How does is allow zero resistance?
Applying a voltage to a superconducting body above its critical temperature
would mean Cooper Pairs would not form and the electrons in the body
would be occupying a range of different energy states. Some electrons
would be at their lowest possible energy state – the ground state – and
others, having bumped into an atom, would be excited to a higher energy
state.
Now let’s bring the superconducting body to below its critical
temperature. Cooper Pairs form from the electrons, and as bosons, all the
Cooper Pairs in the body occupy a new boson ground state. This new ground
state is even less energetic than the original fermion ground state of the
electrons. Left between these two energy states is an energy gap on the order
of 0.001 eV in which no possible states exist for the Cooper Pair. On the occasion
that a Cooper Pair bumps into an atom, the collision would have to overcome
the energy gap to excite the Cooper Pair and cause any resistance.
In general, if a superconductor is at a temperature where its thermal
energy is less than its energy gap, no collisions between Cooper Pairs and
other atoms would have enough energy to excite the Cooper Pair above the
energy gap (and convert it back into electrons) to make it lose any energy at
all. Therefore it can be said that below this temperature – the critical
temperature – the superconductor has zero resistance.
High-Temperature Superconductors
At first glance, superconductors seem to be the holy grail of electricity
transmission, but they run into problems on the practical side. The nature of
conventional superconductors requires that temperatures be extremely
cold; near absolute zero. If superconductors were to be used as power line
cables, advanced cooling systems would be required to maintain the
superconducting state, thus increasing costs, wasting energy, and defeating
the original purpose of superconducting cables. Today, the development of
a superconductor with a high critical temperature that does not require a
separate cooling system is the subject of great research and new
innovation is being made in this area every day, whether it be through
gold-silver composite materials or graphite grains soaked in water. What’s
for sure is that many superconductors remain undiscovered, and it will be
up to us to find them.