Dear Sir,
I am a PhD student of Hong Kong University of Science and Technology. I
want to use KWANT to caculate Hall resistance of a Hall bar structure.We
can get the conductance between 6 electrodes, but how to get hall
resistance? Can you give me some help? Thank you very much.
Best Regards,
Zhang Bing

Dear Kwant developers,
I write concerning the group velocites
of the modes in the leads.
In particular, I wonder how Kwant calculates them.
I see two possibilities (leads along x):
1) knowing the dispersion along x, from the usual definition v(kx) =
\partial E(kx) / \partial kx;
2) working equivalently in the real space basis, and in particular on
a unitary cell
of a lead, one can calculate vx also as:
vx = <\psi |i [H, \hat{x}] | \psi>,
being \psi the wavefunction of the mode and
H the Hamiltonian respectively, both defined on the unitary cell of
the lead, and \hat{x}
the position operator.
The second approach can be useful also to estimate the expectation
value of the velocities in the direction orthogonal to the leads (say
when close boundary conditions are assumed).
Does Kwant utilizes directly one of these two strategies ?
Thank you very much and best regards
L. L.

Hi Ousmane et al,
I actually want the block of unit cells to be perpendicular to the
scattering region as in the Wanted_System.png, attached. Note that it is a
representative plot, I didn't produce it via Kwant but I want to attach the
red lead to the black region in that direction, not like in
Unwanted_System.png, which is also attached and produced via the code:
##########################################
import kwant
import numpy as np
import matplotlib.pyplot as plt
from types import SimpleNamespace
def make_system(a, W, L):
def shape(pos):
(x, y) = pos
return (0 <= y <= W/2 and -x/2 <= y <= (-x + L)/2) # or (-W <= y
<= 0 and 0 <= x <= L)
def onsite(site, par):
return 4 * par.t - par.mu
def hopx(par):
return -par.t
def hopy(par):
return -par.t
# lead
lat = kwant.lattice.square(a, norbs=1)
syst = kwant.Builder()
syst[lat.shape(shape, (0, 0))] = onsite
syst[kwant.builder.HoppingKind((1, 0), lat, lat)] = hopx
syst[kwant.builder.HoppingKind((0, 1), lat, lat)] = hopy
lead = kwant.Builder(kwant.TranslationalSymmetry((-a, -2*a)))
def lead_shape(pos):
(x, y) = pos
return -W <= x <= 0
def lead_hopx(site1, site2, par):
return -par.t
def lead_onsite(site, par):
return 4 * par.t - par.mu
lead[lat.shape(lead_shape, (-2*a, -a))] = lead_onsite
lead[kwant.builder.HoppingKind((1, 0), lat, lat)] = lead_hopx
lead[kwant.builder.HoppingKind((0, 1), lat, lat)] = hopy
syst.attach_lead(lead)
syst = syst.finalized()
return syst
syst = make_system(a=5, W=100, L=100)
kwant.plot(syst)
##########################################
I couldn't make the lead rotated in the perpendicular direction to the
surface. Is there a way to do it?
Thanks,
Barış

Dear kwant researches,
I came across the algorithm described in
https://scipost.org/SciPostPhys.4.5.026, and I think I would benefit a
lot from it. I am wondering whether it is implemented in the new kwant
1.4 library, or is there an implementation publicly available somewhere?
Thanks,
Oleksii

Dear all,
Could anyone provide me the newer version of code *phlead.py* to calculate
the conductance through majorana. The older vesion of code is not working
well with latest version of kwant and it shows a lot of errors. Please help
me in this regard.
Thank you.
Best regards
Naveen
Naveen
Department of Physics & Astrophysics
University of Delhi
New Delhi-110007

Dear all,
I have a code for the Mobius structure, using python scripts. However, I
want to construct a structure by adding hexagonal lattices in a Mobius
structure. How can I do this using Kwant.
Thank you in advance.
Best,
Nuwan,
MSU, Starkville
P.S.: The python script for the mobius structure is as follows:
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.tri as mtri
from mpl_toolkits.mplot3d import Axes3D
fig = plt.figure(figsize=plt.figaspect(0.5))
u = np.linspace(0, 2.0 * np.pi, endpoint=True, num=50)
v = np.linspace(-0.5, 0.5, endpoint=True, num=10)
u, v = np.meshgrid(u, v)
u, v = u.flatten(), v.flatten()
x = (1 + 0.5 * v * np.cos(u / 2.0)) * np.cos(u)
y = (1 + 0.5 * v * np.cos(u / 2.0)) * np.sin(u)
z = 0.5 * v * np.sin(u / 2.0)
tri = mtri.Triangulation(u, v)
ax = fig.add_subplot(1, 2, 1, projection='3d')
ax.plot_trisurf(x, y, z, triangles=tri.triangles)
ax.set_zlim(-1, 1)
plt.show()

Hi Ousmane,
How can I make sure that there is no overlap between the lead and normal
region? Lead_shape() returns -L <= x <= L and we want the lead to satisfy x
<= 0. If we don't use color_site(site), then we would get the attached
plot. The black region not only represents the normal region but also
represents the lead. However, the lead may also cover the region of x > 0
as the function Lead_shape() suggests. Is there another way to check what
part of the shape is scattering region, what part is lead?
Thanks,
--
A. Barış Özgüler
PhD Candidate in Physics
https://home.physics.wisc.edu/ozguler/
University of Wisconsin–Madison
Madison, Wisconsin 53706, USA

Hi Bariş,
it’s possible to attach the lead in that direction. However it’s unclear to me why do you want to do this. Please provide more details about your system.
Regards,
Ousmane

Thanks, Ousmane.
I have attached another figure. Orange is the lead, blue is the scattering
region. Instead of attaching two different leads horizontally and
vertically, is it possible to attach a single lead (like the orange one in
the figure) which is connected to the scattering region both horizontally
and vertically?
Barış