arXiv subjects

Tzong-Jer Yang

Publications and source records attributed to Tzong-Jer Yang.

4 recordsLinked to original sources

arXiv2008

Coherent control of spontaneous emission of a three-level atom in a coherent photonic band gap reservoir

By studying the fluorescence and optical properties of a three-level system, we propose a new point of view on the coherent control of these spectra. With the definite phase difference between the fields of the air band and dielectric band in photonic band gap (PBG) reservoirs, the spectra of spontaneous emission, absorption, and dispersion exhibit the coherent property and quantum interference effect. This coherent interference depending on the position of the embedded atom and the width of band gap causes the coupling of the free-space light and the PBG light to result in blue shift of spectra and the appearance of dark lines and kinks. By coherently controlling the position-dependent dispersion, we can tune the frequency of slow light.

cond-mat.mtrl-sci↗

arXiv2004

Thermoelectric effects in superconductors

It is widely believed that temperature gradient does not induce electric field in the superconductor and consequently that thermoelectric effects do not exist, or are negligible in these materials. This statement is correct only as far as effective electric field or gradient of the electrochemical potential is concerned. In normal metals temperature gradient generates effective electric field, which nulls out thermally induced diffusion current. In superconductor the diffusion current of quasiparticles is canceled a counterflow of supercurrent. Superconducting current induces the true electric field, which can be approximated by gradient of the screened Bernoulli potential. It explains familiar giant thermomagnetic flux observed in superconducting thermocouples. Contactless measurements of thermoelectric effects are suggested.

cond-mat.supr-con↗

arXiv2004

Unified treatment for classical waves in two-dimensional media

A unified treatment for the propagation of classical waves in inhhomogeneous media is proposed. We deal with four kinds of waves, they are the acoustic wave in fluid, the elastic shear wave in two diemnsional solid, and the E- and H-polarized electromagnetic waves in two diemnsional lossless medium. We first show that a universal wave equation governing the wave motion of all these four kinds of waves can be derived. We then introduce an auxiliary field, and give the universal expressions for the energy densities and energy flows of these waves. This unified treatment provides intuitive insights, which may be helpful in understanding the essential physics of various wave phenomena, or useful for designing new photonic and sonic devices.

cond-mat.mtrl-sci↗

arXiv2003

A novel view of plane wave expansion method in photonic crystals

We propose a method derived from the simple plane wave expansion that can easily solve the interface problem between vacuum and a semi-infinite photonic crystal. The method is designed to find the complete set of all the eigenfunctions, propagating or evanescent, of the translation operators $\{{\bf T_R} \}$, at a fixed frequency. With these eigenfunctions and their eigenvalues, the transmitted and reflected waves can be determined. Two kinds of applications are presented for 2D photonic crystals. The first is a selection rule for determine the normal direction of the vacuum-photonic crystal interface to achieve the highest attenuation effect at a gap frequency. The second is to calculate the transmittance and reflectance for a light incident from vacuum to an semi-infinite photonic crystal. As an example we recalculate a system studied previously by K. Sakoda et al. and get results in agreement with theirs.

physics.comp-ph↗