2D material exciton-polariton transport on 2D photonic crystals

Transport of elementary excitations is a fundamental property of 2D semiconductors, important for wide-ranging emergent phenomena and device applications. While exciton transport reported in 2D materials barely exceeds 1-2 $\mu$m, coherent coupling of excitons with photons to form polaritons allows not only greatly enhanced transport length, but also the potential to leverage photonic mode engineering for novel transport properties. However, conventional vertical cavity or waveguide polaritons are difficult to tune or integrate into photonic circuits. Here, we report the transport of transition-metal dichalcogenide polaritons in slab 2D photonic crystals that are highly versatile for tuning, mode-engineering and integration. We show an order-of-magnitude enhancement of the transport length compared to that of bare excitons. We further show the dependence of transport on the polariton dispersion and population dynamics, which we control by varying the photonic crystal design and pumping intensity. Stimulated relaxation observed in the system suggests the potential for forming superfluid polaritons with frictionless transport. These results demonstrate the 2D photonic crystal polariton system as a versatile platform to enhance and manipulate energy transport for novel photonic technologies.