Metal-Insulator Oscillations in a Two-Dimensional Electron-Hole System

Nicholas, R.J.; Takashina, Kei; Lakrimi, M.; Kardynał, Beata; Khym, S.; Mason, Nigel J.; Symons, D.M.; Maude, D. K.; Portal, J. C.

doi:10.1103/physrevlett.85.2364

Cited by 28 publications

(26 citation statements)

References 19 publications

(22 reference statements)

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“…Finally we would like to discuss the similarity and the difference between other bipolar 2D system, such as graphene [4][5][6] and InAs/GaSb system [16], where the QHE has also been studied. In contrast both to our 2D e-h system in HgTe QW and to graphene the InAs/GaSbbased system is not a semimetal since there is a gap resulting from the hybridization of in-plane dispersions of electrons in InAs and holes in GaSb [17].…”

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confidence: 99%

Quantum Hall Effect near the Charge Neutrality Point in a Two-Dimensional Electron-Hole System

et al. 2010

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We study the transport properties of HgT e-based quantum wells containing simultaneously electrons and holes in magnetic field B. At the charge neutrality point (CNP) with nearly equal electron and hole densities, the resistance is found to increase very strongly with B while the Hall resistivity turns to zero. This behavior results in a wide plateau in the Hall conductivity σxy ≈ 0 and in a minimum of diagonal conductivity σxx at ν = νp − νn = 0, where νn and νp are the electron and hole Landau filling factors. We suggest that the transport at the CNP point is determined by electron-hole "snake states" propagating along the ν = 0 lines. Our observations are qualitatively similar to the quantum Hall effect in graphene as well as to the transport in random magnetic field with zero mean value. The quantum Hall effect (QHE) of a two-dimensional (2D) electron gas in a strong magnetic field is one of the most fascinating quantum phenomena discovered in the condensed matter physics. Its basic experimental manifestation is a vanishing longitudinal conductivity σ xx ≈ 0 and a quantization of the Hall conductivity σ xy = ν e 2 h , where ν is the Landau filling factor [1]. The discovery of a 2D electron-hole system in graphene at a finite magnetic field has put a beginning to a series of studies of the properties of the special state realized when the densities of the electrons and holes are equal, the charge neutrality point (CNP) [4][5][6]. In a strong magnetic field the QHE near the CNP reveals a plateau in σ xy with ν = 0 currently associated with the resolution of the spin or the valley splitting of the lowest Landau level (LL) [5,6]. However, the longitudinal resistivity ρ xx at ν = 0 demonstrates different behavior in various but otherwise quite similar samples: in some samples ρ xx shows a rapid divergence at a critical field and, with the temperature decreasing, saturates at a value much larger than the quantum of resistance [6], while in the others it decreases with lowering the temperature [5]. The QHE behavior near the CNP has attracted much theoretical interest and several microscopic mechanisms that might be responsible for these phenomena have been proposed [5,7], however no final quantitative conclusion has been drawn up yet. Graphene remained a unique 2D system with described properties when recently a new 2D system showing similar properties has been discovered. It has been shown [8] that a two-dimensional semimetal exists in undoped HgTe-based quantum wells with an inverse band structure and a (013) surface orientation. In this paper we report the results of our study of the transport properties of the HgTe-based quantum wells near the CNP. At filling factor ν = 0 (CNP) our system goes into a high resistivity state with a moderate temperature dependence markedly different from a thermally activated behavior expected when there is an opening of the Landau gap in the density of states. We suggest that at the CNP the 2D electron-hole gas in our HgTe quantum wells is not homogeneous due to the random potent...

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Quantum Hall Effect near the Charge Neutrality Point in a Two-Dimensional Electron-Hole System

et al. 2010

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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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“…To account for the observed behavior the disorder potential has to be taken into account. A disorder potential comparable to the gap size can locally suppress the insulating state and give rise to carrier hopping between adjacent conducting puddles, leading to a finite resistance [13,14] (see Fig. 4d).…”

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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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“…2 edge channels with broken phase coherence. [22][23][24] To characterize the far infrared photoresponse of the device, we measured the photovoltages ≡ ( − ) with 180 GHz radiation normally incident on the sample through z-cut quartz cryostat windows. A set of Virginia Diodes Inc. Schottky multipliers driven by an RF local oscillator and modulated at 75 Hz with 50% duty cycle provided a peak power of 0 = 3.9 mW.…”

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Far infrared edge photoresponse and persistent edge transport in an inverted InAs/GaSb heterostructure

Dyer

Shi

Olson

et al. 2016

Applied Physics Letters

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Direct current (DC) transport and far infrared photoresponse were studied an InAs/GaSb double quantum well with an inverted band structure. The DC transport depends systematically upon the DC bias configuration and operating temperature. Surprisingly, it reveals robust edge conduction despite prevalent bulk transport in our device of macroscopic size. Under 180 GHz far infrared illumination at oblique incidence, we measured a strong photovoltaic response. We conclude that quantum spin Hall edge transport produces the observed transverse photovoltages.Overall, our experimental results support a hypothesis that the photoresponse arises from direct coupling of the incident radiation field to edge states.

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Metal-Insulator Oscillations in a Two-Dimensional Electron-Hole System

Cited by 28 publications

References 19 publications

Quantum Hall Effect near the Charge Neutrality Point in a Two-Dimensional Electron-Hole System

Quantum Hall Effect near the Charge Neutrality Point in a Two-Dimensional Electron-Hole System

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

Far infrared edge photoresponse and persistent edge transport in an inverted InAs/GaSb heterostructure

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