  Semiconductor nanostructures based on two dimensional electron gases (2DEGs)
have the potential to provide new approaches to sensing, information
processing, and quantum computation. Much is known about electron transport in
2DEG nanostructures and many remarkable phenomena have been discovered (e.g.
weak localization, quantum chaos, universal conductance fluctuations)1,2 - yet
a fundamental aspect of these devices, namely how electrons move through them,
has never been clarified. Important details about the actual pattern of
electron flow are not specified by statistical measures such as the mean free
path. Scanned probe microscope (SPM) measurements allow spatial investigations
of nanostructures, and it has recently become possible to directly image
electron flow through 2DEG devices using newly developed SPM techniques3-13.
Here we present SPM images of electron flow from a quantum point contact (QPC)
which show unexpected dynamical channeling - the electron flow forms
persistent, narrow, branching channels rather than smoothly spreading fans.
Theoretical study of this flow, including electron scattering by impurities and
donor atoms, shows that the channels are not due to deep valleys in the
potential, but rather are caused by the indirect cumulative effect of small
angle scattering. Surprisingly, the channels are decorated by interference
fringes well beyond where the simplest thermal averaging arguments suggest they
should be found. These findings may have important implications for 2DEG
physics and for the design of future nanostructure devices.
