Superconductivity in a mesoscopic double loop: effect of imperfections

Recently determined experimental normal/superconducting phase boundaries of mesoscopic superconducting double loops of Al are analyzed using the network approach generalized to include short-range imperfections. The presence of weakly scattering imperfections results in a dependence T c( Φ/ Φ 0) (of the critical temperature as a function of the relative magnetic flux through the opening of one loop) characterized by a smooth transition between symmetric and antisymmetric states. The best coincidence between the calculated phase boundary and the experimental data is achieved for a configuration with imperfections in all three branches of the double loop.