In order to investigate the influence of different heavy metal ions on the formation of the oxyfluoride glasses and glass ceramics, samples with different Pb F2/Cd F2 ratios have been prepared by the melting quenching...In order to investigate the influence of different heavy metal ions on the formation of the oxyfluoride glasses and glass ceramics, samples with different Pb F2/Cd F2 ratios have been prepared by the melting quenching and thermal treatment method. The different effects of Pb2 tand Cd2ton the glass network structure are investigated by FTIR and Raman spectra. During the formation of glass network structure, Pb2 tprefers to break the Sie Oe Si bond and subsequently bond to F for charge compensation, and Cd2 tprefers to break the SieO eA l bond and is surrounded by O2. Pb2 tand F gather together and form the fluoride nanocrystals,while Cd2 tremains in oxide matrix after thermal treatment. Introduction of proper Cd F2 is important to adjust and control the glass network structure and crystallization process in the fabrication of the transparent glass ceramics.展开更多
Developing moisture-sensitive artificial muscles from industrialized natural fibers with large abundance is highly desired for smart textiles that can respond to humidity or temperature change.However,currently most o...Developing moisture-sensitive artificial muscles from industrialized natural fibers with large abundance is highly desired for smart textiles that can respond to humidity or temperature change.However,currently most of fiber artificial muscles are based on non-common industrial textile materials or of a small portion of global textile fiber market.In this paper,we developed moisture-sensitive torsional artificial muscles and textiles based on cotton yarns.It was prepared by twisting the cotton yarn followed by folding in the middle point to form a self-balanced structure.The cotton yarn muscle showed a torsional stroke of 42.55°/mm and a rotational speed of 720 rpm upon exposure to water moisture.Good reversibility and retention of stroke during cyclic exposure and removal of water moisture were obtained.A moisturesensitive smart window that can close when it rains was demonstrated based on the torsional cotton yarn muscles.This twist-based technique combining natural textile fibers provides a new insight for construction of smart textile materials.展开更多
We present a detailed analysis on mode evolution of gratingcoupled surface plasmonic polaritons （SPPs） on a conical metal tip based on the guidedwave theory. The eigenvalue equations for SPPs modes are discussed, re...We present a detailed analysis on mode evolution of gratingcoupled surface plasmonic polaritons （SPPs） on a conical metal tip based on the guidedwave theory. The eigenvalue equations for SPPs modes are discussed, revealing that cylindrical metal waveguides only support TM01 and HEm1 surface modes. During propagation on the metal tip, the gratingcoupled SPPs are converted to HE31, HE21, HE11 and TM01 successively, and these modes are sequentially cut off except TM01. The TM01 mode further propagates with drastically increasing effective mode index and is converted to localized surface plasmons （LSPs） at the tip apex, which is responsible for plasmonic nanofocusing. The gapmode plasmons can be excited with the focusing TM01 mode by approaching a metal substrate to the tip apex, resulting in further enhanced electric field and reduced size of the plasmonic focus.展开更多
Twisted bilayer graphene(TBG),which has drawn much attention in recent years,arises from van der Waals materials gathering each component together via van der Waals force.It is composed of two sheets of graphene rotat...Twisted bilayer graphene(TBG),which has drawn much attention in recent years,arises from van der Waals materials gathering each component together via van der Waals force.It is composed of two sheets of graphene rotated relatively to each other.Moirépotential,resulting from misorientation between layers,plays an essential role in determining the band structure of TBG,which directly relies on the twist angle.Once the twist angle approaches a certain critical value,flat bands will show up,indicating the suppression of kinetic energy,which significantly enhances the importance of Coulomb interaction between electrons.As a result,correlated states like correlated insulators emerge from TBG.Surprisingly,superconductivity in TBG is also reported in many experiments,which drags researchers into thinking about the underlying mechanism.Recently,the interest in the atomic reconstruction of TBG at small twist angles comes up and reinforces further understandings of properties of TBG.In addition,twisted multilayer graphene receives more and more attention,as they could likely outperform TBG although they are more difficult to handle experimentally.In this review,we mainly introduce theoretical and experimental progress on TBG.Besides the basic knowledge of TBG,we emphasize the essential role of atomic reconstruction in both experimental and theoretical investigations.The consideration of atomic reconstruction in small-twist situations can provide us with another aspect to have an insight into physical mechanism in TBG.In addition,we cover the recent hot topic,twisted multilayer graphene.While the bilayer situation can be relatively easy to resolve,multilayer situations can be really complicated,which could foster more unique and novel properties.Therefore,in the end of the review,we look forward to future development of twisted multilayer graphene.展开更多
Although abundant research on the anisotropy of van der Waals(vd W)materials has been published,we undertake an in-depth study of their optical properties as they have an important guiding role for light control in tw...Although abundant research on the anisotropy of van der Waals(vd W)materials has been published,we undertake an in-depth study of their optical properties as they have an important guiding role for light control in two-dimensional(2D)nanospace.As an example,we study the reflectance of few-layered black phosphorus(BP)in the total internal reflection(TIR)mode in detail.We demonstrate that its optical anisotropy can be changed on a large scale by varying the incident angles,polarization states,and the in-plane rotation angles of the BP samples.Theoretical analysis indicates that the phenomena observed are common to all the atom-thick biaxial crystals,so these conclusions can be widely applied to other anisotropic 2D materials.This research furthers the current understanding of the properties of BP more comprehensively,and provides guidance for developing new optoelectronic applications,especially when BP and other atom-thick biaxial crystals are integrated with TIR devices.展开更多
Photonic analogs of the moirésuperlattices mediated by interlayer electromagnetic coupling are expected to give rise to rich phenomena,such as nontrivial flatband topology.Here,we propose and demonstrate a scheme...Photonic analogs of the moirésuperlattices mediated by interlayer electromagnetic coupling are expected to give rise to rich phenomena,such as nontrivial flatband topology.Here,we propose and demonstrate a scheme to tune the flatbands in a bilayer moirésuperlattice by employing a band offset.The band offset is changed by fixing the bands of one slab while shifting those of the other slab,which is accomplished by modifying the thickness of the latter slab.Our results show that the band-offset tuning not only makes some flatbands emerge and disappear but also leads to two sets of flatbands that are robustly formed even with the change of band offset over a broad range.These robust flatbands form either at the AA-stack site or at the AB-stack site,and as a result,a single-cell superlattice can support a pair of high-quality localized modes with tunable frequencies.Moreover,we develop a diagrammatic model to provide an intuitive insight into the formation of the robust flatbands.Our work demonstrates a simple yet efficient way to design and control complex moiréflatbands,providing new opportunities to utilize photonic moirésuperlattices for advanced light–matter interaction,including lasing and nonlinear harmonic generation.展开更多
Ultraviolet blood irradiation has been used as a physical therapy to treat many nonspeci¯c diseases in clinics;however,the underlying mechanisms remain largely unclear.Neutrophils,the first line of host defense,p...Ultraviolet blood irradiation has been used as a physical therapy to treat many nonspeci¯c diseases in clinics;however,the underlying mechanisms remain largely unclear.Neutrophils,the first line of host defense,play a crucial role in a variety of in°ammatory responses.In the present work,we investigated the effects of ultraviolet light A(UVA)on the immune functions of human neutrophils at the single-cell level by using an inverted°uorescence microscope.N-Formylmethionyl-leucyl-phenylalanine(FMLP),a classic physiological chemotactic peptide,was used to induce a series of immune responses in neutrophils in vitro.FMLP-induced calcium mobilization,migration,and phagocytosis in human neutrophils was significantly blocked after treatment with 365 nm UVA irradiation,demonstrating the immunosuppressive effects of UVA irradiation on neutrophils.Similar responses were also observed when the cells were pretreated with H2O2,a type of reactive oxygen species(ROS).Furthermore,UVA irradiation resulted in an increase in NAD(P)H,a member of host oxidative stress in cells.Taken together,our data indicate that UVA irradiation results in immunosuppression associated with the production of ROS in human neutrophils.展开更多
Vortices are among nature’s most elegant manifestations of order within motion.They appear wherever flow meets rotation—from the microscopic whirlpools of quantum fluids and living cells to the cosmic spirals of gal...Vortices are among nature’s most elegant manifestations of order within motion.They appear wherever flow meets rotation—from the microscopic whirlpools of quantum fluids and living cells to the cosmic spirals of galaxies.Across these vastly different scales,the essence remains the same:a circulating current wrapped around a singularity.In both classical and quantum realms,vortices carrying orbital angular momentum(OAM)have emerged as a unifying concept,realized with photons,electrons,and even cold atoms and molecules.These quantized whirlpools of phase have illuminated fundamental aspects of angular momentum,topology,and coherence,while driving applications in optical manipulation,communications,and quantum information.展开更多
Twist-and-stack engineering provides a programmable degree of freedom for nonlinear optics in two-dimensional materials,yet in a homostructure whose constituents have no second harmonic generation(SHG),how interlayer ...Twist-and-stack engineering provides a programmable degree of freedom for nonlinear optics in two-dimensional materials,yet in a homostructure whose constituents have no second harmonic generation(SHG),how interlayer coupling grants and tunes second-order response remains unclear.Here,we use twisted monolayer-bilayer graphene(t(1+2)LG)and combine microscopic SHG spectroscopy with first-principles differential charge-density analysis to establish a unified"permission-and-resonance"mechanism.Interlayer coupling creates an interlayer charge imbalance within the AB-stacked bilayer,breaking inversion symmetry and thereby permitting an in-plane electric-dipole response.At the same time,the twist angle steers van Hove singularities in the band structure to achieve two-photon resonance,which markedly amplifies the susceptibilityχ^((2)).Experimentally,atθ=13.5°,we obtainχ^((2))=279.4 pm/V,evidencing a highly efficient second-order response.These results identify SHG as a sensitive probe of interlayer coupling and charge redistribution in homostructure van der Waals systems.展开更多
Cobalt-based(Co-based)alloys are widely used in aerospace and machinery applications because of their excellent mechanical properties,where extraordinary wear performance is also desirable to ensure stable operation.H...Cobalt-based(Co-based)alloys are widely used in aerospace and machinery applications because of their excellent mechanical properties,where extraordinary wear performance is also desirable to ensure stable operation.However,there is still scarce information on the tribological mechanism of the cobalt metal building block,especially under different humidities.Insight into the wear mechanism of Co under different humidities is crucial for studying the tribological performance of Co-based alloys as well as their potential applications under various working conditions.Here,we report an investigation of the effect of humidity on the wear behavior of Co.The results revealed that Co exhibited ultralow wear characteristics in a humid air environment(relative humidity(RH)70%),with a wear rate of 2.15×10^(-7)mm^(3)/(N·m),and dramatically increased by three orders of magnitude to 1.47×10^(-4)mm^(3)/(N·m)in the dry environment(~5%RH).Surface analysis revealed that tribochemistry dominated the whole wearing process,with the worn surface almost fully covered by cobalt oxide,Co3O4,when subjected to a humid environment,whereas a small number of oxide layers were observed only within the wear grooves under the RH 5%testing condition.The stripe test results revealed the evolution of this protective oxide generation,and the focused ion beam scanning electron microscopy(FIB-SEM)images of the cross-sections at different sliding stages revealed the role of tribochemistry in triggering such self-protection behavior.Our work provides a fundamental understanding of the wear mechanisms of Co metal,and we anticipate that these findings can offer valuable guidance for further improving the wear performance of cobalt-based alloys in the future.展开更多
Flatbands are of significant interest due to their potential for strong energy confinement and their ability to facilitate strongly correlated physics such as unconventional superconductivity and fractional quantum Ha...Flatbands are of significant interest due to their potential for strong energy confinement and their ability to facilitate strongly correlated physics such as unconventional superconductivity and fractional quantum Hall states.When topology is incorporated into flatband systems,it further enhances flatband mode robustness against perturbations.We present the first realization of doubly degenerate topological flatbands of edge states in chiral-symmetric strained graphene.The flatband degeneracy stems from the merging of Dirac points,achieved by tuning the coupling ratios in a honeycomb lattice with newly discovered twig boundary conditions.The topology of these modes is characterized by the nontrivial winding number,which ensures their robustness against disorder.Experimentally,two types of topological edge states are observed in a strained photonic graphene lattice,consistent with numerical simulations.Moreover,the degeneracy of the topological flatbands doubles the density of states for zero-energy modes,facilitating the formation of compact edge states and providing greater control over edge states and light confinement.Our findings underscore the interplay among lattice geometry,symmetry,and topology in shaping doubly degenerate topological flatbands.This work opens new possibilities for advancements in correlated effects,nonlinear optical phenomena,and efficient energy transfer in materials science,photonic crystals,and quantum devices.展开更多
Links and knots are exotic topological structures that have garnered significant interest across multiple branches of natural sciences.Coherent links and knots,such as those constructed by phase or polarization singul...Links and knots are exotic topological structures that have garnered significant interest across multiple branches of natural sciences.Coherent links and knots,such as those constructed by phase or polarization singularities of coherent light,have been observed in various three-dimensional optical settings.However,incoherent links and knots—knotted or connected lines of coherence singularities—arise from a fundamentally different concept.They are"hidden"in the statistic properties of a randomly fluctuating field,making their presence often elusive or undetectable.Here,we theoretically construct and experimentally demonstrate such topological entities of incoherent light.By leveraging a state-of-the-art incoherent modal-decomposition scheme,we unveil incoherent topological structures from fluctuating light speckles,including Hopf links and Trefoil knots of coherence singularities that are robust against coherence and intensity fluctuations.Our work is applicable to diverse wave systems where incoherence or practical coherence is prevalent,and may pave the way for design and implementation of statistically-shaped topological structures for various applications such as high-dimensional optical information encoding and optical communications.展开更多
Autofocusing beams are powerful photonic tools for manipulating micro/nanoparticles.Here,we propose a special type of dislocated-superimposed swallowtail vortex beam(DSVB)and analyze its propagation properties and opt...Autofocusing beams are powerful photonic tools for manipulating micro/nanoparticles.Here,we propose a special type of dislocated-superimposed swallowtail vortex beam(DSVB)and analyze its propagation properties and optical manipulating capability.By modulating the parameters of the superposition number N and the topological charge l,DSVBs show asymmetric autofocusing propagation phenomena and unconventional orbital angular momentum(OAM),especially for opposite topological charges.Furthermore,when N=|l|,DSVBs form multiple solid focuses while preserving OAM during propagation,suggesting potential applications in multi-point trapping and rotational manipulation.These results deepen the understanding of autofocusing and OAM behaviors,highlighting DSVBs'potential as photonic tools for optical manipulation.展开更多
Crystalline lithium niobate(LN)is an important optical material because of its broad transmission window that spans from ultraviolet to mid-infrared and its large nonlinear and electro-optic coefficients.Furthermore,t...Crystalline lithium niobate(LN)is an important optical material because of its broad transmission window that spans from ultraviolet to mid-infrared and its large nonlinear and electro-optic coefficients.Furthermore,the recent development and commercialization of LN-on-insulator(LNOI)technology has opened an avenue for the realization of integrated on-chip photonic devices with unprecedented performances in terms of propagation loss,optical nonlinearity,and electro-optic tunability.This review begins with a brief introduction of the history and current status of LNOI photonics.We then discuss the fabrication techniques of LNOI-based photonic structures and devices.The recent revolution in the LN photonic industry has been sparked and is still being powered by innovations of the nanofabrication technology of LNOI,which enables the production of building block structures,such as optical microresonators and waveguides of unprecedented optical qualities.The following sections present various on-chip LNOI devices categorized into nonlinear photonic and electro-optic tunable devices and photonic-integrated circuits.Some conclusions and future perspectives are provided.展开更多
Many applications of metasurfaces require an ability to dynamically change their properties in the time domain. Electrical tuning techniques are of particular interest, since they pave a way to on-chip integration of ...Many applications of metasurfaces require an ability to dynamically change their properties in the time domain. Electrical tuning techniques are of particular interest, since they pave a way to on-chip integration of metasurfaces with optoelectronic devices.In this work, we propose and experimentally demonstrate an electro-optic lithium niobate(EO-LN) metasurface that shows dynamic modulations to phase retardation of transmitted light. Quasi-bound states in the continuum(QBIC) are observed from this metasurface. By applying external electric voltages, the refractive index of lithium niobate(LN) is changed by Pockels EO nonlinearity, leading to efficient phase modulations to the transmitted light around the QBIC wavelength. The EO-LN metasurface developed in this study opens up new routes for potential applications in the field of displaying, pulse shaping, and spatial light modulating.展开更多
Optical activity is the rotation of the plane of linearly polarized light along the propagation direction as the light travels through optically active materials.In existing methods,the strength of the optical activit...Optical activity is the rotation of the plane of linearly polarized light along the propagation direction as the light travels through optically active materials.In existing methods,the strength of the optical activity is determined by the chirality of the materials,which is difficult to control quantitatively.Here we numerically and experimentally investigated an alternative approach to realize and control the optical activity with non-chiral plasmonic metasurfaces.Through judicious design of the structural units of the metasurfaces,the right and left circular polarization components of the linearly polarized light have different phase retardations after transmitting through the metasurfaces,leading to large optical activity.Moreover,the strength of the optical activity can be easily and accurately tuned by directly adjusting the phase difference.The proposed approach based on non-chiral plasmonic metasurfaces exhibits large optical activity with a high controllable degree of freedom,which may provide more possibilities for applications in photonics.展开更多
The synergy of a plasmonic tip and fiber-based structure light field excitation can provide a powerful tool for Raman examination. Here, we present a method of Raman spectrum enhancement with an Ag-nanoparticles(Ag-NP...The synergy of a plasmonic tip and fiber-based structure light field excitation can provide a powerful tool for Raman examination. Here, we present a method of Raman spectrum enhancement with an Ag-nanoparticles(Ag-NPs)-coated fiber probe internally excited via an azimuthal vector beam(AVB), which is directly generated in a few-mode fiber by using an acoustically induced fiber grating. Theoretical analysis shows that gap mode can be effectively generated on the surface of the Ag-NPs-coated fiber probe excited via an AVB. The experimental result shows that the intensity of Raman signal obtained with analyte molecules of malachite green by exciting the Ag-NPs-coated fiber probe via an AVB is approximately eight times as strong as that via the linear polarization beam(LPB), and the activity of the AVB-excited fiber probe can reach 10^-11 mol∕L, which cannot be achieved by LPB excitation.Moreover, the time stability and reliability are also examined, respectively.展开更多
The orbital degrees of freedom play a pivotal role in understanding fundamental phenomena in solid-state materials as well as exotic quantum states of matter including orbital superfluidity and topological semimetals....The orbital degrees of freedom play a pivotal role in understanding fundamental phenomena in solid-state materials as well as exotic quantum states of matter including orbital superfluidity and topological semimetals.Despite tremendous efforts in engineering synthetic cold-atom,as well as electronic and photonic lattices to explore orbital physics,thus far high orbitals in an important class of materials,namely,higher-order topological insulators(HOTIs),have not been realized.Here,we demonstrate p-orbital corner states in a photonic HOTI,unveiling their underlying topological invariant,symmetry protection,and nonlinearity-induced dynamical rotation.In a Kagome-type HOTI,we find that the topological protection of p-orbital corner states demands an orbital-hopping symmetry in addition to generalized chiral symmetry.Due to orbital hybridization,nontrivial topology of the p-orbital HOTI is“hidden”if bulk polarization is used as the topological invariant,but well manifested by the generalized winding number.Our work opens a pathway for the exploration of intriguing orbital phenomena mediated by higher-band topology applicable to a broad spectrum of systems.展开更多
Ellipsometry is a powerful method for determining both the optical constants and thickness of thin films.For decades,solutions to ill-posed inverse ellipsometric problems require substantial human-expert intervention ...Ellipsometry is a powerful method for determining both the optical constants and thickness of thin films.For decades,solutions to ill-posed inverse ellipsometric problems require substantial human-expert intervention and have become essentially human-in-the-loop trial-and-error processes that are not only tedious and time-consuming but also limit the applicability of ellipsometry.Here,we demonstrate a machine learning based approach for solving ellipsometric problems in an unambiguous and fully automatic manner while showing superior performance.The proposed approach is experimentally validated by using a broad range of films covering categories of metals,semiconductors,and dielectrics.This method is compatible with existing ellipsometers and paves the way for realizing the automatic,rapid,high-throughput optical characterization of films.展开更多
Higher-order topological insulators(HOTIs)are recently discovered topological phases,possessing symmetry-protected corner states with fractional charges.An unexpected connection between these states and the seemingly ...Higher-order topological insulators(HOTIs)are recently discovered topological phases,possessing symmetry-protected corner states with fractional charges.An unexpected connection between these states and the seemingly unrelated phenomenon of bound states in the continuum(BICs)was recently unveiled.When nonlinearity is added to the HOTI system,a number of fundamentally important questions arise.For example,how does nonlinearity couple higher-order topological BICs with the rest of the system,including continuum states?In fact,thus far BICs in nonlinear HOTIs have remained unexplored.Here we unveil the interplay of nonlinearity,higher-order topology,and BICs in a photonic platform.We observe topological corner states that are also BICs in a laser-written second-order topological lattice and further demonstrate their nonlinear coupling with edge(but not bulk)modes under the proper action of both self-focusing and defocusing nonlinearities.Theoretically,we calculate the eigenvalue spectrum and analog of the Zak phase in the nonlinear regime,illustrating that a topological BIC can be actively tuned by nonlinearity in such a photonic HOTI.Our studies are applicable to other nonlinear HOTI systems,with promising applications in emerging topology-driven devices.展开更多
基金supported by the National Science Fund for Talent Training in Basic Sciences (No. J1103208)
文摘In order to investigate the influence of different heavy metal ions on the formation of the oxyfluoride glasses and glass ceramics, samples with different Pb F2/Cd F2 ratios have been prepared by the melting quenching and thermal treatment method. The different effects of Pb2 tand Cd2ton the glass network structure are investigated by FTIR and Raman spectra. During the formation of glass network structure, Pb2 tprefers to break the Sie Oe Si bond and subsequently bond to F for charge compensation, and Cd2 tprefers to break the SieO eA l bond and is surrounded by O2. Pb2 tand F gather together and form the fluoride nanocrystals,while Cd2 tremains in oxide matrix after thermal treatment. Introduction of proper Cd F2 is important to adjust and control the glass network structure and crystallization process in the fabrication of the transparent glass ceramics.
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFB0307001)the National Natural Science Foundation of China(Grant Nos.U1533122 and 51773094)+4 种基金the Natural Science Foundation of Tianjin,China(Grant No.18JCZDJC36800)the Science Foundation for Distinguished Young Scholars of Tianjin,China(Grant No.18JCJQJC46600)the Fundamental Research Funds for the Central Universities,China(Grant No.63171219)Key Laboratory for Medical Data Analysis and Statistical Research of TianjinState Key Laboratory for Modification of Chemical Fibers and Polymer Materials,Donghua University(Grant No.LK1704)。
文摘Developing moisture-sensitive artificial muscles from industrialized natural fibers with large abundance is highly desired for smart textiles that can respond to humidity or temperature change.However,currently most of fiber artificial muscles are based on non-common industrial textile materials or of a small portion of global textile fiber market.In this paper,we developed moisture-sensitive torsional artificial muscles and textiles based on cotton yarns.It was prepared by twisting the cotton yarn followed by folding in the middle point to form a self-balanced structure.The cotton yarn muscle showed a torsional stroke of 42.55°/mm and a rotational speed of 720 rpm upon exposure to water moisture.Good reversibility and retention of stroke during cyclic exposure and removal of water moisture were obtained.A moisturesensitive smart window that can close when it rains was demonstrated based on the torsional cotton yarn muscles.This twist-based technique combining natural textile fibers provides a new insight for construction of smart textile materials.
基金This work was financially supported by the National Natural Science Foundation of China （NSFC） （61675169, 61377055 and 11634010）, the National Key R＆D Program of China （2017YFA0303800）, and the Fundamental Research Funds for the Central Universities （3102017zy021, 3102017HQZZ 022）.
文摘We present a detailed analysis on mode evolution of gratingcoupled surface plasmonic polaritons （SPPs） on a conical metal tip based on the guidedwave theory. The eigenvalue equations for SPPs modes are discussed, revealing that cylindrical metal waveguides only support TM01 and HEm1 surface modes. During propagation on the metal tip, the gratingcoupled SPPs are converted to HE31, HE21, HE11 and TM01 successively, and these modes are sequentially cut off except TM01. The TM01 mode further propagates with drastically increasing effective mode index and is converted to localized surface plasmons （LSPs） at the tip apex, which is responsible for plasmonic nanofocusing. The gapmode plasmons can be excited with the focusing TM01 mode by approaching a metal substrate to the tip apex, resulting in further enhanced electric field and reduced size of the plasmonic focus.
文摘Twisted bilayer graphene(TBG),which has drawn much attention in recent years,arises from van der Waals materials gathering each component together via van der Waals force.It is composed of two sheets of graphene rotated relatively to each other.Moirépotential,resulting from misorientation between layers,plays an essential role in determining the band structure of TBG,which directly relies on the twist angle.Once the twist angle approaches a certain critical value,flat bands will show up,indicating the suppression of kinetic energy,which significantly enhances the importance of Coulomb interaction between electrons.As a result,correlated states like correlated insulators emerge from TBG.Surprisingly,superconductivity in TBG is also reported in many experiments,which drags researchers into thinking about the underlying mechanism.Recently,the interest in the atomic reconstruction of TBG at small twist angles comes up and reinforces further understandings of properties of TBG.In addition,twisted multilayer graphene receives more and more attention,as they could likely outperform TBG although they are more difficult to handle experimentally.In this review,we mainly introduce theoretical and experimental progress on TBG.Besides the basic knowledge of TBG,we emphasize the essential role of atomic reconstruction in both experimental and theoretical investigations.The consideration of atomic reconstruction in small-twist situations can provide us with another aspect to have an insight into physical mechanism in TBG.In addition,we cover the recent hot topic,twisted multilayer graphene.While the bilayer situation can be relatively easy to resolve,multilayer situations can be really complicated,which could foster more unique and novel properties.Therefore,in the end of the review,we look forward to future development of twisted multilayer graphene.
基金supported by the K. C. Wong Education Foundation (GJTD-2018-08)the Natural Science Foundation of China (NSFC) (Grants 11804334, 51705192)+1 种基金the China Postdoctoral Science Foundation (2017M611325)the National Postdoctoral Program for Innovative Talents (BX201600064)
文摘Although abundant research on the anisotropy of van der Waals(vd W)materials has been published,we undertake an in-depth study of their optical properties as they have an important guiding role for light control in two-dimensional(2D)nanospace.As an example,we study the reflectance of few-layered black phosphorus(BP)in the total internal reflection(TIR)mode in detail.We demonstrate that its optical anisotropy can be changed on a large scale by varying the incident angles,polarization states,and the in-plane rotation angles of the BP samples.Theoretical analysis indicates that the phenomena observed are common to all the atom-thick biaxial crystals,so these conclusions can be widely applied to other anisotropic 2D materials.This research furthers the current understanding of the properties of BP more comprehensively,and provides guidance for developing new optoelectronic applications,especially when BP and other atom-thick biaxial crystals are integrated with TIR devices.
基金supported by Sichuan Science and Technology Program(2023NSFSC0460)the Fundamental Research Funds for the Central Universities(Grant No.ZYGX2020J010)+3 种基金the Open Project Funding of the Ministry of Education Key Laboratory of Weak-Light Nonlinear Photonics(Grant No.OS22-1)the Guangxi Natural Science Foundation(Grant No.2020GXNSFAA297041)the National Key R&D Program of China(Grant No.2022YFA1404800)the National Natural Science Foundation of China(Grant No.12134006).
文摘Photonic analogs of the moirésuperlattices mediated by interlayer electromagnetic coupling are expected to give rise to rich phenomena,such as nontrivial flatband topology.Here,we propose and demonstrate a scheme to tune the flatbands in a bilayer moirésuperlattice by employing a band offset.The band offset is changed by fixing the bands of one slab while shifting those of the other slab,which is accomplished by modifying the thickness of the latter slab.Our results show that the band-offset tuning not only makes some flatbands emerge and disappear but also leads to two sets of flatbands that are robustly formed even with the change of band offset over a broad range.These robust flatbands form either at the AA-stack site or at the AB-stack site,and as a result,a single-cell superlattice can support a pair of high-quality localized modes with tunable frequencies.Moreover,we develop a diagrammatic model to provide an intuitive insight into the formation of the robust flatbands.Our work demonstrates a simple yet efficient way to design and control complex moiréflatbands,providing new opportunities to utilize photonic moirésuperlattices for advanced light–matter interaction,including lasing and nonlinear harmonic generation.
基金This work was supported by the National Natural Science Foundation of China(No.11204142),the National Basic Research Program of China (No.2013CB328702)International S&T Cooperation Program of China (2011DFA52870)+1 种基金the 111 Project(No.B07013),the National Science Fund for Talent Training in Basic Sciences(No.J1103208),the PCSIRT (IRT0149)the Social Development Fund of Ge'ermu Science and Technology Bureau and the State Key Laboratory of Medicinal Chemical Biology.
文摘Ultraviolet blood irradiation has been used as a physical therapy to treat many nonspeci¯c diseases in clinics;however,the underlying mechanisms remain largely unclear.Neutrophils,the first line of host defense,play a crucial role in a variety of in°ammatory responses.In the present work,we investigated the effects of ultraviolet light A(UVA)on the immune functions of human neutrophils at the single-cell level by using an inverted°uorescence microscope.N-Formylmethionyl-leucyl-phenylalanine(FMLP),a classic physiological chemotactic peptide,was used to induce a series of immune responses in neutrophils in vitro.FMLP-induced calcium mobilization,migration,and phagocytosis in human neutrophils was significantly blocked after treatment with 365 nm UVA irradiation,demonstrating the immunosuppressive effects of UVA irradiation on neutrophils.Similar responses were also observed when the cells were pretreated with H2O2,a type of reactive oxygen species(ROS).Furthermore,UVA irradiation resulted in an increase in NAD(P)H,a member of host oxidative stress in cells.Taken together,our data indicate that UVA irradiation results in immunosuppression associated with the production of ROS in human neutrophils.
基金supported by the National Key R&D Program of China(2022YFA1404800)the National Natural Science Foundation of China(W2541003 and 12134006).
文摘Vortices are among nature’s most elegant manifestations of order within motion.They appear wherever flow meets rotation—from the microscopic whirlpools of quantum fluids and living cells to the cosmic spirals of galaxies.Across these vastly different scales,the essence remains the same:a circulating current wrapped around a singularity.In both classical and quantum realms,vortices carrying orbital angular momentum(OAM)have emerged as a unifying concept,realized with photons,electrons,and even cold atoms and molecules.These quantized whirlpools of phase have illuminated fundamental aspects of angular momentum,topology,and coherence,while driving applications in optical manipulation,communications,and quantum information.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12574339,12574457,and 12174207)Tianjin Science and Technology Project(Grant No.24ZXZSSS00120)。
文摘Twist-and-stack engineering provides a programmable degree of freedom for nonlinear optics in two-dimensional materials,yet in a homostructure whose constituents have no second harmonic generation(SHG),how interlayer coupling grants and tunes second-order response remains unclear.Here,we use twisted monolayer-bilayer graphene(t(1+2)LG)and combine microscopic SHG spectroscopy with first-principles differential charge-density analysis to establish a unified"permission-and-resonance"mechanism.Interlayer coupling creates an interlayer charge imbalance within the AB-stacked bilayer,breaking inversion symmetry and thereby permitting an in-plane electric-dipole response.At the same time,the twist angle steers van Hove singularities in the band structure to achieve two-photon resonance,which markedly amplifies the susceptibilityχ^((2)).Experimentally,atθ=13.5°,we obtainχ^((2))=279.4 pm/V,evidencing a highly efficient second-order response.These results identify SHG as a sensitive probe of interlayer coupling and charge redistribution in homostructure van der Waals systems.
基金financial support from the Shenzhen Key Laboratory of Intelligent Robotics and Flexible Manufacturing Systems(No.ZDSYS20220527171403009)the Open Fund of the State Key Laboratory of Intelligent Green Vehicles and Mobility under Project No.KFY2404,Guangdong Basic and Applied Basic Research Foundation(No.2024A1515240041)the Shenzhen Science and Technology Innovation Commission(No.20231115111658002).
文摘Cobalt-based(Co-based)alloys are widely used in aerospace and machinery applications because of their excellent mechanical properties,where extraordinary wear performance is also desirable to ensure stable operation.However,there is still scarce information on the tribological mechanism of the cobalt metal building block,especially under different humidities.Insight into the wear mechanism of Co under different humidities is crucial for studying the tribological performance of Co-based alloys as well as their potential applications under various working conditions.Here,we report an investigation of the effect of humidity on the wear behavior of Co.The results revealed that Co exhibited ultralow wear characteristics in a humid air environment(relative humidity(RH)70%),with a wear rate of 2.15×10^(-7)mm^(3)/(N·m),and dramatically increased by three orders of magnitude to 1.47×10^(-4)mm^(3)/(N·m)in the dry environment(~5%RH).Surface analysis revealed that tribochemistry dominated the whole wearing process,with the worn surface almost fully covered by cobalt oxide,Co3O4,when subjected to a humid environment,whereas a small number of oxide layers were observed only within the wear grooves under the RH 5%testing condition.The stripe test results revealed the evolution of this protective oxide generation,and the focused ion beam scanning electron microscopy(FIB-SEM)images of the cross-sections at different sliding stages revealed the role of tribochemistry in triggering such self-protection behavior.Our work provides a fundamental understanding of the wear mechanisms of Co metal,and we anticipate that these findings can offer valuable guidance for further improving the wear performance of cobalt-based alloys in the future.
基金supported by the National Key R&D Program of China(Grant No.2022YFA1404800)the National Natural Science Foundation of China(Grant Nos.12134006,12274242+2 种基金12474387)the Natural Science Foundation of Tianjin(Grant No.21JCJQJC00050)the 111 Project in China(Grant No.B23045)。
文摘Flatbands are of significant interest due to their potential for strong energy confinement and their ability to facilitate strongly correlated physics such as unconventional superconductivity and fractional quantum Hall states.When topology is incorporated into flatband systems,it further enhances flatband mode robustness against perturbations.We present the first realization of doubly degenerate topological flatbands of edge states in chiral-symmetric strained graphene.The flatband degeneracy stems from the merging of Dirac points,achieved by tuning the coupling ratios in a honeycomb lattice with newly discovered twig boundary conditions.The topology of these modes is characterized by the nontrivial winding number,which ensures their robustness against disorder.Experimentally,two types of topological edge states are observed in a strained photonic graphene lattice,consistent with numerical simulations.Moreover,the degeneracy of the topological flatbands doubles the density of states for zero-energy modes,facilitating the formation of compact edge states and providing greater control over edge states and light confinement.Our findings underscore the interplay among lattice geometry,symmetry,and topology in shaping doubly degenerate topological flatbands.This work opens new possibilities for advancements in correlated effects,nonlinear optical phenomena,and efficient energy transfer in materials science,photonic crystals,and quantum devices.
基金supported by the National Key Research and Development Program of China(No.2022YFA1404800)National Natural Science Foundation of China(No.12174280,No.12204340,No.12192254,No.92250304,No.12434012,No.W2441005)Priority Academic Program Development of Jiangsu Higher Education Institutions,and Postgraduate Research&Practice Innovation Programof Jiangsu Province(KYCX24_3287).
文摘Links and knots are exotic topological structures that have garnered significant interest across multiple branches of natural sciences.Coherent links and knots,such as those constructed by phase or polarization singularities of coherent light,have been observed in various three-dimensional optical settings.However,incoherent links and knots—knotted or connected lines of coherence singularities—arise from a fundamentally different concept.They are"hidden"in the statistic properties of a randomly fluctuating field,making their presence often elusive or undetectable.Here,we theoretically construct and experimentally demonstrate such topological entities of incoherent light.By leveraging a state-of-the-art incoherent modal-decomposition scheme,we unveil incoherent topological structures from fluctuating light speckles,including Hopf links and Trefoil knots of coherence singularities that are robust against coherence and intensity fluctuations.Our work is applicable to diverse wave systems where incoherence or practical coherence is prevalent,and may pave the way for design and implementation of statistically-shaped topological structures for various applications such as high-dimensional optical information encoding and optical communications.
基金supported by the Guangxi Natural Science Foundation(No.2024GXNSFAA0103144)the National Natural Science Foundation of China(Nos.12474290 and 62475047)+2 种基金the Sichuan Science and Technology Program(No.2023NSFSC0460)the Open Project Funding of the Ministry of Education Key Laboratory of Weak-Light Nonlinear Photonics(No.OS22-1)the Special Funding for Guangxi Bagui Youth Scholars(Yi Liang)。
文摘Autofocusing beams are powerful photonic tools for manipulating micro/nanoparticles.Here,we propose a special type of dislocated-superimposed swallowtail vortex beam(DSVB)and analyze its propagation properties and optical manipulating capability.By modulating the parameters of the superposition number N and the topological charge l,DSVBs show asymmetric autofocusing propagation phenomena and unconventional orbital angular momentum(OAM),especially for opposite topological charges.Furthermore,when N=|l|,DSVBs form multiple solid focuses while preserving OAM during propagation,suggesting potential applications in multi-point trapping and rotational manipulation.These results deepen the understanding of autofocusing and OAM behaviors,highlighting DSVBs'potential as photonic tools for optical manipulation.
基金Natural Basic Research Program of China(2019YFA0705000)National Natural Science Foundation of China(11674181,11674340,11734009,11822410,11874154,11874375,61590934,61761136006)+5 种基金Key Research Program of Frontier Sciences(QYZDJ-SSWSLH010)Key Project of the Shanghai Science and Technology Committee(17JC1400400,18DZ1112700)Strategic Priority Research Program of Chinese Academy of Sciences(XDB16030300)Higher Education Discipline Innovation Project(B07013)Program for Changjiang Scholars and Innovative Research Team(IRT_13R29)State Key Laboratory of Advanced Optical Communication Systems and Networks(2019GZKF03006).
文摘Crystalline lithium niobate(LN)is an important optical material because of its broad transmission window that spans from ultraviolet to mid-infrared and its large nonlinear and electro-optic coefficients.Furthermore,the recent development and commercialization of LN-on-insulator(LNOI)technology has opened an avenue for the realization of integrated on-chip photonic devices with unprecedented performances in terms of propagation loss,optical nonlinearity,and electro-optic tunability.This review begins with a brief introduction of the history and current status of LNOI photonics.We then discuss the fabrication techniques of LNOI-based photonic structures and devices.The recent revolution in the LN photonic industry has been sparked and is still being powered by innovations of the nanofabrication technology of LNOI,which enables the production of building block structures,such as optical microresonators and waveguides of unprecedented optical qualities.The following sections present various on-chip LNOI devices categorized into nonlinear photonic and electro-optic tunable devices and photonic-integrated circuits.Some conclusions and future perspectives are provided.
基金supported by the Guangdong Major Project of Basic and Applied Basic Research (Grant No.2020B0301030009)the National Key R&D Program of China (Grant Nos.2017YFA0305100,2017YFA0303800,and 2019YFA0705000)+5 种基金the National Natural Science Foundation of China (Grant Nos.92050114,91750204,61775106,11904182,12074200,and 11774185)the 111 Project (Grant No.B07013)PCSIRT (Grant No.IRT0149)the Open Research Program of Key Laboratory of 3D Micro/Nano Fabrication and Characterization of Zhejiang ProvinceFundamental Research Funds for the Central Universities (Grant Nos.010-63201003,01063201008,and 010-63201009)Tianjin Youth Talent Support Program。
文摘Many applications of metasurfaces require an ability to dynamically change their properties in the time domain. Electrical tuning techniques are of particular interest, since they pave a way to on-chip integration of metasurfaces with optoelectronic devices.In this work, we propose and experimentally demonstrate an electro-optic lithium niobate(EO-LN) metasurface that shows dynamic modulations to phase retardation of transmitted light. Quasi-bound states in the continuum(QBIC) are observed from this metasurface. By applying external electric voltages, the refractive index of lithium niobate(LN) is changed by Pockels EO nonlinearity, leading to efficient phase modulations to the transmitted light around the QBIC wavelength. The EO-LN metasurface developed in this study opens up new routes for potential applications in the field of displaying, pulse shaping, and spatial light modulating.
基金supported by the National Basic Research Program(973 Program)of China(2012CB921900)the Chinese National Key Basic Research Special Fund(2011CB922003)+3 种基金the Natural Science Foundation of China(11574163,61378006,11304163 and 91323304)the Program for New Century Excellent Talents in University(NCET-13-0294)the 111 project(B07013)the National Science Fund for Talent Training in Basic Sciences(J1103208).
文摘Optical activity is the rotation of the plane of linearly polarized light along the propagation direction as the light travels through optically active materials.In existing methods,the strength of the optical activity is determined by the chirality of the materials,which is difficult to control quantitatively.Here we numerically and experimentally investigated an alternative approach to realize and control the optical activity with non-chiral plasmonic metasurfaces.Through judicious design of the structural units of the metasurfaces,the right and left circular polarization components of the linearly polarized light have different phase retardations after transmitting through the metasurfaces,leading to large optical activity.Moreover,the strength of the optical activity can be easily and accurately tuned by directly adjusting the phase difference.The proposed approach based on non-chiral plasmonic metasurfaces exhibits large optical activity with a high controllable degree of freedom,which may provide more possibilities for applications in photonics.
基金National Natural Science Foundation of China(NSFC)(61675169,61675171,11634010)National Key R&D Program of China(2017YFA0303800)+1 种基金Natural Science Basic Research Plan in Shaanxi Province of China(2018JM6036)Shaanxi Provincial Key R&D Program(2018KW-009)
文摘The synergy of a plasmonic tip and fiber-based structure light field excitation can provide a powerful tool for Raman examination. Here, we present a method of Raman spectrum enhancement with an Ag-nanoparticles(Ag-NPs)-coated fiber probe internally excited via an azimuthal vector beam(AVB), which is directly generated in a few-mode fiber by using an acoustically induced fiber grating. Theoretical analysis shows that gap mode can be effectively generated on the surface of the Ag-NPs-coated fiber probe excited via an AVB. The experimental result shows that the intensity of Raman signal obtained with analyte molecules of malachite green by exciting the Ag-NPs-coated fiber probe via an AVB is approximately eight times as strong as that via the linear polarization beam(LPB), and the activity of the AVB-excited fiber probe can reach 10^-11 mol∕L, which cannot be achieved by LPB excitation.Moreover, the time stability and reliability are also examined, respectively.
基金the National Key R&D Program of China(2022YFA1404800)the National Natural Science Foundation of China(12134006,12274242)+4 种基金the Natural Science Foundation of Tianjin(21JCJQJC00050)the QuantiXLie Center of Excellence,a project co-financed by the Croatian Government and the European Union through the European Regional Development Fund the Competitiveness and Cohesion Operational Programme(KK.01.1.1.01.0004)the 66 Postdoctoral Science Grant of Chinathe NSERC Discovery Grantthe Canada Research Chair Programs.
文摘The orbital degrees of freedom play a pivotal role in understanding fundamental phenomena in solid-state materials as well as exotic quantum states of matter including orbital superfluidity and topological semimetals.Despite tremendous efforts in engineering synthetic cold-atom,as well as electronic and photonic lattices to explore orbital physics,thus far high orbitals in an important class of materials,namely,higher-order topological insulators(HOTIs),have not been realized.Here,we demonstrate p-orbital corner states in a photonic HOTI,unveiling their underlying topological invariant,symmetry protection,and nonlinearity-induced dynamical rotation.In a Kagome-type HOTI,we find that the topological protection of p-orbital corner states demands an orbital-hopping symmetry in addition to generalized chiral symmetry.Due to orbital hybridization,nontrivial topology of the p-orbital HOTI is“hidden”if bulk polarization is used as the topological invariant,but well manifested by the generalized winding number.Our work opens a pathway for the exploration of intriguing orbital phenomena mediated by higher-band topology applicable to a broad spectrum of systems.
基金the National Key R&D Program of China(2017YFA0305100,2017YFA0303800,and 2019YFA0705000)National Natural Science Foundation of China(92050114,62076140,91750204,61775106,11904182,61633012,11711530205,11374006,12074200,and 11774185)+6 种基金Guangdong Major Project of Basic and Applied Basic Research(2020B0301030009)111 Projea(B07013)PCSIRT(IRT0149)Open Research Program of Key Laboratory of 3D Micro/Nano Fabrication and Characterization of Zhejiang ProvinceTianjin Youth Talent Support ProgramFundamental Research Funds for the Central Universities(010-63201003,010-63201008,and 010-63201009)。
文摘Ellipsometry is a powerful method for determining both the optical constants and thickness of thin films.For decades,solutions to ill-posed inverse ellipsometric problems require substantial human-expert intervention and have become essentially human-in-the-loop trial-and-error processes that are not only tedious and time-consuming but also limit the applicability of ellipsometry.Here,we demonstrate a machine learning based approach for solving ellipsometric problems in an unambiguous and fully automatic manner while showing superior performance.The proposed approach is experimentally validated by using a broad range of films covering categories of metals,semiconductors,and dielectrics.This method is compatible with existing ellipsometers and paves the way for realizing the automatic,rapid,high-throughput optical characterization of films.
基金This research is supported by the National Key R&D Program of China under Grant No.2017YFA0303800the National Natural Science Foundation(11922408,91750204,11674180)+2 种基金PCSIRT,and the 111 Project(No.B07013)in ChinaD.B.acknowledges support from the 66 Postdoctoral Science Grant of ChinaD.J.and H.B.acknowledge support in part by the Croatian Science Foundation Grant No.IP-2016-06-5885 SynthMagIA and the QuantiXLie Center of Excellence,a project co-financed by the Croatian Government and European Union through the European Regional Development Fund-the Competitiveness and Cohesion Operational Programme(Grant KK.01.1.1.01.0004)。
文摘Higher-order topological insulators(HOTIs)are recently discovered topological phases,possessing symmetry-protected corner states with fractional charges.An unexpected connection between these states and the seemingly unrelated phenomenon of bound states in the continuum(BICs)was recently unveiled.When nonlinearity is added to the HOTI system,a number of fundamentally important questions arise.For example,how does nonlinearity couple higher-order topological BICs with the rest of the system,including continuum states?In fact,thus far BICs in nonlinear HOTIs have remained unexplored.Here we unveil the interplay of nonlinearity,higher-order topology,and BICs in a photonic platform.We observe topological corner states that are also BICs in a laser-written second-order topological lattice and further demonstrate their nonlinear coupling with edge(but not bulk)modes under the proper action of both self-focusing and defocusing nonlinearities.Theoretically,we calculate the eigenvalue spectrum and analog of the Zak phase in the nonlinear regime,illustrating that a topological BIC can be actively tuned by nonlinearity in such a photonic HOTI.Our studies are applicable to other nonlinear HOTI systems,with promising applications in emerging topology-driven devices.
