Valley filter and valve effect by strong electrostatic potentials in graphene

Juan Juan Wang,Su Liu,Jun-Feng Liu,Jun Wang

doi:10.1038/s41598-017-10460-5

Juan Juan Wang, Su Liu + Show 2 more

Open Access

https://doi.org/10.1038/s41598-017-10460-5

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Abstract

We report a theoretical study on the valley-filter and valley-valve effects in the monolayer graphene system by using electrostatic potentials, which are assumed to be electrically controllable. Based on a lattice model, we find that a single extremely strong electrostatic-potential barrier, with its strength exceeding the hopping energy of electrons, will significantly block one valley but allow the opposite valley flowing in the system, and this is dependent on the sign of the potential barrier as well as the flowing direction of electrons. In a valley-valve device composed of two independent potential barriers, the valley-valve efficiency can even amount to 100% that the electronic current is entirely prohibited or allowed by reversing the sign of one of potential barriers. The physics origin is attributed to the valley mixing effect in the strong potential barrier region. Our findings provide a simple electric way of controlling the valley transport in the monolayer graphene system.

Highlights

The valley transport in 2D graphene-like materials has attracted much attention of researchers, because it is expected that the valley degree of freedom of electrons can exert the same effect as the electron spin in carrying and manipulating information[1,2,3]
Since we focus on the valley filter and valve effects, which are induced by the possible valley-mixing effect in the strong potential barrier, a lattice model is employed to describe the system
It is shown that the electrostatic potential V0/t < 0.2 near the Dirac point E = 0 does not lead to serious valley splitting of the electron transmissions

Summary

Model and Method

We first consider a simple two-terminal device in Fig. 1(a), where an electrostatic-potential barrier V0 is constructed in pristine graphene and connects directly with the left and right graphene leads. The electron transporting is assumed along the zigzag edge of graphene as shown, because in this case, the wavefunctions of electrons are clearly valley-separated, i.e., the propagating wavevectors of two valleys are different and one can construct the valley-dependent self-energy of leads. The energy diagram of the armchair-edge graphene is plotted, where the valley is shown degenerate around Dirac points. This implicates that the valley transport should heavily depend on the propagation direction of electrons in the graphene lattice, e.g., along the zigzag-edge or the armchair edge. A valley-valve device similar to the spin-valve one is considered as schematically shown, where two opposite potential barriers are put onto the monolayer graphene, which may be regarded as an antiparallel configuration. Vve should critically depend on the efficiency of the valley filtering effect in a single barrier region which is relied on V0

Results and Discussions

Conclusion

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