  Superconductivity is a phenomenon where electrical current flows without
friction. The current standard theory for it is the BCS
(Bardeen-Cooper-Schrieffer) theory, which explains it as due to the energy gap
formation by the electron-pairing, and the key ingredient for the supercurrent
generation is the gauge symmetry breaking brought about by it. It was thought
that superconductivity was fully understood by this standard theory; however,
the discovery of superconductivity in cuprates in 1986 changed this situation,
showing a number of experimental results that contradict the standard theory.
It is also notable that the standard theory contradicts in the supecurrent
carrier mass in the London moment; the predicted mass is an effective mass,
while the experimental value is the free electron mass. The above
contradictions suggest the necessity for a fundamental revision for the theory
of superconductivity. Here we show that the required revision may be achieved
by using the Berry phase formalism. It was developed after the establishment of
the BCS theory, and provides a way to detect emergent gauge fields. A
self-referencing phase factor on the wave function detected by the Berry phase
formalism explains the supercurrent generation in the conventional and cuprate
superconductors. It gives rise to a gauge field that enables the gauge symmetry
breaking in the standard theory interpretation.
