Long-Lived Direct and Indirect Interlayer Excitons in van der Waals Heterostructures

TLDR

The study investigates photoluminescence of interlayer excitons in monolayer MoSe₂/WSe₂ heterostructures at low temperatures. The authors attribute the observations to two types of interlayer excitons: one indirect in real space but direct in reciprocal space, and another indirect in both spaces. The measurements reveal a doublet of interlayer excitons with long lifetimes up to 100 ns, exhibiting temperature‑ and power‑dependent shifts—including a blue‑shift with higher excitation power—and suggest long‑lived interlayer states that may support bosonic many‑body interactions.

Abstract

We investigate the photoluminescence of interlayer excitons in heterostructures consisting of monolayer MoSe2 and WSe2 at low temperatures. Surprisingly, we find a doublet structure for such interlayer excitons. Both peaks exhibit long photoluminescence lifetimes of several ten nanoseconds up to 100 ns at low temperatures, which verifies the interlayer nature of both. The peak energy and linewidth of both show unusual temperature and power dependences. In particular, we observe a blue-shift of their emission energy for increasing excitation powers. At a low excitation power and low temperatures, the energetically higher peak shows several spikes. We explain the findings by two sorts of interlayer excitons; one that is indirect in real space but direct in reciprocal space, and the other one being indirect in both spaces. Our results provide fundamental insights into long-lived interlayer states in van der Waals heterostructures with possible bosonic many-body interactions