Observation of the Spin-Orbit Gap in Bilayer Graphene by One-Dimensional Ballistic Transport

Banszerus, Luca; Frohn, Benedikt; Fabian, Thomas; Somanchi, Sowmya; Epping, Alexander; Müller, Marvin; Neumaier, Daniel; Watanabe, Kenji; Taniguchi, Takashi; Libisch, Florian; Beschoten, Bernd; Hassler, Fabian; Stampfer, Christoph

doi:10.1103/physrevlett.124.177701

Cited by 59 publications

(56 citation statements)

References 37 publications

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“…Although the single-particle spectrum in BLG QDs has been intensively studied in recent years 9 – 11 , the low-energy spin-valley coupling in BLG QDs has remained experimentally unexplored. This is certainly partly due to the high energy resolution required, as theoretical studies predict an intrinsic spin-orbit (SO) coupling in graphene and BLG of around Δ SO ≈ 24 μ eV 12 – 16 and only recently, experiments have – partly indirectly – reported values in the range between 40 and 80 μ eV 17 , 18 . Moreover, our current knowledge with respect to a possible mixing of and states is very limited.…”

Section: Introductionmentioning

confidence: 99%

Spin-valley coupling in single-electron bilayer graphene quantum dots

et al. 2021

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Understanding how the electron spin is coupled to orbital degrees of freedom, such as a valley degree of freedom in solid-state systems, is central to applications in spin-based electronics and quantum computation. Recent developments in the preparation of electrostatically-confined quantum dots in gapped bilayer graphene (BLG) enable to study the low-energy single-electron spectra in BLG quantum dots, which is crucial for potential spin and spin-valley qubit operations. Here, we present the observation of the spin-valley coupling in bilayer graphene quantum dots in the single-electron regime. By making use of highly-tunable double quantum dot devices we achieve an energy resolution allowing us to resolve the lifting of the fourfold spin and valley degeneracy by a Kane-Mele type spin-orbit coupling of ≈ 60 μeV. Furthermore, we find an upper limit of a potentially disorder-induced mixing of the $$K$$ K and $$K^{\prime}$$ K ′ states below 20 μeV.

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Section: Introductionmentioning

confidence: 99%

Spin-valley coupling in single-electron bilayer graphene quantum dots

et al. 2021

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“…The device studied in this work consists of a BLG flake encapsulated between two crystals of hexagonal boron nitride (hBN), placed on a graphite gate using the conventional van der Waals stacking technology. [6] Similar to previous work studying BLG gate-defined quantum point contacts [7][8][9] and QDs, [10][11][12][13][14][15] two layers of gold gates are evaporated on top: A pair of split gates (SGs) is used to form a 150 nm wide conducting channel connecting the source and drain reservoirs of the device (see Figure 1a). On top, separated by a 30 nm thick film of atomic layer deposited Al 2 O 3 , we place a gold finger gate (FG) with a width of 70 nm (see Figure 1a,b).…”

Section: Fabricationmentioning

confidence: 99%

“…[16][17][18] Similar to recent works, we can form a QD underneath the FG by locally overcompensating the applied back gate voltage. [9][10][11]13,14] A small n-doped island is created underneath the FG, which is separated from the p-doped channel by the bandgap acting as a tunnel barrier (see schematic in Figure 1a). [13,11] We measure the current through the device as a function of V FG (Figure 1c).…”

Section: To Bothmentioning

confidence: 99%

Electrostatic Detection of Shubnikov–de Haas Oscillations in Bilayer Graphene by Coulomb Resonances in Gate‐Defined Quantum Dots

Banszerus

Fabian

Möller

et al. 2020

Physica Status Solidi (b)

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A gate‐defined quantum dot in bilayer graphene is utilized as a sensitive probe for the charge density of its environment. Under the influence of a perpendicular magnetic field, the charge carrier density of the channel region next to the quantum dot oscillates due to the formation of Landau levels. This is experimentally observed as oscillations in the gate‐voltage positions of the Coulomb resonances of the nearby quantum dot. From the frequency of the oscillations, the charge carrier density in the channel is extracted, and from the amplitude the shift of the quantum dot potential. These experimental results are compared with an electrostatic simulation of the device and good agreement is found.

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“…Layered hBN is a perfect substrate for graphene spintronics, allowing for giant mobilities in graphene/hBN structures 6 , ultralong spin lifetimes 1,4,11,14,64 , for extracting spin-orbit gaps in bilayer graphene 65 , or for revealing surprisingly strong spin-orbit anisotropy also in bilayer graphene 66,67 . On the other hand, hBN induces only a weak SOC in graphene 5 to be able to investigate proximity effects.…”

Section: Introductionmentioning

confidence: 99%

Graphene on two-dimensional hexagonal BN, AlN, and GaN: Electronic, spin-orbit, and spin relaxation properties

et al. 2021

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We investigate the electronic band structure of graphene on a series of two-dimensional hexagonal nitride insulators hXN, X = B, Al, and Ga, with first principles calculations. A symmetry-based model Hamiltonian is employed to extract orbital parameters and spin-orbit coupling (SOC) from the low-energy Dirac bands of the proximitized graphene. While commensurate hBN induces the staggered potential of about 10 meV into the Dirac band structure, less lattice-matched hAlN and hGaN disrupt the Dirac point much less, giving the staggered gap below 100 µeV. Proximitized intrinsic SOC surprisingly does not increase much above the pristine graphene value of 12 µeV, it stays in the window of (1-16) µeV, depending strongly on stacking. However, Rashba SOC increases sharply with increasing the atomic number of the boron group, with calculated maximal values of 8, 15, and 65 µeV for B, Al, and Ga-based nitrides, respectively. The individual Rashba couplings depend also strongly on stacking, vanishing in symmetrically-sandwiched structures, and can also be tuned by a transverse electric field. The extracted spin-orbit parameters were used as input for spin transport simulations based on Chebyschev expansion of the time-evolution operator, yielding interesting predictions for the electron spin relaxation. Spin lifetime magnitudes and anisotropies depend strongly on the specific (hXN)/graphene/hXN system, and can be efficiently tuned by an applied external electric field as well as the carrier density in the graphene layer. A particularly interesting case for experiments is graphene/hGaN, in which the giant Rashba coupling is predicted to induce spin lifetimes of 1-10 ns, short enough to dominate over other mechanisms, and lead to the same spin relaxation anisotropy as that observed in conventional semiconductor heterostructures: 50%, meaning that out-of-plane spins relax twice as fast as in-plane spins.

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Observation of the Spin-Orbit Gap in Bilayer Graphene by One-Dimensional Ballistic Transport

Cited by 59 publications

References 37 publications

Spin-valley coupling in single-electron bilayer graphene quantum dots

Spin-valley coupling in single-electron bilayer graphene quantum dots

Electrostatic Detection of Shubnikov–de Haas Oscillations in Bilayer Graphene by Coulomb Resonances in Gate‐Defined Quantum Dots

Graphene on two-dimensional hexagonal BN, AlN, and GaN: Electronic, spin-orbit, and spin relaxation properties

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