Exploring matter wave scattering by means of the phase diagram

For matter wave scattering from passive quantum obstacles, we propose a phase diagram in terms of phase and modulus of scattering coefficients to explore all possible directional scattering patterns. In the phase diagram, we can not only have the physical bounds on scattering coefficients for all channels, but also indicate the competitions among absorption, extinction, and scattering cross sessions. With help of this phase diagram, we discuss different scenarios to steer scattering probability distribution, through the interference between $s$- and $p$-channels. In particular, we reveal the required conditions to implement a quantum scatterer, i.e., a quantum dot in semiconductor matrix, with a minimum (or zero) value in the scattering probability toward any direction. Our results provide a guideline in designing quantum scatterers with controlling and sensing matter waves.Comment: 6 pages, 3 figure

Revisit Kerker's conditions by means of the phase diagram

For passive electromagnetic scatterers, we explore a variety of extreme limits on directional scattering patterns in phase diagram, regardless of details on the geometric configurations and material properties. By demonstrating the extinction cross-sections with the power conservation intrinsically embedded in phase diagram, we give an alternative interpretation for Kerker first and second conditions, associated with zero backward scattering (ZBS) and nearly zero forward scattering (NZFS). The physical boundary and limitation for these directional radiations are illustrated, along with a generalized Kerker condition with implicit parameters. By taking the dispersion relations of gold-silicon core-shell nanoparticles into account, based on the of phase diagram, we reveal the realistic parameters to experimentally implement ZBS and NZFS at optical frequencies.Comment: 8 pages, 4 figure

Unidirectional polarization beam splitters via exceptional points and finite periodicity of Non-Hermitian PT-symmetry

We present a theoretical study of a novel polarization beam splitter (PBS), different to conventional time-reversal symmetry one, where can be totally reflected at two opposite sides with one specific linearly polarized light incident and can be transparent at only one side with its orthogonal linearly polarized light incident. %In addition, intensity of totally reflected beam would suffer from different The mechanism we employ is by both an exceptional point and finite periodicity of Non-Hermitian PT-symmetry. To be more specific, we design such PBS made of a finite periodic structure in which each unit cell has a delicate balance gain and loss in spatial distribution. In order to have one linearly polarized light totally reflected, the corresponding polarized unit cell has to be operated at some PT-symmetry phase of reflection band. To have single-sided transparent for its orthogonal polarized light, the corresponding polarized unit cell should be designed at an exceptional point as well as has asymmetric reflectance. Interestingly, such single-sided transparent phenomenon is independent of total number of unit cell. We believe this asymmetry PBS may excite a new route to polarization control

Particle Size Effects of TiO2 Layers on the Solar Efficiency of Dye-Sensitized Solar Cells

Large particle sizes having a strong light scattering lead to a significantly decreased surface area and small particle sizes having large surface area lack light-scattering effect. How to combine large and small particle sizes together is an interesting work for achieving higher solar efficiency. In this work, we investigate the solar performance influence of the dye-sensitized solar cells (DSSCs) by the multiple titanium oxide (TiO2) layers with different particle sizes. It was found that the optimal TiO2 thickness depends on the particle sizes of TiO2 layers for achieving the maximum efficiency. The solar efficiency of DSSCs prepared by triple TiO2 layers with different particle sizes is higher than that by double TiO2 layers for the same TiO2 thickness. The choice of particle size in the bottom layer is more important than that in the top layer for achieving higher solar efficiency. The choice of the particle sizes in the middle layer depends on the particle sizes in the bottom and top layers. The mixing of the particle sizes in the middle layer is a good choice for achieving higher solar efficiency