2
1 Introduction
Fig. 1.1 Cross-sections of superconducting wires: a multi-filamentary Nb 3 Sn wire (provided by
Showa Cable Systems Co., Ltd.), b Bi-2223 tape (provided by Sumitomo Electric Industries, Ltd.),
and c rare-earth barium copper oxide (REBCO) coated conductor (provided by Furukawa Electric
Co., Ltd. and SuperPower Inc.)
Fig. 1.2 3 T superconducting MRI system (provided by Canon Medical Systems Corporation)
Superconductivity is a peculiar phenomenon in solid state physics. For this reason,
almost half a century was needed for solution to the mechanism of superconductivity
after its discovery in 1911. In the meanwhile, the theory of quantum mechanics was
completed in the 1920s. The great physicists who contributed to the development
of quantum mechanics could not solve the problem of superconductivity. This was
because the appearance of superconductivity was contradictory to the Pauli exclusion
principle based on symmetry of the wave functions of particles. Superconductivity is
a phenomenon of electrons that carry non-dissipative current. The superconducting
state was speculated to be one of condensed states in which many electrons stay in
the same state with the same energy. Such a state is only achieved, however, for Bose
1 Introduction
Fig. 1.1 Cross-sections of superconducting wires: a multi-filamentary Nb 3 Sn wire (provided by
Showa Cable Systems Co., Ltd.), b Bi-2223 tape (provided by Sumitomo Electric Industries, Ltd.),
and c rare-earth barium copper oxide (REBCO) coated conductor (provided by Furukawa Electric
Co., Ltd. and SuperPower Inc.)
Fig. 1.2 3 T superconducting MRI system (provided by Canon Medical Systems Corporation)
Superconductivity is a peculiar phenomenon in solid state physics. For this reason,
almost half a century was needed for solution to the mechanism of superconductivity
after its discovery in 1911. In the meanwhile, the theory of quantum mechanics was
completed in the 1920s. The great physicists who contributed to the development
of quantum mechanics could not solve the problem of superconductivity. This was
because the appearance of superconductivity was contradictory to the Pauli exclusion
principle based on symmetry of the wave functions of particles. Superconductivity is
a phenomenon of electrons that carry non-dissipative current. The superconducting
state was speculated to be one of condensed states in which many electrons stay in
the same state with the same energy. Such a state is only achieved, however, for Bose