Type I superconductor

Type I superconductor

Type I superconductors are superconductors that cannot be penetrated by magnetic flux lines (Meißner-Ochsenfeld effect). As such, they have only a single critical temperature at which the material ceases to superconduct, becoming resistive. The origin of their superconductivity is fully explained by BCS theory. Elementary superconductors, such as aluminium and lead are typical Type I superconductors.

Type I Superconductivity

As explained by BCS theory, type I superconductivity is exhibited by materials with a regularly structured lattice. This allows electrons to be coupled over a relatively large distance (compared to the size of an atom). These pairings are called Cooper pairs.

Though normally electrons exhibit Coulomb repulsion when displayed to each other, when they interact within a lattice, via a phonon interaction they display an attractive force. As this is not a normal state for an electron pair to be in, it is only achieved at very low temperatures. This is because, modeling it as a bond, it has a low bond energy, thus requiring very little force to break it. As such, if the temperature of the material is too high, the energy in the vibrations of the lattice are sufficient to break the bond.

The reason for this force of attraction is an effect known as 'the mattress effect'. [G. Vidali, 1993. Superconductivity: The next revolution? Cambridge University Press, Cambridge.] This comes about due to spins of electrons. As an electron passes through a lattice, the attractive forces between it and the protons in the nuclei of the atoms cause a ripple in the lattice structure. This means that there are ripples through much of the lattice. These ripples are vibrations called 'phonons'.The ripples induced throughout the lattice will affect other electrons passing through it. This creates the weak link between two electrons being affected by one phonon.This coupling means that even if one electron is presented with resistance the effect of the resistance is minimized as it is 'pulled along' by the other electron.

This type of superconductivity is normally exhibited by pure metals, e.g. aluminium, lead or mercury. (Alloys are typically of Type II.)

References

ee also

*Type II superconductor


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