The energy gap of a superconductor

Superconductors:

• It is a material showing perfect conductivity and the Meissner when cooled below down a transition temperature known as critical temperature (T_C).
• Meissner effect is the phenomenon of complete expulsion of magnetic field lines from the interior of the superconductor when it is cooled down below critical temperature.

Properties of a superconductor:

• Zero resistance
• Infinite conductivity
• Meissner effect
• Perfect diamagnetism behavior

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Energy gap in a superconductor:

• The energy gap in a superconductor is an order of 10^-4 eV.
• If a conventional superconducting material is cooled from its metallic state into the superconducting state, then the superconducting energy gap becomes zero at critical temperature (T_c).
• This energy gap is mainly due to electron-electron interactions with opposite spins, which are generally observed at low temperatures. 
• At transition temperature (Tc), the energy gap reduces to zero because pairing is dissolved. 
• The energy gap is maximum at 0° K because pairing is complete at this temperature.