Fluorescence Intermittency in Monolayer WSe_2

Fluorescence intermittent dynamics of single quantum emitters in monolayer WSe2 are investigated via measuring spectrally resolved time traces and time-dependent fluorescence intensity trajectories. Analysis of fluorescence trajectories and spectral shifting reveal a correlation between the fluorescence intermittency and spectral diffusion.A model of an inverse power law can be used to understand the observed blinking dynamics.     

Effect of Hydrostatic Pressure on Interband Transitions in Coupled Quantum Wires

We calculate the exciton binding energy and interband optical absorption in a rectangular coupled quantum wire under the hydrostatic pressure in the effective-mass approximation, using the variational approach. It is found that the interband optical absorption strongly depend on the hydrostatic pressure and the coupling parameter, and that the magnitude of the absorption coefficient for the HH1-E1 transition in the coupled quantum wire is larger than that of the single quantum wire.     

Strain Tunable Berry Curvature Dipole,Orbital Magnetization and Nonlinear Hall Effect in WSe_2 Monolayer

The electronic topology is generally related to the Berry curvature,which can induce the anomalous Hall effect in time-reversal symmetry breaking systems.Intrinsic monolayer transition metal dichalcogenides possesses two nonequivalent K and K’ valleys,having Berry curvatures with opposite signs,and thus vanishing anomalous Hall effect in this system.Here we report the experimental realization of asymmetrical distribution of Berry curvature in a single valley in monolayer WSe₂ via applying uniaxial strain to break C_3v symmetry.As a result,although the Berry curvature itself is still opposite in K and K’ valleys,the two valleys would contribute equally to nonzero Berry curvature dipole.Upon applying electric field E,the emergent Berry curvature dipole D would lead to an out-of-plane orbital magnetization M ∝ D·E,which further induces an anomalous Hall effect with a linear response to E²,known as nonlinear Hall effect.We show the strain modulated transport properties of nonlinear Hall effect in monolayer WSe₂ with moderate hole-doping by gating.The second-harmonic Hall signals show quadratic dependence on electric field,and the corresponding orbital magnetization per current density M/J can reach as large as 60.In contrast to the conventional Rashba-Edelstein effect with in-plane spin polarization,such current-induced orbital magnetization is along the out-of-plane direction,thus promising for high-efficient electrical switching of perpendicular magnetization.     

Scattering and Transmission by a Monolayer of Spheres: A Study on the Monolayer Structure

The angular distribution of scattered light and the transmission of radiation through a monolayer of monodisperse spherical particles at variable particle concentration are studied. The scattering of light by a single particle is calculated with the classical Lorentz‐Mie theory. For a monolayer of mono‐dispersed spherical particles, if the monolayer density is less than 0.5 and the particle size parameter is larger than 5, effects from multiple scattering and dependent scattering can be excluded so that only steric interactions are considered. It is found that the scattering pattern, especially in the forward and backward directions, and the transmission are strongly dependent on the monolayer density.     

Biaxial strain-induced enhancement in the thermoelectric performance of monolayer WSe_2

The effects of biaxial strain on the electronic structure and thermoelectric properties of monolayer WSe_2 have been investigated by using first-principles calculations and the semi-classical Boltzmann transport theory. The electronic band gap decreases under strain, and the band structure near the Fermi level of monolayer WSe_2 is modified by the applied biaxial strain. Furthermore, the doping dependence of the thermoelectric properties of n-and p-doped monolayer WSe_2 under biaxial strain is estimated. The obtained results show that the power factor of n-doped monolayer WSe_2 can be increased by compressive strain while that of p-doping can be increased with tensile strain. Strain engineering thus provides a direct method to control the electronic and thermoelectric properties in these two-dimensional transition metal dichalcogenides materials.     

Asymptotics of the Interband Light Absorption Coefficient near the Band Edge for an Alloy-Type Model

We find the asymptotics of the interband light absorption coefficient of an alloy-type model in the case when the ground-state energies of the electron and the hole Hamiltonians are finite.     

压强对二硼化镁超导电性的影响

基于强耦合理论的 Mc Millan公式 ,研究了压强对 Mg B2 超导电性的影响 ,得到了与实验趋于一致的结果 ,进一步表明了 Mg B2 的超导机制应在 BCS理论框架下讨论。并同时探讨了压强对 Mg B2 超导电性影响的物理机制     

Influence of Electric and Magnetic Fields on Interband Luminescence in Semiconductor Quantum Wires

Optics and Spectroscopy - Interband optical transitions in quantum wires have been theoretically investigated in the model of parabolic potential in electric and magnetic fields directed...     

Influence of Partial Coherent Light on the Transmission Spectrum and Goos-Hänchen Shift in Rydberg Atomic Medium

A cold atomic medium(Rydberg medium) with cascade configuration under the blockade mechanism is considered. A partial coherent light(PCL) beam is incident on the medium, which makes an angle θ with z-axis. We study the influence of PCL field on the transmission spectrum and find high transmission of probe field for PCL field.Conversely, it is investigated that the transparency of probe field decrease for coherent light field. The transmission of probe field is also studied via beam width of PCL field and investigated high transmission of probe field for small beam width and vice versa. Interestingly, the Goos-H?nchen shift(GHS) in the transmitted light(TL) is studied for PCL field. Large negative and positive GHS in the TL are investigated for PCL field and small beam width of PCL field.     

浅水湖泊中介质吸收系数的反演

基于在太湖、天目湖观测的水下光场资料,假定在水体中无内光源及无非弹性散射的情况下,通过水体中向上、向下的辐照度廓线分布,及由此确定的漫射反射率、漫射衰减系数,较为成功地反演了水体中介质的固有光学参数--吸收系数,且在较大程度上降低了由波浪及船舶阴影所带来的误差.同时将该反演结果与通过定量滤膜技术测定的结果进行了比较,二者吻合得较好.该方法有利于研究进入水体的太阳辐射能在各介质之间的分配及水生生态系统对水下光场的响应、大型浅水湖泊中蓝藻水华的暴发机理、提高二类水体水质定量遥感精度.     

几种半导体在高压下的金属化相变

 在金刚石压砧装置上，采用我们建立的电阻测量方法，研究了半导体InP_0.97As_0.03、InP_0.5As_0.5、Ga_0.76In_0.24As和Ga_0.24In_0.76As在室温下、16 GPa内的电阻与压力的关系。工作中，对测量技术进行了一些改进，采用微机进行测量控制和数据记录。实验结果表明，这些样品在测量的压力范围内，均发生了金属化相变。它们的相变压力分别为：10.3、9.7、13.5~14.6和10~10.4 GPa左右。这些实验结果在过去发表的文章中未见报导过。     

A Numerical Method for the Calculation of Transmission Coefficient

A numerical method is presented for calculating the quantum-mechanical transnmission coefficient of one-dimensional problems with potentials of arbitrary shapes. The method is demonstrated to give very accurate results on two solvabie examples. The numerical error in the calculated transmission coefficient is proportional to the second power of integration step size for potentials without discontinuities; for potentials with discontinuities, the dependence is linear.     

Transmission Fluctuation Spectrometry in Concentrated Suspensions Part One: Effects of the Monolayer Structure

The theory of transmission fluctuation spectrometry (TFS) was recently developed for particle size analysis in dilute flowing particle suspensions, whereby the statistical transmission fluctuations are used to extract the particle size distribution and particle concentration.     

Influence of Defects on First Order Structural Phase Transitions

The influence both of symmetry-breaking ("random local field") defects and of symmetry conserving ("random local transition temperature") ones on first order phase transitions is studied within the Landau theory. It is shown that an explicit account, for the elasticity effects, is important in the case of symmetry-breaking defects: the discontinuity of the order parameter at the transition increases due to the defects when the elasticity effects are taken into account but it decreases when they are neglected. For the symmetry-conserving defects, the account for the elasticity does not change the results qualitatively: the defects always diminish the discontinuity of the order parameter. The phase transition temperature always decreases due to the randomness induced by the two types of defects.     

Study of the Influence of Magnetic Fields on the Properties of Polar Liquids

The behavior of water and ethanol under the action of a weak magnetizing field is studied by the methods of high-frequency dielectric metering.     

Influence of Quantal and Statistical Fluctuations on Phase Transitions in Finite Nuclei

Investigations on thermal evolution of pairing-phase transition and shape-phase transition in light nuclei are made as a function of pair gap, deformation, temperature and angular momentum using a finite temperature statistical approach with main emphasis to fluctuations. The occurrence of a peak structure in the specific heat predicted as signals of the pairing-phase and shape-phase transitions are reviewed and it is found that they are not actually true phase
transitions and it is only an artifact of the mean field models. Since quantal number and spin fluctuations and statistical fluctuations in pair gap, deformation degrees of freedom and energy when incorporated, it wash out the pairing-phase transition and smooth out the shape-phase transition. Phase transitions due to collapse of pair gap and deformation is discussed and a clear picture of pairing-phase transition in light nuclei is presented in which pairing transition is reconciled.