Spin Transport Properties In Zigzag Silicene Nanoribbons

The spin transport properties of pristine and substitutionally edge-doped zigzag silicene nanoribbons (ZSiNRs) are investigated using the nonequilibrium Green’s function (NEGF) method combined with the density functional theory (DFT). The geometric optimization is carried out by the Atomistix ToolKits (ATK) package. All structures are fully relaxed until the forces are smaller than0.02eV/A on each atom. Doping effects of elements from groups IIIA and VA, in a parallel (P) or antiparallel (AP) magnetic configuration of the two electrodes, are discussed. The two edges can be spin polarized in the same and opposite directions referred to as the ferromagnetic (FM) and antiferro-magnetic (AFM) state, respectively. By switching on and off the external magnetic field, we may convert the metallic ferromagnetic (FM) ZSiNRs into insulating antiferromagnetic (AFM) ZSiNRs. In a two probe system, the magnetizations of the two electrodes can be aligned in a P or AP configuration according to the directions that the two electrodes spin polarized. The magnetic configurations of the two electrodes considered are FM-P, FM-AP, AFM-P and AFM-AP.At equilibrium, the electronic structures and linear spin transport properties of pristine and substitutionally edge-doped zigzag silicene nanoribbons (ZSiNRs) are investigated. In the ferromagnetic state, even-or odd-width ZSiNRs exhibit a drastically different magnetoresistance. In an odd-width edge-doped ZSiNRs a large magnetoresistance occurs compared to that in a pristine ZSiNRs. The situation is reversed in even-width ZSiNRs. These phenomena result from the drastic changes in the conductance in the antiparallel configuration. In order to explain these changes, we calculate corresponding local density of states (LDOS) of Fermi energy and the molecular projected self-consistant Hamiltonian (MPSH) eigenstates. In addition, we find that the wider an odd-width edge-doped ZSiNRs is, the larger the magnetoresistance would be. What’s more, we find that different edge-doping position may cause drastically different linear conductance and magnetoresistance. If the edge-doping position is in the middle of the center rigion, the lenth of the center rigion has almost no influence on the linear conductance and magnetoresistance. We also take the doped center rigions as super cells and calculate their energy bands which can match well with their conductance curves in parallel magnetic configurations.For the nonequilibrium case, we study the nonlinear spin transport properties of pristine and substitutionally edge-doped zigzag silicene nanoribbons (ZSiNRs). In the FM-P and FM-AP configuration, I-V (current-voltage) characteristics of pristine and edge-doped ZSiNRs are metallic except for pristine even-width ZSiNRs in their FM-AP configuration that exhibiting semiconductor properties. In the AFM-P and AFM-AP configuration, I-V characteristics of pristine and edge-doped ZSiNRs are similar to semiconductor. In the FM-AP configuration, the pristine4-ZSiNRs shows a spin filter effect (SFE) with a spin filter ratio close to100%in the bias voltage range [-0.6,0.6] V. To explain this phenomena, we plot the contour maps of conductance vs bias voltage and energy. Besides, the energy bands of the left and right electrodes at various bias voltages are discussed. Among all the cases considered, only in B edge-doped4-ZSiNRs we observe very weak negative differential resistance (NDR) at their ferromagnetic states.