Yue E. Xie

Electron transport of L-shaped graphene nanoribbons

L-shaped graphene nanoribbons (LGNRs) are important components of nanoelectronics and nanocircuits. By using the Green’s function method, we study the transport properties of LGNRs, which consist of a semi-infinite armchair edged nanoribbon (AGNR) and a semi-infinite zigzag edged nanoribbon (ZGNR). The width of AGNR determines whether the LGNR is metallic or not. The LGNR with a small included angle has high reflectance to the electrons, while the LGNR with a large included angle is nearly reflectionless. These are opposite to the transport characteristics of the LGNRs, which consist of two semi-infinite ZGNRs. As to the right-angle LGNR, its transport properties are associated with the width of ZGNR. The increase of width will decrease the conductance around the Fermi energy and simultaneously induce sharp conductance dips. In addition, an interesting spatially resolved local density of state is found in the right-angle LGNR.

Electron transport of folded graphene nanoribbons

Recently, the AA-stack bilayer graphene nanoribbon (BGN) with a closed edge is observed in experiment. This new type of GN, we called folded GN (FGN), can be formed by folding a monolayer GN (MGN). Electron transport of the folded structures with different edges is studied. The FGNs show unique transport properties different from those of MGNs and BGNs. A metallic MGN with armchair edge (MAGN) is still metallic after folding. However, a semiconducting MAGN can be either semiconducting or metallic after folding, which depends on the width of MAGN and strength of interlayer coupling in the folded structure. The energy gap decreases with the increase of the coupling strength or width. As to the MGNs with zigzag edge (MZGNs), after folding they exhibit interesting conductance characteristics. The conductance steps around the Dirac point are even multiple of G0=2e2/h, while other conductance steps are odd multiple of G0. It indicates that the electron transport around the Dirac point in zigzag-edged FGNs (FZGN...

Spin transistor based on T-shaped graphene junctions

We propose a spin device based on a T-shaped graphene junction (TGJ) in which a ferromagnetic insulator and a metallic gate are deposited on the sidearm. Spin transport properties of the TGJ are studied by using the Green’s function method. It is found that spin-polarized transport can be achieved both far away from and near the Dirac point. The spin polarization far away from the Dirac point is correlated with the quasi-bound states in the junction, while the spin polarization near the Dirac point is due to the destruction of edge states. By varying the strength of the potential, i.e., the gate voltage on the sidearm, the spin polarization can be tuned quasi-periodically from −100% to 100%. In addition, the size of the sidearm also shows obvious influence on the spin polarization of TGJ.