Nonlocal Transport Near Charge Neutrality Point in a Two-Dimensional Electron-Hole System

Gusev, G. M.; Olshanetsky, E. B.; Квон, З. Д.; Levin, A. D.; Михайлов, Н. Н.; Dvoretsky, S. A.

doi:10.1103/physrevlett.108.226804

Cited by 40 publications

(40 citation statements)

References 26 publications

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“…2(a) and 4(a) in this region is caused by scattering between counterpropagating chiral edge states, which is enhanced in the magnetic field. Such large resistance is observed also in nonlocal magnetotransport measurements in similar samples, 21 which provides an additional confirmation of the picture of counterpropagating chiral edge modes in high magnetic fields.…”

Section: Theory and Discussionsupporting

confidence: 64%

Unconventional Hall effect near charge neutrality point in a two-dimensional electron-hole system

Raichev¹,

Gusev

Olshanetsky

et al. 2012

Phys. Rev. B

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The transport properties of the two-dimensional system in HgTe-based quantum wells containing simultaneously electrons and holes of low densities are examined. The Hall resistance, as a function of perpendicular magnetic field, reveals an unconventional behavior, different from the classical Nshaped dependence typical for bipolar systems with electron-hole asymmetry. The quantum features of magnetotransport are explained by means of numerical calculation of Landau level spectrum based on Kane Hamiltonian. The origin of the quantum Hall plateau σxx = 0 near the charge neutrality point is attributed to special features of Landau quantization in our system.

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Section: Theory and Discussionsupporting

confidence: 64%

Unconventional Hall effect near charge neutrality point in a two-dimensional electron-hole system

Raichev¹,

Gusev

Olshanetsky

et al. 2012

Phys. Rev. B

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“…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.…”

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confidence: 99%

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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“…Beyond the topological insulator properties, that manifest themselves, the fate of topological edge states at finite magnetic field has not been investigated so far. Similarly to other semi-metals like graphene [9,10] or CdHgTe/HgTe quantum wells [11,12], electron and hole Landau levels (LLs) can coexist close to the CNP [13,14]. A detailed understanding of the expected hybridization of LLs [15] and its manifestation in a transport experiment is still missing.…”

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confidence: 99%

Insulating State and Giant Nonlocal Response in anInAs/GaSbQuantum Well in the Quantum Hall Regime

et al. 2014

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We present transport measurements performed in InAs/GaSb double quantum wells. At the electron-hole crossover tuned by a gate voltage, a strong increase in the longitudinal resistivity is observed with increasing perpendicular magnetic field. Concomitantly with a local resistance exceeding the resistance quantum by an order of magnitude, we find a pronounced non-local resistance signal of almost similar magnitude. The co-existence of these two effects is reconciled in a model of counter-propagating and dissipative quantum Hall edge channels providing backscattering, shorted by a residual bulk conductivity.An InAs/GaSb double quantum well (QW) sandwiched between two AlSb barriers shows a peculiar band alignment [1]. A QW for electrons in InAs and a QW for holes in GaSb coexist next to each other. If the QWs thicknesses are small enough, a hybridization gap is expected to open at the charge neutrality point (CNP) [2,3]. Depending on the QWs' thicknesses and on the perpendicular electric field, a rich phase diagram is predicted [4]. It should be possible to electrically tune the sample from standard conducting phases to insulating, semimetallic or topological insulator phases. Recent work on InAs/GaSb QWs showed signatures of topological phases in micron-sized Hall bars at zero magnetic field [5][6][7], as expected for the quantum spin Hall insulator regime [8]. Beyond the topological insulator properties, that manifest themselves, the fate of topological edge states at finite magnetic field has not been investigated so far. Similarly to other semi-metals like graphene [9,10] or CdHgTe/HgTe quantum wells [11,12], electron and hole Landau levels (LLs) can coexist close to the CNP [13,14]. A detailed understanding of the expected hybridization of LLs [15] and its manifestation in a transport experiment is still missing.Here we present magnetotransport measurements performed on gated InAs/GaSb double QWs. At high magnetic fields, in the electron and hole regimes, we observe the formation of standard LLs. Close to the CNP a peculiar state forms in which electrical transport is governed by counter-propagating edge channels of highly dissipative nature. We investigate the transport properties in this regime using different measurement configurations, and as a function of magnetic field and temperature.The experiments were performed on two devices (named device A and device B) obtained from the same wafer as described in Ref. 16. In Ref. 17 a nominally identical structure was used, and a hybridization gap of 3.6 meV was reported. Hall bar structures were fabricated by photolithography and argon plasma etching. Device A consisted of a single Hall bar with a width of 25 µm and a separation between lateral arms of 50 µm.Device B consisted of two Hall bars in series, oriented perpendicularly to each other. Their width is 25 µm and the lateral voltage probes have various separations, the shortest being 50 µm . Device A was covered by a 200 nm thick Si 3 N 4 insulating layer, device B by a 40 nm thick HfO 2 layer. On both sampl...

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Nonlocal Transport Near Charge Neutrality Point in a Two-Dimensional Electron-Hole System

Cited by 40 publications

References 26 publications

Unconventional Hall effect near charge neutrality point in a two-dimensional electron-hole system

Unconventional Hall effect near charge neutrality point in a two-dimensional electron-hole system

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

Insulating State and Giant Nonlocal Response in anInAs/GaSbQuantum Well in the Quantum Hall Regime

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