Superconductivity

Superconductivity is the phenomenon by which certain materials, when cooled below a critical temperature, exhibit exactly zero electrical resistance and expel magnetic fields from their interior — the Meissner effect. Discovered in 1911 by Heike Kamerlingh Onnes in mercury, superconductivity remained unexplained for nearly half a century until the BCS theory of 1957 identified its microscopic origin: electrons form bound pairs — Cooper pairs — mediated by lattice vibrations (phonons), and these pairs condense into a macroscopic quantum state that moves through the lattice without scattering. From the perspective of spontaneous symmetry breaking, superconductivity is the breaking of electromagnetic gauge symmetry: the Cooper pair condensate acquires a phase, and the photon gains an effective mass inside the superconductor, which is why magnetic fields cannot penetrate. This same mechanism — gauge symmetry breaking giving mass to force carriers — was later adapted to particle physics as the Higgs mechanism, making superconductivity not merely a technological marvel but a prototype for how the universe generates mass.