Proximity effect (atomic physics)

At the atomic level, when two atoms come into proximity, the highest energy, or valence, orbitals of the atoms change substantially and the electrons on the two atoms reorganize. One way to probe a correlated state is through the proximity effect. This phenomenon occurs when the correlations present in one degenerate system "leak" into another one with which it is in chemical equilibrium. See also quantum tunneling, Casimir effect, van der Waals force.