Full-size Photo Gallery

A Hall probe fabricated in a GaAs/AlGaAs heterojunction. A 50 µA current is passed through two opposite arms of the "cross"; the other two arms are used to measure the resulting Hall voltage. The width of the arms of the cross is about 1 µm.

A magnetic image, made using scanning Hall probe microscopy, of a sample with a square array of holes which act as pinning centers for vortices. The magnetic field is such that half of the holes contain vortices.Throughout most of the visible field these vortices form a "checkerboard" pattern, with every other hole occupied. Because of the limited resolution of the probe, these uniform checkerboard areas appear faint. But along "grain boundaries", where the black (occupied) squares of the checkboard abut other black squares, a distinct boundary of alternating black and white lines is clearly visible. if these formed a perfectly periodic array themselves the image would be a uniform grey, but defects (in the form of domain walls) are visible in this picture.

A bifurcation diagram for flux droplets passing beneath a fixed Hall probe. As the driving current is increased, the time intervals between succesive pulses changes in a complex way. At low and high currents, a broad distribution of pulse sizes is observed. These distributions have been found to be consistent with deterministic chaos. For medium currents, only periodic trains of flux tubes are observed.