Excited States in Bilayer Graphene Quantum Dots

Kurzmann, Annika; Eich, Marius; Overweg, Hiske; Mangold, M.; Herman, František; Rickhaus, Peter; Pisoni, Riccardo; Lee, Yongjin; Garreis, Rebekka; Tong, Chuyao; Watanabe, Kenji; Taniguchi, Takashi; Ensslin, Klaus; Ihn, Thomas

doi:10.1103/physrevlett.123.026803

Cited by 90 publications

(116 citation statements)

References 44 publications

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“…The source and drain edge contacts are realized by a Reactive Ion Etching process and Cr (10nm)/Au (50nm) deposition [8]. The few-layer graphite at the bottom of the stack plays the role of a high quality back gate (BG) [9,10]. Figure 1a shows a sketch of the device structure.…”

Section: Device Fabricationmentioning

confidence: 99%

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Tunable Valley Splitting due to Topological Orbital Magnetic Moment in Bilayer Graphene Quantum Point Contacts

et al. 2020

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We experimentally determine the energy spectrum of a quantum point contact realized by a suitable gate geometry in bilayer graphene. Using finite bias spectroscopy we measure the energy scales arising from the lateral confinement as well as the Zeeman splitting and find a spin g-factor gs ∼ 2. The valley g-factor is highly tunable by vertical electric fields, gv ∼ 40 − 120. The results are quantitatively explained by a calculation considering topological magnetic moment and its dependence on confinement and the vertical displacement field. arXiv:1911.05968v1 [cond-mat.mes-hall]

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Section: Device Fabricationmentioning

confidence: 99%

“…The confinement potential and the gap are chosen in accordance with recent experiments and corresponding simulations [9,13,14] to be of the form…”

Section: Theorymentioning

confidence: 99%

Tunable Valley Splitting due to Topological Orbital Magnetic Moment in Bilayer Graphene Quantum Point Contacts

et al. 2020

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“… 43 This value is in contrast to the maximum extracted g v of around 17 which has also been observed in earlier works. 29 The slightly smaller average valley g -factor in the model compared to that from the experiment might be due to the specific potential shape, strain, 44 additional valley splitting, or effects which are not captured by the single particle Hamiltonian. The small electron hole asymmetry might be explained by the different QD size for electrons and holes.…”

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confidence: 95%

Electron–Hole Crossover in Gate-Controlled Bilayer Graphene Quantum Dots

et al. 2020

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Electron and hole Bloch states in bilayer graphene exhibit topological orbital magnetic moments with opposite signs, which allows for tunable valley-polarization in an out-of-plane magnetic field. This property makes electron and hole quantum dots (QDs) in bilayer graphene interesting for valley and spin-valley qubits. Here, we show measurements of the electron–hole crossover in a bilayer graphene QD, demonstrating opposite signs of the magnetic moments associated with the Berry curvature. Using three layers of top gates, we independently control the tunneling barriers while tuning the occupation from the few-hole regime to the few-electron regime, crossing the displacement-field-controlled band gap. The band gap is around 25 meV, while the charging energies of the electron and hole dots are between 3 and 5 meV. The extracted valley g -factor is around 17 and leads to opposite valley polarization for electrons and holes at moderate B -fields. Our measurements agree well with tight-binding calculations for our device.

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“…none of the QDs is empty. Thus, the description in the single particle picture is no longer valid and interaction effects such as exchange are becoming relevant [26], leading to the observation of an enriched spectrum of available transitions. Under the influence of an out-of-plane field (B = 0.25 T, see Fig.…”

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Single-Electron Double Quantum Dots in Bilayer Graphene

et al. 2020

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We present transport measurements through an electrostatically defined bilayer graphene double quantum dot in the single electron regime. With the help of a back gate, two split gates and two finger gates we are able to control the number of charge carriers on two gate-defined quantum dot independently between zero and five. The high tunability of the device meets requirements to make such a device a suitable building block for spin-qubits. In the single electron regime, we determine interdot tunnel rates on the order of 2 GHz. Both, the interdot tunnel coupling, as well as the capacitive interdot coupling increase with dot occupation, leading to the transition to a single quantum dot. Finite bias magneto-spectroscopy measurements allow to resolve the excited state spectra of the first electrons in the double quantum dot; being in agreement with spin and valley conserving interdot tunneling processes.Electrostatically defined quantum dots (QDs) offer a compelling platform for spin-qubit-based quantum computation [1]. For that purpose, QDs in semiconductor heterostructures mainly based on GaAs [2, 3] and silicon [4,5] have been studied intensively. For example, high-fidelity single-qubit [6] and two-qubit [7-9] gate operations have been recently demonstrated for silicon qubit devices. Graphene has been early identified as an alternative attractive material platform for spin-qubits thanks to its low nuclear spin densities, weak hyperfine coupling and weak spinorbit interaction promising long spin decoherence times [10]. Physically etched graphene quantum devices including quantum dots [11,12] and double quantum dots (DQDs) [13,14] have been studied for about a decade. Major achievements include the implementation of charge detection [15,16], the observation of spin-states [12] and the measurement of charge relaxation times [17]. However, the influence of disorder, in particular edge disorder [18,19], prevented a precise control of the number of charge carriers on individual QDs making spin-qubit implementation impossible.The advancements in ultra-clean van der Waals heterostructures and in particular the use of local graphite gates allowed for the development of electrostatically defined bilayer graphene (BLG) quantum point contacts [20-23], quantum dots [24-26] and double quantum dots (DQDs) [27,28]. While single-electron and hole occupation has been demonstrated recently for individual QDs [24], the number of charge carriers in DQDs could not be controlled yet [27,28]. The precise control of the number of charge carriers is, however, a requirement for qubit operations in a semiconductor QD device.Here, we show single electron occupation of a bilayer graphene DQD. The electrostatically defined DQD allows for a high tunability of the electrochemical potential such that we can precisely control the number of electrons on * These authors contributed equally to this work. a Corresponding author: luca.banszerus@rwth-aachen.de each of the QDs independently down to zero. The gate voltages tune the interdot tunnel couplin...

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Excited States in Bilayer Graphene Quantum Dots

Cited by 90 publications

References 44 publications

Tunable Valley Splitting due to Topological Orbital Magnetic Moment in Bilayer Graphene Quantum Point Contacts

Tunable Valley Splitting due to Topological Orbital Magnetic Moment in Bilayer Graphene Quantum Point Contacts

Electron–Hole Crossover in Gate-Controlled Bilayer Graphene Quantum Dots

Single-Electron Double Quantum Dots in Bilayer Graphene

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