1.3 Energy Dissipation in Superconductors
7
phenomena can be derived from first principles. This fact strongly suggests theoretically that, if there is not energy dissipation, it contradicts the first law of thermodynamics. The contradiction has only been pointed out from the experimental
viewpoint. It can be recognized from the above discussion that there are two kinds of
irreversibility: One originates from the breaking of time reversal symmetry, in spite
of the restriction by the common equation of motion, and the other originates from a
difference in the equation between just before and just after unstable motion of flux
lines. The irreversibility in superconductors belongs to the latter type. Thus, the electromagnetic phenomena in superconductors are deeply associated with fundamental
aspects of physics.
Here, we emphasize a series of special electromagnetic phenomena called the
“longitudinal magnetic field effect” in superconductors. One of them represents a
significant increase in the critical current density. The magnetic field produced by
a current is directed perpendicular to the current. A longitudinal magnetic field is a
magnetic field applied parallel to a superconducting wire and it is empirically known
that a state in which the local current and the magnetic field are parallel to each other
is attained. This state is called the force-free state, since the Lorentz force on the flux
lines is zero. If a simple superposition is assumed for the magnetic field between
the applied field and the self-field of the current, there is no change in the Lorentz
force, resulting in no change in the critical current density. As will be shown later, the
longitudinal magnetic field effect is a quite new electromagnetic phenomenon that
has not been discussed in terms of the usual electromagnetism, and it will add a new
page to electromagnetism. Hence, the introduction of superconductivity is expected
to greatly influence electromagnetism.
Thus, the electromagnetic phenomena in superconductors are important, not
only from scientific, but also from technological aspects. Even a primitive perfect
diamagnetism in superconductors is not described in textbooks of electromagnetism,
however. Such a situation should be corrected. In this book it is emphasized how
elementary electromagnetism changes by introducing perfect diamagnetism in superconductors. If we reach a conclusion, the analogy between electricity and magnetism
becomes perfectly rigid, just as in the case where a picture of a jigsaw puzzle is
completed by adding a missing piece. Maxwell’s theory was completed in the 19th
century. Although superconductivity had not been discovered at that time, the framework of electromagnetism was compatible with superconductivity, as if it had already
been discovered. Since the zero resistivity is easily derived for a material with perfect
diamagnetism using Maxwell’s equations, it was, in principle, possible to predict the
superconductor in the 19th century, even if it might be an imaginary material.
1.4 Contents of This Book
The contents of this book are briefly introduced here. It is also recommended to read
the introduction at the beginning of each chapter.
7
phenomena can be derived from first principles. This fact strongly suggests theoretically that, if there is not energy dissipation, it contradicts the first law of thermodynamics. The contradiction has only been pointed out from the experimental
viewpoint. It can be recognized from the above discussion that there are two kinds of
irreversibility: One originates from the breaking of time reversal symmetry, in spite
of the restriction by the common equation of motion, and the other originates from a
difference in the equation between just before and just after unstable motion of flux
lines. The irreversibility in superconductors belongs to the latter type. Thus, the electromagnetic phenomena in superconductors are deeply associated with fundamental
aspects of physics.
Here, we emphasize a series of special electromagnetic phenomena called the
“longitudinal magnetic field effect” in superconductors. One of them represents a
significant increase in the critical current density. The magnetic field produced by
a current is directed perpendicular to the current. A longitudinal magnetic field is a
magnetic field applied parallel to a superconducting wire and it is empirically known
that a state in which the local current and the magnetic field are parallel to each other
is attained. This state is called the force-free state, since the Lorentz force on the flux
lines is zero. If a simple superposition is assumed for the magnetic field between
the applied field and the self-field of the current, there is no change in the Lorentz
force, resulting in no change in the critical current density. As will be shown later, the
longitudinal magnetic field effect is a quite new electromagnetic phenomenon that
has not been discussed in terms of the usual electromagnetism, and it will add a new
page to electromagnetism. Hence, the introduction of superconductivity is expected
to greatly influence electromagnetism.
Thus, the electromagnetic phenomena in superconductors are important, not
only from scientific, but also from technological aspects. Even a primitive perfect
diamagnetism in superconductors is not described in textbooks of electromagnetism,
however. Such a situation should be corrected. In this book it is emphasized how
elementary electromagnetism changes by introducing perfect diamagnetism in superconductors. If we reach a conclusion, the analogy between electricity and magnetism
becomes perfectly rigid, just as in the case where a picture of a jigsaw puzzle is
completed by adding a missing piece. Maxwell’s theory was completed in the 19th
century. Although superconductivity had not been discovered at that time, the framework of electromagnetism was compatible with superconductivity, as if it had already
been discovered. Since the zero resistivity is easily derived for a material with perfect
diamagnetism using Maxwell’s equations, it was, in principle, possible to predict the
superconductor in the 19th century, even if it might be an imaginary material.
1.4 Contents of This Book
The contents of this book are briefly introduced here. It is also recommended to read
the introduction at the beginning of each chapter.