,形成零维方形金字塔结构.(C_(16)H_(28)N)_(2)SbCl_(5)在低能辐照(400 nm)时在633 nm处呈现宽带橙色发射,具有97.8%的近单位光致发光量子效率.有趣的是,(C_(16)H_(28)N)_(2)SbCl_(5)在高能辐照(300 nm)时在477 nm处显示出一个额外的发射峰,这是由自旋-轨道耦合的二重态转变为两个独立的自束缚激子形成的.变温拉曼光谱显示了多声子耦合的特征,这证明(C_(16)H_(28)N)_(2)-SbCl_(5)中存在强烈的非谐性电子-声子相互作用.变温发射光谱和密度泛函理论计算表明,所观察到的双峰发射源于[SbCl_(5)]2−单元中的单重态和三重态自束缚激子.结合(C_(16)H_(28)N)_(2)SbCl_(5)的高效发光和优异的稳定性,我们还制备了超高显色指数为96.6的稳定白光发光二极管.

Reconfigurable nano-kirigami metasurfaces by pneumatic pressure

Tunable/reconfigurable metasurfaces that can actively control electromagnetic waves upon external stimuli are of great importance for practical applications of metasurfaces.Here,we demonstrate a reconfigurable nano-kirigami metasurface driven by pneumatic pressure operating in the near-infrared wavelength region.The metasurfaces consist of combined Archimedean spirals and are fabricated in a free-standing gold/silicon nitride nanofilm by employing focused ion beam(FIB)lithography.The deformable spirals are instantly transformed from two dimensional(2 D)to three-dimensional(3 D)by the FIB-based nano-kirigami process.The 2 D–to–3 D transformation induces a dramatic irreversible change of the plasmonic quadruple modes and results in significant modulation in reflection by 137%.The suspended porous nano-kirigami metasurface is further integrated with an optofluidics device,with which the optical resonance is reversibly modulated by the pneumatic pressure.This work provides a strategy for tunable/reconfigurable metasurfaces,which are useful to build a promising lab-ona-chip platform for microfluidics,biological diagnostics,chemical sensing,and pressure monitoring.

Dual-Color Lasing Lines from EMPs in Diluted MagneticSemiconductor CdS:NiI Structure

Have one ever seen a semiconductor that can issue two-color lasing lines? The diluted magnetic semiconductor (DMS) can do this.Here, we have observed dual lasing lines of 530 nm and 789 nm from a DMS structure of CdS:NiI, in which the excitonic magneticpolaron (EMP) and localized excitonic magnetic polaron (LEMP) are excitations out of ferromagnetic (NiS)x nanocluster and NiI2nanoclusters within CdS lattice;both of them could lead to the collective EMP state at high excitation and therein produce coherentemission lines simultaneously. This occurrence is due to the superposition of EMP near CdS bandedge and the combination of thecharge-transfer band of (NiI)n cluster with the LEMP within CdS lattice by overcoming the strong electron correlation of NiI clusterin a DMS structure, evidenced also by ab initio calculation. This finding opens a way to understand the collective behaviour of spincoupled excitons in DMS and to find novel applications in the spin-related quantum technology.