Cutting monolayer graphene into flexible spin filters

Graphene is an atomically thin two-dimensional material which is well suited for kirigami-like cutting. We constructed a class of four-zigzag-edged parallelogram-shaped cutting graphenes as scattering region, forming an angle of 60° with electrodes. Based on the first-principles transport calculations, we have illustrated that this system has perfect spin filtering effect, which arises from hybrid spin states in occupied orbitals and bias-induced spin reversal in one of zigzag edges connecting to the electrodes. The spin filtering effect is reinforced with increasing the length of scattering region below a critical value, beyond which the effect may disappear. Fortunately, curling the cutting graphenes into three-dimensional helical structures can maintain the desirable transport properties in a much larger critical size. The results suggest that monolayer graphene can be tailored into perfect flexible spin filters, which may lead to important applications in spintronics and flexible electronics.