Large‐Scale Mapping of Moiré Superlattices by Hyperspectral Raman Imaging

Lin, Kai-Qiang; Höller, Johannes; Bauer, Jonas; Parzefall, Philipp; Scheuck, Marten; Peng, Bo; Korn, Tobias; Bange, Sebastian; Lupton, John M.; Schüller, Christian

doi:10.1002/adma.202008333

Cited by 54 publications

(71 citation statements)

References 35 publications

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“…From theory, IP and OP optical transition dipoles are predicted for both R-and H-type stacking [16,30]. We note that structural deformations are likely to occur in our samples due to an atomic reconstruction [42], since all measured samples exhibit a ro-tational alignment of ∆φ 0 • within the given uncertainties. As a result, the ideal Moiré pattern is reconstructed and the crystal structure is expected to exhibit laterally extended areas of high symmetry [28].…”

Section: Discussionmentioning

confidence: 65%

Optical dipole orientation of interlayer excitons in MoSe$_{2}$-WSe$_{2}$ heterostacks

Sigl,

Troue,

Katzer

et al. 2021

Preprint

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We report on the far-field photoluminescence intensity distribution of interlayer excitons in MoSe2-WSe2 heterostacks as measured by back focal plane imaging in the temperature range between 1.7 K and 20 K. By comparing the data with an analytical model describing the dipolar emission pattern in a dielectric environment, we are able to obtain the relative contributions of the in-and out-of-plane transition dipole moments associated to the interlayer exciton photon emission. We determine the transition dipole moments for all observed interlayer exciton transitions to be (99 ± 1)% in-plane for R-and H-type stacking, independent of the excitation power and therefore the density of the exciton ensemble in the experimentally examined range. Finally, we discuss the limitations of the presented measurement technique to observe correlation effects in exciton ensembles.

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Section: Discussionmentioning

confidence: 65%

Optical dipole orientation of interlayer excitons in MoSe$_{2}$-WSe$_{2}$ heterostacks

Sigl,

Troue,

Katzer

et al. 2021

Preprint

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“…Along our discussion, we have assumed the individual layers of the 2D moiré sample as rigid objects, however, to reach an experimental realization, it is important to take atomic reconstruction into account. It is known that, for samples with small stacking angles, atoms within each layer try to adjust the stacking landscape forming commensurate regions [17,[66][67][68]. This effect increases interlayer adhesion and leads to higher friction between layers that hinders the possibility to modify the atomic registry [32][33][34].…”

Section: How To Avoid Atomic Reconstruction In Strain Tuning Experimentsmentioning

confidence: 99%

Moiré straintronics: a universal platform for reconfigurable quantum materials

Kögl¹,

Soubelet²,

Brotons-Gisbert³

et al. 2022

Preprint

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Large scale two-dimensional (2D) moiré superlattices are driving a revolution in designer quantum materials. The electronic interactions in these superlattices, strongly dependent on the periodicity and symmetry of the moiré pattern, critically determine the emergent properties and phase diagrams. To date, the relative twist angle between two layers has been the primary tuning parameter for a given choice of constituent crystals. Here, we establish strain as a powerful mechanism to insitu modify the moiré periodicity and symmetry. We develop an analytically exact mathematical description for the moiré lattice under arbitrary in-plane heterostrain acting on any bilayer structure. We demonstrate the ability to fine-tune the moiré lattice near critical points, such as the magic angle in bilayer graphene, or fully reconfigure the moiré lattice symmetry beyond that imposed by the unstrained constituent crystals. Due to this unprecedented simultaneous control over the strength of electronic interactions and lattice symmetry, 2D heterostrain provides a powerful platform to engineer, tune, and probe strongly correlated moiré materials.

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“…Since the discovery of flat electronic bands in twisted bilayer graphene [20], such moiré materials have emerged as rich systems to investigate the properties of correlated electrons, excitons and phonons [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]. For example, at small twist angles phonon properties are significantly modified as a consequence of large atomic re-constructions [38,41,42] which result in the localization of incipient phason modes [43] and optical phonon modes [43][44][45][46][47][48][49]. To date, however, the chirality of phonons in twisted bilayer systems has not been studied.…”

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confidence: 99%

Chiral valley phonons and flat phonon bands in moiré materials

Maity,

Mostofi,

Lischner

2021

Preprint

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We investigate the chirality of phonon modes in twisted bilayer WSe2. We demonstrate distinct chiral behavior of the K/K valley phonon modes for twist angles close to 0 • and close to 60 • . Moreover, we discover two sets of well-separated chiral valley modes in moiré lattices for angles close to 60 • . These emergent moiré chiral valley phonons originate from inversion symmetry breaking at the moiré scale. We also find similar emergent chiral modes in moiré patterns of strain-engineered bilayer WSe2 and MoSe2/WSe2 heterostructure. Furthermore, we observe the flattening of bands near the phononic band-gap edges for a broad range of twist angles in twisted bilayer WSe2. Our findings, which are expected to be generic for moiré systems composed of two-dimensional materials that break inversion symmetry, are relevant for understanding electron-phonon and exciton-phonon scattering, and for designing phononic crystals to mimic behaviors of electrons in moiré materials.

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Large‐Scale Mapping of Moiré Superlattices by Hyperspectral Raman Imaging

Cited by 54 publications

References 35 publications

Optical dipole orientation of interlayer excitons in MoSe$_{2}$-WSe$_{2}$ heterostacks

Optical dipole orientation of interlayer excitons in MoSe$_{2}$-WSe$_{2}$ heterostacks

Moiré straintronics: a universal platform for reconfigurable quantum materials

Chiral valley phonons and flat phonon bands in moiré materials

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