Study Of The Transport Properties Of Double Mesoscopic Ring

Recently,with the rapid advances of the nano-technology,it is possible to shape structures like dots,rings,etc,in which the mean free path of the electron is larger than the sample dimension.That the electron transport in such sys-tem is governed by quantum mechanics and results in many interesting quantum phenomena.Mesoscopic system is the hot topic of physics research in which the design and fabrication of quantum devices have attracted much of researcher's attention.In this work,we have made a detailed investigation on the transmission property in the double Mesoscopic ring.Based on the observation of the scatter-ing features of the double Aharonov-Bohm(AB)ring,we propose a device model with tunable flux-independent conductance in a T-shaped structure composed of open Aharonov-Bohm ring.Our arm is to explore the physical properties of the double Mesoscopic ring and provide theoretical background for the quantum device design based on these properties.At the beginning of this dissertation,we introduce the research evolution of Mesoscopic ring,some important characteristic lengths and some typical ef-fects,including Aharonov-Bohm effect,Aharonov-Casher effect,universal conduc-tance fluctuations,weak localization effect,coulomb blockade effect and quantum hall effect.Then,some theoretical methods are presented in chapter 2,including Landauer-Büttiker theory,scattering wave function method,scattering-matrix method,Green's function and quantum waveguide theory.In the section of the scattering wave function method,as a direct application of scattering wave func-tion method,we study spin accumulation effect in a two-terminal system with Rashba form of spin-orbit coupling,the results obtained in linear transport regime is in consistent with other theoretical as well as recent experimental results.In the third part,we provide a brief introduction of the transmission properties of the double AB ring without impurity.Using the quantum waveguide theory,we cal-culate the transmission coefficient of the double AB ring with one impurity and two impurities,respectively.We show that for different value of the kl(where k is the wave vector,l is the length of single ring)the dependence of the transmis-sion properties on impurities.Especially,when kl=2nπ,(n=0,1,…),impurities nearly have no influence on the transmission.Our investigation extends the ex-isting explanation of the transport properties of the double AB ring,which is valuable in designing quantum device.In the fourth part,we study the properties of multi-terminal double AC ring,including the transmission properties and the spin polarization effect.We show that non-polarized electrons entering through one arm can induce spin polarization of the outgoing waves on other arms.We can control the distribution of the spin by controlling the gate voltage and changing the value of the ka.This investigation is helpful in design of mesoscopic devices aiming at spintronics application.We propose a device model with tunable flux-independent conductance in a T—shape structure based on the scattering features of the double AB ring in the fifth part.Using the quantum waveguide theory,we investigate the properties of the transmission.When kl₃=(2n+1)π,(n=0,1,…) of the left double ring and kl₄=2nπ,(n=1,2,…)of the right double rings,We can control the transmission coefficient of one output by changing the value of kl₂.The transmission coefficient versus magnetic flux is quite flat.And the other output is flux-independent reflection,expectφ/φ₀=±n,(n=0,1,…).It is no-ticeable that this system is nonsensitive to the slight departure of the structure, thus it keeps its properties.This investigation can be used to supply a physical model and theoretical validity in designing a stable quantum device.Finally,we summary the whole work,and give an outlook of some problem in the future study.