Detection of spin currents by a three-terminal zigzag graphene nanoribbon junction

We propose a theoretical approach to detect spin currents by converting them into measurable charge currents or potentials in a three-terminal zigzag graphene nanoribbon (ZR) junction. By means of the Keldysh Green's function technique, we demonstrate that when pure spin currents are flowing into the middle region of a nonmagnetic n-doped/normal/p-doped (n/N/p) ZR junction or a ferromagnetic/normal/ferromagnetic (F/N/F) ZR junction, nonzero charge currents could be induced in the ZR terminals due to the combination of the spin-dependent chemical potential splitting and the valley-valve effect in the even-chain ZR. The induced charge currents can be affected by some system parameters such as the Fermi energy, the tunneling strength and the magnetization. It is also shown that the spin-polarized direction of the spin currents can be deduced from the charge currents in the F/N/F ZR junction. Our proposal may provide a useful way to indirectly detect pure spin currents in a graphene-based spin device.