Superconducting microcircuit and fluxoid quantization: A new quantum interferometer

Detailed solutions of the nonlinear Ginzburg-Landau equations are presented for a superconducting ring connected to two long leads. We assume a homogeneous wire of transverse dimension smaller than the coherence length {ξ} and penetration depth {λ}. This circuit behaves in much the same way as an ordinary superconducting quantum-interference device when the ring diameter is of order of magnitude of {ξ}(t), even though it contains no Josephson junctions. The normal-superconducting phase boundary of this device can be shifted with temperature and thus could be used to measure accurately small temperature differences. The proximity effect near a node and the equivalence of the nonlinear solutions of the above circuit with circuits of different geometries and transport or shielding currents are discussed.