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Coherent branched flow in a two-dimensional electron gas


Semiconductor nanostructures based on two-dimensional electron gases (2DEGs) could form the basis of future devices for sensing, information processing and quantum computation. Although electron transport in 2DEG nanostructures has been well studied, and many remarkable phenomena have already been discovered (for example, weak localization, quantum chaos, universal conductance fluctuations1,2), fundamental aspects of the electron flow through these structures have so far not been clarified. However, it has recently become possible to image current directly through 2DEG devices using scanning probe microscope techniques3,4,5,6,7,8,9,10,11,12,13. Here, we use such a technique to observe electron flow through a narrow constriction in a 2DEG—a quantum point contact. The images show that the electron flow from the point contact forms narrow, branching strands instead of smoothly spreading fans. Our theoretical study of this flow indicates that this branching of current flux is due to focusing of the electron paths by ripples in the background potential. The strands are decorated by interference fringes separated by half the Fermi wavelength, indicating the persistence of quantum mechanical phase coherence in the electron flow. These findings may have important implications for a better understanding of electron transport in 2DEGs and for the design of future nanostructure devices.

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Figure 1: Experimental set-up.
Figure 2: Experimental images of electron flow. a, Image of electron flow from one side of a QPC at T = 1.7 K, biased on the G = 2e2/h conductance step.
Figure 3: Calculated electron flow. a, Surface plot of the random potential for computed electron flow, including contributions from impurities, donors, and gates; green areas are low and white areas are high potential.
Figure 4: Calculated tip scan. a, Quantum-mechanical flux through a random potential.


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This work was supported in part at Harvard University by the Office of Naval Research/Augmentation Awards for Science and Engineering Research Training (ONR/AASERT), by ONR and by the National Science Foundation through grants for the Materials Research Science and Engineering Center and for the Institute for Theoretical Atomic and Molecular Physics at Harvard University and Smithsonian Astrophysical Observatory. Work at the University of California Santa Barbara was supported by the NSF Science and Technology Center QUEST.

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Correspondence to R. M. Westervelt.

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Topinka, M., LeRoy, B., Westervelt, R. et al. Coherent branched flow in a two-dimensional electron gas. Nature 410, 183–186 (2001).

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