Figure 2: A schematic of the proposed valley filter. An incoming electron (with angle of incidence $\alpha$) approaching a line defect in graphene having components in both valleys $K$ and $K^{\prime }$ transmits the defect, for instance, preferentially in valley $K$ for a large angle of incidence, whereas the component in $K^{\prime }$ will be reflected in a specular way. This effect could be used to produce a valley-polarized current out of an unpolarized stream of electrons.