Interlayer electron–phonon coupling in WSe2/hBN heterostructures

Choi, Jin; Kim, Jonghwan; Suh, Joonki; Shi, Zhiwen; Chen, Bin; Fan, Xi; Kam, Matthew; Watanabe, Kenji; Taniguchi, Takashi; Tongay, Sefaattin; Zettl, Alex; Wu, Junqiao; Wang, Feng

doi:10.1038/nphys3928

Cited by 200 publications

(221 citation statements)

References 32 publications

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“…This represents a major breakthrough since MoS 2 is the most abundant TMDC found in nature. For comparison, PL and reflectivity give neutral exciton linewidth down to 4 meV in hBN encapsulated WSe 2 MLs [52][53][54][55], a material which so far has been considered to have superior optical compared to MoS 2 .…”

Section: Neutral Exciton Transition In Pl and Reflectivitymentioning

confidence: 99%

Excitonic Linewidth Approaching the Homogeneous Limit in MoS2 -Based van der Waals Heterostructures

et al. 2017

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The strong light-matter interaction and the valley selective optical selection rules make monolayer (ML) MoS 2 an exciting 2D material for fundamental physics and optoelectronics applications. But, so far, optical transition linewidths even at low temperature are typically as large as a few tens of meV and contain homogeneous and inhomogeneous contributions. This prevented in-depth studies, in contrast to the bettercharacterized ML materials MoSe 2 and WSe 2 . In this work, we show that encapsulation of ML MoS 2 in hexagonal boron nitride can efficiently suppress the inhomogeneous contribution to the exciton linewidth, as we measure in photoluminescence and reflectivity a FWHM down to 2 meV at T ¼ 4 K. Narrow optical transition linewidths are also observed in encapsulated WS 2 , WSe 2 , and MoSe 2 MLs. This indicates that surface protection and substrate flatness are key ingredients for obtaining stable, high-quality samples. Among the new possibilities offered by the well-defined optical transitions, we measure the homogeneous broadening induced by the interaction with phonons in temperature-dependent experiments. We uncover new information on spin and valley physics and present the rotation of valley coherence in applied magnetic fields perpendicular to the ML.

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Section: Neutral Exciton Transition In Pl and Reflectivitymentioning

confidence: 99%

Excitonic Linewidth Approaching the Homogeneous Limit in MoS2 -Based van der Waals Heterostructures

et al. 2017

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“…Optical features in hBN sandwiched WSe2 heterostructures are further complicated by inter-material exciton-phonon coupling that results in hybrid modes that do not appear in the optical spectra of either hBN or WSe2 alone [30,31]. To confirm that the new emission feature we observe is from the 2s exciton, we performed two more control experiments.…”

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confidence: 99%

Superior Valley Polarization and Coherence of 2s Excitons in Monolayer WSe2

et al. 2018

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We report experimental observation of 2s exciton radiative emission from monolayer tungsten diselenide, enabled by hexagonal boron nitride protected high-quality samples. The 2s luminescence is highly robust and persists up to 150K, offering a new quantum entity for manipulating the valley degree of freedom. Remarkably, the 2s exciton displays superior valley polarization and coherence than 1s under similar experimental conditions. This observation provides evidence that the Coulomb-exchange-interactiondriven valley-depolarization process, the Maialle-Silva-Sham mechanism, plays an important role in valley excitons of monolayer transition metal dichalcogenides. 71.35.Cc 3The coupled spin-valley physics [1] in monolayer (1L) transition metal dichalcogenide (TMDC) semiconductors has inspired great strides towards realizing valleytronic devices harnessing these two-dimensional (2D) materials [2][3][4][5]. The two energetically degenerate 1L-TMDC valleys with opposite angular momentum can be selectively populated with circularly polarized optical excitation, and the valley polarization can be detected both optically [2][3][4] and electrically [5]. Further, coherent superposition of valley excitons can be generated with linearly polarized light [6] or a sequence of laser pulses with opposite circular polarization [7], which allows for rotation of the valley pseudospin with magnetic Zeeman effect or optical Stark effect [8,9]. Such coherent manipulations of valley pseudospin are at the heart of future quantum valleytronic devices, and requires thorough understanding and efficient control of various valley depolarization and decoherence processes.In general, intervalley scattering can occur due to both extrinsic mechanisms such as disorder scattering, and intrinsic mechanisms such as the Coulomb exchange interaction [10]; the competition between these different valley relaxation channels is a topic under active debate [7,[11][12][13]. So far many of the valleytronic studies focus on the 1s exciton, the ground state of Coulomb-bound electron-hole pairs, which is readily accessible in 2D TMDC monolayers [2][3][4][5][6][7][8][9]14]. Excitons also have higher energy states that form the hierarchical Rydberg-like series [15][16][17], similar to a hydrogen atom. It is desirable to access the valley pseudospin of these higher quantum number exciton states, which in previous studies have been employed to demonstrate the exceptionally large exciton binding energy [15][16][17][18][19] and to probe exciton internal quantum transitions [20]. Yet it is relatively challenging to generate radiative emission from these states, as can be understood from Kasha's rule [21]: photon emission quantum yield is appreciable only for the lowest energy excited state, which for the charge neutral exciton, is the 1s state. In this Letter, we report that with efficient removal of disorder and phonon scattering channels, the 2s exciton luminescence from monolayer tungsten diselenide (1L-WSe2) becomes accessible for valleytronic investigat...

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“…This assembly can be used to create an almost unlimited number of combinations and extraordinary properties [1][2][3] for novel multifunctional electronic and optoelectronic devices. This assembly can be used to create an almost unlimited number of combinations and extraordinary properties [1][2][3] for novel multifunctional electronic and optoelectronic devices.…”

Section: Optical Memorymentioning

confidence: 99%

“…A charge trapping layer acting as a floating gate, instead of charge trapping at the materials/SiO 2 interface, can be introduced via gold nanoparticle/crosslinked poly(4-vinylphenol)/MoS 2 heterojunction-FETs, which significantly increase both the switching on/off ratio (≈10 6 ) and retention time (>10 4 s). This assembly can be used to create an almost unlimited number of combinations and extraordinary properties [1][2][3] for novel multifunctional electronic and optoelectronic devices. [30] Despite the long retention time and high on/off ratios of the recently developed vdWs heterostructure-based optical memory 2D van der Waals (vdWs) heterostructures exhibit intriguing optoelectronic properties in photodetectors, solar cells, and light-emitting diodes.…”

mentioning

confidence: 99%

Two‐Terminal Multibit Optical Memory via van der Waals Heterostructure

et al. 2018

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cells, [11] and memory. [12,13] Recently, vdWs heterostructure-based nonvolatile optical memory have been investigated for broad potential applications in imaging sensors, [14] logic gates, [15] optoelectronic demodulators, [16] and synaptic devices for neuromorphic systems. [17,18] These 2D vdWs materials and their hybrids are considered to be an ideal platform for nonvolatile optical memory owing to their strong light-matter interactions [19][20][21] and significant photogenerated charge trapping derived from their very large surface-to-volume ratio. [22][23][24] In addition, the mechanical strength and atomic thickness of 2D vdWs materials allow for device miniaturization in flexible and wearable optoelectronics. [25][26][27] The demonstration of 2D vdWs materials-based optical memory in the FETs of few-layer copper indium selenide (CuIn 7 Se 11 ) has been reported [14] along with hybrids of graphene/MoS 2[5] on a silicon substrate. These devices exhibit low optical switching on/off ratios (<1 [5] and ≈10 [14] ), high off-currents (≈400 µA [5] and 20 pA [14] ), and short retention times (50 s [14] ), preventing their use in high quality image sensors and multilevel storage devices.Using oxygen plasma treatments to create more charge trap sites at SiO 2 surface, monolayer MoS 2 -FET-based optical memory on silicon substrate has exhibited a long retention time of ≈10 4 s. [28] However, the data storage capacity of eight levels of the material remains limited for practical applications due to moderate switching on/off ratio of ≈4700. Importantly, the memory function of these devices relies on charge trapping of photoexcited carriers in defects and impurities on either the surface or material/SiO 2 interface. [5,28] This results in short retention times and sensitivity to environmental factors. A charge trapping layer acting as a floating gate, instead of charge trapping at the materials/SiO 2 interface, can be introduced via gold nanoparticle/crosslinked poly(4-vinylphenol)/MoS 2 heterojunction-FETs, which significantly increase both the switching on/off ratio (≈10 6 ) and retention time (>10 4 s). [29] Similarly, by storing charge in the hexagonal boron nitride (h-BN) dielectric layer, the WSe 2 /h-BN-FET-based optical memory on silicon also exhibited a high on/off ratio of 1.1 × 10 6 , realizing a data storage capability of up to 128 distinct states. [30] Despite the long retention time and high on/off ratios of the recently developed vdWs heterostructure-based optical memory 2D van der Waals (vdWs) heterostructures exhibit intriguing optoelectronic properties in photodetectors, solar cells, and light-emitting diodes. In addition, these materials have the potential to be further extended to optical memories with promising broadband applications for image sensing, logic gates, and synaptic devices for neuromorphic computing. In particular, high programming voltage, high off-power consumption, and circuital complexity in integration are primary concerns in the development of three-terminal optical memory devices....

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Interlayer electron–phonon coupling in WSe2/hBN heterostructures

Cited by 200 publications

References 32 publications

Excitonic Linewidth Approaching the Homogeneous Limit in MoS2 -Based van der Waals Heterostructures

Excitonic Linewidth Approaching the Homogeneous Limit in MoS2 -Based van der Waals Heterostructures

Superior Valley Polarization and Coherence of 2s Excitons in Monolayer WSe2

Two‐Terminal Multibit Optical Memory via van der Waals Heterostructure

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