Yuchen Xu

Low lattice thermal conductivity of stanene.

A fundamental understanding of phonon transport in stanene is crucial to predict the thermal performance in potential stanene-based devices. By combining first-principle calculation and phonon Boltzmann transport equation, we obtain the lattice thermal conductivity of stanene. A much lower thermal conductivity (11.6 W/mK) is observed in stanene, which indicates higher thermoelectric efficiency over other 2D materials. The contributions of acoustic and optical phonons to the lattice thermal conductivity are evaluated. Detailed analysis of phase space for three-phonon processes shows that phonon scattering channels LA + LA/TA/ZA ↔ TA/ZA are restricted, leading to the dominant contributions of high-group-velocity LA phonons to the thermal conductivity. The size dependence of thermal conductivity is investigated as well for the purpose of the design of thermoelectric nanostructures.

Effective medium theory for random media composed of two-layered spheres

We study the effective index of random media composed of two-layered spheres by using the energy-density coherent potential approximation method. As expected from the Ewald-Oseen extinction theorem, in the long-wavelength limit, the optical properties of a random medium composed of two-layered spheres are identical to those of a random medium composed of the corresponding pure spheres, while in the Mie-scattering region, the single-scattering resonances lead to an overall shift of the effective refractive index with the modified volume fraction.

Light transport in quasi-one-dimensional disordered waveguides composed of locally two-dimensional random square lattices

We present a numerical study on the light transport properties which are modulated by the disorder strength in quasi-one-dimensional disordered waveguide which consists of periodically arranged scatterers with random dielectric constant. The transport mean free path is found to stay inversely proportional to the square of the relative fluctuation of the dielectric constant as in the 1D and 2D cases but with . The transport properties of light through a sample with a fixed size can be modulated from ballistic to localized regime as well, and a generalized scaling function is defined to determine the light transport status in such a sample. The calculation of the diffusion coefficient and the energy density profile of the most transmitted eigenchannel clearly exhibits the transition of transport behaviour from diffusion to localization.Abstract We present numerical studies on the light transport properties which are tuned by the disorder strength in quasi-one-dimensional disordered waveguides consisting of periodically arranged scatterers with random dielectric constant. The transport mean free path is found to be inversely proportional to the square of the relative fluctuation of the dielectric constant as in the 1D and 2D cases but the proportionality coefficient is between those of 1D and 2D. The transport properties of light through a sample with a fixed size can be tuned from ballistic to localized regime as well, and a generalized scaling function is introduced to determine the light transport status in such a sample. The calculation of the energy density profile of the most transmitted eigenchannel clearly exhibits the transition of transport behaviour from diffusion to localization.

Light transmission properties in inhomogeneously‐disordered random media

We present a numerical study on the light transport properties and statistics of transmission channels in random media with inhomogeneous disorder. For the case of longitudinal inhomogeneity of disorder we find that the statistics of the transmission channels is independent of the inhomogeneity and the system can be equivalent to a counterpart with homogeneous disorder strength, both of which have the same statistical distribution of the transmission channels. However, for the case of transverse inhomogeneity of disorder, such equivalence does not exist, moreover, the transmission eigenvalues are pushed to the two ends of the distribution and the distribution of the total transmission is broadened since the spatial structure gives rise to larger and smaller transmitted incident channels.

Light transmission properties in inhomogeneously-disordered random media: Light transmission properties in inhomogeneously-disordered random media

We present a numerical study on the light transport properties and statistics of transmission channels in random media with inhomogeneous disorder. For the case of longitudinal inhomogeneity of disorder we find that the statistics of the transmission channels is independent of the inhomogeneity and the system can be equivalent to a counterpart with homogeneous disorder strength, both of which have the same statistical distribution of the transmission channels. However, for the case of transverse inhomogeneity of disorder, such equivalence does not exist, moreover, the transmission eigenvalues are pushed to the two ends of the distribution and the distribution of the total transmission is broadened since the spatial structure gives rise to larger and smaller transmitted incident channels.

Behaviour of light transmission channels in random media with inhomogeneous disorder

We present a numerical study on the light transport properties and statistics of transmission channels in random media with inhomogeneous disorder. For the case of longitudinal inhomogeneity of disorder we find that the statistics of the transmission channels is independent of the inhomogeneity and the system can be equivalent to a counterpart with homogeneous disorder strength, both of which have the same statistical distribution of the transmission channels. However, for the case of transverse inhomogeneity of disorder, such equivalence does not exist, moreover, the transmission eigenvalues are pushed to the two ends of the distribution and the distribution of the total transmission is broadened since the spatial structure gives rise to larger and smaller transmitted incident channels.

Representation and focusing properties of higher-order radially polarized Laguerre–Gaussian beams

A method based on higher-order Poincaré sphere was proposed to represent the states of polarization of higher-order radially polarized Laguerre–Gaussian (LG) vectorial beams (VBs). And the focusing properties of such LG beams of different radial orders focused by a high-NA lens were discussed. By tuning the ratio of the pupil radius to the waist of the incident beams, some cage-like or needlelike electric intensity field is generated in the focal region for several specific LG VBs with high order. Modulated by diffractive optical elements, the shape of the focal field shows novel behaviors such as splitting of cage-like modes, which provides potentially a more flexible control over micro-particles.

Modelling the optical properties of lossless multilayered spheres

Improved formulae for the Mie scattering of three-layered spheres are presented. By means of comparisons between the scattering cross-sections of three-layered spheres and two-layered spheres, the influence of Mie resonances on the curves of the scattering cross-sections when varying the radius of the core layer is investigated. The transport properties of random media composed of two-layered spheres are investigated as well.