In superconductor, the superconductivity will happen when the temperature of the metal is achieved below the critical temperature. the value of the critical temperature or Tc is different from material to material. when the material is in superconducting states, the resistance in that material is zero. The simplest method to measure the electrical resistance of a sample of some material is to place it in an electrical circuit in series with a current source I and measure the resulting voltage V across the sample. The resistance of the sample is given by Ohm's lawas R = V/I. If the voltage is zero, this means that the resistance is zero and that the sample is in the superconducting state.
The table below shows the different of critical temperature between material.
What are the different between superconductor and normal conductor?
In a normal conductor, an electrical current may be visualized as a fluid of electrons moving across a heavy ionic lattice. When the current moving inside the material, the electrons are colliding between the ions in the lattice and some current is absorbed by the lattice. Because of the kinetic energy, some energy are converted into heat.
The situation is different in a superconductor. In a conventional superconductor, the electronic fluid cannot be resolved into individual electrons. Instead, it consists 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 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.
The picture below show us one of the example of the arrangement of superconductor atoms.
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