Electronic correlations in twisted bilayer graphene near the magic angle

Choi, Youngjoon; Kemmer, Jeannette; Peng, Yang; Thomson, Alex; Arora, Harpreet Singh; Polski, Robert; Zhang, Yiran; Ren, Haowen; Alicea, Jason; Refael, Gil; Oppen, Felix von; Watanabe, Kenji; Taniguchi, Takashi; Nadj-Perge, Stevan

doi:10.1038/s41567-019-0606-5

Cited by 654 publications

(635 citation statements)

References 42 publications

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“…Figure S8 shows quantum oscillations near charge neutrality measured at 30 mK between contacts A and B, a region not exhibiting the QAH effect. The Landau Fan diagram shows clear gapped states with fillings ν = +2, 4,8,12,16,24,32. We use these quantum oscillations to determine the capacitance of the device C = 4.1 × 10 −4 F/m 2 .…”

Section: Quantum Oscillationsmentioning

confidence: 99%

Intrinsic quantized anomalous Hall effect in a moiré heterostructure

Serlin

Tschirhart

Polshyn

et al. 2020

Science

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1,242

967

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We report the observation of a quantum anomalous Hall effect in twisted bilayer graphene showing Hall resistance quantized to within .1% of the von Klitzing constant h/e 2 at zero magnetic field. The effect is driven by intrinsic strong correlations, which polarize the electron system into a single spin and valley resolved moiré miniband with Chern number C = 1. In contrast to extrinsic, magnetically doped systems, the measured transport energy gap ∆/kB ≈ 27 K is larger than the Curie temperature for magnetic ordering TC ≈ 9 K, and Hall quantization persists to temperatures of several Kelvin. Remarkably, we find that electrical currents as small as 1 nA can be used to controllably switch the magnetic order between states of opposite polarization, forming an electrically rewritable magnetic memory.

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Section: Quantum Oscillationsmentioning

confidence: 99%

Intrinsic quantized anomalous Hall effect in a moiré heterostructure

Serlin

Tschirhart

Polshyn

et al. 2020

Science

Self Cite

1,242

967

View full text Add to dashboard Cite

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“…Even more recent experiments have revealed unexpected features of magic-angle TBG close to CN, such as the presence large spectral gaps at fractional filling [6], the appearance of alternating superconducting and insulating phases on an increase of the occupation of the conduction bands [7] as well as evidence of charge ordering and broken rotational symmetry [8,9].…”

Section: Introductionmentioning

confidence: 99%

“…A number of recent theoretical studies have addressed * tommaso.cea@imdea.org † Niels.Walet@manchester.ac.uk; http://bit.ly/nielswalet ‡ francisco.guinea@manchester.ac.uk this topic [26][27][28][29][30][31][32][33][34][35], suggesting this can lead o the formation of novel strongly-correlated phases. The proliferation of these singularities, due to the increasing number of band-crossings in the flat bands as we decrease the twist angle in TBG [9,34,36,37], can further enhance van Hove peaks in the DOS. In addition, the strong filling dependence of the electronic compressibility observed in Ref.…”

Section: Introductionmentioning

confidence: 99%

Electronic band structure and pinning of Fermi energy to Van Hove singularities in twisted bilayer graphene: A self-consistent approach

2019

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The emergence of flat bands in twisted bilayer graphene leads to an enhancement of interaction effects, and thus to insulating and superconducting phases at low temperatures, even though the exact mechanism is still widely debated. The position and splitting of the flat bands is also very sensitive to the residual interactions. Moreover, the low energy bands of twisted graphene bilayers show a rich structure of singularities in the density of states, van Hove singularities, which can enhance further the role of interactions. We study the effect of the long-range interactions on the bandwidth and the van Hove singularities of the low energy bands of twisted graphene bilayers. Reasonable values of the long-range electrostatic interaction lead to a band dispersion with a significant dependence on the filling. The change of the shape and position of the bands with electronic filling implies that the van Hove singularities remain close to the Fermi energy for a broad range of fillings. This result can be described as an effective pinning of the Fermi energy at the singularity. arXiv:1906.10570v2 [cond-mat.str-el]

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“…In Refs. [10][11][12], spatially resolved properties of the insulating states were studied using scanning tunneling microscopy (STM) experiments. Recently, transport experiments were also performed at larger temperatures, and revealed an interesting broad temperature range with a large and linearly increasing resistivity [13,14].…”

Section: Introductionmentioning

confidence: 99%

Symmetry breaking and skyrmionic transport in twisted bilayer graphene

2020

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Motivated by recent low-temperature magnetoresistance measurements in twisted bilayer graphene aligned with hexagonal Boron Nitride substrate, we perform a systematic study of possible symmetry breaking orders in this device at a filling of two electrons per Moiré unit cell. We find that the surprising non-monotonic dependence of the resistance on an out-of-plane magnetic field is difficult to reconcile with particle-hole charge carriers from the low-energy bands in symmetry broken phases. We invoke the non-zero Chern numbers of the twisted bilayer graphene flat bands to argue that skyrmion textures provide an alternative for the dominant charge carriers. Via an effective field-theory for the spin degrees of freedom, we show that the effect of spin Zeeman splitting on the skyrmion excitations provides a possible explanation for the non-monotonic magnetoresistance. We suggest several experimental tests, including the functional dependence of the activation gap on the magnetic field, for our proposed correlated insulating states at different integer fillings. We also discuss possible exotic phases and quantum phase transitions that can arise via skyrmion-pairing on doping such an insulator. arXiv:1908.00986v1 [cond-mat.str-el]

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Electronic correlations in twisted bilayer graphene near the magic angle

Cited by 654 publications

References 42 publications

Intrinsic quantized anomalous Hall effect in a moiré heterostructure

Intrinsic quantized anomalous Hall effect in a moiré heterostructure

Electronic band structure and pinning of Fermi energy to Van Hove singularities in twisted bilayer graphene: A self-consistent approach

Symmetry breaking and skyrmionic transport in twisted bilayer graphene

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