Spin-valve effect in zigzag graphene nanoribbons by defect engineering

We report on the possibility for a spin-valve effect driven by edge defect engineering of zigzag graphene nanoribbons. Based on a mean-field spin-unrestricted Hubbard model, electronic band structures and conductance profiles are derived, using a self-consistent scheme to include gate-induced charge density. The use of an external gate is found to trigger a semiconductor-metal transition in clean zigzag graphene nanoribbons, whereas it yields a closure of the spin-split band gap in the presence of Klein edge defects. These features could be exploited to make charge- and spin-based switches and field-effect devices.

Figure 1

(Color online) Band structures of the clean ZGNR with (a) $V_g=0$ and (b) $V_g=1.5\text{V}$ for both up and down (degenerate) spins. Band structures of the ZGNR with one Klein edge when (c) $V_g=0$ and (d) $V_g=1.5\text{V}$ for up (red dotted) and down (black solid) spins. The schematic shows few unit cells of the clean ZGNR on the left. On the right, three Klein defect edges in an otherwise clean ZGNR have been shown for clarity.

Figure 2

Spin-degenerate (up and down) conductance of the ZGNR with respect to the incident energy of the electrons $\left(E\right)$ scaled by $E_F^g$ for (a) $V_g=0$ and (b) $V_g=1.5\text{V}$.

Figure 3

(Color online) (a) Variation in the band gap over the entire Brillouin zone with $V_g$. (b) The total number of up (red dashed) and down electrons (black solid) with respect to $V_g$. Dotted lines are marked at $V_g=0$ and $V_g=1.5\text{V}$ for clarity.

Figure 4

(Color online) Conductance of the Klein-edged ZGNR with respect to the incident energy of the electrons $\left(E\right)$ scaled by $E_F^g$ for (a) $V_g=0$ and (b) $V_g=1.5\text{V}$. Dashed (red) lines refer to the spin-up conductance and solid (black) lines refer to the spin-down conductance.