Transition-metal oxyhalides MOX(M=Fe,Cr,V;O=oxygen,X=F,Cl,Br,I),an emerging type of two-dimensional(2D)van der Waals materials,have been both theoretically and experimentally demonstrated to possess unique electronic ...Transition-metal oxyhalides MOX(M=Fe,Cr,V;O=oxygen,X=F,Cl,Br,I),an emerging type of two-dimensional(2D)van der Waals materials,have been both theoretically and experimentally demonstrated to possess unique electronic and magnetic properties.However,the intrinsic in-plane anisotropic properties of 2D VOCl still lacks in-depth re-search,especially optical anisotropy.Herein,a systematic Raman spectroscopic study is performed on VOCl single-crystal with different incident laser polarization at various temperatures.The polarized-dependent Raman scattering spectra reveal that the Ag mode of VOCl show a 2-lobed shape in parallel polarization configuration while a 4-lobed shape in vertical configuration.In addition,the temperature-dependent and thickness-dependent Raman scattering spectra confirm a rela-tively weak van der Waals interaction between each layers among VOCl single crystal.These findings might provide better understanding on the in-plane anisotropic phenomenon in VOCl layers,thus will accelate further application of 2D single crystals for nanoscale angle-dependent optoelectronics.展开更多
Two-dimensional(2D)van der Waals(vdW)magnetic materials with strong in-plane anisotropy can make possible novel applications such as optospintronics and strain sensors.In this work,the strong in-plane optical anisotro...Two-dimensional(2D)van der Waals(vdW)magnetic materials with strong in-plane anisotropy can make possible novel applications such as optospintronics and strain sensors.In this work,the strong in-plane optical anisotropy in 2D vdW antiferromagnet VOCl has been systematically investigated.The optical brightness and absorption coefficient exhibit evident periodic variation with the change of incident polarization,unveiling the strong in-plane anisotropic optical absorption.The Raman intensity in this material shows obvious dependence on the polarization angle of incident laser,demonstrating that the phonon properties possess strong in-plane anisotropy.Besides,we have also realized in-situ visualization of in-plane optical reflection anisotropy in this material.Moreover,the strong second harmonic generation(SHG)signal can only be detected when the incident polarization is along specific in-plane crystal orientations,illustrating the presence of strong in-plane nonlinear optical anisotropy.These findings will benefit the applications of VOCl in the field of polarization-dependent electronics and spintronics.展开更多
We have measured the in-plane optical anisotropy (IPOA) of (1120) ZnO (a-plane) on (10]-2) sapphire (r-plane) by reflectance difference spectroscopy (RDS) at room temperature. Giant IPOA has been observed ...We have measured the in-plane optical anisotropy (IPOA) of (1120) ZnO (a-plane) on (10]-2) sapphire (r-plane) by reflectance difference spectroscopy (RDS) at room temperature. Giant IPOA has been observed be- tween the light polarized direction parallel and perpendicular to the c axis of ZnO, since the symmetry of a-plane is C2v. A sharp resonance has been observed near the fundamental band gap, which is induced by the polarization- depend band gap shift. The sharp line shape is attributed to the exciton transition. The spectra fitting and differential spectra indicate the polarization-depend band energies. The giant IPOA is possible enhanced by anisotropy strain along and perpendicular to the c axis in the a-plane.展开更多
The Al-Mg-Mn alloy sheets with and without trace Sc and Zr were investigated by means of tensile test, X-ray diffraction, optical microscope, and transmission electron microscope. The indexes of in-plane anisotropy (...The Al-Mg-Mn alloy sheets with and without trace Sc and Zr were investigated by means of tensile test, X-ray diffraction, optical microscope, and transmission electron microscope. The indexes of in-plane anisotropy (IIPA) of their tensile mechanical properties were calculated and their inverse pole figures were obtained by Harris method. The two alloy sheets have the same law of in-plane anisotropy and remarkable in-plane anisotropy of mechanical properties, and the IIPA of the alloy sheet with Sc and Zr is bigger than that of the alloy sheet without Sc and Zr. The relationships of the in-plane anisotropy and the anisotropy of the crystallographic texture were analyzed based on the model of monocrystal. It is the common action of the anisotropy of crystallography and microstructures that causes the in-plane anisotropy of their mechanical properties, but the major cause is the { 110 }〈112〉 crystallographic texture. The trace Sc and Zr can promote the formation and stabilization of the { 110 } 〈 112〉 texture, inhibit the formation of the { 100 } 〈001 〉 texture, and increase the in-plane anisotropy of the alloy sheet containing trace Sc and Zr.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
Amorphous Sm-Co films with uniaxial in-plane anisotropy have great potential for application in information-storage media and spintronic materials.The most effective method to produce uniaxial inplane anisotropy is to...Amorphous Sm-Co films with uniaxial in-plane anisotropy have great potential for application in information-storage media and spintronic materials.The most effective method to produce uniaxial inplane anisotropy is to apply an in-plane magnetic field during deposition.However,this method inevitably requires more complex equipment.Here,we report a new way to produce uniaxial in-plane anisotropy by growing amorphous Sm-Co films onto(011)-cut single-crystal substrates in the absence of an external magnetic field.The tunable anisotropy constant,kA,is demonstrated with variation in the lattice parameter of the substrates.A kA value as high as about 3.3×10^4J·m^-3 was obtained in the amorphous Sm-Co film grown on a LaAlO3(011)substrate.Detailed analysis indicated that the preferential seeding and growth of ferromagnetic(FM)domains caused by the anisotropic strain of the substrates,along with the formed Sm-Co,Co-Co directional pair ordering,exert a substantial effect.This work provides a new way to obtain in-plane anisotropy in amorphous Sm-Co films.展开更多
Prototypical three-dimensional(3D)topological Dirac semimetals(DSMs),such as Cd3As2 and Na3Bi,contain electrons that obey a linear momentum-energy dispersion with different Fermi velocities along the three orthogonal...Prototypical three-dimensional(3D)topological Dirac semimetals(DSMs),such as Cd3As2 and Na3Bi,contain electrons that obey a linear momentum-energy dispersion with different Fermi velocities along the three orthogonal momentum dimensions.Despite being extensively studied in recent years,the inherent Fermi velocity anisotropy has often been neglected in the theoretical and numerical studies of 3D DSMs.Although this omission does not qualitatively alter the physics of light-driven massless quasiparticles in 3D DSMs,it does quantitatively change the optical coefficients which can lead to nontrivial implications in terms of nanophotonics and plasmonics applications.Here we study the linear optical response of 3D DSMs for general Fermi velocity values along each direction.Although the signature conductivity-frequency scaling,σ(ω)∝ω,of 3D Dirac fermion is well-protected from the Fermi velocity anisotropy,the linear optical response exhibits strong linear dichroism as captured by the universal extinction ratio scaling law,Λi j=(vi/v j)^2(where i=j denotes the three spatial coordinates x,y,z,and vi is the i-direction Fermi velocity),which is independent of frequency,temperature,doping,and carrier scattering lifetime.For Cd3As2 and Na3Bi3,an exceptionally strong extinction ratio larger than 15 and covering a broad terahertz window is revealed.Our findings shed new light on the role of Fermi velocity anisotropy in the optical response of Dirac semimetals and open up novel polarization-sensitive functionalities,such as photodetection and light modulation.展开更多
Dipole coupled nanomagnets controlled by the static Zeeman field can form various magnetic logic interconnects.However, the corner wire interconnect is often unreliable and error-prone at room temperature. In this stu...Dipole coupled nanomagnets controlled by the static Zeeman field can form various magnetic logic interconnects.However, the corner wire interconnect is often unreliable and error-prone at room temperature. In this study, we address this problem by making it into a reliable type with trapezoid-shaped nanomagnets, the shape anisotropy of which helps to offer the robustness. The building method of the proposed corner wire interconnect is discussed,and both its static and dynamic magnetization properties are investigated. Static micromagnetic simulation demonstrates that it can work correctly and reliably. Dynamic response results are reached by imposing an ac microwave field on the proposed corner wire. It is found that strong ferromagnetic resonance absorption appears at a low frequency. With the help of a very small ac field with the peak resonance frequency, the required static Zeeman field to switch the corner wire is significantly decreased by ~21 m T. This novel interconnect would pave the way for the realization of reliable and low power nanomagnetic logic circuits.展开更多
The carrier-density-dependent spin relaxation dynamics for modulation-doped GaAs/Al0.3 Gao,TAs quantum wells is studied using the time-resolved magneto-Kerr rotation measurements. The electron spin relaxation time and...The carrier-density-dependent spin relaxation dynamics for modulation-doped GaAs/Al0.3 Gao,TAs quantum wells is studied using the time-resolved magneto-Kerr rotation measurements. The electron spin relaxation time and its in-plane anisotropy are studied as a function of the optically injected electron density, Moreover, the relative strength of the Rashba and the Dresselhaus spin-rbit coupling fields, and thus the observed spin relaxation time anisotropy, is further tuned by the additional excitation of a 532nm continuous wave laser, demonstrating an effective spin relaxation manipulation via an optical gating method.展开更多
Two-dimensional(2D)transition metal dichalcogenides(TMDs)have garnered considerable attention for their promising applications in sensors and optoelectronic devices,owing to their exceptional optical,electronic,and op...Two-dimensional(2D)transition metal dichalcogenides(TMDs)have garnered considerable attention for their promising applications in sensors and optoelectronic devices,owing to their exceptional optical,electronic,and optoelectronic properties.However,the inherent high symmetry of TMD lattices imposes limitations on their functional versatility.Here,we present a strategy to disrupt the C_(3)rotational symmetry of monolayer WSe_(2)by fabricating a heterostructure incorporating WSe_(2)and SiP flakes.Through comprehensive experimental investigations and first-principle calculations,we elucidate that in the WSe_(2)/SiP heterostructure,excitons-both neutral and charged-emanating from WSe_(2)exhibit pronounced anisotropy,which remains robust against temperature variations.Notably,we observe an anisotropic ratio reaching up to 1.5,indicating a substantial degree of anisotropy.Furthermore,we demonstrate the tunability of exciton anisotropy through the application of a magnetic field,resulting in a significant reduction in the anisotropic ratio with increasing field strength,from 1.57 to 1.18.Remarkably,the change in heterojunction anisotropy ratio reaches 24.8%as the magnetic field increases.Our findings elucidate that the perturbation of the C_(3)rotational symmetry of the WSe_(2)monolayer arises from a non-uniform charge density distribution within the layer,exhibiting mirror symmetry.These results underscore the potential of heterostructure engineering in tailoring the properties of isotropic materials and provide a promising avenue for advancing the application of anisotropic devices across various fields.展开更多
The mechanism of action of clearing agents to improve optical imaging of mouse skin during reflectance-mode confocal microscopy was tested.The dermal side of excised dorsal mouse skin was exposed for one hour to salin...The mechanism of action of clearing agents to improve optical imaging of mouse skin during reflectance-mode confocal microscopy was tested.The dermal side of excised dorsal mouse skin was exposed for one hour to saline,glycerin,or 80% DMSO,then the clearing agent was removed and the dermis placed against a glass cover slip through which a confocal microscope measured reflectance at 488 nm wavelength.An untreated control was also measured.The axial attenuation of reflectance signal,R(z_(f))versus increasing depth of focus zf behaved as R=ρexp(−μz_(f) 2G),where ρ is tissue reflectivity and μ is attenuation[cm^(−1)].The factor 2G accounts for the in/out path of photons,and the numerical aperture of the lens.The ρ,μ data were mapped to values of scattering coefficient(μ_(s)[cm^(−1)])and anisotropy of scattering(g).Images showed that glycerin significantly increased the g of dermis from about 0.7 to about 0.99,with little change in the μ_(s) of dermis at about 300cm^(−1).DMSO and saline had only slight and inconsistent effects on g and μ_(s).展开更多
We present the theoretical results of the electronic band structure of wurtzite GaN films under biaxial strains in the (11^-22)-plane. The calculations are performed by the k.p perturbation theory approach through u...We present the theoretical results of the electronic band structure of wurtzite GaN films under biaxial strains in the (11^-22)-plane. The calculations are performed by the k.p perturbation theory approach through using the effectivemass Hamiltonian for an arbitrary direction. The results show that the transition energies decrease with the biaxial strains changing from -0.5% to 0.5%. For films of (11^-22)-plane, the strains are expected to be anisotropic in the growth plane. Such anisotropic strains give rise to valence band mixing which results in dramatic change in optical polarisation property. The strain can also result in optical polarisation switching phenomena. Finally, we discuss the applications of these properties to the (1132) plane GaN-based light-emitting diode and lase diode.展开更多
Using Nd:YAG second harmonic pulse (100 ps), the optical storage properties of two novel polyesters, poly [4'-bis (N, N-oxyethylene) imino-4-nitroazobenzene succinyl] and poly [2'-chloro-4'-bis (N, N-oxyet...Using Nd:YAG second harmonic pulse (100 ps), the optical storage properties of two novel polyesters, poly [4'-bis (N, N-oxyethylene) imino-4-nitroazobenzene succinyl] and poly [2'-chloro-4'-bis (N, N-oxyethylene) imino-4-nitroazobenzene succinyl] have been studied by multiwave mixing. The high-order diffractions of the orientation gratings induced by anisotropy via the reorientation of nitroazobenzene groups and optical information storage with long-term stability have been realized by multiwave mixing in their films. Up to 3rd order forward diffraction was detected in two wave mixing, while up to 4th order backward diffraction was observed in degenerated four wave mixing. The recording mechanism was explained by the trans-cis-trans isomerization cycles of azobenzene groups. The isomerization of these azobenzene groups probably undergoes with inversion mechanism under the experimental conditions. The information recorded in these films has been kept for more than 6 months.展开更多
We present the specific ab-initio calculations that detail the variations of perovskite BaZrO3 caused by in-plane strain. Specifically, the internal relaxation, which was not captured in the widely used biaxial strain...We present the specific ab-initio calculations that detail the variations of perovskite BaZrO3 caused by in-plane strain. Specifically, the internal relaxation, which was not captured in the widely used biaxial strain model, was included in a complementary manner to lattice relaxation. Density functional theory as well as a hybrid functional method based on a plane wave basis set was employed to calculate the lattice structure, elastic constants, electronic properties and optical properties of perovskite BaZrO3. The lattice parameter c exhibited a clear linear dependence on the imposed in-plane strain, but the Poisson's ratio caused by internal relaxation was smaller than the elastic deformation, indicating an "inelastic" or "plastic" relaxation manner caused by the introduction of internal relaxation. As a result, the related electronic and optical properties of perovskite BaZrO3 were also strongly affected by the in-plane strain, which revealed an effective way to adjust the properties of perovskite BaZrO3 via internal relaxation.展开更多
The magnetization reversal process of Fe/MgO (001) thin film is investigated by combining transverse and longi- tudinal hysteresis loops. Owing to the competition between domain wall pinning energy and weak uniaxial...The magnetization reversal process of Fe/MgO (001) thin film is investigated by combining transverse and longi- tudinal hysteresis loops. Owing to the competition between domain wall pinning energy and weak uniaxial magnetic anisotropy, the typical magnetization reversal process of Fe ultrathin film can take place via either an "l-jump" process near the easy axis, or a "2-jump" process near the hard axis, depending on the applied field orientation. Besides, the hysteresis loop presents strong asymmetry resulting from the variation of the detected light intensity due to the quadratic magneto-optic effect. Furthermore, we modify the detectable light intensity formula and simulate the hysteresis loops of the Kerr signal. The results show that they are in good agreement with the experimental data.展开更多
二维Ag2S是一种具有间接宽带隙的半导体材料,由其在平面内和平面外具有独特的力学性质,因此受到了人们的广泛关注.本文基于密度泛函理论进行了第一性原理计算,研究了二维Ag2S的电子、光学性质的变化.二维Ag2S具有较强的方向各异性,通过...二维Ag2S是一种具有间接宽带隙的半导体材料,由其在平面内和平面外具有独特的力学性质,因此受到了人们的广泛关注.本文基于密度泛函理论进行了第一性原理计算,研究了二维Ag2S的电子、光学性质的变化.二维Ag2S具有较强的方向各异性,通过不同浓度的O取代S替换掺杂,发现随着O浓度的增加,带隙值出现先增大后减小的现象;由于O元素的引入,使二维Ag2S结构对称性降低,引起能带及光吸收、光反射的分布离散化.y方向4.56~5.36 e V处光吸收及光反射峰随掺杂浓度增加逐渐减小,且出现明显的蓝移.展开更多
基金Project financially supported by National Natural Science Foundation of China (Grant No. U1932201)the International Partnership Program (Grant No. 211134KYSB20190063)+3 种基金the CAS (Chinese Academy of Sciences) Collaborative Innovation Program of Hefei Science Center (Grant No. 2020HSCCIP002)the University Synergy Innovation Program of Anhui Province, China (Grant No. GXXT-2020-002)the Youth Innovation Promotion Association of CAS (Grant No. 2022457)the USTC Research Funds of the Double First-Class Initiative (YD2310002004)
文摘Transition-metal oxyhalides MOX(M=Fe,Cr,V;O=oxygen,X=F,Cl,Br,I),an emerging type of two-dimensional(2D)van der Waals materials,have been both theoretically and experimentally demonstrated to possess unique electronic and magnetic properties.However,the intrinsic in-plane anisotropic properties of 2D VOCl still lacks in-depth re-search,especially optical anisotropy.Herein,a systematic Raman spectroscopic study is performed on VOCl single-crystal with different incident laser polarization at various temperatures.The polarized-dependent Raman scattering spectra reveal that the Ag mode of VOCl show a 2-lobed shape in parallel polarization configuration while a 4-lobed shape in vertical configuration.In addition,the temperature-dependent and thickness-dependent Raman scattering spectra confirm a rela-tively weak van der Waals interaction between each layers among VOCl single crystal.These findings might provide better understanding on the in-plane anisotropic phenomenon in VOCl layers,thus will accelate further application of 2D single crystals for nanoscale angle-dependent optoelectronics.
基金S.X.Y.is supported by the National Natural Science Foundation of China(NSFC)(No.51972007).
文摘Two-dimensional(2D)van der Waals(vdW)magnetic materials with strong in-plane anisotropy can make possible novel applications such as optospintronics and strain sensors.In this work,the strong in-plane optical anisotropy in 2D vdW antiferromagnet VOCl has been systematically investigated.The optical brightness and absorption coefficient exhibit evident periodic variation with the change of incident polarization,unveiling the strong in-plane anisotropic optical absorption.The Raman intensity in this material shows obvious dependence on the polarization angle of incident laser,demonstrating that the phonon properties possess strong in-plane anisotropy.Besides,we have also realized in-situ visualization of in-plane optical reflection anisotropy in this material.Moreover,the strong second harmonic generation(SHG)signal can only be detected when the incident polarization is along specific in-plane crystal orientations,illustrating the presence of strong in-plane nonlinear optical anisotropy.These findings will benefit the applications of VOCl in the field of polarization-dependent electronics and spintronics.
基金Project supported by the State Key Development Program for Basic Research of China(Nos.2013CB619306,2012CB921304)the National Natural Science Foundation of China(No.60990313)the National High Technology Research and Development Program of China(No.2011AA03A101)
文摘We have measured the in-plane optical anisotropy (IPOA) of (1120) ZnO (a-plane) on (10]-2) sapphire (r-plane) by reflectance difference spectroscopy (RDS) at room temperature. Giant IPOA has been observed be- tween the light polarized direction parallel and perpendicular to the c axis of ZnO, since the symmetry of a-plane is C2v. A sharp resonance has been observed near the fundamental band gap, which is induced by the polarization- depend band gap shift. The sharp line shape is attributed to the exciton transition. The spectra fitting and differential spectra indicate the polarization-depend band energies. The giant IPOA is possible enhanced by anisotropy strain along and perpendicular to the c axis in the a-plane.
基金This work was financially supported by the National Key Fundamental Research Development Program (No.G1999064911).
文摘The Al-Mg-Mn alloy sheets with and without trace Sc and Zr were investigated by means of tensile test, X-ray diffraction, optical microscope, and transmission electron microscope. The indexes of in-plane anisotropy (IIPA) of their tensile mechanical properties were calculated and their inverse pole figures were obtained by Harris method. The two alloy sheets have the same law of in-plane anisotropy and remarkable in-plane anisotropy of mechanical properties, and the IIPA of the alloy sheet with Sc and Zr is bigger than that of the alloy sheet without Sc and Zr. The relationships of the in-plane anisotropy and the anisotropy of the crystallographic texture were analyzed based on the model of monocrystal. It is the common action of the anisotropy of crystallography and microstructures that causes the in-plane anisotropy of their mechanical properties, but the major cause is the { 110 }〈112〉 crystallographic texture. The trace Sc and Zr can promote the formation and stabilization of the { 110 } 〈 112〉 texture, inhibit the formation of the { 100 } 〈001 〉 texture, and increase the in-plane anisotropy of the alloy sheet containing trace Sc and Zr.
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 the National Key Research and Development Program of China(2017YFB0702702,2018YFA0305704,2016YFB700903,2017YFA0303601,and 2017YFA0206300)the National Natural Sciences Foundation of China(51531008,51771223,51590880,11674378,51971240,U1832219,and 11934016)+2 种基金the Inner Mongolia Science and Technology Major Project of China 2016the Strategic Priority Research Program(B)Key Programof the Chinese Academy of Sciences(CAS).
文摘Amorphous Sm-Co films with uniaxial in-plane anisotropy have great potential for application in information-storage media and spintronic materials.The most effective method to produce uniaxial inplane anisotropy is to apply an in-plane magnetic field during deposition.However,this method inevitably requires more complex equipment.Here,we report a new way to produce uniaxial in-plane anisotropy by growing amorphous Sm-Co films onto(011)-cut single-crystal substrates in the absence of an external magnetic field.The tunable anisotropy constant,kA,is demonstrated with variation in the lattice parameter of the substrates.A kA value as high as about 3.3×10^4J·m^-3 was obtained in the amorphous Sm-Co film grown on a LaAlO3(011)substrate.Detailed analysis indicated that the preferential seeding and growth of ferromagnetic(FM)domains caused by the anisotropic strain of the substrates,along with the formed Sm-Co,Co-Co directional pair ordering,exert a substantial effect.This work provides a new way to obtain in-plane anisotropy in amorphous Sm-Co films.
基金Project supported by Singapore Ministry of Education(MOE)Tier 2 Grant No.(2018-T2-1-007)USA ONRG Grant No.(N62909-19-1-2047)+2 种基金JL is supported by MOE PhD RSS.KJAO acknowledges the funding support of Xiamen University Malaysia Research Fund,Grant Nos.XMUMRF/2019-C3/IECE/0003 and XMUMRF/2020-C5/IENG/0025the Ministry of Higher Education Malaysia under the Fundamental Research Grant No.Scheme,Grant No.FRGS/1/2019/TK08/XMU/02CZ acknowledges the funding support by the Australian Research Council(Grant No.DP160101474).
文摘Prototypical three-dimensional(3D)topological Dirac semimetals(DSMs),such as Cd3As2 and Na3Bi,contain electrons that obey a linear momentum-energy dispersion with different Fermi velocities along the three orthogonal momentum dimensions.Despite being extensively studied in recent years,the inherent Fermi velocity anisotropy has often been neglected in the theoretical and numerical studies of 3D DSMs.Although this omission does not qualitatively alter the physics of light-driven massless quasiparticles in 3D DSMs,it does quantitatively change the optical coefficients which can lead to nontrivial implications in terms of nanophotonics and plasmonics applications.Here we study the linear optical response of 3D DSMs for general Fermi velocity values along each direction.Although the signature conductivity-frequency scaling,σ(ω)∝ω,of 3D Dirac fermion is well-protected from the Fermi velocity anisotropy,the linear optical response exhibits strong linear dichroism as captured by the universal extinction ratio scaling law,Λi j=(vi/v j)^2(where i=j denotes the three spatial coordinates x,y,z,and vi is the i-direction Fermi velocity),which is independent of frequency,temperature,doping,and carrier scattering lifetime.For Cd3As2 and Na3Bi3,an exceptionally strong extinction ratio larger than 15 and covering a broad terahertz window is revealed.Our findings shed new light on the role of Fermi velocity anisotropy in the optical response of Dirac semimetals and open up novel polarization-sensitive functionalities,such as photodetection and light modulation.
基金Supported by the National Natural Science Foundation of China under Grant No 61302022
文摘Dipole coupled nanomagnets controlled by the static Zeeman field can form various magnetic logic interconnects.However, the corner wire interconnect is often unreliable and error-prone at room temperature. In this study, we address this problem by making it into a reliable type with trapezoid-shaped nanomagnets, the shape anisotropy of which helps to offer the robustness. The building method of the proposed corner wire interconnect is discussed,and both its static and dynamic magnetization properties are investigated. Static micromagnetic simulation demonstrates that it can work correctly and reliably. Dynamic response results are reached by imposing an ac microwave field on the proposed corner wire. It is found that strong ferromagnetic resonance absorption appears at a low frequency. With the help of a very small ac field with the peak resonance frequency, the required static Zeeman field to switch the corner wire is significantly decreased by ~21 m T. This novel interconnect would pave the way for the realization of reliable and low power nanomagnetic logic circuits.
基金Supported by the National Natural Science Foundation Program of China under Grant Nos 11274302,11474276 and 61290303
文摘The carrier-density-dependent spin relaxation dynamics for modulation-doped GaAs/Al0.3 Gao,TAs quantum wells is studied using the time-resolved magneto-Kerr rotation measurements. The electron spin relaxation time and its in-plane anisotropy are studied as a function of the optically injected electron density, Moreover, the relative strength of the Rashba and the Dresselhaus spin-rbit coupling fields, and thus the observed spin relaxation time anisotropy, is further tuned by the additional excitation of a 532nm continuous wave laser, demonstrating an effective spin relaxation manipulation via an optical gating method.
基金the financial support from various sources.These include the National Natural Science Foundation of China(Nos.52373311,62090035,and U19A2090)the Youth Innovation Team of CSU(No.2019012)+8 种基金the Hunan Provincial Science Fund for Distinguished Young Scholars(No.2020JJ2059)the Hunan Province Key Research and Development Project(No.2019GK2233)the Key Program of Science and Technology Department of Hunan Province(Nos.2019XK2001 and 2020XK2001)the Science and Technology Innovation Basic Research Project of Shenzhen(No.JCYJ20190806144418859)the support of the High-Performance Complex Manufacturing Key State Lab Project,Central South University(No.ZZYJKT2020-12)the Australian Research Council(ARC Discovery Project,DP180102976)the support of the National Natural Science Foundation of China(Nos.92263202 and 12374020)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB33000000)the National Key Research and Development Program of China(No.2020YFA0711502).
文摘Two-dimensional(2D)transition metal dichalcogenides(TMDs)have garnered considerable attention for their promising applications in sensors and optoelectronic devices,owing to their exceptional optical,electronic,and optoelectronic properties.However,the inherent high symmetry of TMD lattices imposes limitations on their functional versatility.Here,we present a strategy to disrupt the C_(3)rotational symmetry of monolayer WSe_(2)by fabricating a heterostructure incorporating WSe_(2)and SiP flakes.Through comprehensive experimental investigations and first-principle calculations,we elucidate that in the WSe_(2)/SiP heterostructure,excitons-both neutral and charged-emanating from WSe_(2)exhibit pronounced anisotropy,which remains robust against temperature variations.Notably,we observe an anisotropic ratio reaching up to 1.5,indicating a substantial degree of anisotropy.Furthermore,we demonstrate the tunability of exciton anisotropy through the application of a magnetic field,resulting in a significant reduction in the anisotropic ratio with increasing field strength,from 1.57 to 1.18.Remarkably,the change in heterojunction anisotropy ratio reaches 24.8%as the magnetic field increases.Our findings elucidate that the perturbation of the C_(3)rotational symmetry of the WSe_(2)monolayer arises from a non-uniform charge density distribution within the layer,exhibiting mirror symmetry.These results underscore the potential of heterostructure engineering in tailoring the properties of isotropic materials and provide a promising avenue for advancing the application of anisotropic devices across various fields.
基金the National Institutes of Health(R01-CA113947,R01-HL084013)in the USAsupported by the National Institutes of Health under the Ruth L.Kirschstein National Research Service Award 5-T32-CA106195-05,“Training in the Molecular Basis of Skin Pathobiology”,from the National Cancer Institute and the OHSU Cancer Institutefunded by the National Cancer Institute,CA-069533.
文摘The mechanism of action of clearing agents to improve optical imaging of mouse skin during reflectance-mode confocal microscopy was tested.The dermal side of excised dorsal mouse skin was exposed for one hour to saline,glycerin,or 80% DMSO,then the clearing agent was removed and the dermis placed against a glass cover slip through which a confocal microscope measured reflectance at 488 nm wavelength.An untreated control was also measured.The axial attenuation of reflectance signal,R(z_(f))versus increasing depth of focus zf behaved as R=ρexp(−μz_(f) 2G),where ρ is tissue reflectivity and μ is attenuation[cm^(−1)].The factor 2G accounts for the in/out path of photons,and the numerical aperture of the lens.The ρ,μ data were mapped to values of scattering coefficient(μ_(s)[cm^(−1)])and anisotropy of scattering(g).Images showed that glycerin significantly increased the g of dermis from about 0.7 to about 0.99,with little change in the μ_(s) of dermis at about 300cm^(−1).DMSO and saline had only slight and inconsistent effects on g and μ_(s).
基金Project supported by the National Basic Research Program of China (Grant Nos. 2006CB604908 and 2006CB921607)the National Natural Science Foundation of China (Grant Nos. 60625402,60990313 and 60990311)
文摘We present the theoretical results of the electronic band structure of wurtzite GaN films under biaxial strains in the (11^-22)-plane. The calculations are performed by the k.p perturbation theory approach through using the effectivemass Hamiltonian for an arbitrary direction. The results show that the transition energies decrease with the biaxial strains changing from -0.5% to 0.5%. For films of (11^-22)-plane, the strains are expected to be anisotropic in the growth plane. Such anisotropic strains give rise to valence band mixing which results in dramatic change in optical polarisation property. The strain can also result in optical polarisation switching phenomena. Finally, we discuss the applications of these properties to the (1132) plane GaN-based light-emitting diode and lase diode.
文摘Using Nd:YAG second harmonic pulse (100 ps), the optical storage properties of two novel polyesters, poly [4'-bis (N, N-oxyethylene) imino-4-nitroazobenzene succinyl] and poly [2'-chloro-4'-bis (N, N-oxyethylene) imino-4-nitroazobenzene succinyl] have been studied by multiwave mixing. The high-order diffractions of the orientation gratings induced by anisotropy via the reorientation of nitroazobenzene groups and optical information storage with long-term stability have been realized by multiwave mixing in their films. Up to 3rd order forward diffraction was detected in two wave mixing, while up to 4th order backward diffraction was observed in degenerated four wave mixing. The recording mechanism was explained by the trans-cis-trans isomerization cycles of azobenzene groups. The isomerization of these azobenzene groups probably undergoes with inversion mechanism under the experimental conditions. The information recorded in these films has been kept for more than 6 months.
基金Funded by the National Natural Science Foundation of China(No.51502179)the Colleges and Universities in Hebei Province Science and Technology Research Project(No.YQ2014033)the Hebei Key Discipline Construction Project(B2012210004 and E2013210038)
文摘We present the specific ab-initio calculations that detail the variations of perovskite BaZrO3 caused by in-plane strain. Specifically, the internal relaxation, which was not captured in the widely used biaxial strain model, was included in a complementary manner to lattice relaxation. Density functional theory as well as a hybrid functional method based on a plane wave basis set was employed to calculate the lattice structure, elastic constants, electronic properties and optical properties of perovskite BaZrO3. The lattice parameter c exhibited a clear linear dependence on the imposed in-plane strain, but the Poisson's ratio caused by internal relaxation was smaller than the elastic deformation, indicating an "inelastic" or "plastic" relaxation manner caused by the introduction of internal relaxation. As a result, the related electronic and optical properties of perovskite BaZrO3 were also strongly affected by the in-plane strain, which revealed an effective way to adjust the properties of perovskite BaZrO3 via internal relaxation.
基金supported by the National Natural Science Foundation of China(Grant Nos.11274033,11474015,and 61227902)the Research Fund for the Doctoral Program of Higher Education of China(Grant No.20131102130005)the Beijing Key Discipline Foundation of Condensed Matter Physics
文摘The magnetization reversal process of Fe/MgO (001) thin film is investigated by combining transverse and longi- tudinal hysteresis loops. Owing to the competition between domain wall pinning energy and weak uniaxial magnetic anisotropy, the typical magnetization reversal process of Fe ultrathin film can take place via either an "l-jump" process near the easy axis, or a "2-jump" process near the hard axis, depending on the applied field orientation. Besides, the hysteresis loop presents strong asymmetry resulting from the variation of the detected light intensity due to the quadratic magneto-optic effect. Furthermore, we modify the detectable light intensity formula and simulate the hysteresis loops of the Kerr signal. The results show that they are in good agreement with the experimental data.
文摘二维Ag2S是一种具有间接宽带隙的半导体材料,由其在平面内和平面外具有独特的力学性质,因此受到了人们的广泛关注.本文基于密度泛函理论进行了第一性原理计算,研究了二维Ag2S的电子、光学性质的变化.二维Ag2S具有较强的方向各异性,通过不同浓度的O取代S替换掺杂,发现随着O浓度的增加,带隙值出现先增大后减小的现象;由于O元素的引入,使二维Ag2S结构对称性降低,引起能带及光吸收、光反射的分布离散化.y方向4.56~5.36 e V处光吸收及光反射峰随掺杂浓度增加逐渐减小,且出现明显的蓝移.