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1. Photon correlation of photoluminescence emission of a monolayer WS2

   https://doi.org/10.1364/CLEO_QELS.2018.FTh1F.7  

   Huang, J.; Sarpkaya, I.; Lim, J.; Lee, S-J.; Duan, X.; Wong, C. W.; Htoon, H. (May 2018, CLEO: QELS_Fundamental Science 2018)
2. Observation of moiré excitons in WSe2/WS2 heterostructure superlattices

   https://doi.org/10.1038/s41586-019-0976-y  

   Jin, Chenhao; Regan, Emma C.; Yan, Aiming; Iqbal Bakti Utama, M.; Wang, Danqing; Zhao, Sihan; Qin, Ying; Yang, Sijie; Zheng, Zhiren; Shi, Shenyang; et al (March 2019, Nature)
3. Observation of interlayer plasmon polaron in graphene/WS2 heterostructures

   https://doi.org/10.1038/s41467-024-48186-4  

   Ulstrup, Søren; in_’t_Veld, Yann; Miwa, Jill A; Jones, Alfred_J H; McCreary, Kathleen M; Robinson, Jeremy T; Jonker, Berend T; Singh, Simranjeet; Koch, Roland J; Rotenberg, Eli; et al (December 2024, Nature Communications)

   Abstract Harnessing electronic excitations involving coherent coupling to bosonic modes is essential for the design and control of emergent phenomena in quantum materials. In situations where charge carriers induce a lattice distortion due to the electron-phonon interaction, the conducting states get “dressed, which leads to the formation of polaronic quasiparticles. The exploration of polaronic effects on low-energy excitations is in its infancy in two-dimensional materials. Here, we present the discovery of an interlayer plasmon polaron in heterostructures composed of graphene on top of single-layer WS₂. By using micro-focused angle-resolved photoemission spectroscopy during in situ doping of the top graphene layer, we observe a strong quasiparticle peak accompanied by several carrier density-dependent shake-off replicas around the single-layer WS₂conduction band minimum. Our results are explained by an effective many-body model in terms of a coupling between single-layer WS₂conduction electrons and an interlayer plasmon mode. It is important to take into account the presence of such interlayer collective modes, as they have profound consequences for the electronic and optical properties of heterostructures that are routinely explored in many device architectures involving 2D transition metal dichalcogenides. 

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4. Confinement of long-lived interlayer excitons in WS2/WSe2 heterostructures

   https://doi.org/10.1038/s42005-021-00625-0  

   Montblanch, Alejandro R.-P.; Kara, Dhiren M.; Paradisanos, Ioannis; Purser, Carola M.; Feuer, Matthew S.; Alexeev, Evgeny M.; Stefan, Lucio; Qin, Ying; Blei, Mark; Wang, Gang; et al (December 2021, Communications Physics)

   null (Ed.)

   Abstract Interlayer excitons in layered materials constitute a novel platform to study many-body phenomena arising from long-range interactions between quantum particles. Long-lived excitons are required to achieve high particle densities, to mediate thermalisation, and to allow for spatially and temporally correlated phases. Additionally, the ability to confine them in periodic arrays is key to building a solid-state analogue to atoms in optical lattices. Here, we demonstrate interlayer excitons with lifetime approaching 0.2 ms in a layered-material heterostructure made from WS 2 and WSe 2 monolayers. We show that interlayer excitons can be localised in an array using a nano-patterned substrate. These confined excitons exhibit microsecond-lifetime, enhanced emission rate, and optical selection rules inherited from the host material. The combination of a permanent dipole, deterministic spatial confinement and long lifetime places interlayer excitons in a regime that satisfies one of the requirements for simulating quantum Ising models in optically resolvable lattices. 

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5. Formation of metal vacancy arrays in coalesced WS2 monolayer films

   Hickey, Danielle Reifsnyder; Yilmaz, Dundar E; Chubarov, Mikhail; Bachu, Saiphaneendra; Choudhury, Tanushree H; Miao, Leixin; Qian, Chenhao; Redwing, Joan M; van Duin, Adri C; Alem, Nasim (November 2020, 2D materials)

   null (Ed.)

   Defects have a profound impact on the electronic and physical properties of crystals. For two-dimensional (2D) materials, many intrinsic point defects have been reported, but much remains to be understood about their origin. Using scanning transmission electron microscopy imaging, this study discovers various linear arrays of W-vacancy defects that are explained in the context of the crystal growth of coalesced, monolayer WS2. Atomistic-scale simulations show that vacancy arrays can result from steric hindrance of bulky gas-phase precursors at narrowly separated growth edges, and that increasing the edge separation leads to various intact and defective growth modes, which are driven by competition between the catalytic effects of the sapphire substrate and neighboring growth edge. Therefore, we hypothesize that the arrays result from combined growth modes, which directly result from film coalescence. The connections drawn here will guide future synthetic and processing strategies to harness the engineering potential of defects in 2D monolayers. 

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