Collapse of Landau Levels in Gated Graphene Structures

Gu, Nan; Rudner, Mark S.; Young, Andrea; Kim, Philip; Levitov, L. S.

doi:10.1103/physrevlett.106.066601

Cited by 56 publications

(56 citation statements)

References 18 publications

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“…In this regime, transmission probability is dominated by BLG-BLG anti-Klein tunnelling: the pseudospin mismatch between k || ¼ 0 holes in the GL and k || ¼ 0 electrons in the LGR suppresses transmission through the RBS 28 , resulting in a dip in the normal transmission probability and, ultimately, the suppression of the giant oscillations. in MLG 16,20 , and the smaller Fabry-Pérot oscillations faintly visible in Fig.…”

Section: Transmission Amplitudes and The Conductance Oscillationsmentioning

confidence: 99%

Quantum and classical confinement of resonant states in a trilayer graphene Fabry-Pérot interferometer

et al. 2012

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The advent of few-layer graphene has given rise to a new family of two-dimensional systems with emergent electronic properties governed by relativistic quantum mechanics. The multiple carbon sublattices endow the electronic wavefunctions with pseudospin, a lattice analogue of the relativistic electron spin, whereas the multilayer structure leads to electric-field-effect tunable electronic bands. Here we use these properties to realize giant conductance oscillations in ballistic trilayer graphene Fabry-Pérot interferometers, which result from phase coherent transport through resonant bound states beneath an electrostatic barrier. We confine these states by selectively decoupling them from the leads, resulting in transport via non-resonant states and suppression of the giant oscillations. The confinement is achieved both classically, by manipulating quasiparticle momenta with a magnetic field, and quantum mechanically, by locally varying the pseudospin character of the carrier wavefunctions. Our results illustrate the unique potential of trilayer graphene as a versatile platform for electron optics and pseudospintronics.

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Section: Transmission Amplitudes and The Conductance Oscillationsmentioning

confidence: 99%

Quantum and classical confinement of resonant states in a trilayer graphene Fabry-Pérot interferometer

et al. 2012

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“…In the other extreme when V 0 <<hω c , quantum Hall effect in * sudipta.tifr@gmail.com † deshmukh@tifr.res.in graphene is restored [15]. However, the situation is more complex and little explored when V 0 andhω c have comparable contribution, and we have experimentally probed this regime in graphene.The goal of our work is to extend quantum Hall studies beyond single top-gate in graphene [16][17][18]. Our work is the first experimental report on magnetotransport in multiple top-gates on graphene and we probe the physics of equilibration along the narrow region in graphene defined electrostatically.…”

mentioning

confidence: 99%

“…The goal of our work is to extend quantum Hall studies beyond single top-gate in graphene [16][17][18]. Our work is the first experimental report on magnetotransport in multiple top-gates on graphene and we probe the physics of equilibration along the narrow region in graphene defined electrostatically.…”

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confidence: 99%

“…Large V 0 leads to large E in the region between BG and TG region which modifies the LLs locally. It has been shown by Lukose et al [28] and later extended by Gu et al [18] for the case of a topgate geometry that the LL spectrum and the wavefunctions in crossed E and B are fundamentally modified in graphene, an aspect that is not observable in conventional 2DEGS semiconductors. LL wavefunction is modified in two ways.…”

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Tuning equilibration of quantum Hall edge states in graphene – Role of crossed electric and magnetic fields

Dubey

Deshmukh

2016

Solid State Communications

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We probe quantum Hall effect in a tunable 1-D lateral superlattice (SL) in graphene created using electrostatic gates. Lack of equilibration is observed along edge states formed by electrostatic gates inside the superlattice. We create strong local electric field at the interface of regions of different charge densities. Crossed electric and magnetic fields modify the wavefunction of the Landau Levels (LLs) -a phenomenon unique to graphene. In the region of copropagating electrons and holes at the interface, the electric field is high enough to modify the Landau levels resulting in increased scattering that tunes equilibration of edge states and this results in large longitudinal resistance.Magnetotransport across one-dimensional superlattice (SL) had been studied in two-dimensional electron gas in semiconductor heterostructures (2DEGS) [1][2][3][4][5][6], reporting dissipationless transport across high potential barriers [1] and magnetic commensurability oscillations in longitudinal resistance [3]. The motivation was to study various competing length scales and energy scales between tunable SL potential and quantum Hall system. Graphene offers the advantage of large cyclotron gap allowing quantum Hall effect to be observed at room temperature [7][8][9]. Substrate induced SL in graphene in the presence of magnetic field led to the experimental observation of Hofstadter butterfly physics [10][11][12]. The ability to create abrupt (∼ 10 nm) tunable barriers in graphene allows new aspects to be explored. In addition, new physics, due to the role of crossed electric and magnetic field, that cannot be seen in conventional 2DEGS can be studied in SL structures based on graphene.In this letter, we study magneto transport in an electrostatically defined 1D lateral SL in graphene [13]. In our device we apply a perpendicular magnetic field and periodically modulate the charge carrier density in adjacent "ribbons" of graphene, tuning from an array of p-p' (or n-n' ) to an array of p-n' junctions. Changing the magnetic field allows us to vary l B relative to λ; and changing the gate voltage allows us to tune the SL potential strength relative to LL spacing. The relative abruptness, bipolarity of charge carriers, large modulation and unequally spaced LLs distinguishes the present work from the previous work on 1D SL using 2DEGS systems [1][2][3][4]14].Apart from the length scales, we also study the energy scales involved. The competition between SL amplitude (V 0 ) and LL spacing (hω c , whereh = h/2π, h being the Planck's constant, and ω c is the cyclotron frequency) gives rise to three regimes. When V 0 >>hω c , SL effect dominates giving rise to extra Dirac points [15]. In the other extreme when V 0 <

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“…The advantage of controlling the charge type and electric field locally adds a new dimension to study electron transport 4 to see effects like Klein tunneling 5,6 , Andreev reflection 7 , collapse of Landau levels 8 , Veselago lens 9 and collimation of electrons with top gates 10 . The top gate geometry has been utilized in controlling the edge channels in the quantum Hall regime and with control over local and global carrier density.…”

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confidence: 99%

Dual top gated graphene transistor in the quantum Hall regime

Bhat¹,

Singh²,

Patil³

et al. 2012

Solid State Communications

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We study the effect of local modulation of charge density and carrier type in graphene field effect transistors using a double top gate geometry. The two top gates lead to the formation of multiple p-n junctions. Electron transport measurements at low temperature and in the presence of magnetic field show various integer and fractionally quantized conductance plateaus. We explain these results based on the mixing of the edge channels and find that inhomogeneity plays an important role in defining the exact quantization of these plateaus, an issue critical for the metrology applications of p-n junctions.The electronic properties of graphene have been studied extensively in recent years 1 , including effects like anomalous integer quantum Hall effect 2,3 . The advantage of controlling the charge type and electric field locally adds a new dimension to study electron transport 4 to see effects like Klein tunneling 5,6 , Andreev reflection 7 , collapse of Landau levels 8 , Veselago lens 9 and collimation of electrons with top gates 10 . The top gate geometry has been utilized in controlling the edge channels in the quantum Hall regime and with control over local and global carrier density. Such p-n 6,11 and p-n-p junctions 12 show integer and fractional quantized conductance plateaus. These integer and fractional quantized plateaus have been explained with the reflection and mixing of the edge channels leading to the partition of the current 13 . In this letter, we study electron transport in a graphene multiple lateral heterojunction device with charge density distribution of the type q-q 1 -q-q 2 -q with independent and complete control over both the charge carrier type and density in the three different regions. This is achieved by using a global back gate (BG) to fix the overall carrier type and density and local top gates (TG 1 , TG 2 ) to set the carrier type and density only below their overlap region with the graphene flake. By controlling the density under the two top gates, various conductance plateaus can be observed in quantum Hall regime. We explain these results by mixing and partitioning of the edge channels at the junctions. Our analysis on these two probe devices indicates that aspect ratio and inhomogeneity play an important role in determining the quantization of the conductance plateaus. The issues we explore here are also important in the use of multiple graphene p − n junctions for metrology 14 , use of graphene heterojunctions for collimation 10 and broad field of metamaterials based on graphene heterostructures 15 . The device fabrication starts with the mechanical exfoliation of graphene flakes from graphite 2,3 on 300 nm SiO 2 grown on degenerately doped silicon substrates. Using e-beam lithography, source-drain contacts were fabricated by depositing 10 nm/50 nm of Cr/Au. For the fabrication of top gates, we first spin coat 30 nm of NFC 1400 (JSR Micro) 16 as a buffer layer followed by the 10 nm of HfO 2 using atomic layer deposition to serve as the dielectric. Following this we fabricate ...

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Collapse of Landau Levels in Gated Graphene Structures

Cited by 56 publications

References 18 publications

Quantum and classical confinement of resonant states in a trilayer graphene Fabry-Pérot interferometer

Quantum and classical confinement of resonant states in a trilayer graphene Fabry-Pérot interferometer

Tuning equilibration of quantum Hall edge states in graphene – Role of crossed electric and magnetic fields

Dual top gated graphene transistor in the quantum Hall regime

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