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

Abstract

Gate-tunable quantum-mechanical tunnelling of particles between a quantum confined state and a nearby Fermi 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 dot1,2. Depending on the tunnel-coupling strength3,4, this capability facilitates single spin quantum bits1,2,5 or coherent many-body interactions between the confined spin and the Fermi reservoir6,7. 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 spins8,9, tunnel barriers down to the atomic limit10 or a Fermi reservoir beyond the conventional flat density of states11. However, gate-control of vdW nanostructures12,13,14,15,16 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.

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Fig. 1: Coulomb blockade in a vdW heterostructure device.
Fig. 2: Strong tunnel coupling between a quantum dot and a tunable Fermi reservoir in a vdW heterostructure.
Fig. 3: Strong tunnel coupling between a quantum dot and a tunable Fermi reservoir at high magnetic field.
Fig. 4: Magneto-optics of neutral and charged excitons in WSe2 quantum dots.

Data availability

Data described in this paper are presented in the Supplementary Materials and are available online at https://researchportal.hw.ac.uk/en/persons/brian-d-gerardot.

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Acknowledgements

This work is supported by the EPSRC (grant nos. EP/L015110/1, EP/P029892/1 and EP/M013472/1) and the ERC (grant nos. 307392 and 725920) and the EU Horizon 2020 research and innovation program under grant agreement no. 820423. Growth of hBN crystals by K.W. and T.T. was supported by the Elemental Strategy Initiative conducted by the MEXT, Japan and the CREST (grant no. JPMJCR15F3), JST. Device fabrication by M.G. and K.S.B. was made possible with support the National Science Foundation, award no. DMR-1709987. B.D.G. is supported by a Wolfson Merit Award from the Royal Society and a Chair in Emerging Technology from the Royal Academy of Engineering.

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B.D.G. conceived and supervised the project. A.B. fabricated the samples, assisted by S.K., R. Picard, M.G. and K.S.B. K.W. and T.T. supplied the hBN crystals. M.B.-G. and A.B. performed the experiments, assisted by S.K. and R. Proux. M.B.-G. analysed the data and developed the theoretical model, assisted by B.D.G. M.B.-G. and B.D.G. cowrote the paper with input from all authors.

Corresponding authors

Correspondence to Mauro Brotons-Gisbert or Brian D. Gerardot.

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Supplementary Figures 1–10

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Brotons-Gisbert, M., Branny, A., Kumar, S. et al. Coulomb blockade in an atomically thin quantum dot coupled to a tunable Fermi reservoir. Nat. Nanotechnol. 14, 442–446 (2019). https://doi.org/10.1038/s41565-019-0402-5

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