Quantum-Confined Stark Effect in a MoS<sub>2</sub> Monolayer van der Waals Heterostructure

Roch, Jonas G.; Leisgang, Nadine; Froehlicher, Guillaume; Makk, Péter; Watanabe, Kenji; Taniguchi, Takashi; Schönenberger, Christian; Warburton, Richard J.

doi:10.1021/acs.nanolett.7b04553

Cited by 68 publications

(88 citation statements)

References 35 publications

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“…where d InSe and d BN are the respective total thicknesses of the InSe and hBN in the stack, and ε InSe /ε BN ≈ 4.9 is the ratio between the out-of-plane dielectric constants of InSe and hBN. This leads to a clearly pronounced quadratic red shift of the lowest subband s energy seen in Fig.2g,h, similar to previously the observed quantum confined Stark effect in MoS 2 monolayers [24]. At the same time, subbands in the middle of the spectrum (c 1 , c 2 for 4L and c 1 , c 2 , c 3 for 5L) remain almost constant, whereas the highest subband is blue shifted.…”

Section: Resultssupporting

confidence: 88%

Ultra-thin van der Waals crystals as semiconductor quantum wells

et al. 2020

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Control over the electronic spectrum at low energy is at the heart of the functioning of modern advanced electronics: high electron mobility transistors, semiconductor and Capasso terahertz lasers, and many others. Most of those devices rely on the meticulous engineering of the size quantization of electrons in quantum wells. This avenue, however, hasnt been explored in the case of 2D materials. Here we transfer this concept onto the van der Waals heterostructures which utilize few-layers films of InSe as quantum wells. The precise control over the energy of the subbands and their uniformity guarantees extremely high quality of the electronic transport in such systems. Using novel tunnelling and light emitting devices, for the first time we reveal the full subbands structure by studying resonance features in the tunnelling current, photoabsorption and light emission. In the future, these systems will allow development of elementary 1 arXiv:1910.04215v2 [cond-mat.mes-hall] 31 Oct 2019 blocks for atomically thin infrared and THz light sources based on intersubband optical transitions in few-layer films of van der Waals materials.

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Section: Resultssupporting

confidence: 88%

Ultra-thin van der Waals crystals as semiconductor quantum wells

et al. 2020

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“…This result confirms the spatial structure of the interlayer complexes, where electrons and holes reside in different layers. The observed tuning range is orders of magnitude larger than the ones reported for TMD intralayer exciton lines [42][43][44], and similar, yet slightly larger, to the one recently observed for interlayer excitons in homobilayer structures [45]. We finally note that a similar design with only thin hBN layers as top and bottom dielectric spacers would yield a shift as high as 500 meV before reaching the breakdown of hBN [46].…”

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Tuning of impurity-bound interlayer complexes in a van der Waals heterobilayer

et al. 2019

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Due to their unique two-dimensional nature, charge carriers in semiconducting transition metal dichalcogenides (TMDs) exhibit strong unscreened Coulomb interactions and sensitivity to defects and impurities. The versatility of van der Waals layer stacking allows spatially separating electrons and holes between different TMD layers with staggered band structure, yielding interlayer few-body excitonic complexes whose nature is still debated. Here we combine quantum Monte Carlo calculations with spectrally and temporally resolved photoluminescence measurements on a top-and bottom-gated MoSe2/WSe2 heterostructure, and identify the emitters as impurity-bound interlayer excitonic complexes. Using independent electrostatic control of doping and out-of-plane electric field, we demonstrate control of the relative populations of neutral and charged complexes, their emission energies on a scale larger than their linewidth, and an increase of their lifetime into the microsecond regime. This work unveils new physics of confined carriers and is key to the development of novel optoelectronics applications.Transition metal dichalcogenides form a new class of semiconducting twodimensional (2D) materials that display strongly bound electron-hole complexes [1-4] -such as excitons and trions -and original valley physics [5][6][7][8] up to room temperature. Furthermore, their unique layered structure allows them to be stacked in van der Waals heterostructures with atomically sharp and clean interfaces [9][10][11]. The combination of those novel properties with the versatility of layer engineering opens up new avenues for roomtemperature excitonic complex formation and manipulation [12][13][14]. In particular, the model case of TMD heterobilayers with type-II (staggered) band alignment exhibits, upon light excitation, ultrafast charge transfer between layers [15][16][17] and luminescence at energies lower than the one generated by intralayer complexes [18][19][20][21][22]. This is interpreted as the formation of interlayer excitons where electrons and holes reside in different layers due to the staggered band alignment [22][23][24][25][26]. Promising properties of those emitters have been demonstrated, such as long lifetime [20,[27][28][29] and long spin-valley population time [29,30], establishing them as good candidates to achieve coherent manipulation [31][32][33][34]. Yet, clear identification of the nature of these emitters and in situ control over them are crucial challenges that still need to be overcome.In the case of individual monolayer TMDs, electrostatic tuning of the carrier density using a single gate has been key to unveiling the competition between delocalized excitonic complexes (neutral and charged excitons), as well as the presence of impurity-bound local states [5,35,36]. However, in heterobilayer junctions this standard approach is insufficient to achieve unambiguous identification and control over the complexes [20,37,38]. This can be understood considering the spatial separation between electrons and holes resid...

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“…Near V g = 0 V, we observe three spectrally narrow lines corresponding to the neutral excitons (X 0 ) of three different optically active quantum dots (labelled A to C). Notably, the neutral exciton energy of dots A, B and C is independent of the vertical electric field across the device, demonstrating minimal quantum confined Stark effect for these WSe 2 quantum dots, in contrast to previous reports for WSe 2 quantum dots 21 but similar to two-dimensional excitons in TMDs 22 . At V g ≈ −7 V (dot A) and V g ≈ −13 V (dots B and C), the emission energy changes abruptly as a second electron overcomes the electron-electron Coulomb energy (U ee ) and tunnels into the quantum dot (schematically represented in the top part of Fig.…”

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Coulomb blockade in an atomically thin quantum dot coupled to a tunable Fermi reservoir

et al. 2019

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Gate-tunable quantum-mechanical tunnelling of particles between a quantum confined state and a nearbyFermi reservoir of delocalized states has underpinned many advances in spintronics and solid-state quantum optics. The prototypical example is a semiconductor quantum dot separated from a gated contact by a tunnel barrier. This enables Coulomb blockade, the phenomenon whereby electrons or holes can be loaded one-by-one into a quantum dot 1,2 . Depending on the tunnel-coupling strength 3,4 , this capability facilitates single spin quantum bits 1,2,5 or coherent many-body interactions between the confined spin and the Fermi reservoir 6,7 . Van der Waals (vdW) heterostructures, in which a wide range of unique atomic layers can easily be combined, offer novel prospects to engineer coherent quantum confined spins 8,9 , tunnel barriers down to the atomic limit 10 or a Fermi reservoir beyond the conventional flat density of states 11 . However, gatecontrol of vdW nanostructures 12-16 at the single particle level is needed to unlock their potential. Here we report Coulomb blockade in a vdW heterostructure consisting of a transition metal dichalcogenide quantum dot coupled to a graphene contact through an atomically thin hexagonal boron nitride (hBN) tunnel barrier. Thanks to a tunable Fermi reservoir, we can deterministically load either a single electron or a single hole into the quantum dot. We observe hybrid excitons, composed of localized quantum dot states and delocalized continuum states, arising from ultra-strong spin-conserving tunnel coupling through the atomically thin tunnel barrier. Probing the charged excitons in applied magnetic fields, we observe large gyromagnetic ratios (∼8). Our results establish a foundation for engineering next-generation devices to investigate either novel regimes of Kondo physics or isolated quantum bits in a vdW heterostructure platform. Supplementary Figure 5. Lineshape evolution of the excitons states as a function of the gate voltage.Photoluminescence spectra of quantum dots A and B for different applied gate voltage values measured at T = 3.8 K. The green and red labels indicate the charged exciton states for quantum dots A and B, respectively. Labels X 1-, X 0 , X 1+ and X H represent the negatively charged, neutral, positively charged and hybrid excitons, respectively. For comparison purposes, some spectra have been multiplied by the corresponding factors indicated at the left part of the figure.

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Quantum-Confined Stark Effect in a MoS₂ Monolayer van der Waals Heterostructure

Cited by 68 publications

References 35 publications

Ultra-thin van der Waals crystals as semiconductor quantum wells

Ultra-thin van der Waals crystals as semiconductor quantum wells

Tuning of impurity-bound interlayer complexes in a van der Waals heterobilayer

Coulomb blockade in an atomically thin quantum dot coupled to a tunable Fermi reservoir

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Quantum-Confined Stark Effect in a MoS2 Monolayer van der Waals Heterostructure

Cited by 68 publications

References 35 publications

Ultra-thin van der Waals crystals as semiconductor quantum wells

Ultra-thin van der Waals crystals as semiconductor quantum wells

Tuning of impurity-bound interlayer complexes in a van der Waals heterobilayer

Coulomb blockade in an atomically thin quantum dot coupled to a tunable Fermi reservoir

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Quantum-Confined Stark Effect in a MoS₂ Monolayer van der Waals Heterostructure