  We study the interaction between single apex atoms in a metallic contact,
using the break junction geometry. By carefully 'training' our samples, we
create stable junctions in which no further atomic reorganization takes place.
This allows us to study the relation between the so-called jump out of contact
(from contact to tunnelling regime) and jump to contact (from tunnelling to
contact regime) in detail. Our data can be fully understood within a relatively
simple elastic model, where the elasticity k of the electrodes is the only free
parameter. We find 5 < k < 32 N/m. Furthermore, the interaction between the two
apex atoms on both electrodes, observed as a change of slope in the tunnelling
regime, is accounted for by the same model.
