Spin Transport Properties Of Multi-terminal Semiconductor Mesoscopic Rings

Semiconductor mesoscopic rings have the advantages of high electron mobility and long spin coherence time.In semiconductor mesoscopic rings,the interaction of spin-orbit coupling(SOC)and quantum interference can be exploited as to control and manipulate the spin degree of freedom.Based on two-terminal rings,a series of spintronic device models,such as spin filter,spin flip and spin switch,have been proposed.However,due to the phase-locking effect,magnetic field is usually used to realize spin manipulation in two-terminal devices.From a practical point of view,people expect to get spintronic devices controlled only by electric field.People naturally think of multi-terminal ring devices.At the same time,in order to realize quantum logic operation and more quantum control,quantum ring arrays and polygonal quantum network models have been proposed and successfully fabricated in experiments.Three-terminal rings(TTRs)and four-terminal rings(FTRs)are the basic units of quantum ring networks.In the past decade,many theoretical and experimental studies have been carried out on multi-terminal rings.The results show that the spintronic devices based on multi-terminal rings can be controlled by electric field,and the logical calculation function can be realized by adding a magnetic field.Therefore,semiconductor multi-terminal rings have great potential value in spintronic devices and logic calculation.This paper reviews the research background of semiconductor mesoscopic rings.By reviewing the studies of two-and multi-terminal rings,several scientific problems are raised.Focusing on these scientific problems,this paper studies the spin transport properties of one-dimensional(1D)TTRs and FTRs.The main research contents and results are as follows:1.Based on quantum wave guide theory,the transmission amplitudes of 1D TTRs and FTRs are derived analytically,and the results are extended to weak magnetic field by perturbation theory.It is found that:(1)For TTRs and asymmetrical FTRs,the conductance curves present typical resonance and antiresonance characteristics,and there are two kinds of conductance zeros.The generation and evolution of the zeros are related to the phase coherence of the electron,the time reversal symmetry(TRS)and the spin reversal symmetry(SRS)of the system.(2)Two kinds of symmetry relations have been found in the conductances,the spin conductances and the spin polarizations of the multi-terminal rings.One is related tothe symmetry of the system,and the other is related to the commensurability of the configuration parameters,both are related to the TRS of the system and the inherent symmetry of the ring.(3)For the FTRs with axial or central symmetry,the phase-locking effect has been found in terminal 2 and the spin polarization is zero.(4)Under weak magnetic field,the Zeeman effect destroys both the TRS and the SRS,and all the conductance zeros are lifted.The branch conductance and total conductance of the system exhibit typical AB oscillation,and the Zeeman effect can change the amplitude of the conductances.Whether the structure is symmetrical or not,the total conductance is always the even function of the magnetic field.(5)With the increase of the strength of the RSOC,the effect of Zeeman splitting on the conductance decreases rapidly until it can be neglected.2.Using the tight-binding model and the Green's function method,the spin transport properties of multi-terminal rings are studied,the disorder effect and the interplay between the RSOC and the Dresselhaus SOC(DSOC)are considered.It is found that:(1)The disorder effect breaks the strict symmetry of the quantum ring structure,and destroys the phase coherence of the electron.Therefore,it produces weak anisotropic conductances,and lifts all of the conductance zeros.(2)The interplay between RSOC and DSOC destroys the inherent symmetry of the quantum ring.Therefore,neither of the two kinds of symmetry relations is valid,and obvious anisotropic conductances are produced at the symmetric outputs.Moreover,the phase-locking effect of the terminal 2 of the FTRs with axial symmetry is released,while that of the FTRs with central symmetry persists.