Dear Mohamed, it seems that you have defined your bilayer lattice in 3d. If so you have to avoid using the z-axis in your system. For the current you need to define a lattice as 2d shape (ie x and y axis for instance). From the tight binding side, it does not matter if one sets two layers on each other (ie z=0 for boath) and then adds the hopping between each layer. I hope this helps, otherwise it would be great if you share your script to find out the issue. Best, Adel Le lun. 12 juil. 2021 à 12:44, <mohamad.mirzakhani@gmail.com> a écrit :

Dear all, I have written a code in Kwant for a bilayer graphene quantum dot (in 2D manner) to calculate some electronic properties. I can get the results correctly for, e.g, conductance, spectrum, and LDOS. But there is a problem in plotting CURRENT density and I get the following error.

~~ need at least one array to concatenate

Has anyone had a similar experience ? The current density part of code is: ________________________________________________________________ ### Current plot params = dict(B=Bfield, r0=[0,0], h0=0) wf = kwant.wave_function(syst, energy=0.01, params=params) psi = wf(0)[0]

J_0 = kwant.operator.Current(syst) current = J_0(psi, params=params) kwant.plotter.current(syst, current) _________________________________________________________________