Hello,
I want to create a graphene-like system with periodic BC at transverse
direction. I'm following
the discussion at
https://www.mail-archive.com/kwant-discuss@kwant-project.org/msg00036.html.
For nearest-neighbor hopping, it works. There is hopping between the upper
and lower side.
But when I add NNN hopping using:
A,B=graphene.sublattices
sys[A.neighbors()]=hopp_qsvh
sys[B.neighbors()]=hopp_qsvh
The NNN hopping doesn't exist between the upper and lower side.
Is there any way to solve it?
Thank you,
Yuhao
Attached is the code:
import numpy as np
import kwant
X,Y = 4, 4
s0=np.identity(2)
sz=np.array([[1,0],[0,-1]])
graphene = kwant.lattice.honeycomb(1,'b')
A,B=graphene.sublattices
def rectangle(pos):
x, y = pos
return -X/2 < x < X/2
def onsite_qsvh(site):
x,y=site.pos
if y<0:
onsite_a = .4*s0
onsite_b = -.4*s0
return onsite_a if site.family == A else onsite_b
else:
return np.zeros([2,2])
def hopp_qsvh(site1,site2):
x1,y1=site1.pos
x2,y2=site2.pos
hop_a = .4*1j*sz
hop_b = -.4*1j*sz
if (y1+0.1)*(y2+0.1)>0 and y1+0.1>0:
return hop_a if site1.family == A else hop_b
else:
return np.zeros([2,2])
sym = kwant.TranslationalSymmetry(graphene.vec((-Y/2,Y)))
anc = kwant.Builder(sym)
anc[graphene.shape(rectangle,(0, 0))] = None
anc[graphene.neighbors()] = None
sys = kwant.Builder()
sys[anc.sites()] = onsite_qsvh
sys[((a, sym.to_fd(b)) for a, b in anc.hoppings())] = -s0
sys[A.neighbors()]=hopp_qsvh
sys[B.neighbors()]=hopp_qsvh
sys = sys.finalized()
kwant.plot(sys,fig_size=(20, 10))
Hello everybody!
We recently added a new section to the Kwant website [1] that contains
links to pieces of code that "extend" Kwant in some cool way. If you've
used Kwant in a way that you feel may be useful to the wider community
make sure to get in touch so that we can add it to the website. The best
way to do that is to make a post to the Kwant development mailing list
[2] with a link to your code and a few sentences describing what it
enables you to do.
Happy Kwanting,
Joe
[1]: https://kwant-project.org/extensions
[2]: mailto:kwant-devel@kwant-project.org
Sorry I only just saw this email; please remember to "reply All" so that
the email gets sent to the mailing list too!
> Thanks. But except the PBC imposed on transverse direction, I need
> attach the lead on longitude direction. So I want the transverse size
> of sample to be finite.
>
Ah I see. In this case your could consider using 'kwant.wraparound' [1].
In your case you would want to set the 'keep' paramter to '0' to keep
the 0th translational symmetry in the wrapped around system. Using
wraparound in this way will produce a Builder with a single
(longitudinal) translational symmetry that you may use as a lead. The
produced Builder will have an (additional) parameter 'k_y'; the
transverse momentum. Don't be confused by the name; it will also work
when the "wrapped" symmetry vector was not in the "y" direction!
There were already several people on the mailing list who used
wraparound, so you could also search the archives. If it's still not
clear after this post back to this thread.
Happy Kwanting,
Joe
[1]:
https://kwant-project.org/doc/1/reference/generated/kwant.wraparound.wrapar…
