Van der Waals heterostructures constructed of 2-dimensional (2-D) materials such as single layer transition metal dichalcogenides (TMDs) have sparked wide interest because of their large excitonic binding energy, allowing the exploration of novel quantum optical effects in a solid-state system and new opto-electronic devices.
In this talk, I will discuss our results in van der Waals heterostructures formed by stacking together two different TMDs (forming a staggered heterojunction) encapsulated with hexagonal boron nitride (h-BN) with electrical contacts in each layer and a dual gate configuration.
Interlayer excitons, with electrons and holes residing in spatially separated quantum wells, have long lifetimes (> 200 nanoseconds, 5 orders of magnitude longer than intralayer exciton lifetimes). Because of their repulsive Coulomb interaction, they “diffuse” across the entire sample (20 m long) driven by interaction, allowing their manipulation towards condensation. We used local electric fields to localize interlayer excitons, and increase their local exciton densities to few 1012 cm-2 allowing the observation of signatures of Mott transitions. Also, we observed and manipulated long-lived charged interlayer excitons, by electrostatically doping the sample. When the chemical potential reaches the second conduction band in a TMD (MoSe2) we demonstrated the electrical tunability from spin-singlet to spin-triplet charged interlayer excitons. Our long-lived charged interlayer excitons can be used as carriers for quantum information.
Our results pave the way for novel optoelectronic devices as well as a step towards a solid-state platform for generating and exploring Bose-Einstein condensates at high temperatures, near-infrared tunable lasers and light emitting diodes.
Speaker: Luis Jauregui, UC Irving
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