**Magnetic Moments of 4d-Surface Impurities on Noble Metal
Surfaces**

.
In our group we use the coherence of the conduction electrons
to investigate solid state properties. Conduction electron
interference permits us, for example, to determine the time
development of the electron spin orientation on a picosecond
time scale. This method is particularly suited to detect and
investigate magnetic impurities in metals. It is by a factor of
100 more sensitive than competing methods. We discovered this
method accidentally in the late 70's when investigating
the anomalous Hall effect
of Pd films, covered with magnetic impurities /1/. In the 80's
this phenomenon became rather famous under the name
**quantum interference** or **weak localization **.
In the following the basic physics is explained in simple steps.
For a more detailed discussion see the review article /2/.

## The Underlying Physics

** The Drunken Sailor **
Assume that you have a city with streets like a chess board. In
the center of the town is a bar which is crowded with drunken
sailors. Now assume that all the sailors leave the bar at the
time t=0. In Fig.1 we follow the path of such a sailor. At each
corner he makes a random turn because he does not remember where
he came from. There is a finite probability that the sailor
returns (by accident) back to the original bar. As a matter of
fact the bouncer (in front of the bar) sees quite a few sailors
passing by. Although each sailor walks randomly through the city
the number of sailors which return accidentally to the bar is
inversely proportional to the passed time, i.e. proportional to
1/t.

Fig.1: The random walk of a drunken sailor who returns accidentally
to his starting point (the bar). Muggers reduce the number of
returning sailors.
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