Quantum Hall Effect, Screening, and Layer-Polarized Insulating States in Twisted Bilayer Graphene

Sanchez-Yamagishi, Javier; Taychatanapat, Thiti; Watanabe, Kenji; Taniguchi, Takashi; Yacoby, Amir; Jarillo‐Herrero, Pablo

doi:10.1103/physrevlett.108.076601

Cited by 140 publications

(203 citation statements)

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“…This interlayer capacitance has been applied in previous studies on twisted bilayer graphene [38][39][40] . Here we estimate this interlayer capacitance C in B25.3 mF cm À 2 with the interlayer dielectric constant B10e 0 and interlayer spacing B0.35 nm 38,40 .…”

Section: Mos 2 Vertical Heterostructural Capacitance Devicesmentioning

confidence: 99%

Probing the electron states and metal-insulator transition mechanisms in molybdenum disulphide vertical heterostructures

et al. 2015

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The metal-insulator transition is one of the remarkable electrical properties of atomically thin molybdenum disulphide. Although the theory of electron-electron interactions has been used in modelling the metal-insulator transition in molybdenum disulphide, the underlying mechanism and detailed transition process still remain largely unexplored. Here we demonstrate that the vertical metal-insulator-semiconductor heterostructures built from atomically thin molybdenum disulphide are ideal capacitor structures for probing the electron states. The vertical configuration offers the added advantage of eliminating the influence of large impedance at the band tails and allows the observation of fully excited electron states near the surface of molybdenum disulphide over a wide excitation frequency and temperature range. By combining capacitance and transport measurements, we have observed a percolation-type metal-insulator transition, driven by density inhomogeneities of electron states, in monolayer and multilayer molybdenum disulphide. In addition, the valence band of thin molybdenum disulphide layers and their intrinsic properties are accessed.

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Section: Mos 2 Vertical Heterostructural Capacitance Devicesmentioning

confidence: 99%

Probing the electron states and metal-insulator transition mechanisms in molybdenum disulphide vertical heterostructures

et al. 2015

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“…The sequence demonstrates that interlayer coupling is too weak to split the layer degeneracy. We conclude that the twist angle is large enough to model the system as two monolayer graphene sheets conducting in parallel (26,27).In low-disorder samples, electron exchange interactions can break the graphene spin-valley degeneracy, leading to quantum Hall ferromagnetism (28-30). We indeed observe such degeneracy breaking at higher field as a sequence of plateaus at all integer multiples of e 2 /h from -4 to 4 (B = 4 T, Figure 1E).…”

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confidence: 99%

“…The quantum Hall effect is a sensitive probe of electron degeneracy and the underlying symmetries of the Landau levels; as such, the graphene quantum Hall effect is different for monolayers (23,24), AB-stacked bilayers (25), and twisted bilayers (26). In a perpendicular magnetic field, each layer of the twisted bilayer will develop chiral 1d edge states which originate from the bulk Landau levels.…”

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Helical edge states and fractional quantum Hall effect in a graphene electron–hole bilayer

et al. 2016

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†These authors contributed equally to this work. AbstractA quantum Hall edge state provides a rich foundation to study electrons in 1-dimension (1d) but is limited to chiral propagation along a single direction. Here, we demonstrate a versatile platform to realize new 1d systems made by combining quantum Hall edge states of opposite chiralities in a graphene electron-hole bilayer. Using this approach, we engineer helical 1d edge conductors where the counterpropagating modes are localized in separate electron and hole layers by a tunable electric field. These helical conductors exhibit strong nonlocal transport signals and suppressed backscattering due to the opposite spin polarizations of the counterpropagating modes. Moreover, we investigate these electron-hole bilayers in the fractional quantum Hall regime, where we observe conduction through fractional and integer edge states of opposite chiralities, paving the way towards the realization of 1d helical systems with fractional quantum statistics.A helical 1d conductor is an unusual electronic system where forward and backward moving electrons have opposite spin polarizations. Theoretically, a helical state can be realized by combining two quantum Hall edge states with opposite chiralities and opposite spin polarizations (1,2). Most experimental efforts though have focused on materials with strong spin-orbit coupling(3-5), which avoids the need for magnetic fields. However, an approach based on quantum Hall edge states offers greater flexibility in system design with less dependence on material parameters. Moreover, a quantum Hall platform could harness the unique statistics of fractional quantum Hall states. Recent proposals have predicted that such a system, in the form of a fractional quantum spin Hall state(6-8), could host fractional generalizations of Majorana bound states.To simultaneously realize two quantum Hall states with opposite chiralities, it is necessary to have coexisting electron-like and hole-like bands. Such electron-hole quantum Hall states are observed in semi-metals but suffer from low hole-mobilities (9, 10). In this respect, graphene is an attractive system because it has high carrier mobilities and is electron-hole symmetric. In fact, the graphene electron and hole bands can be inverted by the Zeeman effect to realize helical states (11,12), but requires very large magnetic fields (13,14). A similar outcome could be realized more easily in a bilayer system, where an electric field can dope one layer into the electron band and the other into the hole band. In a moderate magnetic field, this electronhole bilayer will develop quantum Hall edge states with opposite chiralities in each layer. Here, we demonstrate a graphene electron-hole bilayer, which we use to realize a helical 1-dimensional conductor made from quantum Hall edge states.All studied devices consist of two monolayer graphene flakes stacked together using a dry transfer process (15,16). The stacking results in a rotational misalignment, or twist, between the layers. The domin...

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“…In Bernal stacking, the charge carriers of the graphene bilayer have a parabolic energy spectrum and exhibit chirality that resembles those associated with spin 1. However, a twist between the two layers splits the parabolic band touching into two Dirac cones [13][14][15][16][19][20][21][22][23][24] and changes the chirality of the low-energy quasiparticles to those of spin 1/2 [18,25]. This provides a facile route to tune the electronic properties of graphene bilayer.…”

Section: Introductionmentioning

confidence: 99%

In-plane chiral tunneling and out-of-plane valley-polarized quantum tunneling in twisted graphene trilayer

Qiao

2014

Phys. Rev. B

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Quantum Hall Effect, Screening, and Layer-Polarized Insulating States in Twisted Bilayer Graphene

Cited by 140 publications

References 37 publications

Probing the electron states and metal-insulator transition mechanisms in molybdenum disulphide vertical heterostructures

Probing the electron states and metal-insulator transition mechanisms in molybdenum disulphide vertical heterostructures

Helical edge states and fractional quantum Hall effect in a graphene electron–hole bilayer

In-plane chiral tunneling and out-of-plane valley-polarized quantum tunneling in twisted graphene trilayer

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