Structure of the moiré exciton captured by imaging its electron and hole

Karni, Ouri; Barré, Elyse; Pareek, Vivek; Georgaras, Johnathan D; Man, Michael K. L.; Sahoo, Chakradhar; Bacon, David R.; Zhu, Xing; Ribeiro, Henrique B.; O'Beirne, Aidan L; Hu, Jenny; Abdullah, Amir; Abdelrasoul, Mohamed; Chan, Nicholas S.; Karmakar, Arka; Winchester, Andrew; Kim, Bumho; Watanabe, Kenji; Taniguchi, Takashi; Barmak, K.; Madéo, Julien; Jornada, Felipe H. da; Heinz, Tony F.; Dani, Keshav M.

doi:10.1038/s41586-021-04360-y

Cited by 61 publications

(37 citation statements)

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“…Furthermore, by analyzing the excitonic envelope wavefunction in momentum-space (Figure 9b) and in real-space, an excitonic root-mean-square (RMS) radius was estimated by 1.4 nm (the real-space envelope function is imaged in Figure 9c). This value is consistent with the radius obtained by previous magneto-optical measurements [111] with the differences explained by the differences in the dielectric screening between the samples [6,15] . The subsequent measurements by S. Dong, M. Puppin, et al on the K-K exciton in bulk TMDCs obtained a Bohr radius of 1.74 nm, translating to an RMS radius of 2.13 nm [108] , consistent with the expectation of increased dielectric screening in bulk samples, which results in weaker excitonic binding.…”

Section: Tr-tof-mm Observations Of Excitonssupporting

confidence: 92%

Through the Lens of a Momentum Microscope: Viewing Light‐Induced Quantum Phenomena in 2D Materials

2022

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Van der Waals (vdW) materials at their two-dimensional limit are diverse, flexible, and unique laboratories to study fundamental quantum phenomena and their future applications. Their novel properties rely on their pronounced Coulomb interactions, variety of crystal symmetries and spinphysics, and the ease of incorporation of different vdW materials to form sophisticated heterostructures. In particular, the excited state properties of many two-dimensional semiconductors and semi-metals are relevant for their technological applications, particularly those that can be induced by light. In this paper, we review the recent advances made in studying out-of-equilibrium, light-induced, phenomena in these materials using powerful, surface-sensitive, time-resolved photoemission-based techniques, with a particular emphasis on the emerging multi-dimensional photoemission spectroscopy technique of time-resolved momentum microscopy. We discuss the advances this technique has enabled in studying the nature and dynamics of occupied excited states in these materials. Then, we project for the future research directions opened by these scientific and instrumental advancements, studying the physics of two-dimensional materials and the opportunities to engineer their band-structure and band-topology by laser fields.

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Section: Tr-tof-mm Observations Of Excitonssupporting

confidence: 92%

Through the Lens of a Momentum Microscope: Viewing Light‐Induced Quantum Phenomena in 2D Materials

2022

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“…An important parameter less well studied is the nature of the excitons at the nanoscale level. Nanoscale modulation or confinement of the center of mass of interlayer excitons has been recently probed in momentum space by using ultrafast angle-resolved photoemission electron spectroscopy (ARPES) ( 12 ). Similarly, the coupling and decoupling of interlayer excitons and phonons was probed by means of ultralow-frequency tip-enhanced Raman spectroscopy ( 13 ).…”

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confidence: 99%

Hyperspectral imaging of exciton confinement within a moiré unit cell with a subnanometer electron probe

Susarla

Naik

Blach

et al. 2022

Science

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Electronic and optical excitations in two-dimensional systems are distinctly sensitive to the presence of a moiré superlattice. We used cryogenic transmission electron microscopy and spectroscopy to simultaneously image the structural reconstruction and associated localization of the lowest-energy intralayer exciton in a rotationally aligned WS 2 -WSe 2 moiré superlattice. In conjunction with optical spectroscopy and ab initio calculations, we determined that the exciton center-of-mass wave function is confined to a radius of approximately 2 nanometers around the highest-energy stacking site in the moiré unit cell. Our results provide direct evidence that atomic reconstructions lead to the strongly confining moiré potentials and that engineering strain at the nanoscale will enable new types of excitonic lattices.

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“…111,[114][115][116] A number of recent TR-ARPES experiments are conducted on monolayers or bilayers positioned on a dielectric substrate such as SiO 2 or hBN. 45,87,109,117,118 The electrical grounding is achieved either by placing an electrode on the side of the monolayer crystal or by contacting through a very thin hBN layer on a highly doped Si substrate. The dielectric substrates will maintain photoexcited charge carriers at higher densities with longer lifetimes on hundreds of ps timescale.…”

Section: Development Of 2d Materials Samplesmentioning

confidence: 99%

Time- and angle-resolved photoemission spectroscopy (TR-ARPES) of TMDC monolayers and bilayers

Liu

2023

Chem. Sci.

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Structure of the moiré exciton captured by imaging its electron and hole

Cited by 61 publications

References 50 publications

Through the Lens of a Momentum Microscope: Viewing Light‐Induced Quantum Phenomena in 2D Materials

Through the Lens of a Momentum Microscope: Viewing Light‐Induced Quantum Phenomena in 2D Materials

Hyperspectral imaging of exciton confinement within a moiré unit cell with a subnanometer electron probe

Time- and angle-resolved photoemission spectroscopy (TR-ARPES) of TMDC monolayers and bilayers

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