Approaching the intrinsic photoluminescence linewidth in transition metal dichalcogenide monolayers

Ajayi, Obafunso; Ardelean, Jenny; Shepard, Gabriella D.; Wang, Jue; Antony, Aldrin; Taniguchi, Takeshi; Watanabe, Kenji; Heinz, Tony F.; Strauf, Stefan; Zhu, Xiaoyang; Hone, James

doi:10.1088/2053-1583/aa6aa1

Cited by 301 publications

(316 citation statements)

References 35 publications

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“…Also, all timeresolved experiments using pulsed laser, such as pumpprobe spectroscopy, time-resolved PL, and four-wave mixing [12,31,36,90,91], will benefit from these samples with much higher threshold for optical damage as compared to uncapped samples. Note added in proof.-Narrow linewidth emission in hBN encapsulated samples is also reported in [92].…”

Section: Discussionmentioning

confidence: 74%

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: Discussionmentioning

confidence: 74%

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

et al. 2017

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“…In the current case, there is no obvious candidate for the continuum excitation. Although the broad exciton lines may suggest that the exciton states themselves might serve as a 'continuum', recent reports that the homogeneous linewidth of the excitons in TMDs is very narrow [58][59][60], indicating that the commonly observed broad exciton linewidth is mainly due to inhomogeneous broadening that would not qualify as the 'continuum' for Fano resonance.…”

Section: Discussionmentioning

confidence: 99%

Excitation energy dependence of Raman spectra of few-layer WS2

2017

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ABSTRACT:Raman spectra of few-layer WS 2 have been measured with up to seven excitation energies, and peculiar resonance effects are observed. The two-phonon acoustic phonon scattering signal close to the main E 2g 1 peak is stronger than the main peaks for excitations near the A or B exciton states. The lowfrequency Raman spectra show a series of shear and layer-breathing modes that are useful for determining the number of layers. In addition, hitherto unidentified peaks (X 1 and X 2 ), which do not seem to depend on the layer thickness, are observed near resonances with exciton states. The polarization dependences of the two peaks are different: X 1 vanishes in cross polarization, but X 2 does not. At the resonance with the A exciton state, the Raman-forbidden, lowest-frequency shear mode for odd number of layers appears as strong as that for the allowed case of even number of layers. This mode also exhibits a strong BreitWigner-Fano line shape and an anomalous polarization behavior at this resonance.

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“…One of the most studied amongst such heterostructures is a TMD monolayer encapsulated by two hexagonal boron nitride 4 (hBN) flakes: this "passivated" monolayer exhibits enhanced carrier mobility (19,20) and reduced photoluminescence linewidth (21,22).…”

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Large Excitonic Reflectivity of MonolayerMoSe2Encapsulated in Hexagonal Boron Nitride

et al. 2018

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scattering has emerged as a method for overcoming these limitations and for controlling light at the atomic scale (3-11). For instance, highly reflective mirrors based on individual quantum emitters have been demonstrated by coupling them to optical cavities and nanophotonic waveguides (3-8). Such resonant mirrors feature very unusual properties due to their extraordinary nonlinearity down to the single-photon level (3-8). A two-dimensional (2D) layer of emitters, such as atomic lattices or excitons (9-11), has also been predicted to act as an efficient mirror when the incident light is resonant with the resonance frequency of the system. Such atomically thin mirrors represent the ultimate miniaturization limit of a reflective surface, and could enable unique applications ranging from quantum nonlinear optics (9-11) to topological photonics (12,13).This Report demonstrates that transition metal dichalcogenide (TMD) monolayers can act as atomically thin, electrically switchable, resonant mirrors. These materials are direct-bandgap semiconductors that support tightly bound excitons. Excitonic transitions in TMD monolayers exhibit large oscillator strengths (14-16), resulting in large radiative linewidths compared to excitons in other semiconductor systems. In addition, the excitonic response in monolayers can be controlled electrically via gate-induced doping and by shifting the chemical potential (17)(18)(19).Importantly, these monolayers can be easily integrated with other 2D materials via Van der Waals stacking to improve their quality or add new functionalities. One of the most studied amongst such heterostructures is a TMD monolayer encapsulated by two hexagonal boron nitride 4 (hBN) flakes: this "passivated" monolayer exhibits enhanced carrier mobility (19,20) and reduced photoluminescence linewidth (21,22).Our experiments make use of a device that consists of an hBN-passivated molybdenum diselenide (MoSe 2 ) monolayer placed on an oxide-covered silicon (Si) substrate, and we measure its reflectivity with a normally incident laser beam (Figs. 1A and 1B). The doped Si substrate is used as a gate electrode: by applying a gate voltage (V g ), MoSe 2 monolayers can be made intrinsic or n-doped. When a monochromatic laser beam is tuned to the exciton resonance, we observe substantial reflection from a monolayer device (M1) at V g < 10 V at T = 4 K (Fig. 1C).The reflection contrast between the monolayer region and the substrate disappears at V g > 20 V ( Fig. 1D), indicating that the reflection can be turned off electrically. When we illuminate another monolayer device (M2) with a supercontinuum laser and spectrally resolve the reflection, we find that both the magnitudes and wavelength positions of the reflectance peaks change with V g (Fig. 1E). When the monolayer is intrinsic (V g < 10 V), the reflection is dominated by a peak at the wavelength of the neutral exciton transition. When MoSe 2 is n-doped (V g > 20 V), however, the reflection by the neutral exciton disappears, and a new, weaker, reflectance peak ap...

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Approaching the intrinsic photoluminescence linewidth in transition metal dichalcogenide monolayers

Cited by 301 publications

References 35 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

Excitation energy dependence of Raman spectra of few-layer WS2

Large Excitonic Reflectivity of MonolayerMoSe2Encapsulated in Hexagonal Boron Nitride

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