Study On The Spin Transport Of Semiconductor Heterostructure Quantum Wire With Spin-Orbit Coupling

Spintronics is a rising crossing research area of several subjects,such as physics,informatics etc..The research object of spintronics is electron spin freedom and its target is to develop new type of spin electric devices substituting traditional electric devices,therefore,the research about spintronic has important scientific significance and background of application,and has been made progress for recent ten years.In this thesis we study spin polarization,spin accumulation,spin current and its induced electric field,and spin polarization dependent transport of a semiconductor heterostructure quantum wire(QW) with spin-orbit coupling(SOC) using scattering matrix method.The thesis consists of six chapters and is organized as follows:Chapter 1 is the part of introduction.We first give a summary of spintronics and the present research in semiconductor spintronics,respectively.Then we summarize briefly the main research contexts of the thesis.Chapter 2 gives the preparative knowledge for the thesis.We first introduce the knowledge semiconductor heterostructure,some typical artificial low dimensional structures and scattering matrix method,respectively.Then we deduce the expression of Rashba and Dresselhaus SOC(RSOC and DSOC) Hamitonian and calculate the corresponding electron structure for the heterostructure,respectively. Finally,we summarize research works about experimental observation of SOC effect.In chapter 3,we have mainly studied spin polarization and its induced spin accumulation of a SOC QW.First,using perturbation theory method,we have obtained the accurate solution of electron transverse wavefunctions in the coexis- tence of RSOC and DSOC for the parabolic or hard-wall potential confining QW, respectively.Furthermore,using the scattering matrix method,we deduce transmission and reflection matrices for the QW system connected to two normal leads, and obtain corresponding wavefunctions expressions.Finally,using the definition of local spin polarization,we calculate the components of spin polarization〈S_i〉(i=x,y,z) of the parabolic and hard-wall confining potential QW for different SOC cases,respectively.Our consequences indicate that,along the transverse direction of different confining potential QW,when the RSOC only exists,the out-of-plane spin polarization〈S_z〉indicates intrinsic spin accumulation,however, for the case of DSOC,〈S_z〉shows same direction spin polarization and indicates no spin accumulation.Moreover,when the two SOCs coexist in the hard-wall confined QW,the influence of RSOC on〈S_z〉is larger than that of DSOC,and when increasing the ratio of Rashba and Dresselhaus strength,〈S_z〉will gradually evolve into spin accumulation from same direction spin polarization.Finally,three spin polarization components〈S_i〉(except for〈S_z〉for the RSOC case with hard-wall confining potential) present intrinsic oscillations along the longitudinal direction of QW,and this character may be used to distinguish intrinsic spin accumulation from extrinsic one.In chapter 4,we have mainly investigated spin current and spin-current-induced electric field of a hard-wall confining potential QW with RSOC or DSOC, respectively.First,using the accurate solution of transverse wavefunctions in chapter 3,we deduce the linear and angular spin current densities for the RSOC or DSOC QW,respectively,and discuss the influences of the number of propagation mode and SOC strength on the nonzero spin current density elements.Then using the nonzero elements,we get spin-current-induced electric field for the RSOC or DSOC QW,respectively.Our consequences reveal that there exist two nonzero linear spin current density elements when the RSOC or DSOC exists,and the strengths of nonzero spin current density elements and spin-current-induced electric field for the RSOC QW are larger than that for the DSOC QW.And the strength of spin-current-induced electric field for the RSOC or DSOC QW is measurable with today's technology which takes a way of detecting spin current.In chapter 5,using scattering matrix method and Landauer-B(u|¨)ttiker formula, we have calculated spin dependent conductance and spin polarization P_z of hardwall potential confined QW system for the cases of RSOC,DSOC and two SOCs, respectively.Our results indicate that,for the above three SOC cases,the spin dependent conductance and spin polarization P_z present oscillation structures near the subband edges,and the quantized conductance plateaus are determined by the number of propagation mode in the two leads.Moreover,the splitting of spin-up and spin-down conductance plateaus for the SOC QW induces spin polarization (P_z≠0),and a large SOC strength destroy the conductance plateaus for the wider QW.Furthermore,when the two SOCs coexist and increasing the ratio of Rashba and Dresselhaus coefficients,the relative strength between spin-up and spin-down conductance is changed,therefore,the sign of P_z can be altered accordingly.The above results indicate that the spin dependent conductance and P_z are strongly dependent on the SOC strength,and which is the physical basis for spin transistor.Chapter 6 is the part of summary of our work.The innovation points of the thesis are pointed out but for a brief outlook of this research field and our rear works.