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What did the discovery of the Meissner effect reveal about superconductors?

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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 discovery of the Meissner effect in 1933 fundamentally changed the scientific understanding of superconductivity. Prior to this, it was widely believed that superconductors were simply materials with zero electrical resistance that otherwise behaved like normal materials.1

The Meissner effect revealed that a superconductor is actually a highly diamagnetic substance that actively expels magnetic fields from its interior when cooled below its transition temperature. This discovery proved that superconductivity is not merely a state of perfect conductivity, but a distinct thermodynamic state characterized by the expulsion of magnetic flux.21

This insight was critical for the development of electromagnetic theories of superconductors, as it allowed physicists to account for the electromagnetic penetration depth and provided a foundation for later advancements, such as the BCS theory and the understanding of quantization of magnetic flux.1