Valley Valve And Valley Transistor In Graphene

The valley degree of freedom as a novel degree has been well known to researchers in recent years,which forms a new subject called valleytronics.Generating and manipulating valley polarized current effectively is the main challenge in this field.Compared with traditional devices,valley-transistor preforms batter in response and energy saving.Valley transistor embodies great potential in applications.We use the green function method to study the valley transport properties caused of graphene under strain and/or in the presence of a graphene-In₂Te₂ superlattice?GS?structure.Valley valve and valve transistor are the two main parts in valleytronic device applications.Strain as well as GS structure have been regarded as two effective ways to manipulate valley degree.Our device is based on graphene with two leads which are under uniaxial strain.We first employ the same strains on the two leads,and then change the direction of one of them.We find that strains with contrary directions heavily affect valley transport,even shut down the transmission when the electron energy E is smaller than the difference of hopping energy induced by strain.This device can be called valley valve.We then consider a GS structure as the device area which is connected by two strained graphene leads.The GS structure generates a pseudovalley exchange field,which opens an energy gap determined by onsite energy of carbon atoms.In the transport gap of valley valve,the pseudovalley exchange field can precess valleys periodically when the electron energy is much larger than the GS energy gap.We find the valleys,manipulated by both onsite energy?_A and the length L of central GS area,precess periodically in real space.We realized the function of this kind of valley transistor.The results in this paper may shed new light on valleytronic devices.