Experimental Techniques

A constant electron current through a normal conductor is affected by local elastic scattering at defects as well as nonlocal inelastic phonon scattering. Both effects contribute to the global potential drop which is usually observed: they constitute Ohm’s law. Although this concept is well established for macroscopic solids, it has not yet been tested on the atomic scale, e.g. around an individual scattering center. To tackle this question, we have studied the gradient of the electrochemical potential ìec in a current-carrying 2-d electron gas confined in a layer of silver atoms on terraces of atomically smooth. At mon- atomic steps the drop in ìec extends over less than 1 nm. It has been modeled with known macroscopic conductivity parameters of the 2DEG and a step transmission coefficient T=0.2 according to Landauer’s ballistic conductance concept [Ref.4].