Nonequilibrium electron distribution and nonlocal resistance in a two-dimensional electron gas at high magnetic fields

Komiyama, S.; Nii, Hideaki

doi:10.1016/0921-4526(93)90312-t

Cited by 46 publications

(30 citation statements)

References 24 publications

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“…6 Its success has been partly legitimated by its ability to include contact effects 7 and to explain adiabatic magnetotransport features 8 -such as the disappearance of peaks in the Shubnikov-de Haas ͑SdH͒ oscillations, the extension of quantum Hall plateaus to lower magnetic fields, and the existence of nonlocal resistances. 9 In this Rapid Communication, we manage a comparison between magnetotransport and scanning force microscopy investigations on Hall bar samples showing adiabatic transport features without the use of gates. The SFM measurements present potential distributions from which we conclude that the incompressible strip in front of alloyed contacts possesses different insulating properties depending of the orientation relatively to the crystal axes of the underlying heterostructure.…”

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confidence: 99%

Cryogenic scanning force microscopy of quantum Hall samples: Adiabatic transport originating in anisotropic depletion at contact interfaces

et al. 2010

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Anisotropic magnetoresistances and intrinsic adiabatic transport features are generated on quantum Hall samples based on an ͑Al,Ga͒As/GaAs heterostructure with alloyed Au/Ge/Ni contacts. We succeed to probe the microscopic origin of these transport features with a cryogenic scanning force microscope by measuring the local potential distribution within the two-dimensional electron system ͑2DES͒. These local measurements reveal the presence of an incompressible strip in front of contacts with insulating properties depending on the orientation of the contact/2DES interface line relatively to the crystal axes of the heterostructure. Such an observation gives another microscopic meaning to the term "nonideal contact" used in context with the Landauer-Büttiker formalism applied to the quantum Hall effect.Few cryogenic scanning force microscopy ͑SFM͒ measurements exist on probing the electrostatic potential distribution in two-dimensional electron systems ͑2DES͒ realized in ͑Al,Ga͒As/GaAs heterostructures under quantum Hall conditions. 1,2 Those results measured over the whole 2DES demonstrated the important role of compressible and incompressible strips 3,4 for the current distribution in quantum Hall samples. Despite of these experimental findings, the edgestate picture 5 remains the widely used model to describe the magnetotransport in quantum Hall devices, also in the context of topological insulators. 6 Its success has been partly legitimated by its ability to include contact effects 7 and to explain adiabatic magnetotransport features 8 -such as the disappearance of peaks in the Shubnikov-de Haas ͑SdH͒ oscillations, the extension of quantum Hall plateaus to lower magnetic fields, and the existence of nonlocal resistances. 9 In this Rapid Communication, we manage a comparison between magnetotransport and scanning force microscopy investigations on Hall bar samples showing adiabatic transport features without the use of gates. The SFM measurements present potential distributions from which we conclude that the incompressible strip in front of alloyed contacts possesses different insulating properties depending of the orientation relatively to the crystal axes of the underlying heterostructure. This result shows how to include contacts and interpret adiabatic features in terms of compressible/incompressible strips and what is the microscopic origin of anisotropy in magnetoresistances.The samples used here are based on an ͑Al,Ga͒As/GaAs heterostructure containing the 2DES at the heterojunction interface 60 nm below the surface. The electron density and mobility at 1.3 K are 3.6ϫ 10 15 m −2 and 160 m 2 ͑V s͒ −1 , respectively. Such conditions lead to high electron mobility samples with an electron mean-free path l Ϸ 13 m, which is three times larger than in Ref. 2. Our Hall bars as depicted in Fig. 1 are defined by optical lithography and wet etching. Au/Ge/Ni film is alloyed to achieve low resistive contacts to the 2DES by following our standard recipe. 10 After annealing, the remaining 2DES has a size of about 10 m w...

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confidence: 99%

Cryogenic scanning force microscopy of quantum Hall samples: Adiabatic transport originating in anisotropic depletion at contact interfaces

et al. 2010

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“…The effect has already been observed in the 1980's, where its physical mechanism was attributed to non-ideal contacts234, but without providing clear evidence for this hypothesis. Later, the overshoot effect was attributed to the decoupling of the spin-split states within the same LL at odd filling factors by Richter and Wheeler5, or, alternatively by the scattering between edge states together with spin-orbit interaction by Komiyama and Nii6. Recently, the overshoot effect has been investigated in Si/SiGe heterostructures as a function of current and temperature12.…”

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Anomalous resistance overshoot in the integer quantum Hall effect

Kendirlik

Sirt

Kalkan

et al. 2013

Sci Rep

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In this work we report on experiments performed on smooth edge-narrow Hall bars. The magneto-transport properties of intermediate mobility two-dimensional electron systems are investigated and analyzed within the screening theory of the integer quantized Hall effect. We observe a non-monotonic increase of Hall resistance at the low magnetic field ends of the quantized plateaus, known as the overshoot effect. Unexpectedly, for Hall bars that are defined by shallow chemical etching the overshoot effect becomes more pronounced at elevated temperatures. We observe the overshoot effect at odd and even integer plateaus, which favor a spin independent explanation, in contrast to discussion in the literature. In a second set of the experiments, we investigate the overshoot effect in gate defined Hall bar and explicitly show that the amplitude of the overshoot effect can be directly controlled by gate voltages. We offer a comprehensive explanation based on scattering between evanescent incompressible channels.T he overwhelming interest to utilize quantum mechanics in applied technologies finds one of its first manifestations in the integer quantized Hall effect (IQHE) 1 . The magnetic field dependence of the transport coefficients of a two dimensional electron system (2DES) provides a possibility to standardize resistance in units of the von Klitzing constant h/e 2 , where h is the Planck constant and e is the elementary charge. However, an unexpected non-monotonic magnetic field dependence of the Hall resistance at the low-field-end of the quantized plateaus, known as the overshoot effect, remains a puzzle despite of both theoretical and experimental efforts in various material systems including GaAs/AlGaAs heterostructure 2-6 as well as Si/SiGe 7-13 and Si metal oxide semiconductor field effect transistors 14 . The utilization of the quantized Hall effect as a resistance standard is hindered by such anomalies, especially because their physical mechanism is not well understood. The overshoot effect is observed in these material systems at various filling factors n, defined by the number of occupied quantized (spin resolved) Landau levels (LL) below the Fermi energy. The effect has already been observed in the 1980's, where its physical mechanism was attributed to non-ideal contacts 2-4 , but without providing clear evidence for this hypothesis. Later, the overshoot effect was attributed to the decoupling of the spin-split states within the same LL at odd filling factors by Richter and Wheeler 5 , or, alternatively by the scattering between edge states together with spin-orbit interaction by Komiyama and Nii 6 . Recently, the overshoot effect has been investigated in Si/SiGe heterostructures as a function of current and temperature 12 . These experimental results have been elegantly explained within the screening theory of the integer quantized Hall effect, which explicitly takes into account the direct Coulomb interaction between charge carriers. In this approach the overshoot effect is described using co-existing (curr...

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“…53 Another is a group of transport phenomena in which traces of the Fermi-surface current can be simply identified, as in the case discussed in the above. The latter category also includes nonlocal resistances observed in a 2DEG system in magnetic-field ranges outside the QHE regime 13,14,54 and the geometry-dependent anomalous magnetoresistances observed in very pure bulk metals at strong magnetic fields. 55,56 …”

Section: Connection To Experimentsmentioning

confidence: 99%

“…On the other hand, there is a series of experiments, which provides definite proof of the presence of edge current and in which the results are analyzed by invoking only the edge current. [8][9][10][11][12][13][14] The present authors stressed earlier that the discussion in terms of the edge current is completely independent of the presence of the bulk Hall current. 15 Beenaker and van Houten also write ''the study of local current distribution does not prove or disprove edgechannel formulation.''…”

Section: Introductionmentioning

confidence: 96%