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Coherence and Coulomb blockade near a quantum point contact in the quantum Hall regime

Benoit Hackens (Louvain-Bélgica)

In macroscopic two-dimensional electron systems (2DES) in the quantum Hall (QH) regime, electrons are transmitted through spatially separated edge states, and localized electron states in the bulk do not contribute to electron transport. In this situation, close to integer filling factors, the longitudinal resistance vanishes. Several local-probe experiments confirmed this picture, and yielded images of localized states in the bulk of macroscopic 2DESs . The situation is different in mesoscopic samples fabricated from 2DES: instead of vanishing, the high magnetic field magnetoresistance is decorated with a rich spectrum of oscillations with a broad range of periodicities. To explain these observations, recent theories invoke Coulomb interactions and tunneling between edge states and “Quantum Hall islands” (QHIs), constituted by edge states looping around hills or dips in the electrostatic potential . Thanks to low temperature scanning gate microscopy, we recently managed to locate and manipulate the active QHIs in a mesoscopic quantum ring. This technique thus allows to elucidate complex patterns of magnetoresistance oscillations in mesoscopic quantum Hall interferometers. Here, we report on unexpected manifestations of coherent electron transport through QHIs. We observe Coulomb blockade (CB) diamonds in some cases. However, for some particular QHIs, our data reveal that CB diamonds are replaced by a “checkerboard” interference pattern, indicative of coherent electron transport.