Twist angle dependent interlayer transfer of valley polarization from excitons to free charge carriers in WSe2/MoSe2 heterobilayers
Frank Volmer, Manfred Ersfeld, Paulo E. Faria, Lutz Waldecker, Bharti Parashar, Lars Rathmann, Sudipta Dubey, Iulia Cojocariu, Vitaliy Feyer, Kenji Watanabe, Takashi Taniguchi, Claus M. Schneider, Łukasz Pluciński, Christoph Stampfer, Jaroslav Fabian, Bernd Beschoten
Abstract
Abstract Transition metal dichalcogenides (TMDs) have attracted much attention in the fields of valley- and spintronics due to their property of forming valley-polarized excitons when illuminated by circularly polarized light. In TMD-heterostructures it was shown that these electron-hole pairs can scatter into valley-polarized interlayer exciton states, which exhibit long lifetimes and a twist-angle dependence. However, the question how to create a valley polarization of free charge carriers in these heterostructures after a valley selective optical excitation is unexplored, despite its relevance for opto-electronic devices. Here, we identify an interlayer transfer mechanism in twisted WSe 2 /MoSe 2 heterobilayers that transfers the valley polarization from excitons in WSe 2 to free charge carriers in MoSe 2 with valley lifetimes of up to 12 ns. This mechanism is most efficient at large twist angles, whereas the valley lifetimes of free charge carriers are surprisingly short for small twist angles, despite the occurrence of interlayer excitons.