  Superconductivity is a phenomena where an external-feeding current flows
through the system without voltage drop. This indicates the existence of an
energy minimum under the current feeding boundary condition. Although it is
believed that superconductivity is explained by the BCS theory that attributes
the origin of superconductivity to the electron pair formation, such an energy
minimum has never been obtained by it. We have found such a minimum in the
system exhibiting spin twisting itinerant motion of electrons with the Rashba
spin-orbit interaction, but without referring to the electron pairing. The
supercurrent is shown to have the London equation form that exhibits the flux
quantum $h/2e$. This supercurrent generation mechanism may be the one actually
occurring in real superconductors instead of the one explained by the BCS
theory.
