Hi Joe,
And how can I set lead1's potential correctly? What is wrong in my script
zigzag.py? I have the same function onsite both for scattering region and
for leads:
def *potential*( site, _U ):
x, y = site.pos
return _U if x >= 0 else 0
def *onsite*( site, _U=0 ):
return eps + *potential*( site, _U )
syst = kwant.Builder()
syst[graphene.shape(stripe, (0,0))] = *onsite*
***
sym1 = kwant.TranslationalSymmetry(graphene.vec((2, -1)))
def lead1_shape(pos):
x, y = pos
return abs(y) <= 0.5*_W
lead1 = kwant.Builder(sym1)
lead1[graphene.shape(lead1_shape, (0, 0))] = *onsite*
Sincerely,
Jambulat
2017-03-29 12:06 GMT+03:00 Joseph Weston <[email protected]>:
> Hi,
>
> > Joe, great thanks for Your explaination. It would be quite hard for me to
> > understand from the code documentation that it is the submatrix method is
> > the thing which I need. But could You say is the function below
> calculates
> > averaged over all modes transparency adequately?
> >
> > tblock = smatrix.submatrix( 1, 0 )
> >
> > def transparency( tblock ):
> > return ( 0 if tblock.shape[0] == 0 else
> > np.sum( np.abs( tblock )**2 )/tblock.shape[0] )
>
> Seems correct
>
> > I want to use it to check the results obtained analytically in the case
> of
> > the wave falling on a potential barrier in infinite graphene. But now I
> see
> > that 'transparency' depends on the length of the scattering region L
> > despite of that the scattering is expected only at the line x=0. What
> > should I do for obtaining more reliable results, to leave only one-two
> unit
> > cells inside scattering region, or maybe make scattering region more
> long?
> > Also it's a bit strange that 'transparency' is zero for potential
> barriers
> > higher than scattering energy for the case of quite wide nanoribbons
> > (W=100nm). According to theory, if I'm not mistaken, electron at any case
> > is able to pass through a barrier in graphene, when the barrier is higher
> > than its energy, electron just becomes a hole. In some sense this is
> > approved by experiment, conductivity of the graphene FET saturates with
> > increasing of gate voltage (e.g. see
> > http://pubs.acs.org/doi/abs/10.1021/nl204088b ). But doing the similar
> > simulations in Kwant I obtain conductivity cut-off for big voltages. You
> > can see the graphs here:
> > https://preview.ibb.co/crtEFa/graphene.png
> > https://ibb.co/jZr1va (better resolution)
> > I'm also attaching the scripts which have generated this graphs, but I'm
> > not certain that they are not be banned. But it would be great if You
> check
> > them and find that I did there something wrong.
>
> In your 'zigzag.py' script you apply potential for all x >= 0 in the
> scattering region (in both the left and the right leads there is a 0
> potential). As you increase L, you increase the length of the
> barrier so it does not surprise me that the transmission drops to 0.
>
> Happy Kwanting,
>
> Joe
>
