Long-distance decay-less spin transport in indirect excitons in a van der Waals heterostructure.

In addition to its fundamental interest, the long-distance spin transport is essential for spintronic devices. However, the spin relaxation caused by scattering of the particles carrying the spin limits spin transport. We explored spatially indirect excitons (IXs) in van der Waals heterostructures composed of atomically thin layers of transition-metal dichalcogenides as spin carries. We observed the long-distance spin transport: the spin polarized excitons travel over the entire sample,  ~10 micron away from the excitation spot, with no spin density decay. This transport is characterized by the 1/e decay distances reaching  ~100 micron. The 1/e decay distances are extracted from fits over the  ~10 micron sample size. The emergence of long-distance spin transport is observed at the densities and temperatures where the IX transport decay distances and, in turn, scattering times are strongly enhanced. The suppression of IX scattering suppresses the spin relaxation and enables the long-distance spin transport.