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| 2. |
- Krause, R., et al.
(författare)
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Microscopic Understanding of Ultrafast Charge Transfer in van der Waals Heterostructures
- 2021
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 127:27
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Tidskriftsartikel (refereegranskat)abstract
- Van der Waals heterostructures show many intriguing phenomena including ultrafast charge separation following strong excitonic absorption in the visible spectral range. However, despite the enormous potential for future applications in the field of optoelectronics, the underlying microscopic mechanism remains controversial. Here we use time- and angle-resolved photoemission spectroscopy combined with microscopic many-particle theory to reveal the relevant microscopic charge transfer channels in epitaxial WS2/graphene heterostructures. We find that the timescale for efficient ultrafast charge separation in the material is determined by direct tunneling at those points in the Brillouin zone where WS2 and graphene bands cross, while the lifetime of the charge separated transient state is set by defect-assisted tunneling through localized sulphur vacancies. The subtle interplay of intrinsic and defect-related charge transfer channels revealed in the present work can be exploited for the design of highly efficient light harvesting and detecting devices.
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| 3. |
- Sandner, Fabian, et al.
(författare)
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Femtosecond nanoscopy of charge carrier dynamics in van der Waals heterostructures
- 2022
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Ingår i: Optics InfoBase Conference Papers.
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Konferensbidrag (refereegranskat)abstract
- Ultrafast polarization nanoscopy traces the femtosecond interlayer tunneling and the density-dependent Mott transition of strongly bound excitons in custom-tailored van der Waals heterostructures with subcycle temporal and nanometer spatial resolution.
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| 4. |
- Siday, Thomas, et al.
(författare)
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Ultrafast Nanoscopy of an Exciton Mott Transition in Twisted Bilayer WSe 2
- 2022
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Ingår i: International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz. - 2162-2027 .- 2162-2035. ; August
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Konferensbidrag (refereegranskat)abstract
- The density-driven transition of an exciton gas into a plasma of unbound electron-hole pairs has provided a compelling testbed for exploring many-body physics. Here, we use ultrafast polarization nanoscopy to trace a Mott transition of excitons in a twisted bilayer of WSe2. An initially monomolecular recombination of optically dark excitons continuously evolves into bimolecular recombination of unbound electrons and holes as the density is increased. Furthermore, we reveal directly how the Mott transition varies on nanometer length scales, demonstrating how the technique is indispensable in the study of intrinsically disordered van der Waals materials.
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| 5. |
- Siday, Thomas, et al.
(författare)
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Ultrafast Nanoscopy of High-Density Exciton Phases in WSe 2
- 2022
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 22:6, s. 2561-2568
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Tidskriftsartikel (refereegranskat)abstract
- The density-driven transition of an exciton gas into an electron-hole plasma remains a compelling question in condensed matter physics. In two-dimensional transition metal dichalcogenides, strongly bound excitons can undergo this phase change after transient injection of electron-hole pairs. Unfortunately, unavoidable nanoscale inhomogeneity in these materials has impeded quantitative investigation into this elusive transition. Here, we demonstrate how ultrafast polarization nanoscopy can capture the Mott transition through the density-dependent recombination dynamics of electron-hole pairs within a WSe2 homobilayer. For increasing carrier density, an initial monomolecular recombination of optically dark excitons transitions continuously into a bimolecular recombination of an unbound electron-hole plasma above 7 × 1012 cm-2. We resolve how the Mott transition modulates over nanometer length scales, directly evidencing the strong inhomogeneity in stacked monolayers. Our results demonstrate how ultrafast polarization nanoscopy could unveil the interplay of strong electronic correlations and interlayer coupling within a diverse range of stacked and twisted two-dimensional materials.
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| 6. |
- Zizlsperger, Martin, et al.
(författare)
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Ultrafast nanoscopy of an excitonic insulator-metal transition in twisted bilayer WSe 2
- 2022
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Ingår i: CLEO: QELS_Fundamental Science in Proceedings Conference on Lasers and Electro-Optics. - 9781557528209 - 9781957171050
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Konferensbidrag (refereegranskat)abstract
- Many-body interactions between excitons in a transition-metal dichalcogenide bilayer drive a transition into an electron-hole liquid at high densities. Using ultrafast polarization nanoscopy, we unveil spatiotemporal dynamics of this continuous Mott transition on the nanoscale.
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