Electric Control of Interlayer Excitons Dynamics in van der Waals Heterostructures

Van der Waals (vdW) heterostructures built of 2-dimensional (2D) materials, such as single layer transition metal dichalcogenides (TMDs) and boron nitride (h-BN), have generated wide interest to investigate novel optoelectronic devices. The large excitonic binding energy of TMDs and their intrinsic 2D nature allow for interesting ways to explore novel quantum optical effects in TMDs. We will discuss our recent results of vdWs heterostructures formed by stacking together two different TMDs (a type-II heterostructure) encapsulated with h-BN with electrical contacts and dual gate configuration. Using an optical excitation, we generate excitons with the electron and the hole each residing in the two different TMDs (interlayer excitons, IE). Thus, IEs have a dipole moment oriented out-of-plane and are repulsive in nature, because of the Coulomb interaction. With increasing excitation power, we create a large density of IEs (5x10¹¹ cm^-2) and observe long diffusion ~ 20µm even at elevated temperatures (T = 60K). Because the IEs diffuse from areas of larger density and temperature (the excitation spot), to regions outside the hot generation spot, they create a cold gas of bosons. A large density of IEs is important for novel optoelectronic devices such as IE condensates and lasers.