Wang Fu-He

First-principles study of electronic properties and stability of Nb5SiB2 (001) surface

The density functional calculations are performed to study the electronic structure and stability of Nb5SiB2 (001) surface with different terminations. The calculated cleavage energies along the (001) planes in Nb5SiB2 are 5.015 J m−2 and 6.593 J m−2 with the break of Nb—Si and Nb—NbB bonds, respectively. There exists a close correlation between the surface relaxation including surface ripple and the cleavage energy: the larger the cleavage energy, the larger the surface relaxation. Moreover, the surface stability of the Nb5SiB2 (001) with different terminations has been investigated by the chemical potential phase diagram. Prom a thermodynamics point of view, the four terminations can be stabilized under different conditions. In chemical potential space, NbB (Nb) and Nb (Si) terminations are just stable in a small area, whereas Si (Nb) and Nb (NbB) terminations are stable in a large area (the letters in brackets represent the subsurface atoms).

Ultra-narrow bandwidth optical filters consisting of one-dimensional photonic crystals with anomalous dispersion materials

We present a new type of optical filter with an ultra-narrow bandwidth and a wide field-of-view (FOV). This kind of optical filter consists of one-dimensional photonic crystal (PC) incorporating an anomalous-dispersion-material (ADM) with, for instance, an anomalous dispersion of 6P(3/2) <- 6S(1/2) hyperfine structure transition of a caesium atom. The transmission spectra of optical filters are calculated by using the transfer-matrix method. The simulation results show that the designed optical filter has a bandwidth narrower than 0.33GHz and a wide FOV of +/- 30 degrees as well. The response of transmission spectrum to an external magnetic field is also investigated.

Correspondence between oscillations and emitted photon closed-orbits in spontaneous emission rate of an atom near a dielectric slab

We study the oscillations in the spontaneous emission rate of an atom near a dielectric slab. The emission rate is calculated as a function of system size using quantum electrodynamics. It exhibits multi-periodic oscillations. Four frequencies of the oscillations are extracted by Fourier transforms. They agree with actions of photon closed-orbits going away and returning to the atom. These oscillations are explained as manifestations of quantum interference effects between the emitted photon wave near the atom and the returning photon waves travelling along various closed-orbits.