  The velocity field composed of the Berry connection from many-body wave
functions and electromagnetic vector potential explains the energy-momentum
balance during the reversible superconducting-normal phase transition in the
presence of an externally applied magnetic field. In this formalism, forces
acting on electrons are the Lorentz force and force expressed as the gradient
of the kinetic energy. In the stationary situation, they balance; however, an
infinitesimal imbalance of them causes a phase boundary shift. In order to
explain the energy balance during this phase boundary shift, the electromotive
force of the Faraday's magnetic induction type is considered for the Berry
connection. This theory assumes that supercurrent exists as a collection of
stable quantized loop currents, and the transition from the superconducting to
normal phase is due to the loss of their stabilizations through the thermal
fluctuation of the winding numbers of the loop currents. We argue that an
abrupt change of loop current states with integral quantum numbers should be
treated as a quantum transition; then, the direct conversion of the quantized
loop currents to the magnetic field occurs; consequently, the Joule heat
generation does not occur during the phase transition.
