Hi Richard,

Andreev conductivity isn't expected to be symmetric outside of the
gap, so that's correct. For a related discussion check out
https://arxiv.org/abs/1905.05438

Best,
Anton

On Tue, 16 Feb 2021 at 10:32, Richard Gerhard Hess
<richardgerhard.hess@unibas.ch> wrote:
>
> Dear all,
>
>
> I have a question regarding the conductance in normal-superconductor junctions. I expect the conductance to be particle-hole symmetric, since the scattering region and the leads obey PHS. However, downloading the tutorial 2.6 and extending the energy interval, for which the conductance is calculated, to negative values, results in a  not particle-hole symmetric conductance spectrum above the gap. The conductance takes larger values for  positive energies above the gap.  Removing the superconducting lead and choosing a long superconducting section leads to the same sub-gap conductance. This was already discussed in the Kwant forum and makes sense to me. However, in this setup I observe a symmetric spectrum for large energies. The conductance for negative and positive energies agree. What is reason for this behaviour?
>
>
> The code "3_advanced_concepts", which was shared in the recent  Kwant workshop, gives the same result. I mean the Majorana part and not the topological insulator example. This effect of broken PHS is strongly pronounced near the topological phase transition, since the gap closes. If I consider a NSN junction, then I observe even not particle hole symmetric sub gap states: The sub-gap states are at the same bias but do not have always the same peak height in the conductance.
>
>
>
> Why does this happen? Maybe it is obvious, but I can not see it right now. The PHS is not broken! What I am missing here and what is the physical explanation?
>
>
> Best regards,
>
> Richard
>
>