  In a semiclassical view superconductivity is attributed exclusively to the
advance of atoms' outer s electrons through the nuclei of neighbor atoms in a
solid. The necessary progression of holes in the opposite direction has the
electric and magnetic effect as if two electrons were advancing instead of each
actual one. Superconductivity ceases when the associated lateral oscillation of
the outer s electrons extends between neighbor atoms. If such overswing occurs
already at T = 0, then the material is a normal conductor. Otherwise, lateral
overswing can be caused by lattice vibrations at a critical temperature Tc or
by a critical magnetic field Bc. Lateral electron oscillations are reduced -
and Tc is increased - when the atoms of the outer s electrons are squeezed, be
it in the bulk crystal, in a thin film, or under external pressure on the
sample. The model is applied to alkali metals and alkali-doped fullerenes.
Aluminum serves as an example of a simple metal with superconductivity.
Application of the model to transition metals, intertransitional alloys and
compounds of transition metals with other elements sheds light on the pattern
of their critical temperature. More examples of the squeeze effect are provided
by the superconductivity of PdH, MgB2, borocarbides, ferropnictides, and
organic charge-transfer salts. The model also provides the superconduction
mechanism in the oxide superconductors, exemplified by YBa2Cu3O7. Finally the
model suggests which steps to take in order to reach superconductivity at room
temperature and above.
