查看更多>>摘要：Physical properties such as the conductivity are usually classified according to the symmetry of the underlying system using Neumann's principle,which gives an upper bound for the number of independent components of the corresponding property tensor.However,for a given Hamiltonian,this global approach usually can not give a definite answer on whether a physical effect such as spin Hall effect(SHE)exists or not.It is found that the parity and types of spin-orbit interactions(SOIs)are good indicators that can further reduce the number of independent components of the spin Hall conductivity for a specific system.In terms of the parity as well as various Rashba-like and Dresselhaus-like SOIs,we propose a local approach to classify SHE in two-dimensional(2D)two-band models,where sufficient conditions for identifying the existence or absence of SHE in all 2D magnetic point groups are presented.
查看更多>>摘要：We concentrate on the skin effects and topological properties in the multi-layer non-Hermitian Su-Schrieffer-Heeger(SSH)structure,by taking into account the nonreciprocal couplings between the different sublattices in the unit cells.Following the detailed demonstration of the theoretical method,we find that in this system,the skin effects and topological phase transitions induced by nonreciprocal couplings display the apparent parity effect,following the increase of the layer number of this SSH structure.On the one hand,the skin effect is determined by the parity of the layer number of this SSH system,as well as the parity of the band index of the bulk states.On the other hand,for the topological edge modes,such an interesting parity effect can also be observed clearly.Next,when the parameter disorders are taken into account,the zero-energy edge modes in the odd-layer structures tend to be more robust,whereas the other edge modes are easy to be destroyed.In view of these results,it can be ascertained that the findings in this work promote to understand the influences of nonreciprocal couplings on the skin effects and topological properties in the multilayer SSH lattices.
查看更多>>摘要：Engineering phonon transport in low-dimensional materials has great significance not only for fundamental research,but also for thermal management applications of electric devices.However,due to the difficul-ties of micro and nano processing and characterization techniques,the work on tuning phonon transport at nanoscale are scarce.In this work,by introducing Ar+plasma,we probed the phonon transport in two-dimen-sional(2D)layered semiconductor PdSe2 under different defect concentra-tions.By using thermal bridge method,the thermal conductivity was measured to decrease by 50％after a certain Ar+irradiation,which implied a possible phase transition.Moreover,Raman characterizations were performed to show that the Raman sensitive peaks of PdSe2 was red-shifted and finally became disappeared with the increase of defect concen-tration."Defect engineering"proves be a practical strategy in tuning the phonon thermal transport in low-dimensional materials,thus providing guidance for potential application in designing thermoelectric devices with various emerging materials.
查看更多>>摘要：We examine the electronic and transport properties of a new phase PdSe monolayer with a puckered structure calculated by first-principles and Boltzmann transport equation.The spin-orbit coupling is found to play a negligible effect on the electronic properties of PdSe monolayer.The lattice thermal conductivity of PdSe monolayer exhibits remarkable anisotropic characteristic due to anisotropic phonon group velocity along different directions and its intrinsic structure anisotropy.The compromised electronic mobility despite a relatively low thermal conduction results in a moderate ZT value but significantly anisotropic thermoelectric perfor-mance in single-layer PdSe.The present work suggests that the remarkable thermal transport anisotropy of PdSe monolayer can be used for thermal management,and enhance the scope of possibilities for heat flow manipu-lation in PdSe based devices.The sizeable puckered cages and wiggling lattice implies it an ideal platform for ionic and molecular engineering for thermoelectronic applications.
查看更多>>摘要：Decreasing of layer thickness causes the decrease of polarization until it disappears due to the existence of depolarization field.Therefore,the search for strong piezoelectric materials is highly desirable for multifunc-tional ultra-thin piezoelectric devices.Herein,we propose a common strat-egy for achieving strong piezoelectric materials through the electronic asymmetry induced by the intrinsically asymmetric atomic character of different chalcogen atoms.Accordingly,in the tetrahedral lattice struc-tures,for example,M4X3Y3(M=Pd/Ni,X/Y=S,Se or Te,X ≠ Y)monolayers are proved to display excellent out-of-plane piezoelectricity.Ni4Se3Te3 possesses the largest piezoelectric coefficient d33 of 61.57 pm/V,which is much larger than that of most 2D materials.Enhancing the electronic asymmetry further increases the out-of-plane piezoelectricity of Janus M4X3Y3 materials.Correspondingly,the out-of-plane piezoelectricity is positively correlated with the ratio of electronegativity difference(Red)and the electric dipole moment(P).This work provides alternative materials for energy harvesting nano-devices or self-energized wearable devices,and supplies a valuable guideline for predicting 2D materials with strong out-of-plane piezoelectricity.
查看更多>>摘要：Metasurfaces and metagratings offer new platforms for electromagnetic wave control with significant responses.However,metasurfaces based on abrupt phase change and resonant structures suffer from the drawback of high loss and face challenges when applied in water waves.Therefore,the application of metasurfaces in water wave control is not ideal due to the limi-tations associated with high loss and other challenges.We have discovered that non-resonant metagratings exhibit promising effects in water wave control.Leveraging the similarity between bridges and metagratings,we have successfully developed a water wave metagrating model inspired by the ancient Luoyang Bridge in China.We conduct theoretical calculations and simulations on the metagrating and derive the equivalent anisotropic model of the metagrating.This model provides evidence that the metagrating has the capability to control water waves and achieve unidirectional surface water wave.The accuracy of our theory is strongly supported by the clear observation of the unidirectional propagation phenomenon during simulation and experiments conducted using a reduced version of the metagrating.It is the first time that the unidi-rectional propagation of water waves has been seen in water wave metagrating experiment.Above all,we realize the water wave metagrating experiment for the first time.By combining complex gratings with real bridges,we explore the physics embedded in the ancient building—Luoyang Bridge,which are of great significance for the water wave metagrating design and provide a new method for analyzing the effects of water waves on bridges.At the same time,this discovery also provides a new idea for ocean cargo transportation,ocean garbage cleaning,and the development and protection of ancient bridges.
查看更多>>摘要：Vortex beam with fractional orbital angular momentum(FOAM)is the excellent candidate for improving the capacity of free-space optical(FSO)communication system due to its infinite modes.Therefore,the recognition of FOAM modes with higher resolution is always of great concern.In this work,through an improved EfficientNetV2 based convolutional neural network(CNN),we experimentally achieve the implementation of the recognition of FOAM modes with a resolution as high as 0.001.To the best of our knowledge,it is the first time this high resolution has been achieved.Under the strong atmospheric turbulence(AT)(Cn=10-15 m-2/3),the recognition accuracy of FOAM modes at 0.1 and 0.01 resolution with our model is up to 99.12％and 92.24％for a long transmission distance of 2000 m.Even for the resolution at 0.001,the recognition accuracy can still remain at 78.77％.This work provides an effective method for the recogni-tion of FOAM modes,which may largely improve the channel capacity of the free-space optical communication.
查看更多>>摘要：Atom interferometer has been proven to be a powerful tool for precision metrology.Here we propose a cavity-aided nonlinear atom interferometer,based on the quasi-periodic spin mixing dynamics of an atomic spin-1 Bose-Einstein condensate trapped in an optical cavity.We unravel that the phase sensitivity can be greatly enhanced with the cavity-mediated nonlinear interaction.The influence of encoding phase,splitting time and recombining time on phase sensitivity are carefully studied.In addition,we demonstrate a dynamical phase transition in the system.Around the criticality,a small cavity light field variation can arouse a strong response of the atomic condensate,which can serve as a new resource for enhanced sensing.This work provides a robust protocol for cavity-enhanced metrol-ogy-ogy.
查看更多>>摘要：Boson sampling has been theoretically proposed and experimentally demonstrated to show quantum computational advantages.However,it still lacks the deep understanding of the practical applications of boson sampling.Here we propose that boson sampling can be used to efficiently simulate the work distribution of multiple identical bosons.We link the work distribution to boson sampling and numerically calculate the transi-tion amplitude matrix between the single-boson eigenstates in a one-dimensional quantum piston system,and then map the matrix to a linear optical network of boson sampling.The work distribution can be efficiently simulated by the output probabilities of boson sampling using the method of the grouped probability estimation.The scheme requires at most a poly-nomial number of the samples and the optical elements.Our work opens up a new path towards the calculation of complex quantum work distribu-tion using only photons and linear optics.
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