Improvement of valley splitting and valley injection efficiency for graphene/ferromagnet heterostructure**Project supported by the National Key R&D Program of China (Grant No. 2017YFF0206104), the National Natural Science Foundation of China (Grant No. 51871018), Beijing Laboratory of Metallic Materials and Processing for Modern Transportation, the Opening Project of Key Laboratory of Microelectronics Devices & Integrated Technology, Institute of Microelectronics of Chinese

Abstract

The valley splitting has been realized in the graphene/Ni heterostructure with the splitting value of 14 meV, and the obtained valley injecting efficiency from the heterostructure into graphene was 6.18% [Phys. Rev. B 92 115404 (2015)]. In this paper, we report a way to improve the valley splitting and the valley injecting efficiency of the graphene/Ni heterostructure. By intercalating an Au monolayer between the graphene and the Ni, the split can be increased up to 50 meV. However, the valley injecting efficiency is not improved because the splitted valley area of graphene moves away from the Fermi level. Then, we mend the deviation by covering a monolayer of Cu on the graphene. As a result, the valley injecting efficiency of the Cu/graphene/Au/Ni heterostructure reaches 10%, which is more than 60% improvement compared to the simple graphene/Ni heterostructure. Then we theoretically design a valley-injection device based on the Cu/graphene/Au/Ni heterostructure and demonstrate that the valley injection can be easily switched solely by changing the magnetization direction of Ni, which can be used to generate and control the valley-polarized current.