Visualization of moiré superlattices

McGilly, L. J.; Kerelsky, Alexander; Finney, Nathan; Shapovalov, Konstantin; Shih, En-Min; Ghiotto, Augusto; Zeng, Yan; Moore, Samuel L.; Wu, Wenjing; Bai, Yusong; Watanabe, Kenji; Taniguchi, Takashi; Stengel, Massimiliano; Lin, Zhifang; Hone, James; Zhu, Xiaoyang; Basov, D. N.; Dean, Cory; Dreyer, Cyrus E.; Pasupathy, Abhay

doi:10.1038/s41565-020-0708-3

Cited by 241 publications

(259 citation statements)

References 33 publications

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“…In this case, electrostatic domains can be detected directly in the AFM phase image by applying a dc bias, which allows faster scanning as compared to other electrostatic modes. ac-EFM and KPFM, which are generally slower and more demanding (they require to record an additional image using a second lock-in and, in the case of KPFM, a second feedback control 24 ), yielded the same information (see Supplementary Figs. [4][5][6][7][8][9]. Figure 1 shows representative images taken from one of our twisted-hBN samples, in which the top hBN crystal has regions of 4-, 8-and 12-layer thickness (also see Supplementary Fig.…”

Section: Resultsmentioning

confidence: 99%

“…ne of the most promising avenues for controlling the properties of van der Waals (vdW) heterostructures is to adjust the angle between the stacked two-dimensional (2D) crystals. Such rotational control has allowed the observation of long-lived excitonic states 1 , resonant tunnelling 2,3 and highly correlated electronic states [4][5][6][7] , including superconductivity in twisted bilayer graphene, among many other exciting effects, and various microscopic techniques have been shown to visualize moiré superlattices in twisted crystals [8][9][10] . At the same time, the twist-dependent electronic properties of hexagonal boron nitride (hBN), one of the most used crystals for engineering vdW heterostructures, have been overlooked so far.…”

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confidence: 99%

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Charge-polarized interfacial superlattices in marginally twisted hexagonal boron nitride

et al. 2021

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When two-dimensional crystals are brought into close proximity, their interaction results in reconstruction of electronic spectrum and crystal structure. Such reconstruction strongly depends on the twist angle between the crystals, which has received growing attention due to interesting electronic and optical properties that arise in graphene and transitional metal dichalcogenides. Here we study two insulating crystals of hexagonal boron nitride stacked at small twist angle. Using electrostatic force microscopy, we observe ferroelectric-like domains arranged in triangular superlattices with a large surface potential. The observation is attributed to interfacial elastic deformations that result in out-of-plane dipoles formed by pairs of boron and nitrogen atoms belonging to opposite interfacial surfaces. This creates a bilayer-thick ferroelectric with oppositely polarized (BN and NB) dipoles in neighbouring domains, in agreement with our modeling. These findings open up possibilities for designing van der Waals heterostructures and offer an alternative probe to study moiré-superlattice electrostatic potentials.

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Section: Resultsmentioning

confidence: 99%

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confidence: 99%

Charge-polarized interfacial superlattices in marginally twisted hexagonal boron nitride

et al. 2021

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“…1). The latter emerges at small twist angle, where the overall band width Mott insulation 8 ; superconductivity 7 ; correlated QAH insulator 22,23 Two-orbital extended Hubbard model Twisted double bilayer graphene Ferromagnetic insulator superconductivity 12,13 ; triplet pairing 108 Asymmetric p x -p y Hubbard model 29,30 Twisted bilayer MoS 2 , MoSe 2 Nematic (anti)ferromagnets 29 Domain wall networks Small-angle TBG with domain reconstruction 57,58,66,109 of these families of flat bands is tuned into the millielectronvolt regime. Due to destructive interference within the strongly asymmetric p x -p y Hubbard model itself (meaning that the two orbitals have very different hopping amplitudes), attached at the bottom and top of these flat bands one can find bands with even much lower dispersion.…”

Section: Realizing Model Quantum Hamiltonians In Van Der Waals Heteromentioning

confidence: 99%

Moiré heterostructures as a condensed-matter quantum simulator

et al. 2021

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Twisted van der Waals heterostructures have latterly received prominent attention for their many remarkable experimental properties and the promise that they hold for realizing elusive states of matter in the laboratory. We propose that these systems can, in fact, be used as a robust quantum simulation platform that enables the study of strongly correlated physics and topology in quantum materials. Among the features that make these materials a versatile toolbox are the tunability of their properties through readily accessible external parameters such as gating, straining, packing and twist angle; the feasibility to realize and control a large number of fundamental many-body quantum models relevant in the field of condensed-matter physics; and finally, the availability of experimental readout protocols that directly map their rich phase diagrams in and out of equilibrium. This general framework makes it possible to robustly realize and functionalize new phases of matter in a modular fashion, thus broadening the landscape of accessible physics and holding promise for future technological applications.

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“…In addition, ultra-high vacuum and/or cryogenic temperatures are needed for the lattice imaging. Moiré superlattices have also been imaged using atomic force microscopy (AFM) operated in the piezoresponse force microscopy mode, here sub-5 nm resolution has been achieved 14 . However, this method, like STM, still requires the AFM tip in direct contact with the region of interest of the heterostructure, thereby preventing any top protecting layer encapsulation or top gates.…”

Section: Introductionmentioning

confidence: 99%

In situ nanoscale imaging of moiré superlattices in twisted van der Waals heterostructures

et al. 2020

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Direct visualization of nanometer-scale properties of moiré superlattices in van der Waals heterostructure devices is a critically needed diagnostic tool for study of the electronic and optical phenomena induced by the periodic variation of atomic structure in these complex systems. Conventional imaging methods are destructive and insensitive to the buried device geometries, preventing practical inspection. Here we report a versatile scanning probe microscopy employing infrared light for imaging moiré superlattices of twisted bilayers graphene encapsulated by hexagonal boron nitride. We map the pattern using the scattering dynamics of phonon polaritons launched in hexagonal boron nitride capping layers via its interaction with the buried moiré superlattices. We explore the origin of the double-line features imaged and show the mechanism of the underlying effective phase change of the phonon polariton reflectance at domain walls. The nano-imaging tool developed provides a non-destructive analytical approach to elucidate the complex physics of moiré engineered heterostructures.

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Visualization of moiré superlattices

Cited by 241 publications

References 33 publications

Charge-polarized interfacial superlattices in marginally twisted hexagonal boron nitride

Charge-polarized interfacial superlattices in marginally twisted hexagonal boron nitride

Moiré heterostructures as a condensed-matter quantum simulator

In situ nanoscale imaging of moiré superlattices in twisted van der Waals heterostructures

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