Controlling thermal hysteresis in superconducting weak-links and micron size superconducting quantum interference devices

Micron size-Superconducting Quantum Interference Devices (micro-SQUIDs) are the most suitable probes for nano-scale magnetism. Hysteresis in the current-voltage characteristics of such devices has been a limiting factor and my thesis explores ways to restrict this hysteretic regime. We have fabricated and studied the current-voltage characteristics of a number of Nb film based weak-link devices and SQUIDs showing a critical current and at least two re-trapping currents. We have proposed a new understanding for the re-trapping currents in terms of thermal instabilities in different portions of the device. We also find that the superconducting proximity effect and the phase-slip processes play an important role in dictating the temperature dependence of the critical current. The proximity effect also helps in widening the temperature range of hysteresis-free characteristics. Finally we demonstrate a control on temperature-range on hysteresis-free characteristics in two ways: 1) By using a parallel shunt resistor in close vicinity of the device, and 2) by reducing the weak-link width.
Thus we demonstrate non-hysteretic regime even down to 1.3 K temperature.