Unconventional excitonic energy transfer in Van der Waals heterostructures

Two-dimensional (2D) Van der Waals quantum materials have shown great promises in next generation optoelectronic, electronic, and photonic applications. Heterostructures (HSs) made of stacking atomically thin layers of transition-metal dichalcogenides (TMDCs) allow us to manipulate the optical and spintronic properties. We fabricated the TMDC HSs of monolayers having the resonance between dark excitonic states. Here, we will present energy transfer (ET) process massively enhancing photoluminescence (PL) and valley polarization (VP) in these TMDC HSs, which is beyond conventional understanding of ET process. We utilize a series of optical and electron spectroscopy techniques complementing by the density functional theory calculations, to describe a massive PL and VP enhancement from the HS area due to an efficient dark excitonic energy transfer (ET) process. The observed data could be understood via phonon-bypass mechanism limiting non-radiative recombination of exciton at Van der Waals HSs.