In this chapter, we review the basic properties of superconductors, illustrating that they go beyond describing a metal without resistance. We develop London's mesoscopic theory of superconductivity as a quantum mechanical description of the charged superfluid, which accounts for the behavior of the superconductor under electromagnetic fields. Using this theory, we explain the flux quantization for supercurrents flowing in closed loops and derive the energetics of the Josephson junction from the tunneling of Cooper pairs.

Starting from a brief introduction to the Meissner effect and other defining properties of superconductivity, Chapter 1 recapitulates the phenomenological theories, including the two-fluid model and the Ginzburg-Landau theory, and the groundbreaking microscopic theory of Bardeen-Cooper-Schrieffer for describing this macroscopic quantum phenomenon. The Cooper pairing and other basic concepts of superconductivity, such as the gap function, off-diagonal long-range order, quasiparticle excitations, coherence length, penetration depth, type-I and type-II superconductors, and phase fluctuations are also introduced, followed by a summary on the classification and experimental identification for the pairing symmetry of high-Tc superconductors.