Off-diagonal long-range order, restricted gauge transformations, and Aharonov-Bohm effect in conductors.

The electrons in a conductor surrounding an external magnetic field are acted on by a vector potential that cannot be removed by a gauge transformation. Nevertheless, a macroscopic normal conductor can experience no Aharonov-Bohm (AB) effect. That is proved by assuming only that a normal conductor lacks off-diagonal long-range order (ODLRO), which means that the electrons lack long-range phase coherence. Then by restricting the Hilbert space to density matrices which lack ODLRO, one can introduce a restricted gauge transformation that removes the interaction of the conductor with the vector potential. Consequently, the AB effect on a beam particle is not shielded by the conductor. {copyright} {ital 1996 The American Physical Society.}