Excitons in a reconstructed moiré potential in twisted WSe2/WSe2 homobilayers

Andersen, Trond I.; Scuri, Giovanni; Sushko, Andrey; Greve, Kristiaan De; Sung, Jiho; Zhou, You; Wild, Dominik S.; Gelly, Ryan J.; Heo, Heeok; Bérubé, Damien; Joe, Andrew Y.; Jauregui, Luis A.; Watanabe, Kenji; Taniguchi, Takashi; Kim, Philip; Park, Hongkun; Lukin, Mikhail D.

doi:10.1038/s41563-020-00873-5

Cited by 141 publications

(133 citation statements)

References 61 publications

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“…To visualize the resulting domain structure, we adopt back-scattered electron channelling contrast imaging (BSECCI), previously used for bulk materials 22 . We find that this techniques provides a high contrast even for twisted bilayers encapsulated under hexagonal boron nitride (hBN) crystals that were several nanometres thick, similar to the recently used channelling-modulated secondary electron imaging 23 . An example of BSECCI in Fig.…”

Section: Main Textsupporting

confidence: 59%

Interfacial ferroelectricity in marginally twisted 2D semiconductors

Weston

Castanon

Enaldiev

et al. 2021

Preprint

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Twisted heterostructures of two-dimensional crystals offer almost unlimited scope for the design of novel metamaterials. Here we demonstrate a room-temperature ferroelectric semiconductor that is assembled using mono- or few- layer MoS2. These van der Waals heterostructures feature broken inversion symmetry, which, together with the asymmetry of atomic arrangement at the interface of two 2D crystals, enables ferroelectric domains with alternating out-of-plane polarisation arranged into a twist-controlled network. The latter can be moved by applying out-of-plane electrical fields, as visualized in situ using channelling contrast electron microscopy. The interfacial charge transfer for the observed ferroelectric domains is quantified using Kelvin probe force microscopy and agrees well with theoretical calculations. The movement of domain walls and their bending rigidity also agrees well with our modelling results. Furthermore, we demonstrate proof-of-principle field-effect transistors, where the channel resistance exhibits a pronounced hysteresis governed by pinning of ferroelectric domain walls. Our results show a potential venue towards room temperature electronic and optoelectronic semiconductor devices with built-in ferroelectric memory functions.

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Section: Main Textsupporting

confidence: 59%

Interfacial ferroelectricity in marginally twisted 2D semiconductors

Weston

Castanon

Enaldiev

et al. 2021

Preprint

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“…In this work, we focus on the samples with the twist angle around 60°due to the following: it has been shown by theoretical analysis 28,29 and transmission electron microscopy (TEM) observations 30,31 that, at a small misalignment angle, the moiré superlattices undergo a strongly structural reconstruction rather than rigidly rotated crystalline lattices. The reconstruction necessarily modifies the electronic and excitonic properties of the twisted bilayers [32][33][34][35][36] . Although this twist angle-dependent reconstruction happens in either near 0°or 60°TB-TMDs, calculations demonstrate that flat bands in near 0°TB-TMDs mainly originate from inhomogeneous hybridization, regardless of the reconstruction.…”

Section: Resultsmentioning

confidence: 99%

Lattice reconstruction induced multiple ultra-flat bands in twisted bilayer WSe2

Feng

et al. 2021

Nat Commun

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Moiré superlattices in van der Waals heterostructures provide a tunable platform to study emergent properties that are absent in the natural crystal form. Twisted bilayer transition metal dichalcogenides (TB-TMDs) can host moiré flat bands over a wide range of twist angles. For twist angle close to 60°, it was predicted that TB-TMDs undergo a lattice reconstruction which causes the formation of ultra-flat bands. Here, by using scanning tunneling microscopy and spectroscopy, we show the emergence of multiple ultra-flat bands in twisted bilayer WSe2 when the twist angle is within 3° of 60°. The ultra-flat bands are manifested as narrow tunneling conductance peaks with estimated bandwidth less than 10 meV, which is only a fraction of the estimated on-site Coulomb repulsion energy. The number of these ultra-flat bands and spatial distribution of the wavefunctions match well with the theoretical predictions, strongly evidencing that the observed ultra-flat bands are induced by lattice reconstruction. Our work provides a foundation for further study of the exotic correlated phases in TB-TMDs.

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“…3d can be considered quite homogeneous, allowing random charge filling of both NN sites and non-NN sites with equal probability. Combining this optical read-out technique with other surface probe microscopy techniques that provide structural information to correlate distinct features of local disorder (for example, strain, ripples, reconstruction and other imperfections) in a moiré superlattice 21 , 23 , 38 would provide valuable new insights into moiré systems. Furthermore, an exciting prospect would be to locally probe long-range charge-ordered states in a fractionally filled moiré lattice, such as correlated Mott insulators and Wigner crystals 15 – 17 .…”

Section: Discussionmentioning

confidence: 99%

Optical read-out of Coulomb staircases in a moiré superlattice via trapped interlayer trions

et al. 2021

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Moiré patterns with a superlattice potential can be formed by vertically stacking two layered materials with a relative twist or lattice constant mismatch. In transition metal dichalcogenide-based systems, the moiré potential landscape can trap interlayer excitons (IXs) at specific atomic registries. Here, we report that spatially isolated trapped IXs in a molybdenum diselenide/tungsten diselenide heterobilayer device provide a sensitive optical probe of carrier filling in their immediate environment. By mapping the spatial positions of individual trapped IXs, we are able to spectrally track the emitters as the moiré lattice is filled with excess carriers. Upon initial doping of the heterobilayer, neutral trapped IXs form charged IXs (IX trions) uniformly with a binding energy of ~7 meV. Upon further doping, the empty superlattice sites sequentially fill, creating a Coulomb staircase: stepwise changes in the IX trion emission energy due to Coulomb interactions with carriers at nearest-neighbour moiré sites. This non-invasive, highly local technique can complement transport and non-local optical sensing techniques to characterize Coulomb interaction energies, visualize charge correlated states, or probe local disorder in a moiré superlattice.

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Excitons in a reconstructed moiré potential in twisted WSe2/WSe2 homobilayers

Cited by 141 publications

References 61 publications

Interfacial ferroelectricity in marginally twisted 2D semiconductors

Interfacial ferroelectricity in marginally twisted 2D semiconductors

Lattice reconstruction induced multiple ultra-flat bands in twisted bilayer WSe2

Optical read-out of Coulomb staircases in a moiré superlattice via trapped interlayer trions

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