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Ballistic point contact (BPC) with zigzag edges in graphene is a maincandidate of a valley filter, in which the polarization of the valley degree offreedom can be selected by using a local gate voltage. Here, we propose todetect the valley filtering effect by Andreev reflection. Because electrons inthe lowest conduction band and the highest valence band of the BPC possessopposite chirality, the inter-band Andreev reflection is strongly suppressed,after multiple scattering and interference. We draw this conclusion by both thescattering matrix analysis and the numerical simulation. The Andreev reflectionas a function of the incident energy of electrons and the local gate voltage atthe BPC is obtained, by which the parameter region for a perfect valley filterand the direction of valley polarization can be determined. The Andreevreflection exhibits an oscillatory decay with the length of the BPC, indicatinga negative correlation to valley polarization.

Probing valley filtering effect by Andreev reflection in zigzag graphene nanoribbon