The Electromagnetic Response In The Mesoscopic Nano-systems

The research of mesoscopic nano-systems is one of very active foreland research fields in the current condensed matter physics. It not only reveals a great deal of novel and marvelous physics properties, but also unfolds widely applied prospects. Moreover, the investigation on the mesoscopic structure will help to explain and verify some basic principles in quantum mechnicices on theory and experiment, respectively. In this thesis, we have systematic investigated the electrons transport and the surface plasmon polarizations in the mesoscopic nano-systems. Actually, these questions come down to the response of structure to the electromagnetic field (or turning potential). Its main purpose is to reveal some new effects and physical mechanisms in these structures. Meanwhile, it will support physics models and theoretical basis for the design and realizing quantum devices, which have excellent performances.Recently, many researches indicate that nanotube transistors will play a very important role in the future microelectronics technology and information systems, and are expected to replace the current silicon transistors into a more performance information materials. At present, there have been many associated reports about the nature of contact in the transport properties of carbon nanotube devices, but the discussions were mainly concentrated in the resistance characteristics of contact, and limited to dc transport. So in order to further study the contact effect in mesoscopic electronic dynamic transport of nano-system, basing on the Buttiker's scattering matrix theory, we discuss the role of wide contacts in the response to the external fields of a structure with barrier. Several physical quantities, such as the distributions of internal potential and charge density, capacitance, dipole and low frequency ac conductance, are calculated. Results show the contact effect on the capacitance is significant in resonant condition. These results and discussions are significant for the practical preparation and development of the nanotubes-based electronic devices. But this method is based on low frequency limits and is limitation in theory. For purpose of studying better the transport properties and the effects of strong correlative interactions between electrons of nano-system, we use the self-consistent field approach to deal with the interaction electrons in the mesoscopic nano-system and derive a set of self-consistent equations for general frequency case within the framework of general linear response theory and random phase approximation (RPA). This method can be used arbitrary shapes and boundary conditions, that is, it is universalistic approach. Basing on this theory, we employ a simple model, namely, a coherent parallel-plate capacitor, to investigate the frequency-dependence of capacitance. Meanwhile, we also obtain the distribution of the internal characteristics potential and the induced charges in this capacitor. For purpose of the size effect in the nano-structure, we will also discuss the distance-dependence of capacitance and compare it with classical geometric capacitance. Results show that the dynamic transports of electrons have close relationship with plasmon-like excitation. In the discussion of size effect, we should take account of the feature of the electrons distribution on the surface of the plates, so we introduce an effective screened length in the discussion.Last, within the framework of the general linear response theory and the dynamic self-consistent field method, we obtain non-local electromagnetic field equations. According to gold, we study emphatically the dispersion relation of the surface plasmon polarization for ultra-thin metal films by means of these equations. We also calculate the induced charge density and current density on the surface of the ultra-thin metal films structure.