Why does the electromagnetic penetration depth grow near the transition temperature?

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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.

The electromagnetic penetration depth in a superconductor represents the small distance that a magnetic field can penetrate into the material's interior. As the temperature of a superconductor approaches its transition temperature ( $T_{c}$ ), the energy gap ( $Δ$ ) for the superconducting electrons decreases, causing the number of thermally excited electrons to increase.12

This reduction in the energy gap and the corresponding increase in thermally excited electrons as the material nears $T_{c}$ leads to a significant increase in the electromagnetic penetration depth, which becomes extremely large as the transition temperature is reached.12