Periodic Reporting for period 1 - 2DValley (Opto-valleytronic moiré polaritons)
Okres sprawozdawczy: 2022-08-01 do 2024-07-31
The emerging field of opto-valleytronics based on two-dimensional (2D) transition metal dichalcogenides (TMDs) has the potential to revolutionize quantum information processing by enabling all-optical quantum photonic circuits with nonlinear and non-reciprocal devices, such as optical switches and isolators. Such devices are inherently difficult to realize because photons generally do not interact and flow in both directions due to time-reversal symmetry. In this action, I proposed to develop novel optical microcavities with embedded TMD heterostructures to achieve photon-photon interaction and directional light propagation. A small twist angle between TMD heterobilayers gives rise to hybrid moiré excitons exhibiting a permanent dipole moment in addition to increased lifetimes and oscillator strengths. Strongly coupled to a microcavity, moiré polaritons emerge with valley-contrasting dipolar optical selection rules. Moiré polaritons exhibit optical nonlinearities induced by the moiré potential. Based on all this, the overriding research objective of the project 2DValley was to develop and investigate novel opto-valleytronic devices utilizing valley-polarized moiré polaritons. Such nonlinear and nonreciprocal opto-valleytronic devices would have potential technological and societal impact by increasing information processing speed, volume, and security.
We developed two fabrication methods for polariton microcavities with transition metal dichalcogenides. One method is based on literature and uses a mechanically extracted piece of mirror. The other method implements a novel scheme for plasmonic lattices. This led to one publication in Nano Letters about a metasurface consisting of a gold nanodisk array strongly coupled to a monolayer of WSe2. Next, we studied a promising material combination MoSe2-WSe2 fully grown by chemical vapor deposition. This material combination shows another limit of moiré physics, atomic reconstruction, over several micron length-scales. Here, the interlayer excitons act as sensors for their atomic registries, with registry-specific optical properties. This work was also published in Nano Letters. Lastly, we investigated the two-dimensional (2D) magnet, CrSBr, which is stable in air and shows intriguing coupled optical, electronic, and magnetic properties. Since at the time there were few reports on excitons in few-layer CrSBr, we started with a fundamental study. We studied samples with single-gated field-effect devices and observed charge-doping for the first time in this material. We demonstrated doping-control of the metamagnetic transition, as well as one-way switching of the magnetization with doping. We also visualized magnetic domain formation all-optically by taking advantage of the coupling of the excitons to the magnetic order. This work has been published in Nature Communications.
We have published three peer-reviewed articles in Nano Letters (2) and Nature Communications (1). These have strongly contributed towards the state of the art.
Nano Letters 2023: This work demonstrated large-area atomic reconstruction in heterobilayers of MoSe2-WSe2. Interlayer excitons have registry specific optical properties and consequently act as sensors of the interlayer stacking. We presented an elaborate study of vertical MoSe2−WSe2 heterobilayers synthesized by chemical vapor deposition with evidence for spatially extended reconstruction into domains of one atomic registry, enclosing a central region of periodically reconstructed nanoscale moiré domains.
Nature Communications 2024: This work studied CrSBr, a layered magnetic semiconductor that has recently grasped the attention of the 2D exciton community. We were among the first groups to explore the magneto-optical properties of few-layer samples, and the first to achieve charge-doping in the form of exciton-charge complexes, which allowed us to demonstrate the doping-dependence of the critical magnetic field of metamagnetic transitions, as well as one-way magnetic switching. Due to the correlation between excitons and magnetic order, the excitons act as sensors for the magnetic order, and we succeeded to visualize magnetic domain formation all-optically. Since many groups have recently started studying this material, I believe our work published in June 2024 will have tremendous impact on this community.
Nano Letters 2024: In this work, we developed a novel fabrication method for gold nanodisk arrays embedded in hexagonal boron nitride and realized a plasmon-exciton-polariton metasurface with a WSe2 monolayer strongly coupled to the surface lattice resonances of the plasmonic array. Remarkably, the metasurface strongly modifies the angular dependence of the polaritonic emission profile, resulting in linearly polarized, directional light emission. This fabrication method provides a solution to the compromise of optical quality of 2D semiconductors in plasmonic cavities and large light-matter coupling strength, resulting from the need for encapsulation in hexagonal boron nitride for the former and minimal distance between the plasmonic resonator and the 2D material for the latter.
Nano Letters 2023: This work demonstrated large-area atomic reconstruction in heterobilayers of MoSe2-WSe2. Interlayer excitons have registry specific optical properties and consequently act as sensors of the interlayer stacking. We presented an elaborate study of vertical MoSe2−WSe2 heterobilayers synthesized by chemical vapor deposition with evidence for spatially extended reconstruction into domains of one atomic registry, enclosing a central region of periodically reconstructed nanoscale moiré domains.
Nature Communications 2024: This work studied CrSBr, a layered magnetic semiconductor that has recently grasped the attention of the 2D exciton community. We were among the first groups to explore the magneto-optical properties of few-layer samples, and the first to achieve charge-doping in the form of exciton-charge complexes, which allowed us to demonstrate the doping-dependence of the critical magnetic field of metamagnetic transitions, as well as one-way magnetic switching. Due to the correlation between excitons and magnetic order, the excitons act as sensors for the magnetic order, and we succeeded to visualize magnetic domain formation all-optically. Since many groups have recently started studying this material, I believe our work published in June 2024 will have tremendous impact on this community.
Nano Letters 2024: In this work, we developed a novel fabrication method for gold nanodisk arrays embedded in hexagonal boron nitride and realized a plasmon-exciton-polariton metasurface with a WSe2 monolayer strongly coupled to the surface lattice resonances of the plasmonic array. Remarkably, the metasurface strongly modifies the angular dependence of the polaritonic emission profile, resulting in linearly polarized, directional light emission. This fabrication method provides a solution to the compromise of optical quality of 2D semiconductors in plasmonic cavities and large light-matter coupling strength, resulting from the need for encapsulation in hexagonal boron nitride for the former and minimal distance between the plasmonic resonator and the 2D material for the latter.