Vortex flow in superconducting devices

We have found an exact vortex current solution for a rectangular neutral superfluid microbridge; this solution is used in a model for vortex flow. Our model includes vortex self-energy effects (i.e. the edge barrier to vortex entry).; Our main theoretical result quantifies the dependence of the critical current (for vortex flow) on the edge barrier. The critical current increases by an order of magnitude if edge barriers are present. Furthermore, the critical current is unlikely to be less than half the depairing current. The critical current may even exceed the depairing current, which means that vortex flow will never happen. Finally, the critical current's magnetic field sensitivity is an order of magnitude lower than previously thought.; Our experiments with YBCO microbridges show that self-heating can occur even at higher temperature operation because of small thermal boundary conductance; we show that modeling self-heating in YBCO requires a more sophisticated treatment of the superconducting to normal state transition. Fortunately, however, self-heating does not totally dominate the device behavior: we found an operating regime in which vortex flow does occur. Our most important experimental results are our critical current and depairing current measurements, which found somewhat lower values than what theory predicts. We show that theory may be reconciled with experiment if a geometric correction factor derived from the normal state resistivity is applied. One implication of this correction factor is that YBCO may be very nonhomogeneous (e.g. filamentary) on a mesoscopic scale. We also find measurement induced damage in YBCO microbridges that is consistent with a filamentary hypothesis.; Our work has important implications for several types of superconducting devices. Their low magnetic sensitivity implies that microbridge vortex flow transistors will have poor performance. Microbridges, however, are useful in SQUID-like circuits and our model can be used to understand how this device operates. Another application of our model is to vortex-flow breakdown in superconducting interconnects. The self-heating effects and thermal properties (e.g. the thermal boundary conductance) that we have observed in YBCO microbridges are relevant to other devices such as bolometers. Finally, if YBCO is intrinsically a nonhomogeneous superconductor, then there may be substantial limitations on the application of YBCO in small scale devices (e.g. too much variation in behavior, damage vulnerability).