Josephson Junctions and Waves

Josephson junctions are experimental constructs with uses in electronics and in particular the creation of the next generation of computers or the faster transmission of data. Josephson junctions are created by sandwiching an insulator (or in fact just a non-superconducting material) between two superconductors. Due to the use of superconductors, current Josephson junctions have a very low operating temperature, but work is being done to raise this and make them practical components.

One of the characteristics of Josephson junctions is the way in which current flows between the two superconductors. The current flows (via quantum tunnelling of Cooper pairs of electrons) even when there is no potential difference. This current is approximated very well by a fast switching between two binary states. The switching time can be significantly faster than that of transistors, this means that computers could theoretically be an order of magnitude faster than they currently are. Logic gates have already been created by combing several Josephson junctions.

Because of the many applications that involve the binary like nature of the current, it is important that we understand how (and when) this switching occurs. A lot of work has already been done to deepen our understanding, however there is an area which (until relatively recently) had not attracted much interest. That is, what happens when we do not consider a perfect Josephson junction but rather consider one with some kind of defect present. Perhaps the most obvious defect would be a scratch in the non-superconducting layer.

It turns out that the presence of such a scratch allows current to behave in different ways. For instance, stationary current need not be monotonic, or, if a pulse of current (information) is travelling towards the defect then it can be trapped by the defect. So if defects can be switched on and off we would be able to delay the propagation of the current. (back)