Valley plasmonics in transition metal dichalcogenides

Groenewald, R. E.; Rösner, Malte; Schönhoff, Gunnar; Haas, Stephan; Wehling, T. O.

doi:10.1103/physrevb.93.205145

Cited by 36 publications

(60 citation statements)

References 45 publications

(70 reference statements)

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“…Moreover, two-dimensional substrates, such as additional layers of TMDCs, can be studied. The two-dimensional plasmons in these materials behave very differently from the three-dimensional plasmon studied in this paper [24] and may open additional possibilities to tailor quasiparticle band gaps and excitons. Beyond that, our results are a first step towards a microscopic understanding of how TMDC excitons can be manipulated by means of more complex plasmonic nanostructures.…”

Section: Resultsmentioning

confidence: 75%

Frequency-dependent substrate screening of excitons in atomically thin transition metal dichalcogenide semiconductors

2018

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Atomically thin layers of transition metal dichalcogenides (TMDCs) exhibit exceptionally strong Coulomb interaction between charge carriers due to the two-dimensional carrier confinement in connection with weak dielectric screening. The van der Waals nature of interlayer coupling makes it easy to integrate TMDC layers into heterostructures with different dielectric or metallic substrates. This allows to tailor electronic and optical properties of these materials, as Coulomb interaction inside atomically thin layers is very susceptible to screening by the environment. Here we theoretically investigate dynamical screening effects in TMDCs due to bulk substrates doped with carriers over a large density range, thereby offering three-dimensional plasmons as tunable degree of freedom. We report a wide compensation of renormalization effects leading to a spectrally more stable exciton than predicted for static substrate screening, even if plasmons and excitons are in resonance. We also find a nontrivial dependence of the single-particle band gap on substrate doping density due to dynamical screening. Our investigation provides microscopic insight into the mechanisms that allow for manipulations of TMDC excitons by means of arbitrary plasmonic environments on the nanoscale. arXiv:1804.01352v1 [cond-mat.mtrl-sci]

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Section: Resultsmentioning

confidence: 75%

Frequency-dependent substrate screening of excitons in atomically thin transition metal dichalcogenide semiconductors

2018

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“…It is obvious that the plasmon mode obtained within DFT-RPA approach for monolayer MoS 2 differs significantly from with that calculated using the low-energy model Hamiltonian. The similar comparison was performed for hole doping in the case of MoS 2 in [72], and they observed strongly reduced plasmon energies and concluded that neglecting the material-specific dielectric function αβ (q) within the minimal three-band model is a severe approximation leading to unrealistic plasmonic properties.…”

Section: Monolayer Mosmentioning

confidence: 65%

Plasmonic Physics of 2D Crystalline Materials

Torbatian

Asgari

2018

Applied Sciences

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Collective modes of doped two-dimensional crystalline materials, namely graphene, MoS 2 and phosphorene, both monolayer and bilayer structures, are explored using the density functional theory simulations together with the random phase approximation. The many-body dielectric functions of the materials are calculated using an ab initio based model involving material-realistic physical properties. Having calculated the electron energy-loss, we calculate the collective modes of each material considering the in-phase and out-of-phase modes for bilayer structures. Furthermore, owing to many band structures and intreband transitions, we also find high-energy excitations in the systems. We explain that the material-specific dielectric function considering the polarizability of the crystalline material such as MoS 2 are needed to obtain realistic plasmon dispersions. For each material studied here, we find different collective modes and describe their physical origins.

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“…These plasmons originate from the short-range Coulomb potential through which electrons transition between valleys. Figures 5 shows ab initio-based model calculations of the electron energy loss spectroscopy (EELS) spectrum, measuring the imaginary part of the inverse dielectric function, for hole-doped MoS 2 , without and with SOC [111]. Here, the momenta are along the Γ − K path in the Brillouin zone and the pronounced maxima in the EELS spectrum correspond to plasmon modes.…”

Section: Intervalley Plasmonsmentioning

confidence: 99%

“…The intervalley Coulomb interaction in ML-TMDs. (a) and (b) Model calculations of the electron energy loss spectroscopy (EELS) spectra for hole-doped MoS 2 without and with SOC, respectively, taken from Ref [111]…”

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confidence: 99%

Dynamical screening in monolayer transition-metal dichalcogenides and its manifestations in the exciton spectrum

Scharf

Tuan

Žutić

et al. 2019

J. Phys.: Condens. Matter

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Monolayer transition-metal dichalcogenides (ML-TMDs) offer exciting opportunities to test the manifestations of many-body interactions through changes in the charge density. The two-dimensional character and reduced screening in ML-TMDs lead to the formation of neutral and charged excitons with binding energies orders of magnitude larger than those in conventional bulk semiconductors. Tuning the charge density by a gate voltage leads to profound changes in the optical spectra of excitons in ML-TMDs. On the one hand, the increased screening at large charge densities should result in a blueshift of the exciton spectral lines due to reduction in the binding energy. On the other hand, exchange and correlation effects that shrink the band-gap energy at elevated charge densities (band-gap renormalization) should result in a redshift of the exciton spectral lines. While these competing effects can be captured through various approximations that model long-wavelength charge excitations in the Bethe-Salpeter Equation, we show that a novel coupling between excitons and shortwave charge excitations is essential to resolve several experimental puzzles.Unlike ubiquitous and well-studied plasmons, driven by collective oscillations of the background charge density in the long-wavelength limit, we discuss the emergence of shortwave plasmons that originate from the short-range Coulomb interaction through which electrons transition between the K and −K valleys. The shortwave plasmons have a finite energy-gap because of the removal of spin-degeneracy in both the valence-arXiv:1801.06217v2 [cond-mat.mtrl-sci] 2. Properties of monolayer transition-metal dichalcogenides ML-TMDs are direct band-gap semiconductors with the conduction band and valence band edges at the K and K = −K points [19]. These time-reversed points define two separate low-energy pockets/valleys in the Brillouin zone. Due to the lack of space inversion symmetry and strong spin-orbit coupling arising from the d orbitals of the transition-metal atoms, the spin degeneracy in these valleys is lifted [24], as shown in Figs. 1(a,c). Whereas the spin splitting ∆ c in the conduction band is typically at most a few 10s of meV, the spin splitting in the valence band can be several 100s meV [24,54,55,56,57]. There are two important aspects to this band structure: First, timereversal symmetry results in a coupling between the spin and valley degrees of freedom, such that the spin ordering in opposite valleys is reversed as illustrated in Figs. 1(a,c). Second, the spin ordering of the conduction band in Mo-based compounds is opposite to the one in W-based compounds, as can be seen by comparing Figs. 1(a) and (c) [24,57,58]. This difference will be shown below to have profound consequences on their optical properties. Due to the large spin-splitting energy of the valence band, one can distinguish between two different series of neutral excitons in absorption experiments: One series involving the top valleys in the valence band, usually denoted as A excitons, and one involving it...

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Valley plasmonics in transition metal dichalcogenides

Cited by 36 publications

References 45 publications

Frequency-dependent substrate screening of excitons in atomically thin transition metal dichalcogenide semiconductors

Frequency-dependent substrate screening of excitons in atomically thin transition metal dichalcogenide semiconductors

Plasmonic Physics of 2D Crystalline Materials

Dynamical screening in monolayer transition-metal dichalcogenides and its manifestations in the exciton spectrum

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