Artificial microstructures,which allow us to control and change the properties of wave fields through changing the geometrical parameters and the arrangements of microstructures,have attracted plenty of attentions in ...Artificial microstructures,which allow us to control and change the properties of wave fields through changing the geometrical parameters and the arrangements of microstructures,have attracted plenty of attentions in the past few decades.Some artificial microstructure based research areas,such as metamaterials,metasurfaces and phononic topological insulators,have seen numerous novel applications and phenomena.The manipulation of different dimensions(phase,amplitude,frequency or polarization)of wave fields,particularly,can be easily achieved at subwavelength scales by metasurfaces.In this review,we focus on the recent developments of wave field manipulations based on artificial microstructures and classify some important applications from the viewpoint of different dimensional manipulations of wave fields.The development tendency of wave field manipulation from single-dimension to multidimensions provides a useful guide for researchers to realize miniaturized and integrated optical and acoustic devices.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
Nonlinear metasurfaces and photonic crystals provide a significant way to generate and manipulate nonlinear signals owing to the resonance-and symmetry-based light-matter interactions supported by the artificial struc...Nonlinear metasurfaces and photonic crystals provide a significant way to generate and manipulate nonlinear signals owing to the resonance-and symmetry-based light-matter interactions supported by the artificial structures.However,the nonlinear conversion efficiency is generally limited by the angular dispersion of optical resonances especially in nonparaxial photonics.Here,we propose a metagrating realizing a quasi-bound-state in the continuum in a flat band to dramatically improve the third harmonic generation(THG)efficiency.A superior operating angular range is achieved based on the interlayer and intralayer couplings,which are introduced by breaking the mirror symmetry of the metagrating.We demonstrate the relation of angular dispersion between the nonlinear and linear responses at different incident angles.We also elucidate the mechanism of these offaxis flat-band-based nonlinear conversions through different mode decomposition.Our scheme provides a robust and analytical way for nonparaxial nonlinear generation and paves the way for further applications such as wide-angle nonlinear information transmission and enhanced nonlinear generation under tight focusing.展开更多
A four-fold-degenerate three-dimensional(3D)Dirac point,represents a degenerate pair of Weyl points carrying opposite chiralities.Moreover,3D Dirac crystals have shown many exotic features different from those of Weyl...A four-fold-degenerate three-dimensional(3D)Dirac point,represents a degenerate pair of Weyl points carrying opposite chiralities.Moreover,3D Dirac crystals have shown many exotic features different from those of Weyl crystals.How these features evolve from 3D Dirac to Weyl crystals is important in research on 3D topological matter.Here,we realized a pair of 3D acoustic Dirac points from band inversion in a hexagonal sonic crystal and observed the surface states and helical interface states connecting the Dirac points.Furthermore,each Dirac point can transition into a pair of Weyl points with the introduction of chiral hopping.The exotic features of the surface states and interface states are inherited by the resulting Weyl crystal.Our work may serve as an ideal platform for exploring exotic physical phenomena in 3D topological semimetals.展开更多
In this study, we investigate the fabrication of periodically poled lithium niobate(PPLN) microdisk cavities on a chip. These resonators are fabricated from a PPLN film with a 16 μm poling period on insulator using c...In this study, we investigate the fabrication of periodically poled lithium niobate(PPLN) microdisk cavities on a chip. These resonators are fabricated from a PPLN film with a 16 μm poling period on insulator using conventional microfabrication techniques.The quality factor of the PPLN microdisk resonators with a 40-μm radius and a 700-nm thickness is 6.7×10~5. Second harmonic generation(SHG) with an efficiency of 2.2×10^(-6) mW(-1) is demonstrated in the fabricated PPLN microdisks. The nonlinear conversion efficiency could be considerably enhanced by optimizing the period and pattern of the poled structure and by improving the cavity quality factors.展开更多
We report the first observation, to the best of our knowledge, of sum-frequency generation in on-chip lithium niobate microdisk resonators. The sum-frequency signal in the 780 nm band, distinct in wavelength from seco...We report the first observation, to the best of our knowledge, of sum-frequency generation in on-chip lithium niobate microdisk resonators. The sum-frequency signal in the 780 nm band, distinct in wavelength from secondharmonic signals, was obtained in lithium niobate microresonators under the pump of two individual 1550 nm band lasers. The sum-frequency conversion efficiency was measured to be 1.4 × 10^(-7) mW^(-1). The dependence of the intensities of the nonlinear signals on the total pump power and the wavelength of one pump laser was investigated while fixing the wavelength of the other. This work paves the way for applications of on-chip lithium niobate microdisk resonators ranging from infrared single-photon detection to infrared spectroscopy.展开更多
Metasurfaces,which are planar arrays of subwavelength artificial structures,have emerged as excellent platforms for the integration and miniaturization of electromagnetic devices and provided ample possibilities for s...Metasurfaces,which are planar arrays of subwavelength artificial structures,have emerged as excellent platforms for the integration and miniaturization of electromagnetic devices and provided ample possibilities for single-dimensional and multi-dimensional manipulations of electromagnetic waves.However,owing to the limited interactions between planar thin metallic nanostructures and electromagnetic waves as well as intrinsic losses in metals,metasurfaces exhibit disadvantages in terms of efficiency,controllability,and functionality.Recent advances in this field show that few-layer metasurfaces can overcome these drawbacks.Few-layer metasurfaces composed of more than one functional layer enable more degrees of design freedom.Hence,they possess unprecedented capabilities for electromagnetic wave manipulation,which have considerable impact in the area of nanophotonics.This article reviews recent advances in few-layer metasurfaces from the viewpoint of their scattering properties.The scattering matrix theory is briefly introduced,and the advantages and drawbacks of few-layer metasurfaces for the realization of arbitrary scattering properties are discussed.Then,a detailed overview of typical few-layer metasurfaces with various scattering properties and their design principles is provided.Finally,an outlook on the future directions and challenges in this promising research area is presented.展开更多
Metasurfaces,whose electromagnetic(EM)responses can be artificially designed,are two-dimensional arrays composed of subwavelength nanostructures.Accompanied by various fascinating developments in the past decade,metas...Metasurfaces,whose electromagnetic(EM)responses can be artificially designed,are two-dimensional arrays composed of subwavelength nanostructures.Accompanied by various fascinating developments in the past decade,metasurfaces have been proved as a powerful platform for the implementation of EM wave manipula-tion.However,the planar monoatomic metasurfaces widely used in previous works have limited design freedoms,resulting in some disadvantages for the realization of high-performance and new functional EM wave control.The latest developments show that few-layer metasurfaces and polyatomic metasurfaces are good alternatives to overcome the drawbacks of planar monoatomic metasurfaces and realize high-efficient,multi-band and broad-band EM functionalities.They provide additional degrees of design freedom via introducing multilayer layouts or combining multiple meta-atoms into a unit cell respectively.Here,recent advances of few-layer and polyatomic metasurfaces are reviewed.The design strategies,EM properties and main advantages of few-layer metasurfaces and polyatomic metasurfaces are overviewed firstly.Then,few-layer metasurfaces and polyatomic metasurfaces in recent progress for EM wave manipulation are classified and discussed from the viewpoint of their design strategy.At last,an outlook on future development trends and potential applications in these fast-developing research areas is presented.展开更多
基金This work was supported by the National Key Research and Development Program of China(2016YFA0301102 and 2017YFA0303800)the National Natural Science Fund for Distinguished Young Scholar(11925403)+2 种基金the National Natural Science Foundation of China(11974193,91856101,and 11774186)Natural Science Foundation of Tianjin for Distinguished Young Scientists(18JCJQJC45700)the China Postdoctoral Science Foundation(2020M680851).
文摘Artificial microstructures,which allow us to control and change the properties of wave fields through changing the geometrical parameters and the arrangements of microstructures,have attracted plenty of attentions in the past few decades.Some artificial microstructure based research areas,such as metamaterials,metasurfaces and phononic topological insulators,have seen numerous novel applications and phenomena.The manipulation of different dimensions(phase,amplitude,frequency or polarization)of wave fields,particularly,can be easily achieved at subwavelength scales by metasurfaces.In this review,we focus on the recent developments of wave field manipulations based on artificial microstructures and classify some important applications from the viewpoint of different dimensional manipulations of wave fields.The development tendency of wave field manipulation from single-dimension to multidimensions provides a useful guide for researchers to realize miniaturized and integrated optical and acoustic devices.
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 National Key Research and Development Program of China(Grant Nos.2021YFA1400601,and 2022YFA1404501)the National Natural Science Fund for Distinguished Young Scholar(Grant No.11925403)the National Natural Science Foundation of China(Grant Nos.12122406,12192253,12274239,12274237,and U22A20258)。
文摘Nonlinear metasurfaces and photonic crystals provide a significant way to generate and manipulate nonlinear signals owing to the resonance-and symmetry-based light-matter interactions supported by the artificial structures.However,the nonlinear conversion efficiency is generally limited by the angular dispersion of optical resonances especially in nonparaxial photonics.Here,we propose a metagrating realizing a quasi-bound-state in the continuum in a flat band to dramatically improve the third harmonic generation(THG)efficiency.A superior operating angular range is achieved based on the interlayer and intralayer couplings,which are introduced by breaking the mirror symmetry of the metagrating.We demonstrate the relation of angular dispersion between the nonlinear and linear responses at different incident angles.We also elucidate the mechanism of these offaxis flat-band-based nonlinear conversions through different mode decomposition.Our scheme provides a robust and analytical way for nonparaxial nonlinear generation and paves the way for further applications such as wide-angle nonlinear information transmission and enhanced nonlinear generation under tight focusing.
基金supported by the National Key Research and Development Program of China(2016YFA0301102 and 2017YFA0303800)the National Natural Science Fund for Distinguished Young Scholars(11925403)+2 种基金the National Natural Science Foundation of China(11974193,91856101,11774186,and 21421001)the Natural Science Foundation of Tianjin for Distinguished Young Scientists(18JCJQJC45700)the Fundamental Research Funds for the Central Universities,Nankai University(63201005).
文摘A four-fold-degenerate three-dimensional(3D)Dirac point,represents a degenerate pair of Weyl points carrying opposite chiralities.Moreover,3D Dirac crystals have shown many exotic features different from those of Weyl crystals.How these features evolve from 3D Dirac to Weyl crystals is important in research on 3D topological matter.Here,we realized a pair of 3D acoustic Dirac points from band inversion in a hexagonal sonic crystal and observed the surface states and helical interface states connecting the Dirac points.Furthermore,each Dirac point can transition into a pair of Weyl points with the introduction of chiral hopping.The exotic features of the surface states and interface states are inherited by the resulting Weyl crystal.Our work may serve as an ideal platform for exploring exotic physical phenomena in 3D topological semimetals.
基金supported by the National Natural Science Foundation of China(Grant Nos.11734009,11674181,11774182,and 11674184)the 111 Project(Grant No.B07013)+1 种基金PCSIRT(Grant No.IRT 13R29)CAS Interdisciplinary Innovation Team
文摘In this study, we investigate the fabrication of periodically poled lithium niobate(PPLN) microdisk cavities on a chip. These resonators are fabricated from a PPLN film with a 16 μm poling period on insulator using conventional microfabrication techniques.The quality factor of the PPLN microdisk resonators with a 40-μm radius and a 700-nm thickness is 6.7×10~5. Second harmonic generation(SHG) with an efficiency of 2.2×10^(-6) mW(-1) is demonstrated in the fabricated PPLN microdisks. The nonlinear conversion efficiency could be considerably enhanced by optimizing the period and pattern of the poled structure and by improving the cavity quality factors.
基金National Natural Science Foundation of China(NSFC)(11374165,11674181,11674184,61475077)Ministry of Science and Technology of the People’s Republic of China(MOST)(2013CB328702)+1 种基金Ministry of Education of the People’s Republic of China(MOE)(B07013)PCSIRT(IRT_13R29)
文摘We report the first observation, to the best of our knowledge, of sum-frequency generation in on-chip lithium niobate microdisk resonators. The sum-frequency signal in the 780 nm band, distinct in wavelength from secondharmonic signals, was obtained in lithium niobate microresonators under the pump of two individual 1550 nm band lasers. The sum-frequency conversion efficiency was measured to be 1.4 × 10^(-7) mW^(-1). The dependence of the intensities of the nonlinear signals on the total pump power and the wavelength of one pump laser was investigated while fixing the wavelength of the other. This work paves the way for applications of on-chip lithium niobate microdisk resonators ranging from infrared single-photon detection to infrared spectroscopy.
基金supported by the National Key Research and Development Program of China(Grant Nos.2016YFA0301102,and 2017YFA0303800)the National Natural Science Fund for Distinguished Young Scholar(Grant No.11925403)+3 种基金the National Natural Science Foundation of China(Grant Nos.11974193,11904181,11904183,91856101,and 11774186)the Natural Science Foundation of Tianjin for Distinguished Young Scientists(Grant No.18JCJQJC45700)the National Postdoctoral Program for Innovative Talents(Grant No.BX20180148)the China Postdoctoral Science Foundation(Grant Nos.2018M640224,and 2018M640229)。
文摘Metasurfaces,which are planar arrays of subwavelength artificial structures,have emerged as excellent platforms for the integration and miniaturization of electromagnetic devices and provided ample possibilities for single-dimensional and multi-dimensional manipulations of electromagnetic waves.However,owing to the limited interactions between planar thin metallic nanostructures and electromagnetic waves as well as intrinsic losses in metals,metasurfaces exhibit disadvantages in terms of efficiency,controllability,and functionality.Recent advances in this field show that few-layer metasurfaces can overcome these drawbacks.Few-layer metasurfaces composed of more than one functional layer enable more degrees of design freedom.Hence,they possess unprecedented capabilities for electromagnetic wave manipulation,which have considerable impact in the area of nanophotonics.This article reviews recent advances in few-layer metasurfaces from the viewpoint of their scattering properties.The scattering matrix theory is briefly introduced,and the advantages and drawbacks of few-layer metasurfaces for the realization of arbitrary scattering properties are discussed.Then,a detailed overview of typical few-layer metasurfaces with various scattering properties and their design principles is provided.Finally,an outlook on the future directions and challenges in this promising research area is presented.
基金This work was supported by the National Key Research and Devel-opment Program of China(2017YFA0303800 and 2016YFA0301102)the National Natural Science Fund for Distinguished Young Scholar(11925403)+2 种基金the National Natural Science Foundation of China(11974193,11904181,11904183,91856101,and 11774186)Natu-ral Science Foundation of Tianjin for Distinguished Young Scientists(18JCJQJC45700)and the China Postdoctoral Science Foundation(2018M640224 and 2021M690084).
文摘Metasurfaces,whose electromagnetic(EM)responses can be artificially designed,are two-dimensional arrays composed of subwavelength nanostructures.Accompanied by various fascinating developments in the past decade,metasurfaces have been proved as a powerful platform for the implementation of EM wave manipula-tion.However,the planar monoatomic metasurfaces widely used in previous works have limited design freedoms,resulting in some disadvantages for the realization of high-performance and new functional EM wave control.The latest developments show that few-layer metasurfaces and polyatomic metasurfaces are good alternatives to overcome the drawbacks of planar monoatomic metasurfaces and realize high-efficient,multi-band and broad-band EM functionalities.They provide additional degrees of design freedom via introducing multilayer layouts or combining multiple meta-atoms into a unit cell respectively.Here,recent advances of few-layer and polyatomic metasurfaces are reviewed.The design strategies,EM properties and main advantages of few-layer metasurfaces and polyatomic metasurfaces are overviewed firstly.Then,few-layer metasurfaces and polyatomic metasurfaces in recent progress for EM wave manipulation are classified and discussed from the viewpoint of their design strategy.At last,an outlook on future development trends and potential applications in these fast-developing research areas is presented.
