Defect Structure of Localized Excitons in a 
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 Monolayer

Zhang, Shuai; Wang, Chenguang; Li, Mingyang; Huang, Di; Li, Lain‐Jong; Ji, Wei; Wu, Shiwei

doi:10.1103/physrevlett.119.046101

Cited by 190 publications

(143 citation statements)

References 38 publications

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“…However, C 3v symmetry is broken for Se W defect, which relaxes to C 2v symmetry after geometrical optimization. Our results are in agreement with previously published results …”

Section: Numerical Resultssupporting

confidence: 94%

“…We now turn to the origin of the defect responsible for the observed single‐photon emission. It has been observed that in CVD‐grown monolayer WSe 2 , the intrinsic defects are centered on the W sites which would indicate four possible defect structures: The W‐vacancy (V W ), the WSe 3 vacancy (V WSe3 ), the antisite defect with W being replaced by Se (Se W ), and the Se 3 vacancy (V Se3 ) . Because the defect calculations require large supercells, and thus less computationally expensive methods, we use DFT, with the use of LDA and restrict our investigation to the V W , V WSe3 , Se W , and the V Se3 defects.…”

Section: Numerical Resultsmentioning

confidence: 99%

“…Many challenges and questions yet remain, for example, the nature of the co‐linearly polarized doublet peaks as well as the wide range of lifetimes for the SQEs in this sample, indicating that more research on the coupling of bright and dark states is necessary to understand the variety of single emitter lifetimes in monolayer WSe 2 . Further studies on long‐lifetime emitters in the presence of high magnetic fields could shed light on the symmetry properties of the defects responsible as well as allow direct observation of potential dark states . The low estimated quantum efficiencies of single emitters in WSe 2 poses yet another challenge, but because of their atomically thin nature, 2D materials do not suffer from the internal reflection losses characteristic of other SQE systems.…”

Section: Resultsmentioning

confidence: 99%

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Ultra‐Long Lifetimes of Single Quantum Emitters in Monolayer WSe₂/hBN Heterostructures

et al. 2019

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Here, ultra‐long lifetimes of defect‐trapped single quantum emitters (SQEs) in monolayer WSe2/hBN heterostructures are reported. The lifetimes of these SQEs are approximately 225 ns, more than two orders of magnitude larger than what has been previously reported for defect‐trapped excitons in WSe2. These SQEs consist of co‐linearly polarized doublet peaks with a fine structure splitting of 0.45 meV. Second‐order correlation measurements show antibunched single‐photon emission with a g(2)(0) value of ≈0.13. Through numerical analysis and modeling, it is shown how such long‐lifetime single emitters can arise from bright and dark exciton coupling in antisite defects on the W sites. Additionally, high‐quality single‐photon emission over a wide range of lifetimes—from 2 ns to over 200 ns—is also reported, suggesting a variety of other possible defect structures present. The flexibility to generate high fidelity single‐photon emission, over a wide range of lifetimes in a single material system, has potential in many optical quantum computing applications from high‐bit‐rate single‐photon sources to quantum memory devices.

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“…However, C 3v symmetry is broken for Se W defect, which relaxes to C 2v symmetry after geometrical optimization. Our results are in agreement with previously published results …”

Section: Numerical Resultssupporting

confidence: 94%

Section: Numerical Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Ultra‐Long Lifetimes of Single Quantum Emitters in Monolayer WSe₂/hBN Heterostructures

et al. 2019

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“…In our recent reports, WS 2, and MoS 2 nanoparticles have shown ferromagnetism when annealed at different temperatures . Moreover, XPS results (Figure ) demonstrate the presence of W vacancies in undoped‐annealed WSe 2 sample, which promotes the electron deficiencies and results in hole (p‐type) doping into WSe 2 . Hence, hole‐mediated ferromagnetism is observed in WSe 2 .…”

Section: Resultsmentioning

confidence: 73%

High Coercivity and Magnetization in WSe₂ by Codoping Co and Nb

Ahmed

Ding

Murmu

et al. 2019

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Introducing ferromagnetism in transition metal dichalcogenides has attracted lots of attention due to the possible applications in spintronics devices. Generally, single magnetic element doping is used to introduce magnetism. However, mostly, weak ferromagnetism is observed. In this work, codoping of two kinds of transition metals (Nb and Co) into WSe2 is used to study its magnetic properties. In detail, single crystal WSe2 is codoped with 4 at% Co and various concentrations of Nb by employing the physical ion implantation method. Raman, X‐ray diffraction and X‐ray photoelectron spectroscopy results reveal the effective substitutional doping of implanted elements (Co and Nb). Magnetic measurements illustrate that both un‐doped and 4 at% Co doped WSe2 show weak ferromagnetism whereas magnetization is strongly enhanced when Co and Nb are codoped into WSe2. The magnetization is comparable with a ferromagnet, which may be attributed to Co, Nb doping and defects. In addition, a large coercivity of ≈1.2 kOe is observed in the 1 at% Nb–4 at% Co codoped WSe2 sample, which may be ascribed to the combined effect of doping‐induced stress, defect‐dictated pinning and anisotropy of NbSe bond owing to the charge transfer between Nb and Se ions.

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“…1(a)]. Here, we demonstrate the effect of symmetry on quasiparticle scattering by atomic vacancies which are among the most common types of defects in 2D TMDs [32][33][34][35][36][37][38]. For this purpose, we perform atomistic density-functional (DFT)-based T -matrix calculations [39] of FT-STS and QPI spectra for vacancies in two archetypal TMDs: the direct gap [44], small SO split MoS 2 , and the indirect gap [17], large SO split [13,14] WSe 2 .…”

mentioning

confidence: 99%

Symmetry-forbidden intervalley scattering by atomic defects in monolayer transition-metal dichalcogenides

et al. 2017

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Intervalley scattering by atomic defects in monolayer transition metal dichalcogenides (TMDs; M X2) presents a serious obstacle for applications exploiting their unique valley-contrasting properties. Here, we show that the symmetry of the atomic defects can give rise to an unconventional protection mechanism against intervalley scattering in monolayer TMDs. The predicted defectdependent selection rules for intervalley scattering can be verified via Fourier transform scanning tunneling spectroscopy (FT-STS), and provide a unique identification of, e.g., atomic vacancy defects (M vs X). Our findings put the absence of the intervalley FT-STS peak in recent experiments in a different perspective.Introduction.-Two-dimensional (2D) monolayers of transition metal dichalcogenides (TMDs; M X 2 ) are promising candidates for spin-and valleytronics applications [1]. Their hallmarks include unique valleycontrasting properties and strong spin-valley coupling [1, 2] exemplified by, e.g., valley-selective optical pumping [3][4][5], a valley-dependent Zeeman effect [6][7][8][9], and the valley Hall effect [10]. Such means to control the valley degree of freedom are instrumental for valleytronics applications.Another prerequisite for a successful realization of valleytronics is a sufficiently long valley lifetime [11,12]; atomic defects are a common limiting factor which can provide the required momentum for intervalley scattering due to their short-range nature. However, as illustrated in Fig. 1(a), the spin-orbit (SO) induced spin-valley coupling in the K, K valleys of 2D TMDs partially protects the valley degree of freedom against relaxation via intervalley scattering by nonmagnetic defects [2]. Due to the small spin-orbit splitting in the conduction band valleys [13,14], only the valence-band valleys fully benefit from this protection. Identification of additional protection mechanisms in the conduction band would hence be advantageous for valleytronics in 2D TMDs.In this work, we demonstrate that besides the spinvalley coupling, the symmetry and position of atomic defects give rise to unconventional selection rules for intervalley quasiparticle scattering in 2D TMDs. As illustrated in Fig. 1(b), we find that for defects with threefold rotational symmetry (C 3 ), e.g., atomic vacancies, intervalley K ↔ K scattering in the conduction band is forbidden for defects centered on the X site while it is allowed for M centered defects. In the valence band, intervalley scattering is forbidden in both cases. Analogous selection rules for the intervalley coupling due to confinement potentials in 2D TMD based quantum dots have previously been noted [15].Our findings can be readily verified with scanning tunneling spectroscopy (STS) which has provided valuable insight to the electronic properties of 2D TMDs [16][17][18][19][20]. In particular, Fourier transform STS (FT-STS) is a powerful method for investigating atomic defects and their scattering properties in 2D materials [21,22]. The measured STS map is a probe of the local density ...

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Defect Structure of Localized Excitons in a WSe2 Monolayer

Cited by 190 publications

References 38 publications

Ultra‐Long Lifetimes of Single Quantum Emitters in Monolayer WSe₂/hBN Heterostructures

Ultra‐Long Lifetimes of Single Quantum Emitters in Monolayer WSe₂/hBN Heterostructures

High Coercivity and Magnetization in WSe₂ by Codoping Co and Nb

Symmetry-forbidden intervalley scattering by atomic defects in monolayer transition-metal dichalcogenides

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Defect Structure of Localized Excitons in a WSe2 Monolayer

Cited by 190 publications

References 38 publications

Ultra‐Long Lifetimes of Single Quantum Emitters in Monolayer WSe2/hBN Heterostructures

Ultra‐Long Lifetimes of Single Quantum Emitters in Monolayer WSe2/hBN Heterostructures

High Coercivity and Magnetization in WSe2 by Codoping Co and Nb

Symmetry-forbidden intervalley scattering by atomic defects in monolayer transition-metal dichalcogenides

Contact Info

Product

Resources

About

Ultra‐Long Lifetimes of Single Quantum Emitters in Monolayer WSe₂/hBN Heterostructures

Ultra‐Long Lifetimes of Single Quantum Emitters in Monolayer WSe₂/hBN Heterostructures

High Coercivity and Magnetization in WSe₂ by Codoping Co and Nb