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Research on Wave Dynamics and Resonance Phenomena in Microstructures

Author: ChenZuo
Tutor: LiChunFang
School: Shanghai University
Course: Radio Physics
Keywords: optics and quantum microstructures resonance phenomenon group delay lateral displacement interference between the wavepackets
CLC: O436
Type: PhD thesis
Year: 2007
Downloads: 161
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Abstract

With the progress of science & technology and the development of information society, information technology such as integrated optics, large-scaled integrated circuits and quantum electronic devices has approached and even reached nanometre scale. Therefore, the research in this field is the forunner and basis for the high technology development in the 21st century. In this Ph. D. dissertation, the investigations of the wave dynamics and its resonance phenomena in the microstructures are presented. The main results given by the author are as follows:(i) The anomalous lateral displacement and its mechanism in the optics microstructures are investigated. Firstly, it is reported that the finite-sized light beam transmitted through a thin dielectric slab experiences four non-geometric effects, such as lateral displacement, angular deflection, modification of waist width, and longitudinal focal shift. Necessary conditions are advanced for the lateral displacement to be backward. The experimental observations of the backward displacement in the microwave region are reported for the first time. Secondly, I have found that the resonance-enhanced lateral displacement of the light beam transmitted through a left-handed slab can also be negative as well as positive. These show that the negative lateral displacement of the finite-sized light beam transmitted through a thin dielectric slab is the result of the interaction of the boundary effects of the slab, and have nothing to do with the negative refractive index itself. Finally, we have investigated the origin of the anomalous displacements in a thin dielectric slab by the interference between the multiple finite-sized light beam.(ii) The lateral displacements of the electron beam and their modulation in the two-dimensional quantum microstructures are investigated. It is found that the displacement of the electron beams transmitting through a two-dimensional semiconductor barrier is quite different from the prediction from Snell’s law for electron waves. It is shown that the displacement can be greatly enhanced by transmission resonance when the incidence angle is less than but close to the critical angle for total reflection. In addition, the lateral displacement of the transmitted electron beam through a semiconductor quantum well can be negative as well as positive. The necessary condition is obtained for the displacement to be negative. More importantly, the positive and negative displacements of the electron beam in transmission through a two-dimensional electron gas can be modulated by a ferromagnetic (FM) stripe under an applied voltage. These phenomena may lead to novel applications in quantum electronic devices.(iii) The anomalous group delay in the quantum structures and its mechanism are investigated. The theoretical and experimental researches have demonstrated that the group delay for quantum particles traveling through a potential well can be negative. Accordingly, the reflection and transmission group delay times are systematically investigated in an asymmetric single quantum barrier. It is found that the reflection times in both evanescent and propagating cases can be negative as well as positive, depending on the relative height of the potential energies on the two sides of the barrier. In evanescent case where the energy of incident particles is less than the height of the barrier, the reflection and transmission group delay times in the opaque limit are both independent of the barrier’s thickness. In the propagating case where the energy of incident particles is larger than the height of the barrier, the group delay times depend periodically on the barrier’s thickness, thus can be greatly enhanced by the transmission resonance. Finally, the physical mechanism of superluminal and even negative group delay in quantum well structure and the nature of Hartman effect in quantum barrier structure are investigated from the viewpoint of interference between multiple finite wave packets, due to the multiple reflections.(iv) The traversal times for Dirac particles through the quantum microstruc-tures are investigated. Firstly, the properties of group delay for Dirac particles traveling through a quantum potential well are investigated. A necessary condition is put forward for the group delay to be negative. It is shown that this negative group delay is closely related to its anomalous dependence on the width of the potential well around the resonance points. Furthermore, a traversal time that has no problem of superluminality for particles to tunnel through potential barriers in the non-relativistic quantum theory is generalized to Dirac’s relativistic quantum theory. Both evanescent and propagating cases are considered. It is shown that the traversal time in the evanescent case has much the same properties as in the non-relativistic quantum theory and thus has no problem of superluminality. It also gets rid of the problem of superluminality in the propagating case. Comparisons with the dwell time, the group delay, and the velocity of monochromatic front are also made.

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