Effects Of Intervalley Scattering On Transport Properties Of Graphene

Recently,the investigation on the valley transport properties of graphene had attracted a great deal of attention.Graphene,with gapless and approximately linear electron spectrum near the Fermi energy is a two-dimensional signal layer of carbon atoms forming a dense honeycomb crystal lattice.There are two inequivalent Dirac points in the first Brillouin zone which are so-called K point and K' point.The K point and K' point are also called K valley and K' valley.Any intervalley scattering between two valleys can cause valley de-coherence.Because of the large distance in momentum space between two valleys,the intervalley scattering always is ignored in previous investigations.However,the sharp potential could cause intervalley scattering,such as square barrier and wells.And then the intervalley scattering causes valley polarization.In this paper the intervalley and intravalley transmission and reflection probabilities in zigzag grapheme nanoribbons with periodic boundary condition were investigated by tight-binding approximate method and Recursive Green's function technique.Due to effect of abrupt barriers and wells,the intervalley distance in momentum space changes small.Therefore,the intervalley scattering will be not ignored.It lead to appearance of valley polarization.The potential of barriers and wells will effect on the valley-dependent transmission and reflection probabilities,then influence on the valley polarization.Valley polarization will increase as the number of barriers and wells increases.In addition,valley polarization is related to the potential strength of barriers and wells.This is because that the potential strength change of barriers and wells can impact on the distance between the two valleys in momentum space as well.Therefore,the intervalley scattering can be indeed caused by the abrupt square barriers and wells.The intervalley scattering caused by the barriers and wells,which is formed by the gate on the surface of graphene,can result in electrical adjustable valley polarization current.These results provide a new investigation direction of valley-polarized transport properties of graphene.