Imaging interlayer exciton superfluidity in a 2D semiconductor heterostructure.

Excitons, which are Coulomb bound electron-hole pairs, are composite bosons and thus at low temperature can form a superfluid state with a single well-defined amplitude and phase. We directly image this macroscopic exciton superfluid state in an hBN-separated MoSe-WSe heterostructure. At high density, we identify quasi-long-range order over the entire active area of our sample, through spatially resolved coherence measurements. By varying the exciton density and sample temperature, we map out the phase diagram of the superfluid. We observe the superfluid phase persisting to a temperature of 15 K, which is in excellent agreement with theoretical predictions. This works paves the way to realizing on chip superfluid structures capable of studying fundamental physical behaviors and quantum devices that use superfluidity.