Twist-angle dependence of moiré excitons in WS2/MoSe2 heterobilayers

Zhang, Long; Zhang, Zhe; Wu, Fengcheng; Wang, Danqing; Gogna, Rahul; Hou, Shaocong; Watanabe, Kenji; Taniguchi, Takashi; Kulkarni, Krishnamurthy; Kuo, T.; Forrest, Stephen R.; Deng, Hui

doi:10.1038/s41467-020-19466-6

Cited by 127 publications

(117 citation statements)

References 52 publications

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“…Our scheme for tuning SHG based on interlayer excitons with a permanent static electric dipole can be applied to a variety of other systems with strong interlayer exciton resonances, such as homobilayer MoSe 2 66 . Very importantly it has been shown recently that several heterobilayer systems host interlayer excitons with static electric dipoles and high optical oscillator strength, for example, MoSe 2 /WS 2 with hybridized conduction states 61,62 , WSe 2 /WS 2 with hybridized valence states 63 , MoS 2 /WS 2 with electrically tunable valence state hybridization 64 and similar predictions of electronic state hybridization for specific twist angles in MoTe 2 /MoSe 2 65 . It can be expected that also in these and other systems SHG can also be efficiently tuned via the Stark effect, as demonstrated here for homobilayer MoS 2 .…”

Section: Discussionmentioning

confidence: 56%

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Interlayer exciton mediated second harmonic generation in bilayer MoS2

et al. 2021

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Second-harmonic generation (SHG) is a non-linear optical process, where two photons coherently combine into one photon of twice their energy. Efficient SHG occurs for crystals with broken inversion symmetry, such as transition metal dichalcogenide monolayers. Here we show tuning of non-linear optical processes in an inversion symmetric crystal. This tunability is based on the unique properties of bilayer MoS2, that shows strong optical oscillator strength for the intra- but also interlayer exciton resonances. As we tune the SHG signal onto these resonances by varying the laser energy, the SHG amplitude is enhanced by several orders of magnitude. In the resonant case the bilayer SHG signal reaches amplitudes comparable to the off-resonant signal from a monolayer. In applied electric fields the interlayer exciton energies can be tuned due to their in-built electric dipole via the Stark effect. As a result the interlayer exciton degeneracy is lifted and the bilayer SHG response is further enhanced by an additional two orders of magnitude, well reproduced by our model calculations. Since interlayer exciton transitions are highly tunable also by choosing twist angle and material combination our results open up new approaches for designing the SHG response of layered materials.

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Section: Discussionmentioning

confidence: 56%

“…3a. Tuning both amplitude and spectral range of the SHG response of the bilayer is a direct consequence of exploiting the properties of interlayer excitons applicable to many van der Waals bilayer systems [61][62][63][64][65][66] and will be further discussed below.…”

Section: Resultsmentioning

confidence: 99%

Interlayer exciton mediated second harmonic generation in bilayer MoS2

et al. 2021

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“…Recently, 2D transition metal dichalcogenides (TMDCs) have attracted increasing attentions due to their unique optical and electrical properties, which bring them wide‐range applications in electronics and optoelectronics related fields. [ 1–7 ] For such purposes, it is essential to realize the controlled synthesis of TMDCs monolayers with large domain size, ideally in an effective and low‐cost way. [ 8–12 ] Chemical vapor deposition (CVD) has proven to be promising for synthesizing high‐quality TMDCs monolayers, due to its excellent controllability, scalability, and cost effectiveness.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast Growth of Large‐Area Uniform, Millimeter‐Size MoSe₂ Single Crystals on Low‐Cost Soda‐Lime Glass

Zhang

Zhu

Wang

et al. 2021

Adv Materials Inter

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2D semiconducting transition metal dichalcogenides (TMDCs) have emerged as essential building blocks for engineering next‐generation integrated electronics. To achieve this, the controllable synthesis of monolayer TMDCs with high crystal quality, low cost, and high yield is crucial, while it remains challenging. Herein, the direct synthesis of large‐area uniform, millimeter‐size monolayer MoSe2 single crystals on a 6‐centimeter‐long soda‐lime glass template, by using a designed “beam‐bridge” assisted metal oxide precursor feeding strategy via chemical vapor deposition (CVD), is reported. Notably, several tenths of millimeter‐scale, triangular‐shaped monolayer MoSe2 single crystals are obtained in one batch within 25 s’ growth, affording so far the fastest growth rate (≈50 µm s−1). This ultrafast growth behavior is proposed to be mediated by the sufficient, homogeneous release of Mo‐based precursor, the catalytic property of sodium atoms on soda‐lime glass substrate, as well as the improved surface kinetics on the molten glass surface. Moreover, the thickness‐controlled growth from monolayer to bilayers is also realized. This work provides brand new insights for the batch production of large single‐crystal TMDCs, which should propel its practical applications in versatile fields.

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“… 17 − 20 Evidence of moiré excitons has been found in van der Waals heterostructures such as WS 2 /MoSe 2 even at bilayers with large twist angles. 21 , 22 Among other 2D layered systems proposed as possible candidates, theoretical predictions have shown the emergence of flat bands on the interlayer twisting of 2D kagomé layers resulting in possible insulating correlated states at higher T c . 23 …”

Section: Introductionmentioning

confidence: 99%

Twisting of 2D Kagomé Sheets in Layered Intermetallics

et al. 2021

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Chemical bonding in 2D layered materials and van der Waals solids is central to understanding and harnessing their unique electronic, magnetic, optical, thermal, and superconducting properties. Here, we report the discovery of spontaneous, bidirectional, bilayer twisting (twist angle ∼4.5°) in the metallic kagomé MgCo 6 Ge 6 at T = 100(2) K via X-ray diffraction measurements, enabled by the preparation of single crystals by the Laser Bridgman method. Despite the appearance of static twisting on cooling from T ∼300 to 100 K, no evidence for a phase transition was found in physical property measurements. Combined with the presence of an Einstein phonon mode contribution in the specific heat, this implies that the twisting exists at all temperatures but is thermally fluctuating at room temperature. Crystal Orbital Hamilton Population analysis demonstrates that the cooperative twisting between layers stabilizes the Co-kagomé network when coupled to strongly bonded and rigid (Ge 2 ) dimers that connect adjacent layers. Further modeling of the displacive disorder in the crystal structure shows the presence of a second, Mg-deficient, stacking sequence. This alternative stacking sequence also exhibits interlayer twisting, but with a different pattern, consistent with the change in electron count due to the removal of Mg. Magnetization, resistivity, and low-temperature specific heat measurements are all consistent with a Pauli paramagnetic, strongly correlated metal. Our results provide crucial insight into how chemical concepts lead to interesting electronic structures and behaviors in layered materials.

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Twist-angle dependence of moiré excitons in WS2/MoSe2 heterobilayers

Cited by 127 publications

References 52 publications

Interlayer exciton mediated second harmonic generation in bilayer MoS2

Interlayer exciton mediated second harmonic generation in bilayer MoS2

Ultrafast Growth of Large‐Area Uniform, Millimeter‐Size MoSe₂ Single Crystals on Low‐Cost Soda‐Lime Glass

Twisting of 2D Kagomé Sheets in Layered Intermetallics

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Twist-angle dependence of moiré excitons in WS2/MoSe2 heterobilayers

Cited by 127 publications

References 52 publications

Interlayer exciton mediated second harmonic generation in bilayer MoS2

Interlayer exciton mediated second harmonic generation in bilayer MoS2

Ultrafast Growth of Large‐Area Uniform, Millimeter‐Size MoSe2 Single Crystals on Low‐Cost Soda‐Lime Glass

Twisting of 2D Kagomé Sheets in Layered Intermetallics

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Ultrafast Growth of Large‐Area Uniform, Millimeter‐Size MoSe₂ Single Crystals on Low‐Cost Soda‐Lime Glass