Valley-polarized Transport Properties Of Monolayer Transition Metal Dichalcogenides Lateral Heterojunction

In 2004,the successful preparation of graphene broke the cognitive limitation that two-dimensional materials cannot exist stably in the scientific community.Since then,various related researches have attracted widespread attention.However,the properties of a single two-dimensional material no longer satisfy the research demands in recent years.People have gradually turned their attention to stacking or seamlessly connecting two different two-dimensional crystals.We choose two different monolayer transition metal dichalcogenides with similar structure to graphene,which can generally be considered as the band gap counterparts of graphene,using their smaller lattice mismatch and identical crystal structure to achieve lateral connection and investigate their valley-polarized transport properties.Two unequal degenerate extremes(usually called valleys)that are far apart and well distributed in the momentum space of the monolayer transition metal dichalcogenides lateral heterojunction,the naturally opened band gap and the superlattice structure that can be connected without external regulation have aroused our great research interest.As an emerging research device that can store and transmit information,valley electronics devices have been a hot issue of research in recent years.We choose two kinds of transition metal dichalcogenides to be alternately connected,one of which acts as a semi-infinite lead,and the direction of zigzag chain direction is chosen as the transport direction.The periodic boundary conditions is done via modifying the hopping between atomic sites by a Bloch phase factor.The valley polarization properties are explored by adjusting the relevant parameters of the heterojunction to control the intervalley scattering.We found that increasing the number of heterojunctions in the scattering region will significantly increase the valley polarizability.This is because the valley-related energy gap is formed by the multi-period structure of the superlattice.The size of the width of a single heterojunction will make the intervalley scattering oscillation obvious,which is related to the overlap of the wave functions of the two wells/barriers of the superlattice.Under the premise of imposing periodic boundary conditions,the change in the number of atoms in the armchair chain direction lattice period is basically independent of valley polarization,but the position of the valley-resolving minigap can be adjusted,so the superlattice can be used as a valley filter.Besides,we selected several monolayer transition metal dichalcogenides to combine them in pairs,and found that the valley polarizability can reach almost perfect 100% under certain conditions,which is a very efficient valley-filter.In addition,two superlattices connected in series can be used as a valley resistance device for electric field control.Such two lateral heterojunctions with relative valley polarization characteristics in series can realize an electrostatically controlled giant valley resistance device.Interestingly,we can control the perfect polarization of a specific valley by adjusting the incident energy,which is of great significance for the study of electron transport in related two-dimensional materials.