Tunable Fermi surface topology and Lifshitz transition in bilayer graphene

Varlet, Anastasia; Mucha-Kruczyński, Marcin; Bischoff, Dominik; Simonet, Pauline; Taniguchi, Takashi; Watanabe, Kenji; Ihn, Thomas; Ensslin, Klaus

doi:10.1016/j.synthmet.2015.07.006

Cited by 38 publications

(35 citation statements)

References 61 publications

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“…Here, p = p(cos ϕ, sin ϕ) is the momentum near the K point, m ≈ γ1 2v 2 ≈ 0.032m e is the effective mass of electrons in gapless BLG, and τ = v3 v ≈ 0.1 parametrizes skew interlayer hopping [8,11]. The dispersion of the lower conduction band (α = 1) in the K − valley is plotted in Fig.…”

Section: Introductionmentioning

confidence: 99%

Influence of minivalleys and Berry curvature on electrostatically induced quantum wires in gapped bilayer graphene

Knothe

Fal’ko

2018

Phys. Rev. B

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We show that the spectrum of subbands in an electrostatically defined quantum wire in gapped bilayer graphene (BLG) directly manifests the minivalley structure and reflects Berry curvature via the associated magnetic moment of the states in the low-energy bands of this two-dimensional material. We demonstrate how these appear in degeneracies of the low-energy minibands and their valley splitting, which develops linearly in a weak magnetic field. Consequently, magnetoconductance of a ballistic point contact connecting two non-gapped areas of a bilayer through a gapped (top and bottom gated) barrier would reflect such degeneracies by the heights of the first few conductance steps developing upon the increase of the doping of the BLG conduction channel (we consider an adiabatic constriction, where conductance is set by the number of propagating ballistic modes in its narrowest part): 8e 2 /h steps in a wide channel in BLG with a large gap, 4e 2 /h steps in narrow channels, all splitting into a staircase of 2e 2 /h steps upon lifting valley degeneracy by a magnetic field.

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Section: Introductionmentioning

confidence: 99%

Influence of minivalleys and Berry curvature on electrostatically induced quantum wires in gapped bilayer graphene

Knothe

Fal’ko

2018

Phys. Rev. B

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“…As soon as the brown lines are crossed (n c,dis = n dis ), the effect of varying dielectric thickness starts to dominate over the intrinsic doping fluctuations due to fabrication residues. These conclusions are important, for example, for doublegated bilayer graphene devices where a high top-gate voltage is applied in order to open a bandgap [32][33][34][35][36][37][38]. Choosing a thick dielectric together with as clean interfaces as possible mitigates these layer thickness fluctuations.…”

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confidence: 99%

Measuring the local quantum capacitance of graphene using a strongly coupled graphene nanoribbon

et al. 2015

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We present electrical transport measurements of a van-der-Waals heterostructure consisting of a graphene nanoribbon separated by a thin boron nitride layer from a micron-sized graphene sheet. The interplay between the two layers is discussed in terms of screening or, alternatively, quantum capacitance. The ribbon can be tuned into the transport gap by applying gate voltages. Multiple sites of localized charge leading to Coulomb blockade are observed in agreement with previous experiments. Due to the strong capacitive coupling between the ribbon and the graphene top layer sheet, the evolution of the Coulomb blockade peaks in gate voltages can be used to obtain the local density of states and therefore the quantum capacitance of the graphene top layer. Spatially varying density and doping are found which are attributed to a spatial variation of the dielectric due to fabrication imperfections.PACS numbers: 71.15. Mb, 81.05.ue, 72.80.Vp One of the advantages of layered materials such as graphene, hexagonal boron nitride (hBN) or various dichalcogenides, is the possibility to fabricate stacks in order to obtain a heterostructure material with new properties. This was recently exploited to fabricate a variety of different device structures [1][2][3][4][5][6][7][8] and to investigate a number of novel effects: localization in super clean systems [9, 10], current drag [11][12][13] and the emergence of superlattices [14][15][16]. Most of these experiments were performed with so-called "double-layer graphene", consisting of two graphene layers separated by a thin insulator layer. In contrast to Bernal-stacked bilayer graphene, charge transfer between the two layers is not possible.Above experiments were conducted with micron-sized graphene sheets. In this paper we develop this idea one step further: we pattern the lower graphene sheet laterally into a nanoribbon (e.g. Refs. [17][18][19][20][21]) and stack an insulator plus a micron-sized graphene sheet on top. This experiment is a crucial step towards fabricating and understanding stacked graphene nanostructures. If the nanoribbon is tuned into the so-called transport gap [17,18], Coulomb blockade can be observed [17,18]. The localized charge in the ribbon serves as a sensitive and local detector for its electrostatic surrounding and allows us to probe properties of the graphene top layer. This is conceptually similar to an SET above a 2DEG [22] and scanning SET measurements [23,24]. Despite using a comparably thick insulator layer (13 nm), we can still reach the regime where the spacing between the layers is smaller than the average distance between two charge carriers within one layer [12].In this paper we present simultaneous electrical transport measurements through a graphene nanoribbon and a graphene sheet (top layer) that are separated by a layer of hBN, and therefore strongly capacitively coupled. By * dominikb@phys.ethz.ch applying gate voltages, we can independently tune both the graphene top layer and the graphene ribbon to their respective Dirac point. If t...

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“…Since the "annihilation" of the two pockets changes the Fermi topology abruptly -from the quadruplyconnected Fermi surface to the doubly-connected one - the Lifshitz transition takes place. It should be noted that it is similar to the Lifshitz transition in the strained bilayer graphene 33,34 . Namely, the dressing field linearly polarized along the x axis effects on BLG similarly to an uniform strain applied along the same axis.…”

Section: Resultsmentioning

confidence: 67%

Optically induced Lifshitz transition in bilayer graphene

2017

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It is shown theoretically that the renormalization of the electron energy spectrum of bilayer graphene with a strong high-frequency electromagnetic field (dressing field) results in the Lifshitz transition -the abrupt change in the topology of the Fermi surface near the band edge. This effect substantially depends on the polarization of the field: The linearly polarized dressing field induces the Lifshitz transition from the quadruply-connected Fermi surface to the doubly-connected one, whereas the circularly polarized field induces the multicritical point, where the four different Fermi topologies may coexist. As a consequence, the discussed phenomenon creates physical basis to control the electronic properties of bilayer graphene with light.

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Tunable Fermi surface topology and Lifshitz transition in bilayer graphene

Cited by 38 publications

References 61 publications

Influence of minivalleys and Berry curvature on electrostatically induced quantum wires in gapped bilayer graphene

Influence of minivalleys and Berry curvature on electrostatically induced quantum wires in gapped bilayer graphene

Measuring the local quantum capacitance of graphene using a strongly coupled graphene nanoribbon

Optically induced Lifshitz transition in bilayer graphene

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