  We consider a superconducting loop with two weak links that encloses a
magnetic flux. The weak links are unequal and are treated as Josephson
junctions with non-sinusoidal phase dependence. We devise a model that takes
into account the fluctuation of the critical currents, due to the fluctuations
of the order parameter in the weak links. These fluctuations are important near
the onset of superconductivity; in this regime they may significantly weaken
and eventually disconnect the superconducting loop. As a consequence of these
fluctuations and of the resistive noise in the junctions, the average dc
voltage does not vanish. Our model can be easily extended to provide a
qualitative description of a recent experiment.

Superconductivity;Statistical Mechanics