  The origin of the anomalous transport feature appearing at conductance G
\approx 0.7 x (2e2/h) in quasi-1D ballistic devices - the so-called 0.7 anomaly
- represents a long standing puzzle. Several mechanisms were proposed to
explain it, but a general consensus has not been achieved. Proposed
explanations are based on quantum interference, Kondo effect, Wigner
crystallization, and more. A key open issue is whether point defects that can
occur in these low-dimensional devices are the physical cause behind this
conductance anomaly. Here we adopt a scanning gate microscopy technique to map
individual impurity positions in several quasi-1D constrictions and correlate
these with conductance characteristics. Our data demonstrate that the 0.7
anomaly can be observed irrespective of the presence of localized defects, and
we conclude that the 0.7 anomaly is a fundamental property of low-dimensional
systems.
