SPECIAL SEMINAR: Interlayer exciton phase transitions in atomically thin semiconductors

Andrew Y. Joe
Harvard University
Wednesday, July 14, 2021
3:00 pm
RH 142

Semiconducting transition metal dichalcogenides (TMDs), when reduced to the two-dimensional (2D) limit, exhibit extraordinary excitonic effects that serve as a versatile platform for optoelectronic studies. Interlayer excitons, where the electron and hole are in separate layers, form dipolar composite bosons across the atomically-thin type-II heterostructures and offer a rich phase diagram for these interacting excitations. Here, we fabricate high-quality TMD heterostructure devices that allow us to have electrical control of interlayer excitons. We can spatially pattern electrostatic gates to create exciton traps, demonstrating spatial control of the excitons, increased lifetimes, and large densities that approach the exciton Mott transition (electron-hole disassociation). We can also electrically generate interlayer excitons while controlling the charge density in the device. We observe a non-trivial increase in the degree of second-order coherence, or g2(t), of the interlayer exciton electroluminescence with increased bias voltage along charge neutrality. Intriguingly, we show that the g2(0) correlations extend over a spatial distance greater than our expected detection spot size and greater than the IE thermal de Broglie wavelength, and can be tuned with the bias voltage. The results presented here are important steps towards realizing the elusive high-temperature exciton condensate.

Luis Jauregui