Highly Strain-Tunable Interlayer Excitons in MoS₂/WSe₂ Heterobilayers

Creators: Cho, Chullhee; Wong, Joeson; Taqieddin, Amir; Biswas, Souvik; Aluru, Narayana R.; Nam, SungWoo; Atwater, Harry A.

Abstract

Interlayer excitons in heterobilayers of transition-metal dichalcogenides (TMDCs) have generated enormous interest due to their permanent vertical dipole moments and long lifetimes. However, the effects of mechanical strain on the optoelectronic properties of interlayer excitons in heterobilayers remain relatively uncharacterized. Here, we experimentally demonstrate strain tuning of Γ–K interlayer excitons in molybdenum disulfide and tungsten diselenide (MoS₂/WSe₂) wrinkled heterobilayers and obtain a deformation potential constant of ∼107 meV/% uniaxial strain, which is approximately twice that of the intralayer excitons in the constituent monolayers. We further observe a nonmonotonic dependence of the interlayer exciton photoluminescence intensity with strain, which we interpret as being due to the sensitivity of the Γ point to band hybridization arising from the competition between in-plane strain and out-of-plane interlayer coupling. Strain engineering with interlayer excitons in TMDC heterobilayers offers higher strain tunability and new degrees of freedom compared to their monolayer counterparts.

Additional Information

© 2021 American Chemical Society. Received: February 21, 2021; Revised: April 26, 2021; Published: April 29, 2021. This work was primarily supported by the "Photonics at Thermodynamic Limits" Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award No. DE-SC0019140, which supported the strained interlayer exciton sample fabrication and experimental optical measurements. C.C. also acknowledges additional support from the NASA Space Technology Research Fellow Grant No. 80NSSC17K0149, and J.W. acknowledges additional support from a National Science Foundation (NSF) Graduate Research Fellowship under Grant No. 1144469. S.N. gratefully acknowledges support from the AFOSR (FA2386-17-1-4071), NSF (MRSEC DMR-1720633 and CMMI-1554019), and ONR YIP (N00014-17-1-2830), which supported additional wrinkled heterobilayer sample fabrication and optical measurements. The density functional theory calculations performed by A.T. and N.R.A. acknowledge support from the NSF (MRSEC DMR-1720633 and CMMI-1921578), ONR (Grant No. N00014-19-1-2596), and the supercomputing resources provided by the Extreme Science and Engineering Discovery Environment (XSEDE) (supported by NSF Grant No. OCI1053575), Blue Waters (supported by NSF Award Nos. OCI-0725070 and ACI-1238993 and the state of Illinois, and as of December, 2019, supported by the National Geospatial-Intelligence Agency), and Frontera computing project at the Texas Advanced Computing Center (supported by NSF Grant No. OAC-1818253). C.C. acknowledges Dr. J. S. Lopez who assisted the X-ray reflectometry analysis. Author Contributions: C.C., J.W., S.N., and H.A.A. developed the ideas. C.C. and J.W. fabricated the samples and performed the measurements, with assistance from S.B. The first-principles simulations were performed by A.T. under the supervision of N.R.A. The manuscript was written by C.C. and J.W., with input from all authors. All authors contributed to the discussion and interpretation of results, as well as the presentation and preparation of the manuscript. The authors declare no competing financial interest.

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