Wen-Quan Sui

Topological asymmetry induced electronic transport in three terminal graphene nanoribbon structure

Topological configurations play an important role in graphene nanoribbon based devices. In this work, the Buttiker’s ac transport theory is used to study an asymmetric three terminal graphene nanoribbon structure. With the help of Green’s function and related parameters, we show that the topological asymmetries can form capacitive and inductive junctions in this three terminal structure. The transport properties are sensitive to the geometric features of the branches of the junctions and the coupling positions. It is believed that this kind of structure can be useful for the future nanoelectronic devices.

Exchange effects on spin-dependent ac transport

Spin-dependent ac transport problem is studied with exchange effects. Spin-spin exchange interaction and charge-charge Coulomb interaction are included simultaneously to determine the landscape of internal potential and the spin-dependent ac conductance. Gauge invariance and charge conservation are still satisfied. But spin current is not conserved. It is found that the exchange effects affect spin conductance dramatically, and hardly influence charge conductance. This shows the role of spin-accumulation in spin-dependent transport.

Capacitive Effects of Gate on Spin-Dependent AC Transport

From the spin-spin interaction, spin-capacitive term is defined in a similar way to the usual charge capacitive term that is due to the charge-charge interaction. The charge and spin capacitive effects between the gate and central channel region are found to play an important role in gate-controlled spin-dependent transport systems. Both the capacitive terms affect systems charge and spin ac transport properties. The behaviors of conductance, density of states, and internal potentials demonstrate the strong involvement of charge and spin in electrons in spin-dependent transport. The purpose of this paper is to draw attention to the Coulomb and exchange interactions in spintronics devices.

Charge Relaxation Resistances in Gated Graphene Nanoribbons

We investigate the charge relaxation resistances in a typical graphene nanoribbon FET (GNRFET). We show that the behavior of the charge relaxation resistances heavily depends on the exerted gate voltage and the structural details of the GNRFET. When there is 0 channel (blocked), 1 channel, and N channels in the GNR as tuned by the gate voltage, the equilibrium charge relaxation resistance is roughly 1, 1/2, and 1/2N of Sharvin-Imry contact resistance (h/2e2), respectively, whereas the nonequilibrium charge relaxation resistance is much smaller. Our results indicate that the charge relaxation resistances characterizing the information of dissipation, RC time and noise can be controlled by the gate voltage.