Questions about the "weak link" of Josephson junction

[zhanhai]

1.
It seems that in some Josephson junctions the insulator part is replaced by a gap, as is the so-called mesa. Is it true?

2.
What does "weak link" exactly means? Somewhere it is said that the connection part is of a thickness of about 10 angstroms. What is the upper limit of the thickness?

Thanks.

 

[marcusl]

1. A gap is an insulator, isn't it?
2. A weak link is a region of the circuit where superconducting current is compromised but not eliminated--Cooper pairs can tunnel through it. The insulator and gap that you mentioned in part 1 are weak links (assuming they're thin enough). Instead of an insulator, one can reduce the width or diameter of the superconductor to accomplish the same thing.

The limit of thickness depends somewhat on the materials. You don't want tunneling to become unlikely enough that the tunneling current (and, therefore, the Josephson effect) disappear.