We start with a single crystal
sapphire wafer and coat it with a thin (~1µm thick) ceramic material called
yttrium barium copper oxide (YBa
2Cu
3O
7-x ).
The ceramic layer has no interesting magnetic or electrical properties
at room temperature. However, when cooled below -185ºC (-301ºF) the
material becomes a
superconductor. It conducts electricity without resistance, with no energy loss. Zero.
Superconductivity and magnetic field do not like each other. When
possible, the superconductor will expel all the magnetic field from
inside. This is the
Meissner effect.
In our case, since the superconductor is extremely thin, the magnetic
field DOES penetrates. However, it does that in discrete quantities
(this is quantum physics after all! ) called flux tubes.
Inside each magnetic flux tube superconductivity is locally destroyed.
The superconductor will try to keep the magnetic tubes pinned in weak
areas (e.g. grain boundaries). Any spatial movement of the
superconductor will cause the flux tubes to move. In order to prevent
that the superconductor remains “trapped” in midair.