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How does the energy gap affect electrons in a superconductor?

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Figure 1: Specific heat in the normal (Cen) and superconducting (Ces) states of a classic superconductor as a function of absolute temperature. The two functions are identical at the transition temperature (Tc) and above Tc. — superconductivity Figure 1: Specific heat in the normal (C_en) and superconducting (C_es) states of a classic superconductor as a function of absolute temperature. The two functions are identical at the transition temperature (T_c) and above T_c.

In a superconductor, the energy gap ( $Δ$ ) represents a range of energy levels that are unavailable to electrons, meaning a finite amount of energy must be supplied to an electron to excite it from its superconducting state.1

According to the BCS theory, electrons in a superconductor form pairs of opposite spin known as Cooper pairs. These pairs are central to the phenomenon of superconductivity, as they move through the material without losing energy to the medium through collisions or phonon excitations.12

The energy gap directly affects these electrons by acting as a binding energy for the Cooper pairs. To break a pair, an amount of energy at least equal to the energy gap must be supplied to each electron, requiring a total energy of at least $2 Δ$ to be delivered to the superconductor. As the temperature of the material increases toward its transition temperature, the energy gap decreases, eventually reaching zero in the normal state, which corresponds to the breaking of these pairs and the loss of superconducting properties.1