Flux-induced vortex in mesoscopic superconducting loops

We predict the existence of a quantum vortex for an unusual situation. We s tudy the order parameter in doubly connected superconducting samples embedd ed in a uniform magnetic field. For samples with perfect cylindrical symmet ry, the order parameter has been known for a long time and no vortices are present in the linear regime. However, if the sample is not symmetric, ther e exist ranges of the field fur which the order parameter vanishes along a line, parallel to the held. In many respects, the behavior of this line is qualitatively different from that of the vortices encountered in type-II su perconductivity. For samples with mirror symmetry, this flux-induced vortex appears at the thin side for small fluxes and at the opposite side for lar ge fluxes. We propose direct and indirect experimental methods which could test our predictions. [S0163-1829(99)01813-5].