Nanoscale lattice dynamics in hexagonal boron nitride moiré superlattices

Moore, Samuel L.; Ciccarino, Christopher J.; Halbertal, Dorri; McGilly, L. J.; Finney, Nathan; Yao, Kaiyuan; Shao, Yinming; Ni, Guangxin; Sternbach, Aaron; Telford, Evan J.; Kim, B. S.; Rossi, S. E.; Watanabe, Kenji; Taniguchi, Takashi; Pasupathy, Abhay; Dean, Cory; Hone, James; Schuck, P. James; Narang, Prineha; Basov, D. N.

doi:10.1038/s41467-021-26072-7

Cited by 46 publications

(47 citation statements)

References 41 publications

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“…A wide range of emerging electronic, magnetic, and topological properties in quantum materials are intimately linked to spatial inversion symmetry. In van der Waals heterostructures, the crystal symmetry can be precisely controlled by interlayer stacking and twisting techniques, providing a knob for programming the electronic bandstructure, [1][2][3] magnetic orders, [4] optical, [5][6][7][8][9][10][11] thermal [12] and phonon properties, [13] atomic reconstruction, [14] etc. Second harmonic generation (SHG) is the lowest-order nonlinear optical response, where the incident laser beam interacts with the material, emitting a frequency-doubled signal.…”

Section: Introductionmentioning

confidence: 99%

Nanoscale Optical Imaging of 2D Semiconductor Stacking Orders by Exciton‐Enhanced Second Harmonic Generation

Yao

Zhang

Yanev

et al. 2022

Advanced Optical Materials

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Second harmonic generation (SHG) is a nonlinear optical response arising exclusively from broken inversion symmetry in the electric‐dipole limit. Recently, SHG has attracted widespread interest as a versatile and noninvasive tool for characterization of crystal symmetry and emerging ferroic or topological orders in quantum materials. However, conventional far‐field optics is unable to probe local symmetry at the deep subwavelength scale. Here, near‐field SHG imaging of 2D semiconductors and heterostructures with the spatial resolution down to 20 nm is demonstrated using a scattering‐type nano‐optical apparatus. It is shown that near‐field SHG efficiency is greatly enhanced by excitons in atomically thin transition metal dichalcogenides. Furthermore, by correlating nonlinear and linear scattering‐type nano‐imaging, nanoscale variations of interlayer stacking order in bilayer WSe2 are resolved, and the stacking‐tuned excitonic light–matter interactions are revealed. This work demonstrates nonlinear optical interrogation of crystal symmetry and structure–property relationships at the nanometer length scales relevant to emerging properties in quantum materials.

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Section: Introductionmentioning

confidence: 99%

Nanoscale Optical Imaging of 2D Semiconductor Stacking Orders by Exciton‐Enhanced Second Harmonic Generation

Yao

Zhang

Yanev

et al. 2022

Advanced Optical Materials

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“…For example, scattering near-field optical microscopy (s-SNOM) uncovered the variation of the in-plane optical phonon frequencies for different stacking in the moiré superlattice of a twisted hBN (t-hBN). 24 Piezo force microscopy revealed strain gradients along moiré stacking domain boundaries, through piezoelectric coupling to an electric field applied between atomic force microscope (AFM) tip and hBN sample. 19 Electrostatic force microscopy (EFM) and kelvin probe force microscopy (KPFM) were performed on t-hBN (1–20L-BN on top of a thicker >30L flake 20 ), addressing the existence of two opposite permanent out-of-plane polarizations emerging from the moiré pattern.…”

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confidence: 99%

Moiré Modulation of Van Der Waals Potential in Twisted Hexagonal Boron Nitride

et al. 2022

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When a twist angle is applied between two layered materials (LMs), the registry of the layers and the associated change in their functional properties are spatially modulated, and a moiré superlattice arises. Several works explored the optical, electric, and electromechanical moiré-dependent properties of such twisted LMs but, to the best of our knowledge, no direct visualization and quantification of van der Waals (vdW) interlayer interactions has been presented, so far. Here, we use tapping mode atomic force microscopy phase-imaging to probe the spatial modulation of the vdW potential in twisted hexagonal boron nitride. We find a moiré superlattice in the phase channel only when noncontact (long-range) forces are probed, revealing the modulation of the vdW potential at the sample surface, following AB and BA stacking domains. The creation of scalable electrostatic domains, modulating the vdW potential at the interface with the environment by means of layer twisting, could be used for local adhesion engineering and surface functionalization by affecting the deposition of molecules or nanoparticles.

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“…Extension of these nonlinear effects to polaritonic modes [94][95][96] beyond those in graphene is a meaningful future direction. For example, monolayer hexagonal boron nitride [97,98] should exhibit strong second order optical nonlinearity due to broken inversion symmetry of the crystal lattice, and would be a natural platform for generating entanglement between the long lived hyperbolic phonon polaritons [99][100][101][102][103][104][105][106][107][108]. Similar nonlinear processes exist for optical phonons in SiC [109], Josephson plasmons in layered superconductors [110][111][112][113] and the collective modes in excitonic insulators [114][115][116][117][118].…”

Section: Discussion and Experimental Outlookmentioning

confidence: 99%

Graphene as a source of entangled plasmons

Sun,

Basov,

Fogler

2021

Preprint

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We analyze nonlinear optics schemes for generating pairs of quantum entangled plasmons in graphene. We predict that high plasmonic field concentration and strong optical nonlinearity of monolayer graphene enables pair-generation rates much higher than those of conventional photonic sources. The first scheme we study is spontaneous parametric down conversion in a graphene nanoribbon. In this second-order nonlinear process a plasmon excited by an external pump splits into a pair of plasmons, of half the original frequency each, emitted in opposite directions. The conversion is activated by applying a dc electric field that induces a density gradient or a current across the ribbon. Another scheme is degenerate four-wave mixing where the counter-propagating plasmons are emitted at the pump frequency. This third-order nonlinear process does not require a symmetrybreaking dc field. We suggest nano-optical experiments for measuring position-momentum entanglement of the emitted plasmon pairs. We estimate the critical pump fields at which the plasmon generation rates exceed their dissipation, leading to parametric instabilities.

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Nanoscale lattice dynamics in hexagonal boron nitride moiré superlattices

Cited by 46 publications

References 41 publications

Nanoscale Optical Imaging of 2D Semiconductor Stacking Orders by Exciton‐Enhanced Second Harmonic Generation

Nanoscale Optical Imaging of 2D Semiconductor Stacking Orders by Exciton‐Enhanced Second Harmonic Generation

Moiré Modulation of Van Der Waals Potential in Twisted Hexagonal Boron Nitride

Graphene as a source of entangled plasmons

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