In a normal conductor, an electrical current may be visualized as a fluid of electrons moving across a heavy ionic lattice. The electrons are
constantly colliding with the ions in the lattice, and during each collision some of the energy carried by the current is absorbed by the lattice and
converted into heat (which is essentially the vibrational kinetic energy of the lattice ions.) As a result, the energy carried by the current is
constantly being dissipated. This is the phenomenon of electrical resistance.
The situation is different in a superconductor. In a conventional superconductor, the electronic fluid cannot be resolved into individual electrons,
instead consisting of bound pairs of electrons known as Cooper pairs. This pairing is caused by an attractive force between electrons from the
exchange of phonons. Due to quantum mechanics, the energy spectrum of this Cooper pair fluid possesses an energy gap, meaning there is a minimum
amount of energy ΔE that must be supplied in order to excite the fluid. Therefore, if ΔE is larger than the thermal energy of the lattice
(given by kT, where k is Boltzmann's constant and T is the temperature), the fluid will not be scattered by the lattice. The Cooper pair fluid
is thus a superfluid, meaning it can flow without energy dissipation. |