Spin and Valley States in Gate-Defined Bilayer Graphene Quantum Dots

Eich, Marius; Herman, František; Pisoni, Riccardo; Overweg, Hiske; Kurzmann, Annika; Lee, Yongjin; Rickhaus, Peter; Watanabe, Kenji; Taniguchi, Takashi; Sigrist, Manfred; Ihn, Thomas; Ensslin, Klaus

doi:10.1103/physrevx.8.031023

Cited by 149 publications

(241 citation statements)

References 39 publications

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“…The g v -factors at lower quantum conductance such as G = 6 and 10 e 2 /h are as small as g v = 40 ∼ 60 and then increase to reach saturation at ∼ 100 for large conductance values. This valley g v -factor is much larger than the spin g-factor of 2, in agreement with results obtained in bilayer graphene quantum dots [13].…”

Section: Spin and Valley Splittingsupporting

confidence: 91%

“…We extract the g-factor from linear fits with ∆ s = g s µ B B , where µ B is the Bohr magneton, g is the Lande g-factor and B the magnetic field. The lines connecting the data points agree with a g-factor of g = 2.16 ± 0.07 , in agreement with the expectation for graphene and previous measurements on graphene quantum dots [13,15,16].…”

Section: Spin and Valley Splittingsupporting

confidence: 91%

“…Next, we discuss how the four-fold degenerate states split in a magnetic field. Zeeman splitting of spin states [6,11,13] occurs for any magnetic field orientation. Valley splitting, on the other hand, is an orbital effect [6], and will therefore only occur for magnetic fields perpendicular to the sample plane.…”

Section: Magnetic Field Dependencementioning

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: Spin and Valley Splittingsupporting

confidence: 91%

Section: Spin and Valley Splittingsupporting

confidence: 91%

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

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“…The obtained conductance traces are qualitatively very similar. A series of Coulomb peaks proofs the formation of a QD below each of the finger gates and the sequence is in agreement with a fourfold shell filling due to spin and valley degeneracy in BLG [24]. With decreasing finger gate voltage, first the QD is fully depleted, then the conductance increases without showing additional Coulomb peaks.…”

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confidence: 73%

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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“…On the other hand, with recent progress in fabrication technologies such as hBN encapsulation and the fabrication of a graphite back gate 3 through an all-dry transfer process, 27 high-quality BLG-based QD devices defined by electrostatically-induced potential barrier have been achieved under a perpendicular electric field. [22][23][24][25] In this work, to study the single-carrier transport in graphene superlattices, we fabricated a BLG/hBN moiré superlattice-based QD device (Figure 1c-e), in which the double dots are defined 3 by geometric patterning and local gating with the contribution of the superlattice potential. Note that widths of constrictions and diameters of the dots were slightly large compared to the previous graphene QD devices, [13][14][15][16][17][18] for avoiding strong potential fluctuation which leads to unstable dot configuration.…”

mentioning

confidence: 99%

Single-Carrier Transport in Graphene/hBN Superlattices

et al. 2020

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Graphene/hexagonal boron nitride (hBN) moiré superlattices have attracted interest for use in the study of many-body effects and fractal physics in Dirac fermion systems. Many exotic transport properties have been intensively examined in such superlattices, but previous studies have not focused on single-carrier transport. The investigation of the single-carrier behavior in these superlattices would lead to an understanding of the transition of singleparticle/correlated phenomena. Here, we show the single-carrier transport in a high-quality bilayer graphene/hBN superlattice-based quantum dot device. We demonstrate remarkable device controllability in the energy range near the charge neutrality point (CNP) and the hole-side satellite point. Under a perpendicular magnetic field, Coulomb oscillations disappear near the CNP, which could be a signature of the crossover between Coulomb blockade and quantum Hall regimes. Our results pave the way for exploring the relationship of single-electron transport and fractal quantum Hall effects with correlated phenomena in two-dimensional quantum materials.

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Spin and Valley States in Gate-Defined Bilayer Graphene Quantum Dots

Cited by 149 publications

References 39 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

Single-Electron Double Quantum Dots in Bilayer Graphene

Single-Carrier Transport in Graphene/hBN Superlattices

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