Dear community,
I am trying to simulate the current in a JJ with kwant. So far current oscillates with a phase rate that scales with bias. However, the averaged current does not depend on bias, as show in the plots below. Any idea what might be causing this? For simplicity, I do not consider any bound states in my calculations. Any suggestions are welcome!
Best, Denise
Parameters: t=1 mu=t Delta=0.02 # superconducting gap N=1 #size of the N region S=10 #size of the S region barrier=1 #barrier in the N region
[image: barrier_1_V_1.5.png] Same parameters but with barrier =2 [image: barrier_2_V_1.5.png] [image: barrier_2_V_0.2.png]
Dear Denise,
 First, bound states are the primary source of Josephson current so you should definitely include them.
 Nevertheless, current should depend on V even without them. There is a subtle issue here of chemical potential versus electrostatic potential. (versus electrochemical potential). We have a section about it in our physics report article. I strongly recommend that you read it. What you want to do is to fix the chemical potential to be the same for both leads which translate into:
occupation_l = tkwant.manybody.make_occupation(mu) occupation_r = tkwant.manybody.make_occupation(mu)
and V should show up only in the electric potential, i.e. in the function phase().
As it is your adding V in the electric potential of the left contact so that at the end of the day yuo have zero net (electrochemical) bias between the two electrodes also they are of different nature (electric versus chemical). I am not sure how mother nature could realize this setup.
 For perfomances, you should avoid nested python functions in the definition of the Hamiltonian.
Other than that it looks good.
Best regards,
Xavier
Le 20 nov. 2019 à 17:52, Denise Puglia dpuglia.eng@gmail.com a écrit :
Dear community,
I am trying to simulate the current in a JJ with kwant. So far current oscillates with a phase rate that scales with bias. However, the averaged current does not depend on bias, as show in the plots below. Any idea what might be causing this? For simplicity, I do not consider any bound states in my calculations. Any suggestions are welcome!
Best, Denise
Parameters: t=1 mu=t Delta=0.02 # superconducting gap N=1 #size of the N region S=10 #size of the S region barrier=1 #barrier in the N region
<barrier_1_V_1.5.png> Same parameters but with barrier =2 <barrier_2_V_1.5.png> <barrier_2_V_0.2.png>
<SIS_v2(1).py>
participants (2)

Denise Puglia

Xavier Waintal