| 1. |
- Thompson, Joshua, 1992, et al.
(author)
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Criteria for deterministic single-photon emission in two-dimensional atomic crystals
- 2020
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In: Physical Review Materials. - 2475-9953. ; 4:8
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Journal article (peer-reviewed)abstract
- The deterministic production of single photons from two-dimensional materials promises to usher in a new generation of photonic quantum devices. In this work, we outline criteria by which single-photon emission can be realized in two-dimensional materials: spatial isolation, spectral filtering, and low excitation of quantum emitters. We explore how these criteria can be fulfilled in atomically thin transition metal dichalcogenides, where excitonic physics dictates the observed photoemission. In particular, we model the effect of defects and localized strain, in accordance with the most common experimental realizations, on the photon statistics of emitted light. Moreover, we demonstrate that an optical cavity has a negative impact on the photon statistics, suppressing the single-photon character of the emission by diminishing the effect of spectral filtering on the emitted light. Our work provides a theoretical framework revealing criteria necessary to facilitate single-photon emission in two-dimensional materials and thus can guide future experimental studies in this field.
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| 2. |
- Thompson, Joshua, 1992, et al.
(author)
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Valley-exchange coupling probed by angle-resolved photoluminescence
- 2022
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In: Nanoscale Horizons. - : Royal Society of Chemistry (RSC). - 2055-6756 .- 2055-6764. ; 7:1, s. 77-84
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Journal article (peer-reviewed)abstract
- The optical properties of monolayer transition metal dichalcogenides are dominated by tightly-bound excitons. They form at distinct valleys in reciprocal space, and can interact via the valley-exchange coupling, modifying their dispersion considerably. Here, we predict that angle-resolved photoluminescence can be used to probe the changes of the excitonic dispersion. The exchange-coupling leads to a unique angle dependence of the emission intensity for both circularly and linearly-polarised light. We show that these emission characteristics can be strongly tuned by an external magnetic field due to the valley-specific Zeeman-shift. We propose that angle-dependent photoluminescence measurements involving both circular and linear optical polarisation as well as magnetic fields should act as strong verification of the role of valley-exchange coupling on excitonic dispersion and its signatures in optical spectra.
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| 3. |
- Garcia-Ruiz, Aitor, et al.
(author)
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Electronic Raman Scattering in Twistronic Few-Layer Graphene
- 2020
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In: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 125:19
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Journal article (peer-reviewed)abstract
- We study electronic contribution to the Raman scattering signals of two-, three- and four-layer graphene with layers at one of the interfaces twisted by a small angle with respect to each other. We find that the Raman spectra of these systems feature two peaks produced by van Hove singularities in moiré minibands of twistronic graphene, one related to direct hybridization of the Dirac states, and the other resulting from band folding caused by moiré superlattice. The positions of both peaks strongly depend on the twist angle, so that their detection can be used for noninvasive characterization of the twist, even in hBN-encapsulated structures.
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| 4. |
- Thompson, Joshua, 1992, et al.
(author)
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Anisotropic exciton diffusion in atomically-thin semiconductors
- 2022
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In: 2D Materials. - : IOP Publishing. - 2053-1583. ; 9:2
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Journal article (peer-reviewed)abstract
- Energy transport processes are critical for the efficiency of many optoelectronic applications. The energy transport in technologically promising transition metal dichalcogenides is determined by exciton diffusion, which strongly depends on the underlying excitonic and phononic dispersion. Based on a fully microscopic theory we demonstrate that the valley-exchange interaction leads to an enhanced exciton diffusion due to the emergence of a linear excitonic dispersion and the resulting decreased exciton-phonon scattering. Interestingly, we find that the application of a uniaxial strain can drastically boost the diffusion speed and even give rise to a pronounced anisotropic diffusion, which persists up to room temperature. We reveal that this behaviour originates from the highly anisotropic exciton dispersion in the presence of strain, displaying parabolic and linear behaviour perpendicular and parallel to the strain direction, respectively. Our work demonstrates the possibility to control the speed and direction of exciton diffusion via strain and dielectric engineering. This opens avenues for more efficient and exotic optoelectronic applications of atomically thin materials.
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| 5. |
- Thompson, Joshua, 1992, et al.
(author)
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Determination of interatomic coupling between two-dimensional crystals using angle-resolved photoemission spectroscopy
- 2020
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 11:1
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Journal article (peer-reviewed)abstract
- Lack of directional bonding between two-dimensional crystals like graphene or monolayer transition metal dichalcogenides provides unusual freedom in the selection of components for vertical van der Waals heterostructures. However, even for identical layers, their stacking, in particular the relative angle between their crystallographic directions, modifies properties of the structure. We demonstrate that the interatomic coupling between two two-dimensional crystals can be determined from angle-resolved photoemission spectra of a trilayer structure with one aligned and one twisted interface. Each of the interfaces provides complementary information and together they enable self-consistent determination of the coupling. We parametrise interatomic coupling for carbon atoms by studying twisted trilayer graphene and show that the result can be applied to structures with different twists and number of layers. Our approach demonstrates how to extract fundamental information about interlayer coupling in a stack of two-dimensional crystals and can be applied to many other van der Waals interfaces.
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