Study Of Spin Transport In Graphene Microstructure With Spin-orbit Coupling

Due its high mobility and potential long spin lifetime, graphene has been known as the first choice for the next generation electronic component materials. Now, a variety of spin-dependent interactions of graphene-based materials are being studied extensively in the experiment. In this research, we study the spin transport characteristics based on graphene modulated by the structure and external field with spin orbit coupling, the purpose is to reveal the physical mechanism of spin transport and explore its applications in spintronics. The major contents and important results are given as follows:(1) using the transfer matrix method, we investigate the spin precession and the spin transport properties of electrons through a graphene-based nanostructure with spatially modulated Rashba spin-orbit coupling(RSOC)and exchange field. It is found that the spin precession is directly related to incident energy, RSOC strength, incident angle, coupling length and exchange field. And the spin precession can be controlled accurately by modulating those parameters. In addition, a wide-angle spin filter can be achieved by parallel and anti-parallel magnetic fields combined with RSOC. In this structure, spin polarization can be achieved too, and the spin polarization is positive and negative for parallel and anti-parallel magnetic field respectively. Both of them increase with increasing RSOC strength and exchange field.(2) we have discussed the spin transport properties through a graphene-based multi-barrier nanostructure with exchange field and Rashba SOC. We found that only if the strength of Rashba SOC equals to exchange field, and moreover, the phase shift, which is induced by Rashba SOC and exchange field, satisfies the condition△θ=(2k+1)π,k=0,1,2... in single barrier, the parallel and anti-parallel magnetic multi-barriers nanostructures is an efficient way to achieve spin rotators and spin filters. In addition, we calculated the Fano factor of graphene-based double barrier with different electrostatic potential, and found the Fano factor for some a spin state electron can be enhanced by electrostatic potential, more important, a plateau of the Fano factor can be formed. However, the Fano factor of another spin state electron is very low in the vicinity of Dirac point and the maximum Fano factor is only about F=1/3.(3) The graphene-based RSOCand strain double junctions have been designed and the spin-polarized transports of electrons through the junctions have been investigated. For the electrons injected from left normal grapheme region, since the resonance depends strongly on the spin wave vector, high spin polarization oscillation is achieved by tuning the Fermi energy. In addition, a positive/negative switching effect for spin polarization can be obtained by tuning the stain strength or the normal grapheme region width. While the spin polarization is negligible for the electrons injected from right normal grapheme region.(4) We have studied spin-dependent transport properties of a graphene nanostructure under the modulations of the strain, RSOC and exchange splitting field. The high spin polarization component perpendicular to the graphene sheet is achieved by the combined effects of the strain and the RSOC. In addition,100%spin polarization can be achieved when the exchange splitting field, strain and RSOC are all present, and the location of the high spin polarization can be tuned by the exchange splitting field.