Control of light-matter interaction in 2D transition metal dichalcogenides via strain engineering
Final Report Abstract
Realizing excitonic many-body phases promises a leap toward next-generation quantum optoelectronics. In the key challenge of artificially tailoring the properties of excitonic systems towards supporting such exotic phases, strain engineering has become one of the most powerful techniques at hand. Opposed to the relatively small effects of growth-induced strain in traditional semiconductors, transition metal-dichalcogenides (TMDs) offer unprecedented potential for strain engineering. Their single layers have been reported to withstand extreme deformations of the lattice unit cell of up to 10% before the deformations become inelastic and the material is permanently damaged. Wrinkling and folding observed in single layer TMD resembles the properties of ultrathin membranes, in stark contrast to the mechanical properties of rigid bulk crystals. Accordingly, various studies report an enormous impact of crystal lattice deformations on the characteristic electronic properties of TMDs; the fundamental band gap, carrier mobilities, optical selection rules, and even spin-orbit effects are all modified under the influence of strain. Notably, the van der Waals (vdW) nature further allows complex nanoscale strain architectures to be readily implemented with essentially arbitrary geometry. Due to reduced dielectric screening and strong Coulomb correlations, two-dimensional (2D) semiconductors are also a highly promising platform for room temperature implementations of exciton-based optoelectronics. While most studies of strain concentrated on funneling excitons or free electrons into localized potential minima, recent reports suggest promising perspectives to manipulate the mobility of excitons via strain tuning. This provides a strong motivation to build strain-induced quasi-1D potentials for mobile exciton quasiparticles in an otherwise fully 2D system. In this project, we realized deterministic strain engineering of both single-particle electronic bandstructure and excitonic many-particle interactions. We were able to create quasi-1D transport channels that confine excitons and simultaneously enhance their mobility through locally suppressed exciton-phonon scattering. Using ultrafast, all-optical injection and time-resolved readout, we achieved highly directional exciton flow with up to 100% anisotropy both at cryogenic and room temperatures (see publication [P1]). Furthermore, we found evidence of a recently unobserved, strain-related electronic state in the optical spectrum of wrinkles in a monolayer WSe2. Resonance with a heavily populated and highly diffusive reservoir of dark excitons gives rise to exceptionally efficient energy transport and luminescence emission. Overall, the demonstrated fundamental modification of exciton transport and localized state properties in deterministically strained 2D materials has broad implications for both basic solidstate science and emerging technologies.
Publications
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Quasi-1D exciton channels in strain-engineered 2D materials. Science Advances, 7(44).
Dirnberger, Florian; Ziegler, Jonas D.; Faria, Junior Paulo E.; Bushati, Rezlind; Taniguchi, Takashi; Watanabe, Kenji; Fabian, Jaroslav; Bougeard, Dominique; Chernikov, Alexey & Menon, Vinod M.
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Relaxing Symmetry Rules for Nonlinear Optical Interactions in Van der Waals Materials via Strong Light–Matter Coupling. ACS Photonics, 9(2), 503-510.
Khatoniar, Mandeep; Bushati, Rezlind; Mekawy, Ahmed; Dirnberger, Florian; Alù, Andrea & Menon, Vinod M.
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Sensing the Local Magnetic Environment through Optically Active Defects in a Layered Magnetic Semiconductor. ACS Nano, 17(1), 288-299.
Klein, Julian; Song, Zhigang; Pingault, Benjamin; Dirnberger, Florian; Chi, Hang; Curtis, Jonathan B.; Dana, Rami; Bushati, Rezlind; Quan, Jiamin; Dekanovsky, Lukas; Sofer, Zdenek; Alù, Andrea; Menon, Vinod M.; Moodera, Jagadeesh S.; Lončar, Marko; Narang, Prineha & Ross, Frances M.
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Spin-correlated exciton–polaritons in a van der Waals magnet. Nature Nanotechnology, 17(10), 1060-1064.
Dirnberger, Florian; Bushati, Rezlind; Datta, Biswajit; Kumar, Ajesh; MacDonald, Allan H.; Baldini, Edoardo & Menon, Vinod M.
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Thermalization of Fluorescent Protein Exciton–Polaritons at Room Temperature. Advanced Materials, 34(15).
Satapathy, Sitakanta; Liu, Bin; Deshmukh, Prathmesh; Molinaro, Paul M.; Dirnberger, Florian; Khatoniar, Mandeep; Koder, Ronald L. & Menon, Vinod M.
