Valley-polarized exciton dynamics in a 2D semiconductor heterostructure

Stacking to prolong valley lifetime In the material MoSe 2 , which, like graphene, has a two-dimensional honeycomb crystal lattice, the electronic structure has two “valleys.” Electrons can be distinguished by the valley they reside in, making them act as potential information carriers. However, electrons easily lose this information by scattering into the other valley. Rivera et al. placed single layers of MoSe 2 and WSe 2 on top of each other and shone circularly polarized light on the structure. The light caused excitons—pairs of electrons and holes—to form so that the hole and electron came from the same valley but different layers. The valley-specific character of such excitons persisted far longer than would be possible in a single layer of either material. Science , this issue p. 688