抄録
The gauge invariance of B.C.S. explanation of the Meissner effect is guaranteed by the inclusion of the collective excitations, as shown by Anderson and Yosida. In this case, however, the current, which can be neglected in B.C.S. calculation, might become to make a finite contribution to the Meissner effect. It is shown that this is actually the case in a system of normal electrons with Coulomb interactions. The situation in superconductors does not seem to differ essentially from that of normal electrons with this respect. This conclusion means that the gauge invariant theory of the Meissner effect cannot be said to be complete unless this difficulty is solved.
Moreover, the canonical transformation leading to the B.C.S. model adds some terms to the current operator. The magnitude of these terms is estimated, and is shown to make a numerically small but finite contribution to the Meissner effect also.
