Josephson Effect: SNS Junction & Self-Generated Current

[chientewu]

Hi,

I am confused about josephson effect. Take SNS for example. If the phase of these two superconductors are different, then there will be a josephson current through the junction. Experimentally, do we measure the current by attach two ends of SNS with a wire? If there is no wire attached to these two ends, will there be a current flowing through the junction? In other words, will there be a self-generated current in it without a loop?

Thanks for you help.

 

[f95toli]

Yes, you measure it by passing a current through the junction and then measuring the voltage across it.

And no, there won't be "self generated" current.
The only time you would get a current through a junction not connected by a wire is if it is part of a loop that is being threaded by a changing flux (i.e. an RF- SQUID).

 

[chientewu]

Thanks for your quick reply. Now I am confused about your statement "measure it by passing a current through the junction and then measuring the voltage across it." It means we have to pass a current through the junction, otherwise there will be no current? Is it correct. Thanks.

 

[f95toli]

Yes, the current-voltage characheristics of JJs are measured in exactly the same way as for example semiconductor diods; you use current source to bias it and then a voltmeter to measure the voltage across it (you can do it the other way aorund, using a voltage source and an ammeter; but this is quite tricky since the impedance of the junction is practically zero when you are on the supercurrent branch).