What is the reason why the experimental IVC curve obtained for a current-biased Josephson tunnel junction (strongly underdamped) differs from the theoretical curve expected when solving the RCJS model using beta_c >> 1 ? I am attaching a picture of a typical experimental curve and the theoretical one obtained for beta_c=5.
Hello, Lucia!
First of all, the RSCJ model is a first-order model in which the dissipative nature of the JJ is only related to the normal resistance of the device. You can see from your simulations that the subgap resistance, or in other words the slope of the IV when returning in the subgap branch, follows the slope of the IV above the switching voltage, related to RN. The RSCJ model can not capture more complex dissipative behaviors for your JJs, which may result in a non-linear behavior or the subgap branch. Your experimental IV curve is much more similar to those that you could capture within a microscopic tunneling modelization of the quasi particles in your device. See for example the Tunnel Junction Microscopic model, which is far better than the RSCJ model when dealing with devices with very large beta.
The knee that you see near the switching voltage, for example, may be due to what are knows as riedel peaks, and the TJM allows you to capture this behavior too, for instance. What is peculiar of your curve is the shape of your subgap branch, which is not simply squarish like most of the standard tunnel JJs in literature, but it shows also an elbow, which is due to the fact that the slope below the switching is not positive, but negative. I've already seen this behavior, but I don't remember what is the physical motivation. However, you can look at our work "electrodynamics of highly spin-polarized Josephson junctions", published in Physical Review Applied, in which we discuss the electrodynamics of JJs and we report several references about the subject. Hope it could help!
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