Recent advances in the isolation and stacking of monolayers of van der Waals materials have provided approaches for the preparation of quantum materials in the ultimate two-dimensional limit1,2. In van der Waals heterostructures formed by stacking two monolayer semiconductors, lattice mismatch or rotational misalignment introduces an in-plane moiré superlattice3. It is widely recognized that the moiré superlattice can modulate the electronic band structure of the material and lead to transport properties such as unconventional superconductivity4 and insulating behaviour driven by correlations5,6,7; however, the influence of the moiré superlattice on optical properties has not been investigated experimentally. Here we report the observation of multiple interlayer exciton resonances with either positive or negative circularly polarized emission in a molybdenum diselenide/tungsten diselenide (MoSe2/WSe2) heterobilayer with a small twist angle. We attribute these resonances to excitonic ground and excited states confined within the moiré potential. This interpretation is supported by recombination dynamics and by the dependence of these interlayer exciton resonances on twist angle and temperature. These results suggest the feasibility of engineering artificial excitonic crystals using van der Waals heterostructures for nanophotonics and quantum information applications.
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The work performed by K.T., J.C., A.H.M. and X. Li was primarily supported by the National Science Foundation (NSF) through the Center for Dynamics and Control of Materials, an NSF MRSEC, under Cooperative Agreement DMR-1720595. X. Li also acknowledges partial support from NSF EFMA-1542747 and the Welch Foundation via grant F-1662. The theoretical work by F.W. was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. J.Q acknowledges support from the China Scholarship Council (grant 201706050068). A.H.M., K.K. and E.T. were supported in part by Army Research Office (ARO) grant W911NF-17-1-0312 (MURI). X. Lu and L.Y. are supported by the Air Force Office of Scientific Research (AFOSR) FA9550-17-1-0304 and NSF DMR-1455346. S.K. was financially supported by National Research Foundation of Korea (NRF) grant funded by the South Korean government (2017R1D1B04036381). K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan and JSPS KAKENHI grant JP15K21722. A.R. and S.K.B. acknowledge support from the NASCENT Engineering Research Centre (ERC) funded by NSF grant EEC-1160494. D.A.S acknowledges support from the NSF Graduate Research Fellowship Program. N.L. acknowledges support from NSF CMMI-1351875. The Texas Nanofabrication Facility, where some of the work was carried out, is a member of the National Nanotechnology Coordinated Infrastructure, which is supported by the NSF (grant ECCS-1542159). This work is an official contribution of NIST, which is not subject to copyright in the United States.
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