Control of interlayer valley excitons in atomically-thin MoSe₂-WSe₂ heterostructures

Atomically thin semiconductors, such as monolayer MoSe₂ and WSe₂, have emerged as novel optoelectronic materials, with coupled spin-valley electronic physics and excitons that are strongly bound at room temperature. It has recently been shown that these materials can form the basis for atomically thin p-n junctions, transistors, light emitting diodes, and low threshold nanolasers. In this presentation, I will discuss optoelectronics and spin effects in heterostructures of MoSe₂and WSe₂, with type-II band alignment, with the lowest conduction band in the MoSe₂ layer, and the highest valence band in the WSe₂ layer. Upon optical excitation, electrons transfer to the MoSe₂ layer and holes transfer to the WSe₂ layer. Due to the strong attractive Coulomb interaction between these spatially separated layers can form interlayer excitons which have many similarities to the spatially indirect excitons of coupled GaAs quantum wells. However, unlike the coupled quantum well system, here the constituent electrons and holes are located in momentum space valleys on the edge of the Brillouin zone. The conduction and valence band valley alignment can be tuned by twist angle between layers to realize optically bright interlayer excitons with an optical selection rule allowing for optical control of the valley degree of freedom. I will discuss the dynamics and spin-valley effects of these bright interlayer excitons.