title: Realization of Valley and Spin Pumps by Scattering at Nonmagnetic Disorders.
abstract: The recent success in optical pumping of valley polarization in two-dimensional transition metal dichalcogenides (TMDs) has greatly promoted the concept of valley-based informatics and electronics. However, between the demonstrated valley polarization of transient electron-hole pair excitations and practical valleytronic operations, there exist obvious gaps to fill, among which is the valley pump of long-lived charge carriers. Here we discover that the quested valley pump of electrons or holes can be realized simply by scattering at the ubiquitous nonmagnetic disorders, not relying on any specific material property. The mechanism is rooted in the nature of the valley as a momentum space index: the intervalley backscattering in general has a valley contrasted rate due to the distinct momentum transfers, causing a net transfer of population from one valley to another. As examples, we numerically demonstrate the sizable valley pump effects driven by charge current in nanoribbons of monolayer TMDs, where the spin-orbit scattering by nonmagnetic disorders also realizes a spin pump for the spin-valley locked holes. Our finding points to a new opportunity towards valley spintronics, turning disorders from a deleterious factor to a resource of valley and spin polarization.
authors.affiliation: Department of Physics and Center of Theoretical and Computational Physics, University of Hong Kong, Hong Kong, China.|School of Science, Hebei University of Science and Technology, Shijiazhuang, Hebei 050018, China.
authors.forename: Xing-Tao
authors.initials: XT
authors.lastname: An
authors.affiliation: Department of Physics and State Key Laboratory of Surface Physics, Fudan University, Shanghai 200433, China.|Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China.|Institute for Nanoelectronics Devices and Quantum Computing, Fudan University, Shanghai 200433, China.
authors.forename: Jiang
authors.initials: J
authors.lastname: Xiao
authors.affiliation: Department of Physics and Center of Theoretical and Computational Physics, University of Hong Kong, Hong Kong, China.
authors.forename: M W-Y
authors.initials: MW
authors.lastname: Tu
authors.affiliation: Department of Physics and Center of Theoretical and Computational Physics, University of Hong Kong, Hong Kong, China.
authors.forename: Hongyi
authors.initials: H
authors.lastname: Yu
authors.affiliation: National Graphene Institute, University of Manchester, Booth St E, Manchester M13 9PL, United Kingdom.
authors.forename: Vladimir I
authors.initials: VI
authors.lastname: Fal'ko
authors.affiliation: Department of Physics and Center of Theoretical and Computational Physics, University of Hong Kong, Hong Kong, China.
authors.forename: Wang
authors.initials: W
authors.lastname: Yao