High-temperature exciton condensation in two-dimensional atomic double layers

Bose-Einstein condensate is the ground state of matter of a dilute gas of bosons, such as atoms cooled to temperatures close to absolute zero. With a much smaller mass than atoms, excitons have been predicted to condense at significantly higher temperatures. The small exciton binding energy in conventional semiconductors has so far limited the condensation temperature to below 1 K. In the past several years, a new class of two-dimensional (2D) semiconductors with much larger exciton binding energy has emerged. In this talk, I will discuss the development of transition metal dichalcogenide double layer structures and electrical injection of interlayer excitons up to 10¹² cm^-2 in the system. We study the electron-hole double layers through the interlayer tunneling and electroluminescence (EL). We observe a threshold dependence of the EL intensity on exciton density, accompanied by a super-Poissonian photon statistics near the threshold, and a large EL enhancement peaked narrowly at equal electron-hole densities. These results provide compelling evidence for interlayer exciton condensation in atomic double layers.