Dear developers, dear all,

I am Guido Menichetti, a Post-Doc at the University of Pisa.

I am currently working on computing the Andreev reflection in a 3D hexagonal 
lattice system, incorporating the spin degree of freedom and utilizing 
wraparound techniques. To facilitate this, I have been following the Kwant 
tutorial available at https://kwant-project.org/doc/1.0/tutorial/tutorial5.

In my approach, I define a "conservation law" to decompose the transmission 
function into four blocks: two for the spin degree of freedom and two for the 
electron-hole degree of freedom. Initially, I successfully ran calculations in 
a 2D system with periodic boundary conditions, perpendicular to the transport 
direction, without encountering any warning messages.

However, when attempting the same calculations in a 3D system with periodic 
boundary conditions in the perpendicular directions, I encountered a warning 
message: "[...] |envs\Kwant-env\lib\site-packages\kwant\system.py:316: 
UserWarning: Hamiltonian breaks Conservation law, ignoring the symmetry in the 
computation
warnings.warn('Hamiltonian breaks ' + name +". 

This warning disappears when I set the superconductor gap Delta (as defined in 
https://kwant-project.org/doc/1.0/tutorial/tutorial5) to 0 (Delta = 0).
The superconducting part is located in the right lead.

I believe the issue does not stem from the Hamiltonian of the scattering 
region. However, I am puzzled by the origin of this warning and its potential 
impact on the results. Could this problem be related to the "wraparound" 
technique in the 3D system?

The only difference between the 2D and 3D systems is the lattice: the 2D system 
lives on a square lattice, while the full 3D system is a hexagonal lattice.

Your insights and guidance on resolving this issue would be greatly appreciated.

Best regards,
Guido Menichetti
University of Pisa

Reply via email to