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Opto-valleytronic imaging of atomically thin semiconductors


Transition metal dichalcogenide semiconductors represent elementary components of layered heterostructures for emergent technologies beyond conventional optoelectronics. In their monolayer form they host electrons with quantized circular motion and associated valley polarization and valley coherence as key elements of opto-valleytronic functionality. Here, we introduce two-dimensional polarimetry as means of direct imaging of the valley pseudospin degree of freedom in monolayer transition metal dichalcogenides. Using MoS2 as a representative material with valley-selective optical transitions, we establish quantitative image analysis for polarimetric maps of extended crystals, and identify valley polarization and valley coherence as sensitive probes of crystalline disorder. Moreover, we find site-dependent thermal and non-thermal regimes of valley-polarized excitons in perpendicular magnetic fields. Finally, we demonstrate the potential of wide-field polarimetry for rapid inspection of opto-valleytronic devices based on atomically thin semiconductors and heterostructures.

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Figure 1: Confocal spectroscopy and imaging of extended MoS2 monolayers grown by chemical vapour deposition.
Figure 2: Raster-scan polarimetry of single- and polycrystalline MoS2.
Figure 3: The valley Zeeman effect in polarimetric imaging.
Figure 4: Wide-field linear and circular polarimetry.


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We thank P.M. Ajayan for support in the establishment of materials synthesis conditions used in this study, P. Altpeter and R. Rath for assistance in the clean room, J.P. Kotthaus, B. Urbaszek and F. Wang for useful discussions, and P. Maletinsky and K. Karrai for valuable input on the manuscript. We gratefully acknowledge funding by the European Research Council under the ERC grant agreement no. 336749, the Volkswagen Foundation, the the Deutsche Forschungsgemeinschaft (DFG) Cluster of Excellence Nanosystems Initiative Munich (NIM), and financial support from the Center for NanoScience (CeNS) and LMUinnovativ.

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A.N. and A.H. conceived the experiments. A.N. built the experimental set-up. H.Y. organized the material aspect and prepared MoS2 flakes on SiO2/Si substrates with support from A.D.M. S.N. and J.Lou provided inputs on growth parameters of MoS2 flakes at the initial stage of the project. A.N., M.N. and H.Y. performed basic characterization of the sample. A.N., J.Lin. and L.C. performed the measurements. A.N., J.Lin., L.C. and A.H. analysed the data. A.N. and A.H. prepared the figures and wrote the manuscript. All authors commented on the manuscript.

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Correspondence to Hisato Yamaguchi or Alexander Högele.

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The authors declare no competing financial interests.

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Neumann, A., Lindlau, J., Colombier, L. et al. Opto-valleytronic imaging of atomically thin semiconductors. Nature Nanotech 12, 329–334 (2017).

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