Electrical tuning of optically active interlayer excitons in bilayer MoS2

Peimyoo, Namphung; Deilmann, Thorsten; Withers, Freddie; Escolar, Janire; Nutting, Darren; Taniguchi, Takashi; Watanabe, Kenji; Taghizadeh, Alireza; Craciun, Monica F.; Thygesen, Kristian Sommer; Russo, Saverio

doi:10.1038/s41565-021-00916-1

Cited by 74 publications

(62 citation statements)

References 35 publications

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“…Because these IXs consist of electrons and holes separated in different layers and valleys, their population lifetimes at low temperature are up to 100 s of nanoseconds 4 , facilitating long-range transport before relaxation. Importantly, IXs have a permanent perpendicular dipole moment so that their energy can be tuned with an out-of-plane electric field 33,34 , thus they can be driven by a lateral gradient of electric-field 35 . Indeed, prototypical TMDC excitonic transistors have been demonstrated based on field-controlled IX diffusion in MoSe 2 /WSe 2 heterobilayers [35][36][37] .…”

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confidence: 99%

Long-range transport of 2D excitons with acoustic waves

Peng

Ripin

et al. 2022

Nat Commun

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Excitons are elementary optical excitation in semiconductors. The ability to manipulate and transport these quasiparticles would enable excitonic circuits and devices for quantum photonic technologies. Recently, interlayer excitons in 2D semiconductors have emerged as a promising candidate for engineering excitonic devices due to their long lifetime, large exciton binding energy, and gate tunability. However, the charge-neutral nature of the excitons leads to weak response to the in-plane electric field and thus inhibits transport beyond the diffusion length. Here, we demonstrate the directional transport of interlayer excitons in bilayer WSe2 driven by the propagating potential traps induced by surface acoustic waves (SAW). We show that at 100 K, the SAW-driven excitonic transport is activated above a threshold acoustic power and reaches 20 μm, a distance at least ten times longer than the diffusion length and only limited by the device size. Temperature-dependent measurement reveals the transition from the diffusion-limited regime at low temperature to the acoustic field-driven regime at elevated temperature. Our work shows that acoustic waves are an effective, contact-free means to control exciton dynamics and transport, promising for realizing 2D materials-based excitonic devices such as exciton transistors, switches, and transducers up to room temperature.

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confidence: 99%

Long-range transport of 2D excitons with acoustic waves

Peng

Ripin

et al. 2022

Nat Commun

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“…The recent emergence of two-dimensional transition metal dichalcogenides (TMDCs) and their van der Waals (vdW) heterostructures offers an unprecedented platform to realize spatially indirect excitons. Indeed, spatially indirect excitons have thus far been demonstrated in a wide variety of TMDC homo-and heterostructures [19], such as MoS 2 /WS 2 [25][26][27], MoS 2 /WSe 2 [28,29], MoSe 2 /WSe 2 [20,22,[30][31][32][33], and bilayer MoS 2 [7,[34][35][36][37][38][39]. Specially, owing to the strongly reduced dielectric screening, spatially indirect excitons in homo-/heterobilayers of TMDCs possess substantial binding energies and show crucial advantages for applications, for example, superfluidity at high temperature [9].…”

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“…To date, the studies of spatially indirect excitons have mainly focused on the momentum-bright species with electrons and holes localized in the same valley of the Brillouin zone (BZ) [7,[19][20][21][22][23][24][25][29][30][31][32][33][34][35][36][37][38][39][40][41][42]. On the other hand, because of the existence of multiple electronic valleys, TMDC homoand heterobilayers can also exhibit spatially indirect excitons with momentum-dark nature (that is, electrons and holes are from different valleys of the BZ) [6,28,[43][44][45].…”

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Spatially indirect intervalley excitons in bilayer WSe2

et al. 2022

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Spatially indirect excitons with displaced wave functions of electrons and holes play a pivotal role in a large portfolio of fascinating physical phenomena and emerging optoelectronic applications, such as valleytronics, exciton spin Hall effect, excitonic integrated circuit, and high-temperature superfluidity. Here, we uncover three types of spatially indirect excitons (including their phonon replicas) and their quantum-confined Stark effects in hexagonal boron nitride encapsulated bilayer WSe 2 by performing electric field-tunable photoluminescence measurements. Because of different out-of-plane electric dipole moments, the energy order between the three types of spatially indirect excitons can be switched by a vertical electric field. Remarkably, we demonstrate, assisted by first-principles calculations, that the observed spatially indirect excitons in bilayer WSe 2 are also momentum indirect, involving electrons and holes from and K/ valleys in the Brillouin zone, respectively. This is in contrast to the previously reported spatially indirect excitons with electrons and holes localized in the same valley. Furthermore, we find that the spatially indirect intervalley excitons in bilayer WSe 2 can exhibit considerable, doping-sensitive circular polarization. The spatially indirect excitons with momentum-dark nature and highly tunable circular polarization may provide a firm basis for the understanding and engineering of technological applications in photonics and optoelectronics.

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“…A particularly attractive feature of interlayer excitons in related homobilayer systems is provided by the permanent dipole moment of layer-indirect excitons [13][14][15] which promotes exciton-exciton dipolar interactions, allows employing electric fields to tune the optical properties via the Stark effect [10,[16][17][18][19][20][21] or implementing exciton trapping and routing [22]. The electrostatic dipole moment depends on the degree of exciton layer delocalization, which in turn is sensitive to the interlayer coupling and thus to the stacking order, as was shown recently by optical absorption for 2H and 3R MoS 2 BLs for transitions involving momentum direct KK excitons [23,24].…”

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Stacking-dependent exciton multiplicity in WSe2 bilayers

Förste

Watanabe

et al. 2021

Preprint

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Twisted layers of atomically thin two-dimensional materials realize a broad range of novel quantum materials with engineered optical and transport phenomena arising from spin and valley degrees of freedom and strong electron correlations in hybridized interlayer bands. Here, we report experimental and theoretical studies of WSe2 homobilayers obtained in two stable configurations of 2H (60° twist) and 3R (0° twist) stackings by controlled chemical vapor synthesis of high-quality large-area crystals. Using optical absorption and photoluminescence spectroscopy at cryogenic temperatures, we uncover marked differences in the optical characteristics of 2H and 3R bilayer WSe2 which we explain on the basis of beyond-DFT theoretical calculations. Our results highlight the role of layer stacking for the spectral multiplicity of momentum-direct intralayer exciton transitions in absorption, and relate the multiplicity of phonon sidebands in the photoluminescence to momentum-indirect excitons with different spin valley and layer character. Our comprehensive study generalizes to other layered homobilayer and heterobilayer semiconductor systems and highlights the role of crystal symmetry and stacking for interlayer hybrid states.

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Electrical tuning of optically active interlayer excitons in bilayer MoS2

Cited by 74 publications

References 35 publications

Long-range transport of 2D excitons with acoustic waves

Long-range transport of 2D excitons with acoustic waves

Spatially indirect intervalley excitons in bilayer WSe2

Stacking-dependent exciton multiplicity in WSe2 bilayers

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