Zero-resistance states induced by electromagnetic-wave excitation in GaAs/AlGaAs Heterostructures

GaAs-based two-dimensional electron gases (2DEGs) show a wealth of remarkable electronic states [1][2][3] , and serve as the basis for fast transistors, research on electrons in nanostructures 4,5 , and prototypes of quantum-computing schemes 6 . All these uses depend on the extremely low levels of disorder in GaAs 2DEGs, with low-temperature mean free paths ranging from microns to hundreds of microns 7 . Here we study how disorder affects the spatial structure of electron transport by imaging electron flow in three different GaAs/AlGaAs 2DEGs, whose mobilities range over an order of magnitude. As expected, electrons flow along narrow branches that we find remain straight over a distance roughly proportional to the mean free path. We also observe two unanticipated phenomena in high-mobility samples. In our highest-mobility sample we observe an almost complete absence of sharp impurity or defect scattering, indicated by the complete suppression of quantum coherent interference fringes.Also, branched flow through the chaotic potential of a high-mobility sample remains stable to significant changes to the initial conditions of injected electrons.Scanning gate microscopy (SGM) images of electron flow in two-dimensional electron gases (2DEGs) [8][9][10][11][12][13][14][15][16][17][18] provide direct spatial information not available in conventional electrical transport measurements. Our SGM studies show how varying disorder affects electron flow, and enable us to infer information about the disorder potential in our different samples. Achieving a detailed picture of the disorder potential 19, 20 may help to understand why exotic electron organization emerges in some 2DEGs and not others, and to aim for ever weaker disorder or even tailored disorder 21 .By analyzing the differences between images of flow in our samples, we find that the highermobility samples are increasingly dominated by small-angle scattering instead of hard-scattering 22 .2 Finally, we investigate an unusual property of electron flow through such a small-angle scattering disorder potential: though the disorder potential is classically chaotic, branches of flow are stable to significant changes in initial conditions.On each of three 2DEG samples defined in GaAs/AlGaAs heterostructures (Table 1), we use a home-built scanning gate microscope to image the flow of electrons emanating from a split-gate quantum point contact (QPC) 23, 24 at 4.2 K, as schematically shown in Fig. 1d. Using a recently established technique 9-15 , we measure the conductance across the QPC while scanning a sharp conducting tip ∼20 nm above the surface of the sample. We negatively bias the tip to create a depletion region in the 2DEG below. When the tip is above a region of high electron flow from the QPC, it backscatters electrons through the QPC, reducing the measured conductance. By scanning the tip and recording the drop in conductance ∆G for each tip location, we thus image electron flow. Images of flow gathered in this way have been found to accurately reproduce the under...

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confidence: 99%

Unexpected features of branched flow through high-mobility two-dimensional electron gases

et al. 2007

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“…Note that the additional term in the differential equation which provides g(B), is the factor (1/B) in the dominator of Equation (32). If this term does not exist, the differential equation has a simple form dB dT = B T and obtains the result previously discussed for the non-degenerate case.…”

Section: Depends On Three Variables S L ≡ S L (T B λ)mentioning

confidence: 66%

“…Thus, the electrons in GaAs are confined in a 1-D potential well of length L in the Z-direction. Therefore, electrons are trapped in 2D space, where a magnetic field along Z-axis can be applied [32].…”

Section: Introductionmentioning

confidence: 99%

Magnetic Engine for the Single-Particle Landau Problem

Peña

González

Núñez

et al. 2017

Entropy

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Abstract:We study the effect of the degeneracy factor in the energy levels of the well-known Landau problem for a magnetic engine. The scheme of the cycle is composed of two adiabatic processes and two isomagnetic processes, driven by a quasi-static modulation of external magnetic field intensity. We derive the analytical expression of the relation between the magnetic field and temperature along the adiabatic process and, in particular, reproduce the expression for the efficiency as a function of the compression ratio.

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Section: Of 15mentioning

confidence: 99%

Magnetic Engine for the Single-Particle Landau Problem

Peña¹,

González²,

Núñez³

et al. 2017

Preprint

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Abstract:We study the effect of the degeneracy factor in the energy levels of the well-known Landau problem for a magnetic engine. The scheme of the cycle is composed of two adiabatic processes and two isomagnetic processes driven by a quasi-static modulation of external magnetic field intensity. We derive the analytical expression of the relation between the magnetic field and temperature along the adiabatic process and, in particular, reproduce the expression for the efficiency as a function of the compression ratio.

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Zero-resistance states induced by electromagnetic-wave excitation in GaAs/AlGaAs Heterostructures

Cited by 106 publications

References 11 publications

Unexpected features of branched flow through high-mobility two-dimensional electron gases

Unexpected features of branched flow through high-mobility two-dimensional electron gases

Magnetic Engine for the Single-Particle Landau Problem

Magnetic Engine for the Single-Particle Landau Problem

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